Dissertations / Theses on the topic 'Electrochemical energy storage and conversion'

With increasing interest in energy storage and conversion devices for automobile applications, the necessity to understand and predict life behavior of rechargeable batteries, PEM fuel cells and super capacitors is paramount. These electrochemical devices are most beneficial when used in hybrid configurations rather than as individual components because no single device can meet both range and power requirements to effectively replace internal combustion engines for automobile applications. A system model helps us to understand the interactions between components and enables us to determine the response of the system as a whole. However, system models that are available predict just the performance and neglect degradation. In the first part of the thesis, a framework is provided to account for the durability phenomena that are prevalent in fuel cells and batteries in a hybrid system. Toward this end, the methodology for development of surrogate models is provided, and Pt catalyst dissolution in PEMFCs is used as an example to demonstrate the approach. Surrogate models are more easily integrated into higher level system models than the detailed physics-based models. As an illustration, the effects of changes in control strategies and power management approaches in mitigating platinum instability in fuel cells are reported. A system model that includes a fuel cell stack, a storage battery, power-sharing algorithm, and dc/dc converter has been developed; and preliminary results have been presented. These results show that platinum stability can be improved with only a small impact on system efficiency. Thus, this research will elucidate the importance of degradation issues in system design and optimization as opposed to just initial performance metrics. In the second part of the thesis, modeling of silicon negative electrodes for lithium ion batteries is done at both particle level and cell level. The dependence of the open-circuit potential curve on the state of charge in lithium insertion electrodes is usually measured at equilibrium conditions. Firstly, for modeling of lithium-silicon electrodes at room temperature, the use of a pseudo-thermodynamic potential vs. composition curve based on metastable amorphous phase transitions with path dependence is proposed. Volume changes during lithium insertion/de-insertion in single silicon electrode particle under potentiodynamic control are modeled and compared with experimental data to provide justification for the same. This work stresses the need for experiments for accurate determination of transfer coefficients and the exchange current density before reasoning kinetic hysteresis for the potential gap in Li-Si system. The silicon electrode particle model enables one to analyze the influence of diffusion in the solid phase, particle size, and kinetic parameters without interference from other components in a practical porous electrode. Concentration profiles within the silicon electrode particle under galvanostatic control are investigated. Sluggish kinetics is established from cyclic voltammograms at different scan rates. Need for accurate determination of exchange current density for lithium insertion in silicon nanoparticles is discussed. This model and knowledge thereof can be used in cell-sandwich model for the design of practical lithium ion cells with composite silicon negative electrodes. Secondly, galvanostatic charge and discharge of a silicon composite electrode/separator/ lithium foil is modeled using porous electrode theory and concentrated solution theory. Porosity changes arising due to large volume changes in the silicon electrode with lithium insertion and de-insertion are included and analyzed. The concept of reservoir is introduced for lithium ion cells to accommodate the displaced electrolyte. Influence of initial porosity and thickness of the electrode on utilization at different rates is quantitatively discussed. Knowledge from these studies will guide design of better silicon negative electrodes to be used in dual lithium insertion cells for practical applications.

In this thesis different materials have been developed to use them in electrochemical cells. The electrochemical cells studied can be divided into two material big groups: solids oxides and acid salts materials. In the first group, materials to use them in electrodes for fuel cells an electrolyzer based on oxygen ion conductor electrolytes were optimized. Pertaining to this group, the influence of doping the Ba0.5Sr0.5Co0.8Fe0.2O3-d perovskite with 3% of Y, Zr and Sc in B position (ABO3-d) was checked. That optimization could reduce the polarization resistance of electrodes and improve the stability with time. Additionally, the limiting mechanisms in the oxygen reduction reaction were determined, and the influence of CO2 containing atmospheres was checked. La2NiO4+d;, pertaining to the Ruddlesden-Popper serie, is a mixed conductor of electron and oxygen ions. This compound was doped in La position (with Nd and Pr) and in Ni position (with Co). The dopants introduced were able to produce structural change and improve the cell performance, reducing in more than one order of magnitude the La1.5Pr0.5Ni0.8Co0.2O4+d; polarization resistance respect to the reference material (La2NiO4+d). In addition, the properties of an electrode based on the pure electronic conductor, La0.8Sr0.2MnO3-d; (LSM), were optimized. The triple phase boundary was enlarged by the addition of a second phase with ionic conductivity. That strategy made possible to reduce the electrode polarization resistance. In order to improve the oxygen reduction reaction, the addition of different catalysts by infiltration was studied. The different infiltrated oxides changed the electrochemistry properties, being the praseodymium oxide the catalyst which made possible a reduction in two orders of magnitude the electrode polarization resistance respects to the composite without infiltration. Furthermore, the efficiency of the cell working in fuel cell and electrolyzer mode was improved. Concerning the materials selected to use as electrodes on proton conductor electrolytes, the efficiency of electrodes based on LSM was optimized by using a second phase with protonic conductivity (La5.5WO12-d) and varying the sintering temperature of the electrode. Finally, the catalytic activity of the cell was boosted by infiltrating samaria doped ceria nanoparticles, achieving higher power densities for the fuel cell. The materials pertaining to the Ruddlesden-Popper series and studied for ionic conductor electrolytes were also used for cathodes in proton conductor fuel cells. After checking the compatibility with the electrolyte material, the influence of different electrode sintering temperatures and air containing atmospheres (dry, H2O y D2O) on the cathode performance was studied. Finally, the electrochemical cells based on acid salts (CsH2PO4) were designed and optimized. In that way, different cell configurations were studied, enabling to obtain thin and dense electrolytes and active electrodes for the hydrogen reduction/oxidation reactions. The thickness of the electrolyte was reduced by using steel and nickel porous supports. Furthermore, an epoxy resin type was added to the electrolyte material to enhance the mechanical properties. The electrodes configuration was modified from pure electronic conductors to composite electrodes. Moreover, copper was selected as an alternative of the expensive platinum working at high operation pressures. The cells developed were able to work with high pressures and with high content of water steam in fuel cell and electrolyzer modes.
En la presente tesis doctoral se han desarrollado materiales para su uso en celdas electroquímicas. Las celdas electroquímicas estudiadas, se podrían separar en dos grandes grupos: materiales de óxido sólido y sales ácidas. En el primer grupo, se optimizaron materiales para su uso como electrodos en pilas de combustible y electrolizadores, basados en electrolitos con conducción puramente iónica. Dentro de este grupo, se comprobó la influencia de dopar la perovskita Ba0.5Sr0.5Co0.8Fe0.2O3-d, con un 3% de Y, Zr y Sc en la posición B (ABO3-d). Esta optimización llevó a la reducción de la resistencia de polarización así como a una mejora de la estabilidad con el tiempo. Así mismo, se determinaron los mecanismos limitantes en la reacción de reducción de oxígeno, y se comprobó la influencia de la presencia de CO2 en condiciones de operación. El La2NiO4+d perteneciente a la serie de Ruddlesden-Popper, es un conductor mixto de iones oxígeno y electrones. Éste, fue dopado tanto en la posición del La (con Nd y Pr) como en la posición del Ni (con Co). Los dopantes introducidos además de producir cambios estructurales, provocaron mejoras en el rendimiento de la celda, reduciendo para alguno de ellos, como el La1.5Pr0.5Ni0.8Co0.2O4+d, en casi un orden de magnitud la resistencia de polarización del electrodo de referencia (La2NiO4+d). De la misma manera, se optimizaron las propiedades del electrodo basado en el conductor electrónico puro La0.8Sr0.2MnO3-d (LSM). La adición de una segunda fase, con conductividad iónica, permitió aumentar los puntos triples (TPB) en los que la reacción de reducción de oxígeno tiene lugar y reducir la resistencia de polarización. Con el fin de mejorar la reacción de reducción de oxígeno, se estudió la adición de nanocatalizadores mediante la técnica de infiltración. Los diferentes óxidos infiltrados produjeron el cambio de las propiedades electroquímicas del electrodo, siendo el óxido de praseodimio el catalizador que consiguió disminuir en dos órdenes de magnitud la resistencia de polarización del composite no infiltrado. De la misma manera, la mejora de la eficiencia del electrodo infiltrado con Pr, mejoró los resultados de la celda electroquímica trabajando como pila (mayores densidades de potencia) y como electrolizador (menores voltajes). En lo que respecta a los materiales seleccionados para su uso como electrodos en electrolitos con conductividad protónica, se optimizó la eficiencia del cátodo basado en LSM, mediante el uso de una segunda fase conductora protónica (La5.5WO12-d) y variando la temperatura de sinterización del electrodo. Finalmente, se mejoró la actividad catalítica mediante la infiltración de nanopartículas de ceria dopada con samario, produciendo mayores densidades de corriente de la pila de combustible. Los materiales pertenecientes a la serie de Ruddlesden-Popper y usados para cátodos en pilas iónicas, fueron empleados también para cátodos en pilas protónicas. Después de comprobar que el material electrolítico (LWO) era compatible con los compuestos de la serie de Ruddlesden-Popper, se estudió la influencia de la temperatura de sinterización de los electrodos en el rendimiento, así como de la composición de la atmosfera de aire (seca, H2O y D2O). Finalmente, se diseñó y optimizó las celdas electroquímicas basadas en sales ácidas (CsH2PO4). En este sentido, se estudiaron diferentes configuraciones de celda, que permitieran obtener un electrolito denso con el menor espesor posible y unos electrodos activos a la reacción de reducción/oxidación de hidrógeno. Se consiguió reducir el espesor del electrolito soportando la celda en discos de acero y níquel porosos. Se añadió una resina tipo epoxi al material electrolítico para aumentar sus propiedades mecánicas. De la misma manera, se cambió la configuración de los electrodos pasando por conductores electrónicos puros a electrodos compuestos por conductores
En la present tesis doctoral es van desenvolupar materials per al seu ús en cel·les electroquímiques. Les cel·les electroquímiques estudiades poden ser dividides en dos grans grups: materials d'òxid sòlid i sals àcides. En el primer grup, es van optimitzar materials per al seu ús com a elèctrodes en piles de combustible i electrolitzadors, basats en electròlits amb conducció purament iònica. Dins d'este grup, es va comprovar la influència de dopar la perovskita Ba0.5Sr0.5Co0.8Fe0.2O3-d amb un 3% de Y, Zr i Sc en la posició B (ABO3-d;). Esta optimització va portar a la reducció de la resistència de polarització així com a una millora de l'estabilitat amb el temps. Així mateix, es van determinar els mecanismes limitants en la reacció de reducció d'oxigen, i es va comprovar la influència de la presència de CO2 en condicions d'operació. El La2NiO4+d pertanyent a la sèrie de Ruddlesden-Popper, és un conductor mixt d'ions oxigen i electrons. Este, va ser dopat tant en la posició del La (amb Nd i Pr) com en la posició del Ni (amb Co). Els dopants introduïts a més de produir canvis estructurals, van provocar millores en el rendiment de la cel·la, reduint per a algun d'ells, com el La1.5Pr0.5Ni0.8Co0.2O4+d, en quasi un ordre de magnitud la resistència de polarització de l'elèctrode de referència (La2NiO4+d). De la mateixa manera, es van optimitzar les propietats de l'elèctrode basat en el conductor electrònic pur La0.8Sr0.2MnO3-d (LSM). L'addició d'una segona fase, amb conductivitat iònica, va permetre augmentar els punts triples (TPB), en els que la reacció de reducció d'oxigen té lloc, i reduir la resistència de polarització. A fi de millorar la reacció de reducció d'oxigen, es va estudiar l'adició de nanocatalitzadors per mitjà de la tècnica d'infiltració. Els diferents òxids infiltrats van produir el canvi de les propietats electroquímiques de l'elèctrode, sent l'òxid de praseodimi el catalitzador que va aconseguir disminuir en dos ordres de magnitud la resistència de polarització del composite no infiltrat. De la mateixa manera, la millora de l'eficiència de l'elèctrode infiltrat amb Pr, va millorar els resultats de la cel·la electroquímica treballant com a pila (majors densitats de potència) i com a electrolitzador (menors voltatges). Pel que fa als materials seleccionats per al seu ús com a elèctrodes en electròlits amb conductivitat protònica, es va optimitzar l'eficiència del càtode basat en LSM, per mitjà de l'ús d'una segona fase conductora protònica (La5.5WO12-d;) i variant la temperatura de sinterització de l'elèctrode. Finalment, es va millorar l'activitat catalítica mitjançant la infiltració de nanopartícules de ceria dopada amb samari, produint majors densitats de corrent de la pila de combustible. Els materials pertanyents a la sèrie de Ruddlesden-Popper i usats per a càtodes en piles iòniques, van ser empleats també per a càtodes en piles protòniques. Després de comprovar que el material electrolític (LWO) era compatible amb els compostos de la sèrie de Ruddlesden-Popper, es va estudiar la influència de la temperatura de sinterització dels elèctrodes en el rendiment, així com de la composició de l'atmosfera d'aire (seca, H2O i D2O). Finalment, es van dissenyar i optimitzar les cel·les electroquímiques basades en sals àcides (CsH2PO4). En este sentit, es van estudiar diferents configuracions de cel·la, que permeteren obtindre un electròlit dens amb el menor espessor possible i uns elèctrodes actius a la reacció de reducció/oxidació d'hidrogen. Es va aconseguir reduir l'espessor de l'electròlit suportant la cel·la en discos d'acer i níquel porosos. Es va afegir una resina tipus epoxi al material electrolític per a augmentar les seues propietats mecàniques. De la mateixa manera, es va canviar la configuració dels elèctrodes passant per conductors electrònics purs a elèctrodes compostos per conductors protònics
Navarrete Algaba, L. (2017). New electrochemical cells for energy conversion and storage [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/78458
TESIS

Metal hydrides hydrogen storage materials have the ability to reversibly absorb and release large amounts of hydrogen at low temperature and pressure. In this study, metal hydride materialsemployed as negative electrodes in Ni-MH batteries are investigated. Attention is on AB5 alloys due to their intermediate thermodynamic properties. However, AB5 alloys a have 
tendency of forming oxide film on their surface which inhibits hydrogen dissociation and penetration into interstitial sites leading to reduced capacity. To redeem this, the materials were micro-encapsulated by electroless deposition with immersion in Pd and Pt baths. PGMs were found to increase activation, electrochemical activity and H2 sorption kinetics of the MH alloys. Between the two catalysts the one which displayed better performance was chosen. The materials were characterized by X-ray difractommetry, and the alloys presented hexagonal CaCu5 &ndash
type 
structure of symmetry P6/mmm. No extra phases were found, all the modified electrodes displayed the same behavior as the parent material. No shift or change in peaks which corresponded to Pd or Pt were observed. Scanning Electron Microscopy showed surface morphology of the materials modified with Pd and Pt particles, the effect of using different reducing agents (i.e., N2H4 and NaH2PO2), and alloys functionalized with &gamma
-aminosopropyltrietheosilane solution prior to Pd deposition. From all the surface modified alloys, Pt and Pd particles were observed on the 
surface of the AB5 alloys. Surface modification without pre-functionalization had non-uniform coatings, but the prefunctionalized exhibited more uniform coatings. Energy dispersive X-ray Spectroscopy and Atomic Absorption Spectroscopy determined loading of the Pt and Pd on the surface of all the alloys, and the results were as follows: EDS ( Pt 13.41 and Pd 31.08wt%), AAS (Pt 0.11 and Pd 0.78wt%). Checking effect of using different reducing agents N2H4 and NaH2PO2 for electroless Pd plating the results were as follows: EDS (AB5_N2H4_Pd- 7.57 and AB5_NaH2PO2_Pd- 31.08wt%), AAS (AB5_N2H4_Pd- 11.27 and AB5_NaH2PO2_Pd- 0.78wt%). For the AB5 alloys pre-functionalized with &gamma
-APTES, the results were: EDS (10.24wt%) and AAS (0.34wt%). Electrochemical characterization was carried out by charge/discharge cycling controlled via potential to test the AB5 alloy. Overpotential for unmodified, Pt and Pd modified 
electrodes were -1.1V, -1.24V, and -1.60V, respectively. Both modified electrodes showed discharge overpotentials at lower values implying higher specific power for the battery in comparison with the unmodified electrodes. However, Pd electrode exhibited higher specific power than Pt. To check the effect of the reducing agent the results were as follows: AB5_ N2H4_Pd (0.4V) and AB5_NaH2PO2_Pd (-0.2V), sodium hypophosphite based alloy showing lower overpotential values, implying it had higher specific power than hydrazine based bath. Alloy prefunctionalized with &gamma
-APTES, the overpotential was (0.28V), which was higher than -0.2V of the alloy without pre-functionalization, which means pre-functionalization with &gamma
-APTES did not improve the performance of the alloy electrode. Polarization resistance of the electrodes was investigated with Electrochemical Impedance Spectroscopy. The unmodified alloy showed high resistance of 
21.6884 while, both Pt and Pd modified electrodes exhibited decrease 14.7397 and 12.1061 respectively, showing increase in charge transfer for the modified electrodes. Investigating the effect of the reducing agent, the alloys exhibited the following results: (N2H4 97.8619 and NaH2PO2 12.1061) based bath. Alloy pre-functionalized with &gamma
-APTES displayed the 
resistance of 9.3128. Cyclic Voltammetry was also used to study the electrochemical activity of the alloy electrodes. The voltammograms obtained displayed the anodic current peak at -0.64V 
o -0.65V for the Pt and Pd modified electrodes, respectively. Furthermore, the electrode which was not coated with Pt or Pd the current peak occurred at -0.59V. The Pd and Pt coated 
alloy electrodes represented lower discharge overpotentials, which are important to improve the battery performance. Similar results were also observed with alloy electrodes Pd modified 
using N2H4 (-0.64V) and NaH2PO2 (-0.65V). For the electrode modified with and without &gamma
-APTES the over potentials were the same (-0.65V). PGM deposition has shown to significantly 
improve activation and hydrogen sorption performance and increased the electro-catalytic activity of these alloy electrodes. Modified electrodes gave better performance than the unmodified 
electrodes. As a result, Pd was chosen as the better catalyst for the modification of AB5 alloy. Based on the results, it was concluded that Pd electroless plated using NaH2PO2 reducing agent 
had better performance than electroless plating using N2H4 as the reducing agent. Alloy electrode pre-functionalized with &gamma
-APTES gave inconsistent results, and this phenomenon needs to 
be further investigated. In conclusion, the alloy modified with Pd employing NaH2PO2 based electroless plating bath exhibited consistent results, and was found to be suitable candidate for 
use in Ni-MH batteries.

The work presented herein involves the development of the scanning electrochemical cell microscopy (SECCM) platform for visualizing electrochemical and (photo)electrochemical activity of processes at electrode surfaces relevant to energy applications. The use of complementary microscopy characterization techniques such as: field emission-scanning electron microscopy (FE-SEM), electron backscatter diffraction (EBSD), atomic force microscopy (AFM) and Raman microscopy provides a correlation between the localized (photo)electrochemical activity (obtained by SECCM) and physical properties of the investigated surfaces. SECCM studies of a polycrystalline platinum surface highlight the significant variations in electrochemical activity that can be measured at electrode surfaces due to variations in localized crystallographic orientation and the presence of grain boundaries. An ostensibly simple redox couple (Fe2+/3+) in two different acidic media on a polycrystalline platinum foil is utilized as a model system and the localized crystallographic orientation of the surface is determined by EBSD analysis. The approach is then extended to room temperature ionic liquids (RTILs) to study the reduction of triiodide (I3-) to iodide (I-) on polycrystalline platinum for the application of dye sensitized solar cells (DSSCs) as a counter electrode. The coupling of illumination with high sensitivity current followers and external lock-in amplifiers to the SECCM setup is described and the resulting platform is demonstrated to allow investigation of (photo)electrochemical systems. Two examples are provided: imaging photo-anodes in DSSCs and electrodeposition and characterization of conjugated polymers on a transparent electrode for organic photovoltaic devices. Finally, photo-SECCM is used for determining structure-activity relationships for (photo)electrocatalysts of conjugated organic polymers by coupling the technique with AFM and Raman spectroscopy, suggesting the technique as a potential high throughput screening platform. The approach is exemplified by investigating poly(3-hexylthiophene) and provides not only a correlation of film morphology and photo-activity but also extracts important information on film growth and aging.

Thesis advisor: Chia-Kuang Tsung
Electrochemical energy storage and conversion applications benefit from the integration of nanostructures into the devices, as they have many more active sites per gram which enables excellent mass utilization of the active species. By controlling the surface of fuel cell catalysts, higher activity and efficiency can be achieved as compared to the bulk counterpart, with multiple catalyst facets of varying activity and efficiency. Nanostructured electrochemical capacitors have enhanced electrolyte diffusion over the surface of the electrode, facilitating high rate capability. Nanostructured materials for energy storage and conversion devices, such as electrochemical capacitors and proton exchange membrane fuel cells, can perform even better with the incorporation of carbon. High surface area carbon can enhance the activity of electrochemical capacitors by improving the conductivity of the electrode and/or enhancing the double layer capacitance. Carbon supports for fuel cell catalysts enable proper dispersion of active material without sacrificing conductivity. The work reported in this thesis is aimed toward improving the performance of electrochemical energy storage and conversion devices through novel incorporation of carbon. Carbon was first used to enhance the performance of electrocatalysts. By wrapping fuel cell catalysts in a porous carbon shell, the activity was increased over its bare and CNT-supported counterparts. The carbon shell synthetic method reported here is a good route to the production of a conductive host for Pd electrocatalysts with good contact and in one step with the formation of the Pd nanoparticles. Carbon was also used to enhance the performance of pseudocapacitors, first by incorporating it into the precursor spray solution in the generation of mesoporous metal oxides and then as a metal-organic framework-derived carbon host with dispersed electrochemically active metal oxides. A carbon network was generated from the pyrolysis of pore directing agents during the decomposition of precursor metal nitrates in the generation of mesoporous manganese oxides in a modified spray pyrolysis approach. The addition of Super P to the precursor spray solution further enhanced the conductivity of the material, enabling the formation of high-performing pseudocapacitors. Lastly, nitrogen-doped carbon cubes produced from thermally-treated parent ZIF-8 cubes were tested as electrochemical capacitors and found to have higher specific capacitance than the nitrogen-doped carbon generated from the parent ZIF-8 rhombic dodecahedra. ZIF-67 cubes were then thermally treated to yield cubic nitrogen-doped carbon hosts for the generated cobalt nanoparticles. Once the cobalt particles were oxidized, the cobalt oxide/carbon hybrid structure exhibited the best pseudocapacitive performance of the ZIF-derived carbon materials tested, exhibiting high specific capacitance and good capacitance retention with increased scan rates and prolonged cycling. Each of the materials tested for electrochemical energy storage and conversion saw an enhancement in performance with the addition of carbon. The results reported here illustrate the importance of carbon in electrochemical cells and the importance of continuing research to modify and improve the methods for carbon production and integration
Thesis (PhD) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Energy storage provides sustainability when coupled with renewable but intermittent energy sources such as solar, wave and wind power, and electrochemical supercapacitors represent a new storage technology with high power and energy density. For inclusion in supercapacitors, transition metal oxide and sulfide electrodes such as RuO2, IrO2, TiS2, and MoS2 exhibit rapid faradaic electron–transfer reactions combined with low resistance. The pseudocapacitance of RuO2 is about 720 F/g, and is 100 times greater than double-layer capacitance of activated carbon electrodes. Due to the two-dimensional layered structure of MoS2, it has proven to be an excellent electrode material for electrochemical supercapacitors. Cathodic electrodeposition of MoS2 onto glassy carbon electrodes is obtained from electrolytes containing (NH4)2MoS4 and KCl. Annealing the as-deposited Mo sulfide deposit improves the capacitance by a factor of 40x, with a maximum value of 360 F/g for 50 nm thick MoS2 films. The effects of different annealing conditions were investigated by XRD, AFM and charge storage measurements. The specific capacitance measured by cyclic voltammetry is highest for MoS2 thin films annealed at 500°C for 3h and much lower for films annealed at 700°C for 1 h. Inclusion of copper as a dopant element into electrodeposited MoS2 thin films for reducing iR drop during film charge/discharge is also studied. Thin films of Cu-doped MoS2 are deposited from aqueous electrolytes containing SCN-, which acts as a complexing agent to shift the cathodic Cu deposition potential, which is much more anodic than that of MoS2. Annealed, Cu-doped MoS2 films exhibit enhanced charge storage capability about 5x higher than undoped MoS2 films. Coal combustion is currently the largest single anthropogenic source of CO2 emissions, and due to the growing concerns about climate change, several new technologies have been developed to mitigate the problem, including oxyfuel coal combustion, which makes CO2 sequestration easier. One complication of oxyfuel coal combustion is that corrosion problems can be exacerbated due to flue gas recycling, which is employed to dilute the pure O2 feed and reduce the flame temperature. Refractory metal diffusion coatings of Ti and Zr atop P91 steel were created and tested for their ability to prevent corrosion in an oxidizing atmosphere at elevated temperature. Using pack cementation, diffusion coatings of thickness approximately 12 and 20 µm are obtained for Ti and Zr, respectively. The effects of heating to 950°C for 24 hr in 5% O2 in He are studied in situ by thermogravimetric analyses (TGA), and ex situ by SEM analyses and depth profiling by EDX. For Ti-coated, Zr-coated and uncoated P91 samples, extended heating in an oxidizing environment causes relatively thick oxide growth, but extensive oxygen penetration greater than 2.7 mm below the sample surface, and eventual oxide exfoliation, are observed only for the uncoated P91 sample. For the Ti- and Zr-coated samples, oxygen penetrates approximately 16 and 56 µm, respectively, below the surface. In situ TGA verifies that Ti-and Zr-coated P91 samples undergo far smaller mass changes during corrosion than uncoated samples, reaching close to steady state mass after approximately four hours.

The role of nanohybrid materials in the fields of polymer composites and electrochemical energy systems is significant since they affect the enhanced physical properties and improved electrochemical performance, respectively. As basic nanomaterials, carbon nanotubes and graphene were utilized due to their outstanding physical properties. With these materials, hybrid nanostructures were generated through a novel synthesis method, modified sol-gel process; namely, carbon nanotubes (CNTs)-maghemite and reduced graphene oxide (rGO)-maghemite nanohybrid materials were developed. In the study on polymer composities, developed CNTs-maghemite (magnetic carbon nanotbues (m-CNTs)) were readily aligned under an externally applied magnetic field, and due to the aligned features of m-CNTs in polymer matrices, it showed much enhanced anisotropic electrical and mechanical properties. In the study on electrochemical energy system (Li-ion batteries), rGO-maghemite were used as anode materials; as a result, they showed improved electrochemical performance for Li-ion batteries due to their specific morphology and characteristics.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references.
All-multiwall carbon nanotube (MWNT) thin films are created by layer-by-layer (LbL) assembly of surface functionalized MWNTs. Negatively and positively charged MWNTs were prepared by surface functionalization, allowing the incorporation of MWNTs into highly tunable thin films via the LbL technique. The pH dependent surface charge on the MWNTs gives this system the unique characteristics of LbL assembly of weak polyelectrolytes, controlling thickness and morphology with assembly pH conditions. We demonstrate that these MWNT thin films have randomly oriented interpenetrating network structure with well developed nanopores using SEM, which is an ideal structure of functional materials for various applications. LbL-MWNT electrodes show high electronic conductivity in comparison with polymer composites with single wall nanotubes, and high capacitive behavior in aqueous electrolyte with precise control of capacity. Of significance, additive-free LbL-MWNT electrodes with thicknesses of several microns can deliver high energy density (200 Wh/kg) at an exceptionally high power of 100 kW/kg in lithium nonaqueous cells. Utilizing the redox reactions on the surface functional groups in a wide voltage window (1.5 - 4.5 V vs. lithium) in nonaqueous electrolytes, asymmetric electrochemical capacitors consisting of LbL-MWNT and either lithium or a lithium titanium oxide negative electrode exhibit gravimetric energy density -5 times higher than conventional electrochemical capacitors with comparable gravimetric power and cycle life. Thin-film LbL-MWNT electrodes could potentially lead to breakthrough power sources for microsystems and flexible electronic devices such as smart cards and ebook readers, while thicker LbL-MWNT electrodes could expand the application of electrochemical capacitors into heavy vehicle and industrial systems, where the ability to deliver high energy at high power will be an enabling technological development. Furthermore, nanoscale pseuduocapactive oxides and electrocatalysts were incorporated into LbL-MWNT electrodes for energy storage and conversion. Inorganic oxides such as MnO2 and RuO2 are incorporated to increase volumetric capacitance in LbLMWNT electrodes using electroless deposition and square wave pulse potential deposition methods. Preliminary results show that we can increase volumetric capacitance of LbLMWNT/ MnO2 and LbL-MWNT/RuO2 composite up to 1000 F/cm3 in aqueous electrolytes. In addition, Pt and Pt/Ru alloy electrocatalysts are introduced into LbL-MWNT electrodes using square wave pulse potential deposition, which show higher CO and methanol oxidation activities. Tailored incorporation of metal and oxide nanoparticles into LbLMWNT electrodes by square wave pulse potential opens a new strategy for novel energy storage and conversion electrodes with superior electrochemical properties.
by Seung Woo Lee.
Ph.D.

The development of better energy conversion and storage devices, such as fuel cells and batteries, is crucial for reduction of our global carbon footprint and improving the quality of the air we breathe. However, both of these technologies face important challenges. The development of lower cost and better electrode materials, which are more durable and allow more control over the electrochemical reactions occurring at the electrode/electrolyte interface, is perhaps most important for meeting these challenges. Hence, full characterization of the electrochemical processes that occur at the electrodes is vital for intelligent design of more energy efficient electrodes.

X-ray absorption spectroscopy (XAS) is a short-range order, element specific technique that can be utilized to probe the processes occurring at operating electrode surfaces, as well for studying the amorphous materials and nano-particles making up the electrodes. It has been increasingly used in recent years to study fuel cell catalysts through application of the Δ&mgr; XANES technique, in combination with the more traditional X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The Δ&mgr; XANES data analysis technique, previously developed and applied to heterogeneous catalysts and fuel cell electrocatalysts by the GWU group, was extended in this work to provide for the first time space resolved adsorbate coverages on both electrodes of a direct methanol fuel cell. Even more importantly, the Δ&mgr; technique was applied for the first time to battery relevant materials, where bulk properties such as the oxidation state and local geometry of a cathode are followed.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.
Cataloged from PDF version of thesis. Vita.
Includes bibliographical references.
We live in an age where our society faces the great challenge of generating, storing and transporting energy in responsible ways that minimize impact to the environment. Significant effort has been spent to develop new technologies capable of (1) efficiently converting renewable energy into usable electricity, (2) storing energy into high performance energy storage devices, and (3) fabricating advanced energy conversion and storage devices using environmentally benign technologies. One of the approaches is to genetically engineer M13 bacteriophage (M13 virus) to display proteins with specific functionalities, which allow the synthesis and organization of hybrid materials in environmentally friendly manners. The primary goal of my Ph.D. thesis has been to develop M13 virus-enabled processes for building the electrodes of advanced energy conversion and energy storage devices, including dye-sensitized solar cells (DSCs), electrochemical capacitors, and perovskite hybrid solar cells (PSCs). In order to fabricate nanostructures for the DSC photoanodes, the M13 viruses were crosslinked into a virus hydrogel that served as a multifunctional 3D scaffold capable of binding gold nanoparticles (AuNPs) to the virus proteins. The AuNP-virus hydrogel was encapsulated in titanium dioxide (TiO₂) to produce a plasmon-enhanced nanowire (NW)-based DSC photoanode that enabled a power conversion efficiency (PCE) of 8.46%. A theoretical model was developed that predicted the experimentally observed trends of plasmon-enhancement. Furthermore, to optimize the surface-to-volume ratio of the photoanodes to maximize PCE, a tunable fabrication process used individual free-floating M13 virus as the template for TiO₂ NWs, and the assynthesized NWs were blended with sacrificial polymer to control the film porosity. The optimized semiconducting mesoporous networks were used as photoanodes in both DSCs and PSCs, and the effects of surface morphology on the photovoltaic properties was experimentally investigated. In order to construct the electrodes of electrochemical capacitors, M13 viruses were genetically programmed to bind single-walled carbon nanotubes (SWNTs) in a controlled fashion by aligning SWNTs along the length of the phage without aggregation. The SWNTs-virus complexes were used as the basis for the formation of crosslinked virus hydrogel scaffolds for the fabrication of porous 3D polyaniline (PANI) nanostructures. The PANI-coated SWNT nanocomposites further improved the electrical conductivity and electrochemical activity of thin films. In addition, by using a fog generator to deliver the crosslinker solution, larger-area virusbased hydrogels were fabricated for versatile material coatings, including PANI, MnOx, Ni, and Ni-MnOx. Lastly, an environmentally-responsible process to fabricate efficient PSCs was developed that recycled lead content from discarded car batteries. Perovskite films, assembled using materials sourced from either recycled battery materials or high-purity commercial reagents, showed the same material characterizations and the identical photovoltaic performance, indicating the practical feasibility of recycling car batteries for lead-based PSCs.
by Po-Yen Chen.
Ph. D.

Les carbones nanostructurés sont très largement utilisés dans les systèmes de stockage et conversion d'énergie par voie électrochimique, par exemple en tant que matériau d'électrode de pile à combustible et de batterie ou encore de supercondensateur. La structure du carbone ainsi que sa chimie de surface sont des paramètres primordiaux et doivent être adaptés aux différentes spécificités de chacune de ces applications. Dans ce cadre général, cette thèse a pour but de développer une nouvelle famille de carbones nanostructurés, les aérogels de carbone cellulosiques. Ces derniers sont obtenus par pyrolyse d'aérogels organiques élaborés à partir d'acétate de cellulose. Pour ce faire, nous avons fait varier les paramètres de synthèse sol-gel ainsi que les conditions de séchage et de pyrolyse (principalement la composition du sol, la nature du catalyseur, la température et l'atmosphère de pyrolyse) afin de générer une vaste palette de structures. Dans un second temps, ces aérogels ont subi différents post-traitements visant à modifier leur chimie de surface et ce, par introduction de groupements fonctionnels oxygénés et azotés. Finalement, les Performances de ces nouveaux aérogels de carbone ont été analysées sous la forme de matériaux d'électrode de supercondensateur
Nanostructured carbons are widely used in electrochemical energy storage and conversion devices, e. G. As electrode material for fuel cells, batteries, or still EDLCs (Electric Double Layer Capacitor). The carbon structure and surface chemistry are crucial parameters and consequently need to be adjusted to the specific application's requirements. This PhD thesis has aimed at developing a new family of nanostructured carbons: aerogels from renewable organic sol-gel precursors, i. E. Pyrolyzed cellulose-acetate-based aerogels. Sol-gel synthesis parameters and drying conditions of the organic gel, as well as pyrolysis parameters (particularly the influence of the sol composition, the type of catalyst used in the sol-gel synthesis step, pyrolysis temperature, and atmosphere) have been varied systematically in order to generate a broad range of structurally different cellulose-acetate-based carbonaceous aerogels. Further, cellulose-acetate-based carbon aerogels have been exposed to different post-treatments (e. G. Introduction of oxygen and nitrogen-containing surface functional groups) to create cellulose-acetate-based carbon aerogels with different surface chemistries. Finally, the performance of these cellulose-acetate-based carbon aerogels has been analyzed as EDLC electrode material

Rechargeable batteries have already conquered the market of portable electronics (i.e., mobile phones and laptops) and are set to further enable the large-scale deployment of electric vehicles and hybrid electric vehicles in a not too distant future. In this context, a deeper understanding of the fundamental processes governing the electrochemical behavior of electrode materials for batteries is required for further development of these applications. The aims of the work described in this thesis have been to investigate how electrochemical properties and structural properties of novel electrode materials relate to each other. In this sense, electrochemical characterization, structural analysis using XRD and their combined simultaneous use via in operando XRD experiments have played a crucial part. The investigations showed that: Two oxohalides, Ni3Sb4O6F6 and Mn2Sb3O6Cl, react with Li-ions in a complex manner involving different types of reaction mechanisms at low voltages in Li half cells. In operando XRD show that both of these materials are reduced in a conversion reaction via an in situ formation of nanocomposites, which proceed to react reversibly with Li-ions in a combination of alloying and conversion reactions. Carbon-coated Na2Mn2Si2O7 was synthesized and characterized as a possible positive electrode material for non-aqueous Na-ion batteries. DFT calculations point to a structural origin of the modest electrochemical behavior of this material. It is suggested that structural rearrangements upon desodiation are associated with large overpotentials. It is demonstrated via an in operando synchrotron XRD study that Fe(CN)6 vacancies in copper hexacyanoferrate (CuHCF) play an important role in the electrochemical behavior toward Zn2+ in an aqueous CuHCF/Zn cell. Furthermore, manganese hexacyanomanganate (MnHCM) is shown to react reversibly with Li+, Na+ and K+ in non-aqueous alkali metal half cells. In contrast to CuHCF, which is a zero-strain material, MnHCM undergoes a series of structural transitions (from monoclinic to cubic) during electrochemical cycling.

The fast pyrolysis plant at RISE – ETC, Piteå produces carbon rich chars in bulk from various sources of biomass as feedstock. These in-house manufactured carbon rich chars were upgraded via pyrolysis as well as chemical activation using KOH to enhance their potential as an electrode material for supercapacitors. Commercial activated charcoal (Merck) was also studied and used as a yardstick for comparing performance of our materials. Investigations using EDX show enrichment in carbon content and very low amounts of impurities in the materials prepared from wood char after specific treatments for upgrading. Two-electrode coin cell apparatus with an aqueous electrolyte was used to determine the electrochemical performance of these materials. Wood char after KOH activation shows a high specific capacitance of ~105 Fg-1 at 2 Ag-1 in galvanostatic charge discharge measurements which outperformed activated charcoal used in this study (~68 Fg-1 at 2 Ag-1). This material was tested in a wide range of conditions (current density ranging from 0.1 Ag-1 to 10 Ag-1) and showed specific capacitance from ~90 Fg-1 (for 10 Ag-1) up to ~118 Fg-1 (for 0.1 Ag-1). Fatigue testing for >20000 cycles showed a remarkably high retention (>96%) of capacitance. Currently, most commercial supercapacitors use activated carbon materials prepared from coconut shells as the active electrode material which are not native to Sweden. In this study, we upgrade wood chars produced at RISE – ETC from biomass sources obtained locally (Sweden and Scandinavia) and demonstrate their applicability as supercapacitor electrode materials.
Den snabba pyrolysanläggningen vid RISE - ETC, Piteå, producerar kolrika kol i bulk från olika källor till biomassa som råvara. Dessa interna tillverkade kolrika karaktärer uppgraderades via pyrolys samt kemisk aktivering med hjälp av KOH för att förbättra deras potential som ett elektrodmaterial för superkondensatorer. Kommersiellt aktivt kol (Merck) studerades och användes som en måttstock för att jämföra våra materials prestanda. Undersökningar med EDX visar berikning av kolinnehåll och mycket låga mängder föroreningar i material som framställts av träkol efter specifika behandlingar för uppgradering. Tvåelektrodmyntcellapparater med en vattenhaltig elektrolyt användes för att bestämma den elektrokemiska prestandan hos dessa material. Träkol efter KOH-aktivering visar en hög specifik kapacitans på ~ 105 Fg-1 vid 2 Ag-1 i galvanostatiska laddningsurladdningsmätningar som överträffade aktivt kol som användes i denna studie (~ 68 Fg-1 vid 2 Ag-1). Detta material testades under ett stort antal betingelser (strömtäthet från 0,1 Ag-1 till 10 Ag-1) och visade specifik kapacitans från ~ 90 Fg-1 (för 10 Ag-1) upp till ~ 118 Fg-1 (för 0,1 Ag-1). Trötthetstestning för > 20000 cykler visade en anmärkningsvärt hög retention (> 96%) av kapacitansen. För närvarande använder de flesta kommersiella superkondensatorer aktivt kolmaterial framställt av kokosnötskal som det aktiva elektrodmaterialet som inte är hemma i Sverige. I den här studien uppgraderar vi träkolor som produceras vid RISE - ETC från biomassakällor erhållna lokalt (Sverige och Skandinavien) och visar deras användbarhet som superkapacitorelektrodmaterial.

Le développement durable nécessite des investissements massifs pour l'exploration et l'utilisation des sources d'énergie renouvelables dans le bilan énergétique. Parmi diverses formes de l’énergie, l'électricité est sans doute la forme la plus souhaitable pour les usages quotidiens. Cependant, en raison de l'intermittence des sources d’énergie renouvelables, l'électricité doit être stockée sous d'autres formes afin de corréler la production éphémère et la consommation en continue. Malgré la présence des systèmes commerciaux de stockage d'énergie, la recherche de nouveaux matériaux et de nouvelles approches pour résoudre ce problème est toujours en cours et attire également une grande attention. Les récents progrès ont poussé la communauté scientifique vers l'utilisation de matériaux à l'échelle nanométrique pour des systèmes de stockage et de conversion de l'énergie. Bien que ces derniers offrent des avantages pour réduire les émissions de gaz à effet de serre, leurs performances sont encore inférieures aux valeurs théoriques. Dans ce contexte, l’ingénierie à l'échelle moléculaire devient cruciale non seulement pour créer un nouveau type d'entités moléculaires mais aussi pour augmenter les performances des matériaux existants. Dans ce contexte, nous proposons d’utiliser une nouvelle famille de matériaux à base de liquides ioniques pour diverses d’applications, comprenant celles dans le domaine énergétique et pour le long terme, dans la fabrication de la peau artificielle, ces objectifs font l’objet de ces travaux de thèse. Cette dissertation est composée de cinq chapitres. Le chapitre 1 présente différents aspects des liquides ioniques (LIs) et des polymères à base de LI décrites dans la littérature. Via ce chapitre, nous envisageons d’atteindre les points suivants : (1) Décrire les utilisations possibles des liquides ioniques en électrochimie ; (2) Discuter des comportements physico-chimiques de ces composés en solution, (3) Montrer l'immobilisation de liquides ioniques (Redox-actifs) sur différents substrats : de couches minces aux polymères et (4) Mettre en évidence les travaux marquant portant sur l’utilisation des polymères ioniques liquides dans diverses applications. Le chapitre 2 présente différentes approches électrochimiques pour l'immobilisation de liquides ioniques rédox à la surface de l'électrode. De plus, les différentes caractéristiques des nouvelles interfaces seront reportées. Le chapitre 3 se concentre sur l'utilisation des polymères LIs comme catalyseurs émergents et comme matrices pour la génération de matériaux hybrides vers l'activation de petites molécules (ORR, OER, HER). Le chapitre 4 étudie la réactivité à l'échelle micro / nanométrique de divers matériaux, y compris les polymères liquides ioniques électro-actifs, en utilisant la microscopie électrochimique à balayage (SECM). Le chapitre 5 présente les résultats préliminaires de la fabrication de substrats flexibles avec des fonctionnalités intéressantes : possibilité de convertir le frottement en électricité et stockage d'énergie en utilisant des liquides ioniques redox polymériques. Ces études ouvrent de nouvelles opportunités pour élaborer des dispositifs flexibles, portables et implantables
Increasing demand of energy requires massive investment for exploration and utilization of renewable energy sources in the energy balance. However, due to the intermittence of the current renewable sources, the generated electricity must be stored under other forms to correlate the fleeting production and the continuous consumption. Despite available commercialized systems, seeking for new materials and new approaches for resolving this problem is still matter of interest for scientific researches. Highlighted advancements have recently oriented the community towards the utilization of nanoscale materials for efficient energy storage and conversion. Although the advantages given by existing nanomaterials for diverse applications, especially in the energy field, their performance is still lower than theoretical purposes. Consequently, tailoring the physical-chemical properties at the molecular scale becomes crucial not only for boosting the activities of the existed materials but also for creating a new type of molecular entities for storing and releasing the energy. Accordingly, this PhD work aim to develop new family of materials based on ionic liquid that exhibits a multifunctionality towards energy applications. Our work is based on the knowhow in surface functionalization and material preparation by simple methods to build up electrochemical systems that can be utilized in various applications. Thus, this thesis will report different results obtained by following this direction and is composed of six chapters: Chapter 1 reports an overview of ionic liquid and polymeric ionic liquid. We propose to review the available literature on the redox-IL from solution to immobilized substrates. Through this chapter, we will achieve the following points: (1) Report the possible uses of ionic liquids in electrochemistry; (2) Discuss about the physical-chemical behaviors of these compounds in solution, (3) Show the immobilization of (Redox-active)–ionic liquids onto different substrates: from thin layer to polymer and (4) Highlight recent advances using polymeric ionic liquids for diverse applications. Chapter 2 will be devoted to different electrochemical assisted approaches for the immobilization of (redox)-ionic liquids to the electrode surface. We will focus on generating a thin layer and polymeric film based ionic liquid. Furthermore, the different characteristics of the new interfaces will be reported. Chapter 3 concentrates on the use of the polymer ionic liquid modified electrodes as emerging catalyst and as template for the generation of hybrid materials towards activation of small molecules. Chapter 4 studies the reactivity at micro/nanometer scale of diverse materials, including single layer graphene, polymeric redox – ionic liquid, using the scanning electrochemical microscopy (SECM). Chapter 5 reports the potential applications of redox ionic liquid and focus on providing the preliminary results towards the fabrication of flexible substrates with interesting functionalities: possibility to convert the friction to electricity and energy storage by using polymeric redox ionic liquids. These studies open a new opportunity to elaborate flexible, wearable and implantable devices. Finally, some concluding remarks are given to summarize different results obtained in the previous chapters. Besides, different perspectives will be given by using ionic liquid as main material for developing different energy storage and conversion systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Electrode materials for rechargeable lithium ion batteries are well-known to undergo significant dimensional changes during lithium-ion insertion and extraction. In the battery community, this has often been looked upon negatively as a degradation mechanism. However, the crystallographic strains are large enough to warrant investigation for use as actuators. Lithium battery electrode materials lend themselves to two separate types of actuators. On one hand, intercalation oxides and graphite provide moderate strains, on the order of a few percent, with moderate bandwidth (frequency). Lithium intercalation of graphite can achieve actuation energy densities of 6700 kJ m-3 with strains up to 6.7%. Intercalation oxides provide strains on the order of a couple percent, but allow for increased bandwidth. Using a conventional stacked electrode design, a cell consisting of lithium iron phosphate (LiFePO4) and carbon achieved 1.2% strain with a mechanical power output of 1000 W m 3 . Metals, on the other hand, provide colossal strains (hundreds of percent) upon lithium alloying, but do not cycle well. Instead, a self-amplifying device was designed to provide continuous, prolonged, one-way actuation over longer time scales. This was still able to achieve an energy density of 1700 kJ n 3, significantly greater than other actuation technologies such as shape-memory alloys and conducting polymers, with displacements approaching 10 mm from a 1 mm thick disc. Further, by using lithium metal as the counterelectrode in an electrochemical couple, these actuation devices can be selfpowered: mechanical energy and electrical energy can be extracted simultaneously.
by Timothy Edward Chin.
Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 119-136).
Electrochemical energy storage will play a pivotal role in our society's energy future, providing vital services to the transportation, grid, and residential markets. Depending on the power and duration requirements of a specific application, numerous electrochemical technologies exist. For the majority of the markets, lithium-ion (Li-ion) batteries are the state-of-the-art technology owing to their good cycle life and high energy density and efficiency. Their widespread penetration, however, is limited by high production cost and inherent safety concerns. Understanding the solid-electrolyte interphase (SEI) which governs the performance and lifetime of these batteries is critical to developing the next generation Li-ion batteries. As an alternative to Li-ion, redox flow batteries store energy in solutions of electroactive species, which are housed in external tanks and pumped to a power-converting electroreactor. This configuration decouples power and energy, improving the safety and flexibility of the system, however, flow battery energy density is inherently lower than Li-ion and expensive ion-selective membranes are required for efficient operation. As a contrast to Li-ion and redox flow batteries, convection batteries harnesses the key benefits of Li-ion batteries and redox flow batteries while overcoming their individual limitations. By incorporating thick electrodes into the cell, the energy density is increased and the cost of the system is reduced. To overcome the diffusive losses in the thick electrodes, electrolyte is pumped through the electrodes, enabling uniform ion transport throughout the porous structure. However, thick electrodes can lead to large ohmic losses in the cell resulting in lower energy efficiency. In this thesis, I discuss my work on understanding the SEI in Li-ion batteries, highlighting the thermodynamics of its origin, characterization of its structure, and strategies for future development. I then detail my work understanding redox active molecules from molecule characterization and mechanistic generation to redox flow cell level engineering. Finally, I highlight my work in the development of the convection battery technology explaining the synthesis of active materials, thick electrode design, and fabrication of the prototype convection cell architecture. Taken together, these projects highlight the theme of achieving low-cost electrochemical energy storage through various technical pathways.
by Thomas J. Carney.
Ph. D.

Storing the fluctuating renewable energy into synthetic fuels or in batteries is meaningful due to the emerging energy crisis. In this thesis, four nanostructured catalysts based on two kinds of metal sulfides, namely Cu2S and SnS2, were produced and optimized to improve their performance towards three key electrochemical energy conversion processes, namely electrochemical oxygen evolution, photoelectrochemical water splitting and lithium-ion batteries. Chapter 1 presented a general introduction to explain the motivation of the thesis topic. In chapter 2, a metallic copper substrate was used as current collector and chemical template to produce Cu2S nanorod arrays for electrochemical oxygen evolution reaction (OER). Suitable characterization tools were applied to investigate the chemical, structural and morphological transformation in OER operation, during which the initial Cu2S nanorod arrays would perform as a “pre-catalyst” that in-situ changed to CuO nanowires. Notably, the Cu2S-derived CuO showed significant improved OER performance compared with that of CuO prepared by directly annealing a Cu(OH)2 precursor, in terms of both activity and stability. Thus obtained electrocatalyst can be ranked among the best Cu-based OER catalysts reported so far. To take advantage of the unlimited solar energy, an ultrathin SnS2 NPL with a suitable band gap around 2.2 eV was produced via a hot-injection solution-based process in chapter 3. The unsatisfied photoelectrochemical (PEC) performance of bare SnS2 motivated me to deposit Pt NPs on its surface as cocatalyst via in-situ reduction of a Pt salt. The resulting SnS2-Pt heterostructures with optimal Pt amount showed significant improvement (six fold) towards PEC water oxidation. Mott-Schottky analysis and PEC impedance spectroscopy (PEIS) were used to analyze in more detail the effect of Pt on the PEC performance. The optimal SnS2-Pt heterostructure presented acceptable performance towards PEC water splitting. However, it still suffered from a moderate stability due to the peel-off of the catalyst layer from the FTO surface. To solve this problem, in chapter 4 we detailed a simple, versatile and scalable amine/thiol- based molecular ink to grow nanostructured SnS2 layers directly on conductive substrates such as FTO, stainless steel and carbon cloth. Such layers on FTO were characterized by excellent photocurrent densities. The same strategy was used to produce SnS2-graphene composites, SnS2-xSex ternary coatings and even phase pure SnSe2 layers. Finally, the potential of this precursor ink to produce gram scale amounts of unsupported SnS2 was also investigated. Apart from the application as a photocatalyst, SnS2 can also be a promising anode material for Li-ion batteries (LIB). In chapter 5, nanostructured SnS2 with different morphologies produced in chapter 3 were tested as LIB anodes firstly to find that thin SnS2 NPLs provided the highest performance. Thereafter, a colloidal synthesis strategy to grow the same SnS2 NPLs within a matrix of porous g-C3N4 (CN) and graphite plates (GPs) was developed and the obtained materials were tested for LIB application. Such hierarchical SnS2/CN/GP composites using SnS2-NPL as active materials, porous CN to provide avenues for electrolyte diffusion and ease the volumetric expansion of SnS2, and GP as “highways” for charge transport displayed excellent rate capabilities (536.5 mAh g-1 at 2.0 A g-1) and an outstanding stability (~99.7 % retention after 400 cycles), which were partially associated with a high pseudocapacitance contribution (88.8 % at 1.0 mV s-1). The excellent electrochemical properties of these nanocomposites were ascribed to the synergy created between the three components. Overall, four nanostructured catalysts based on Cu2S and SnS2 were prepared, and proper optimizations/treatments were defined to improve their catalytic performance. The results shown in this thesis demonstrate the promising application of non-toxic, low cost metal sulfides in electrochemical energy conversion technologies.
En esta tesis, se produjeron y optimizaron cuatro catalizadores nanoestructurados basados en Cu2S y SnS2 para mejorar su rendimiento hacia la conversión de energía electroquímica. El Capítulo 1 presentó una introducción general para explicar la motivación del tema de tesis. En el capítulo 2, las matrices de las nanovarillas de Cu2S se sintetizaron in situ sobre un sustrato de cobre metálico para la reacción electroquímica de evolución de oxígeno (OER). Se aplicaron herramientas de caracterización adecuadas para investigar la transformación en la operación OER, durante la cual las matrices iniciales de las nanovarillas Cu2S in situ cambió a nanohilos de CuO. En particular, el CuO derivado de Cu2S mostró un rendimiento de OER significativamente mejor cuando comparado al de CuO preparado mediante el recocido. En el capítulo 3, se detalló un proceso basado en una solución de inyección en caliente para producir nanoplacas ultrafinas SnS2 (NPL). Posteriormente, se cultivóPt en su superficie mediante la reducción in situ de una sal de Pt. Posteriormente se probó el rendimiento fotoelectroquímico (PEC) de los fotoanodes hacia la oxidación del agua. Los fotoanodes de SnS2-Pt optimizados proporcionaron densidades de fotocorriente significativamente más altas que el SnS2 desnudo (seis veces). Se analizó el efecto de Pt. En el capítulo 4, se informó una tinta molecular simple para cultivar capas de SnS2 nanoestructuradas directamente sobre sustratos conductores. Tales capas nanoestructuradas en FTO se caracterizaron por excelentes densidades de fotocorriente. Se utilize la misma estrategia para producir compuestos de grafeno-SnS2, recubrimientos ternarios SnS2-xSex, capas de SnSe2 de fase pura e incluso polvo de SnS2 a gran escala. En el capítulo 5, el SnS2 nanoestructurado con diferentes morfologías se probaron como ánodos LIB en primer lugar para encontrar que los NPL de SnS2 delgados proporcionaban el mayor rendimiento. Posteriormente, se desarrolló una estrategia de síntesis coloidal para cultivar los mismos NPL de SnS2 dentro de una matriz de g-C3N4 (CN) poroso y placas de grafito (GP) y se probaron para la aplicación LIB. Tales compuestos jerárquicos SnS2/CN/GP mostraron excelentes propiedades electroquímicas, lo que se atribuye a la sinergia creada entre los tres componentes como se investigó.

Utilisée en tant que source d’énergie renouvelable, l’énergie solaire peut permettre de repousser les limites d’autonomie des batteries, tandis que l’utilisation de batteries est nécessaire pour gérer le problème d’intermittence de l’énergie solaire. Le design conventionnel d’une batterie solaire implique l’utilisation d’une unité de stockage et d’une unité de conversion reliées l’une à l’autre par des fils électriques. Dans ce travail, une autre approche est explorée pour permettre la conversion et le stockage de l’énergie dans un dispositif unique qui utilise une électrode de TiO2 anatase en tant qu’électrode de batterie Lithium-ion photo-rechargeable. Des films minces mésoporeux de TiO2 anatase déposés sur substrats de FTO sont utilisés en tant qu’électrode modèle pour permettre le contrôle de l’architecture de l’électrode. Ces films sont préparés en combinant la chimie sol-gel et le procédé de trempage-retrait (dip-coating). Le comportement électrochimique sous illumination de ces électrodes est étudié dans une configuration de batterie Li-ion afin d’apporter la preuve de concept de la photo-recharge de l’électrode de TiO2. Les mécanismes photo-induits ainsi que le destin des photo-charges est analysé en étudiant notamment l’influence de l’architecture de l’électrode et le rôle de l’électrolyte
Sunlight, as abundant clean source of energy, can alleviate the energy limits of batteries, while batteries can address photovoltaic intermittency. Conventional design of solar charging batteries involves the use of batteries and solar modules as two separate units connected by electric wires. In this work, we have studied another approach to harvest and store solar energy simultaneously into a single device, using a TiO2 bi-functional Li-ion battery photo-electrode. The apprehension of an electrode undergoing simultaneous light absorption and Li+ intercalation/extraction is very rich in terms of potentialities. At the same time, the various facets of the electrode evolution are very challenging to track and understand. Mesoporous TiO2 anatase thin film on FTO substrates are used as model electrodes to allow a careful control of the electrode architecture. They are prepared by combining the sol-gel chemistry with the dip-coating process, using the “evaporation induced self-assembly” (EISA) approach. In order to bring the proof of concept of the photo-recharge of the electrode, its electrochemical behaviour under illumination is studied using a Li-ion battery configuration. Photo-induced mechanisms and fate of photo-charges are investigated by studying the influence of the electrode architecture and of the electrolyte

Graphene has great potential for energy storage and conversion applications due to its outstanding electrical conductivity, large surface area and chemical stability. However, the pristine graphene offers unsatisfactory performance as a result of several intrinsic limitations such as aggregation and inertness. The functionalization of graphene is considered as a powerful way to modify the physical and chemical properties of graphene, and improve the material performance, which unfortunately still being preliminary and need further knowledge on controllable functionalization methods and the structure-property relationships. This thesis aims to provide in-depth understanding on these aspects. We firstly explored oxygen-functionalized graphene for supercapacitor electrodes. A mild solvothermal method was developed for graphene preparation from the reduction of graphene oxide; the solvent-dependent reduction kinetics is an interesting finding in this method that could be attributed to the solvent-graphene oxide interactions. Using the solvothermal method, oxygen-functionalized graphene with controlled density of oxygen functional groups was prepared by tuning the reduction time. The oxygen-containing groups, primarily phenols and quinones, reduce the graphene aggregation, improve the wetting properties and introduce the pseudocapacitance. Consequently, excellent supercapacitive performance was achieved. Nitrogen-doped graphene was synthesized by the pyrolysis of graphene oxide with nitrogen-containing molecules and used as an electrocatalyst for oxygen reduction reactions. We achieved the structural control of the nitrogen-doped graphene, mainly the content of graphitic nitrogen, by manipulating the pyrolysis temperature and the structure of nitrogen-containing molecules; these experiments help understand the evolution of the bonding configurations of nitrogen dopants during pyrolysis. Superior catalytic activity of the prepared nitrogen-doped graphene was found, due to the enriched content of graphitic nitrogen that is most active for the oxygen reduction reaction. Moreover, we demonstrated a facile strategy of producing superhydrophobic octadecylamine-functionalized graphite oxide films. The long hydrocarbon chain in octadecylamine reduces the surface energy of the graphene oxide film, resulting in a high water contact angle and low hysteresis. The reaction mechanism and the effect of hydrocarbon chain length were systematically investigated. In addition to the researches on graphene-based materials, some results on advanced carbon nanomaterials and polymer composites for electronic packaging will also be discussed as appendix to the thesis. These include carbon nanotube-based capacitive deionizer and gas sensor, and hexagonal boron nitride-epoxy composites for high thermal conductivity underfill.

Photoelectro analytical chemistry provides an elegant technique by which to explore, amongst others, various industrial and environmental applications. To this end, four areas of photoelectroanalytical chemistry are investigated in order to develop industrially - and environmentally - relevant galvanic and photogalvanic cells, together with exploring the electro-generation of an industrially important molecule and diffusion factors they may affect this generation. The first study is investigated a long-range charge transfer, using tert-butylferrocene (tBuFc) as model hydrophobic system. It is found that the apparent one-dimensional diffusion coefficient depends on the tBuFc loading. It is suggested that an efficient relay mechanism for electron transfer is through the partitioning of the oxidised form between the two subphases, with inter-pseudophase reaction. However, the second study investigated the normal lyotropic liquid crystals (in the lamellar or hexagonal phases) as a route to afford a structured, three-dimensional, quasi-biphasic framework within which electron transfer cascades may take place using cyclic voltammetry. It is shown that these can take place through reagent partitioning between the hydrophobic and hydrophilic subphases, and it is illustrated how the structure and its orientation, the nature of the ionic doping of the framework, and the hydrophobicity of the redox analyte may give rise to changes in the observed voltammetric waveshape. For the case of an artitifical mimic of the first few stages of Photosystem I, it is demonstrated that photo-induced electron transfer is likewise affected by the orientation, and develop a system of photon efficiency of ~0.1%. Thirdly, a novel attempt at power production was attempted with the construction and optimisation of a photogalvanic cell system. A literature review was conducted and a system proposed utilizing 10-methylphenothiazine (NMP) as a light harvester and zinc as a sacrificial electrode with tetrabutylammonium chloride (TBAP) as a supporting electrolyte and chloroform as a mediator. The study aimed to create a cell that could be produced using industrial run-off or other waste water supplies. A series of cells was produced with varying concentrations of both zinc and NMP solutions and the power conversions studied by producing a voltage-current plot for each system. A system that exhibited 9.02% conversion efficiency keep, future studies were conducted to show whether the zinc species effected the power conversion or if silver would act in a similar way. A mechanism was proposed for the power production process and so studies using 2, 4-Dichlorophenol (DCP) rather than chloroform we conducted; it was believed that the dissociation step for DCP was step wise rather than concerted. Lower power production was seen in these cells as predicted by the reaction mechanism. Tris - (4-bromophenyl) - amine (TBA), an alternative light harvester to NMP, was used to see if altering the active chemical agent resulted in efficiency change. Finally , A photogalvanic cell that employs 2,4-dichlorophenol as a fuel source, an N-substituted phenothiazine as light harvester, and sacrificial zinc anode is presented, and shown to afford a ca. 4% light-to-electrical power conversion efficiency in violet light.

Climate change, pollution, unprecedented population growth, geopolitical tensions and rapid technological development are intrinsically connected to the nature, level and availability of global energy, which shapes present and future aspects of human society. Particularly, in a society where global energetic demand is continuously rising and the awareness of the negative impact of fossil fuels on the environment is becoming widespread, the exploitation of renewable sources for the generation of sustainable energy is highly needed. In this regard one key requirement for an effective deployment and expansion of renewable energy in the global energy market is represented by its ability to conveniently convert and store the energy derived from intermittent sources, in order to guarantee a constant supply to the electric grid. The technologies for the energy conversion and storage present various degrees of maturity, each one having specific advantages and disadvantages depending on the type of application and energetic source. This thesis aims to give a tiny contribution to the complex problem of energy conversion and storage, through the design, characterisation and testing of electrocatalytic materials for water electrolysis, photoelectrochemical water splitting and direct methanol fuel cell. It is expected that the first two processes will play an important role in the future as convenient technologies for the conversion of solar and wind power into chemical energy in the form of hydrogen. The third process is regarded as promising way to convert the renewable chemical energy in the form of methanol into electrical energy. At the core of the research lies the design and development of electrocatalysts, which are directly responsible for lowering the reaction overpotentials and ultimately increasing the overall efficiency of the processes. As such, in this thesis three materials were synthesised using straightforward methodologies and evaluated as electrocatalysts for the alkaline hydrogen evolution, the photoelectrochemical oxygen evolution and the alkaline methanol oxidation. Their performances were directly linked to the morphological and structural properties which in turn significantly affected the nature of active sites. For the first work reported in Chapter 3, a material based on a mixed cobalt nickel sulphide nanoparticles supported onto Ni foam showed high activity toward the hydrogen evolution reaction, with a required small overpotentials of 163 mV at a current density of 10 mA/cm2 in 1.0 M KOH electrolyte. This value compares well with the best existing hydrogen evolution reaction electrocatalysts based on non-noble elements. Moreover the catalyst showed good durability which was tested under chronoamperometric conditions, maintaining an optimal performance for 72 hours. The origin of such high activity was attributed to the existence of an optimal nickel-cobalt sulphide ratio at the surface of the electrode, which was obtained by selecting the appropriate temperature and time of thermal annealing of the material. This optimal presence of the biphasic nickel-cobalt sulphide nanoparticles led to high electrochemically active surface area and small charge transfer resistance, as evidenced by the extensive characterisation analysis carried out on these materials. For the second work reported in Chapter 4, a WO3/Co3O4 photoanode was successfully synthesised via a facile sol-gel method and tested for the photoelectrochemical oxygen evolution. It was found that the degree of crystallinity of the cocatalyst influenced heavily the photoelectrochemical activity towards the oxygen evolution. In particular, a poorly crystalline structure of Co3O4 led to an improvement of up to 40% in photocurrent generation compared to the bare WO3. Interestingly, the highly crystalline Co3O4 significantly suppressed the photocurrent generation, as a result of the creation of an unfavourable band alignment, with a dramatic increase in the charge recombination at the interface. Finally, for the third and last work reported in Chapter 5, ultra-small Pt nanoparticles embedded on a 3D structure composed of CeO2, NiO and Ni foam was synthesised and tested as electrocatalyst for the alkaline methanol oxidation reaction. The generated catalyst showed extremely high activity for the alkaline methanol oxidation, with mass and geometric current density values of 1160 mA/mgPt and 202 mA/cm2, whose values are among the highest ever reported for Pt-based materials. It was demonstrated that the unique morphological architecture and existence of a synergistic effect between Pt and adjacent CeO2 nanoparticles contributed decisively to the observed high performance. Particularly the presence of defective and poorly crystalline CeO2 nanoparticles was beneficial to the efficient oxidative removal of the CO from the Pt active sites which resulted in a higher durability of the electrocatalyst. Moreover, the concomitant presence of the superficial Ni(OH)2 was thought to contribute to the supply of OH species to the Pt, which act as reactants for the CO removal. The most active electrocatalyst was subjected to stability test, retaining 40 % of the initial geometric current density after 6 hours, and quite surprisingly the activity could be totally restored through straightforward CV scans in 1.0 M NaOH electrolyte.

This thesis aims at formulating and validating models for electrochemical energy storage devices. More specifically, the devices under consideration are lithium ion batteries and polymer electrolyte fuel cells.

A model is formulated to describe an experimental cell setup consisting of a Li_xNi_0.8Co_0.15Al_0.05O₂ composite porous electrode with three porous separators and a reference electrode between a current collector and a pure Li planar electrode. The purpose of the study being the identification of possible degradation mechanisms in the cell, the model contains contact resistances between the electronic conductor and the intercalation particles of the porous electrode and between the current collector and the porous electrode. On the basis of this model formulation, an analytical solution is derived for the impedances between each pair of electrodes in the cell. The impedance formulation is used to analyse experimental data obtained for fresh and aged Li_xNi_0.8Co_0.15Al_0.05O₂ composite porous electrodes. Ageing scenarios are formulated based on experimental observations and related published electrochemical and material characterisation studies. A hybrid genetic optimisation technique is used to simultaneously fit the model to the impedance spectra of the fresh, and subsequently also to the aged, electrode at three states of charge. The parameter fitting results in good representations of the experimental impedance spectra by the fitted ones, with the fitted parameter values comparing well to literature values and supporting the assumed ageing scenario.

Furthermore, a steady state model for a polymer electrolyte fuel cell is studied under idealised conditions. The cell is assumed to be fed with reactant gases at sufficiently high stoichiometric rates to ensure uniform conditions everywhere in the flow fields such that only the physical phenomena in the porous backings, the porous electrodes and the polymer electrolyte membrane need to be considered. Emphasis is put on how spatially resolved porous electrodes and nonequilibrium water transport across the interface between the gas phase and the ionic conductor affect the model results for the performance of the cell. The future use of the model in higher dimensions and necessary steps towards its validation are briefly discussed.

In this dissertation, diverse strategic designs of energy storage materials were explored. The main aims were: affordability and high-performances. I) on eco-efficient synthesis of 1D intercalation compounds was described; a low-temperature aqueous solution synthesis of nanostructured 1D (molybdenum trioxide) MoO3 was developed. Subsequent self-assembly of the fibers to form large-scale freestanding films in paper-like structure was achieved without any assistance of organic compounds. Indeed, the whole processes, from synthesis to assembly of obtained materials, do not require toxic organic solvents. As an example of the application of our synthesized materials, 1D MoO3, having the width in 50−100 nm, with the length in micro scale, and with thickness in ~10 nm, and the macroscopic oxide papers consisting of 1D MoO3 and carbon materials were applied as the cathode and anode to lithium-ion batteries, respectively. As a cathode material, the 1D MoO3 showed a high rate capability with a stable cycle performance up to 20 A/g due to a short Li+ diffusion path along [101] and less grain boundaries which were achieved by the precise nanostructure control. As an anode material, the composite paper showed the first specific discharge capacity of 800 mAh/g. These findings above indicate not only an affordable, eco-efficient synthesis and assembly of nanomaterials but also show a new attractive strategy towards a possible whole aqueous process for a large-scale fabrication of freestanding oxide papers without any toxic organic solvent. II) a new energy storage principle using polymeric frameworks was investigated. The new energy storage concept can deliver both high power and high energy. This is because of the novel energy storage nature of designed artificial polymeric frameworks which is different from classical energy storage mechanisms. The main novel discovery was as follows; since CTF-1 is linear stepwise p- and n-dopable polymer, therefore, this framework can store energy as a cathode in the wide working potential with both cation below 3 V versus Li/Li+ and anion above 3 V versus Li/Li+ by Faradaic reaction. Due to this feature, CTF-1 can store high specific capacity of 540 mAh/g. As the result the new energy storage concept which can deliver both high power and high energy was discovered by using a novel polymeric cathode. Unlike typical organic electrodes in sodium battery systems, the CTF-1 has a high specific power of 10 kW/kg, specific energy of 500 Wh/kg, and over 7,000 cycle life retaining 80 % of its initial capacity in half-cells. Indeed, all-organic energy storage devices based on CTF-1 suggested a possibility towards an extremely affordable energy storage device. Recent research on such artificial polymeric frameworks suggests their huge variability to utilize different functional structures which could even further increase power and energy even further when using different starting monomers. This would significantly extend the possibilities of electrical energy storage devices for a sustainable society based on our result. From this point of view, our research strategy which combined the experimental and theoretical study would be a model for further development of this field.

Ce travail intitulé « Systèmes Conjugués Fonctionnelle pour la Conversion et le Stockage de l'Energie » porte sur la conception et la synthèse de nouvelles classes de systems π-conjugués fonctionnels pour la conversion photovoltaïque et le développement de nouveaux matériaux microporeux. Après une présentation générales de la structure et des propriétés électroniques des principales classes de systèmes conjugués et plus particulièrement des molécules conjuguées utilisées comme matériaux donneur dans les cellules solaires organiques (CSO), le second chapitre décrit la synthèse et l'étude d'une série de donneurs moléculaires obtenus par greffage de groupes dicyanovinle sur trois types de blocs conjugués rigides : carbazole cyclopentadithiophène et dithiénopyrrole (DTP). L'évaluation de ce systèmes dans des CSOs de type hétérojonction donneur-accepteur bicouche montre que le DTP conduit aux meilleurs résultats. Une étude de l'évolution des propriétés électroniques d'une série d'oligo-DTPs avec la longueur de la chaîne confirme par ailleurs l'intérêt de ce bloc donneur pour la conception de systèmes conjugués à faible bande interdite. Le chapitre suivant traite de la synthèse d'une série de molécules conjuguées de type donneur-accepteur-donneur (D-A-D) construites autour d'un cœur isoindigo ou alcoxy-cyanobithiophène et décrit une première anlyse de leurs potentialités comme matériaux donneurs dans les CSOs. Le quatrième chapitre porte sur la synhtèse d'une séries de molécules 3D issues du greffage de groupes donneurs sur une cœur quaterthiophène de géométrie quasi-tétraédrique engendrée par effet stérique et étudie les relations entre la structure des molécules la mobilité des charges positives dans les matériaux correspondants et les performances dans des CSOs. Enfin le cinquième et dernier chapitre décrit les premières étapes vers la conception et l'utilisation de molécules conjuguées 3D en vue de développer de nouvelles classes de matériaux électroactifs microporeux par polymérisation de systèmes moléculaires 3D munis de groupes terminaux réactifs
This work entitled « Functional Conjugated Systems for Energy Conversion and Storage » involves the design and synthesis of new classes of functional π-conjugated systems for photovoltaic conversion and the development of new microporous materials. After a general introduction to the structure and electronic properties of the major classes of conjugated systems and more particularly conjugated molecules used as donor material in organic solar cells (OSC), the second chapter describes the synthesis and study of a series of molecular donors obtained by grafting dicyanovinylene on three types of conjugated rigid blocks : carbazole, cyclopentadithiophene and dithienopyrrole (DTP). The evaluation of these systems in donor-acceptor bilayer heterojunction OSCs shows that the DTP leads to best results. A study of the evolution of the electronic properties, of a series of oligo-DTPs, with the chain length further confirms the interest of the donor block for low band gap conjugated systems. The next chapter deals with the synthesis of a series of conjugated molecules of donor-acceptor-donor (D-A-D) type, built around a core of isoindigo, and describes a first evaluation of their potential as donor materials in OSCs. The fourth chapter deals with the synthesis of a series of 3D molecules derived from the grafting of donor groupas on a quaterthiophene core with a quasi-tetrehedral geometry caused by steric effect, and examine the relationship between the structure of the molecules, the mobility of positive charges in these materials and their performance in OSCs. Finally the fift and last chapter describes the first steps towards the design and use of 3D conjugated molecules in order to develop new classes of electro-active materials by polymerization of microporous 3D molecular systems provided with reactive end groups

Carbon nanocomposites have been successfully developed and applied in the field of energy storage and conversion such as supercapacitors and lithium ion batteries. The effects of controlled morphologies and structures have been fundamentally studied to enhance the electrochemical performance. The aim of this thesis is to develop facile and effective methods to prepare carbon nanocomposites with appropriate morphologies, compositions, porosities and functionalities to suit their application in energy storage and conversion.

Submitted by Geandra Rodrigues (geandrar@gmail.com) on 2018-03-27T13:46:07Z No. of bitstreams: 1 jonathanhunderdutragherardpinto.pdf: 6016290 bytes, checksum: 50eab93d008d20c4a60c851574b2c6f3 (MD5)
Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-03-27T13:57:34Z (GMT) No. of bitstreams: 1 jonathanhunderdutragherardpinto.pdf: 6016290 bytes, checksum: 50eab93d008d20c4a60c851574b2c6f3 (MD5)
Made available in DSpace on 2018-03-27T13:57:34Z (GMT). No. of bitstreams: 1 jonathanhunderdutragherardpinto.pdf: 6016290 bytes, checksum: 50eab93d008d20c4a60c851574b2c6f3 (MD5) Previous issue date: 2018-02-19
Este trabalho tem como contribuição o desenvolvimento de uma estratégia de equa-lização das tensões em um conversor multinível modular, como parte integrante de um sistema híbrido de armazenamento de energia. O conversor modular multinível realiza a conexão em série de módulos supercapacitores, o que possibilita aumentar a ten-são sem prejudicar a transferência rápida de energia. Em relação à outras topologias, este trabalho permite reduzir a quantidade, volume e massa do elemento magnético da estrutura do conversor. Um banco de baterias de íons de lítio também integra o sistema por intermédio de um conversor estático. Como é a fonte de maior densidade de energia, fornece a potência média requerida pelo carga. A associação com uma fonte de transferência rápida de energia permite aumentar o desempenho dinâmico, a eficiência energética e a vida útil da bateria. Com efeito, tem-se um sistema híbrido de armazenamento de energia que requer estratégias de gestão para múltiplas fontes de suprimento. Os resultados simulados considerando a estimativa da demanda de po-tência de um protótipo de veículo elétrico, são adequados e propiciam os fundamentos necessários para a construção de um protótipo.
This work is a contribution to develop a strategy equalization of tensions in a mo-dular multilevel converter as part of a hybrid system energy storage. The multilevel modular converter realizes the series connection of supercapacitor modules, which al-lows to increase the voltage without cause damages to the quick energy transfer. In relation to other topologies, it allows reduction of the quantity, volume and mass of the magnetic element of the converter structure. A lithium-ion battery bank also integrates the system via a voltage boost converter. This battery is the source of high energy density, which provides the average power required by the load. The association with a fast transfer power source allows for increased dynamic performance, energy efficiency and service life. In fact, there is a hybrid energy storage system that requires mana-gement strategies for multiple sources of supply. The simulated results were obtained considering the power demand estimation of an electric vehicle prototype.

La nature intermittente de l'énergie solaire est souvent résolue par un couplage entre le PV et une batterie. Notre approche plus fondamentale vise à développer des matériaux capables de combiner ces deux fonctions à l'échelle moléculaire. Des nanocristaux de TiO2 de 5 nm ont été synthétisés dans notre groupe, ce qui a permis une réaction quantitative de photorecharge sous illumination standard. Nous présentons ici une étude originale portant sur l'évolution des propriétés optoélectroniques et de la dynamique du transfert de charge dans une électrode de TiO2 à l'aide d'expériences spectroscopiques in operando effectuées pendant le fonctionnement de la batterie. L'augmentation de la valeur de la bande interdite et de l'absorbance a été observée lors de l'insertion du lithium dans TiO2. Un décalage négatif en énergie de la bande de conduction indique un potentiel plus oxydant des trous photogénérés dans le Li0.6TiO2 par rapport au TiO2 initial. En analysant les processus de recombinaison dans Li0.6TiO2, nous avons établi une compétition entre les processus ultra-rapides (gamme ps) de recombinaison directe et de transfert de charge vers Ti3+ dans Li0.6TiO2, ce qui limite potentiellement le rendement de la réaction de photorécharge. Cette étude a été étendue à d'autres matériaux d'insertion généralement utilisés dans les batteries lithium-ion (Li4Ti5O12, LiCoO2, LiFePO4, MoO3, etc.). Les positions de bord de bande, la bande interdite, le type de porteurs de charge et leur concentration ont été mesurées et rassemblées dans une base de données. Basé sur ces résultats, la possibilité de photorécharge induite par la lumière a été évaluée et les premiers résultats discutés
The problem of intermittent nature of solar energy is often addressed by the traditional coupling of the PV and battery units. Our more fundamental approach targets the development of materials able to combine solar energy conversion and storage at the molecular level. The 5 nm anatase TiO2 nanocrystals were synthesized in our group affording a quantitative photorecharge reaction by a sole contribution of illumination. Here, we present a study of the evolution of the optoelectronic properties and dynamics of charge transfer in TiO2 electrode using in situ / in operando experiments performed during the battery functioning (UV-visible, Mott-Schottky, fluorescence spectroscopy). The increase of the bandgap value and the rise of absorbance are observed upon lithium insertion into TiO2. A negative shift of the conduction band indicates a more oxidizing potential of the photogenerated holes in Li0.6TiO2 compared to TiO2. By analysis of the recombination processes in TiO2 upon lithium insertion, we established a competition of the ultra-fast (ps range) processes of direct recombination and charge transfer towards Ti3+ in Li0.6TiO2, potentially limiting the yield of the photorecharge reaction. This study was extended to other insertion materials typically used in lithium-ion batteries (Li4Ti5O12, LiCoO2, LiFePO4, MoO3, etc.). The measured band edge positions, band gap, charge carrier type and concentration were gathered into a database, based on which the fundamental evaluation of the possibility of the light-induced photorecharge was conducted. The first results of the photoelectrochemical study of chosen materials are also discussed

L’energia que s’origina de combustibles fòssils ha permés avenços molt remarcables a la nostra civilització durant el segle passat. No obstant, els combustibles fòssils no son il·limitats i suposen una font d’increment del diòxid de carboni a l’atmòsfera, amb els seus conseqüents efectes ambientals nocius. Millorar la eficiencia dels dispositius d’enmagatzematge d’energia i la conversió d’energia solar a hidrògen mitjançant la dissociació de l’aigua són tecnologies clau per encarar problemes energètics i ambientals. Els semiconductors que es presenten en abundància i són beneficiosos pel medi ambient han estat en el punt de mira durant els últims anys donades les seves característiques especifiques com a supercapacitors i dispositius per la dissociació de l’aigua. És conegut que les propietats capacitives dels semiconductors están molt afectades per la seva estructura a la nanoescala i la seva baixa conductivitat, limitant les densitats d’energia i potencia. Així doncs, entendre i manipular l’estructura jeràrquica a la nanoescala és essencial per dissenyar materials nanocompostos per l’emmagatzematge d’energia amb millores en la transferència de càrrega i habilitat de transportar ions electrolítics. Per la dissociació d’aigua fotoelectroquímica (PEC), la recombinació electró-forat al “bulk” i les interfícies juguen un paper molt determinant en l’actuació catalítica. La investigació sobre la modulació de la dinámica de transferencia de càrrega així com el nivell d’energia i la densitat d’estats de superfície sobre la modificació d’un segon semiconductor o catalitzadors per dissociació de l’oxígen (OEV) podrien ser de gran interés. Per altra banda, pels catalitzadors de evolució d’hidrògen (HEC), com la identificació de defectes estructurals, transmisió de fase i les vacants presents en materials 2D juguen un paper de vital interès per optimitzar els catalitzadors per la reacció d’evolució de l’hidrògen (HER) en la dissociació de l’aigua. Aquest treball està dividit en 7 capítols: El Capítol 1 és la part introductòria, que inclou els principis bàsics dels supercapacitors i la dissociació de l’aigua i comenta els factors limitants de les propietats electroquímiques dels semiconductors per aplicacions en supercapacitors i dissociació de l’aigua. El Capítol 2 resumeix les metodologies emprades en aquest treball. Aquest capítol inclou els detalls sobre les configuracions experimentals del TEM, STEM i EELS, processament de dades, simulacions i una introducció a les tècniques electroquímiques com la voltimetria cíclica, espectre d’impedància electroquímica i els models de circuits electrònics per il·lustrar els estats de superficie. La síntesi i els resultats experimentals es presenten en els Capítols 3-6. El Capítol 3 tracta sobre la fabricació de nuclis embrancats de nanocompostos de Fe2O3/PPy com a electrodes negatius per aplicacions en supercapacitors, així com la investigació dels mecanismes de creixement de nanofulles de PPy sobre flocs d’hematita. Al Capítol 4, hem optimitzat les condicions de síntesi, incloent el gruix de ITO, gruix de TiO2, càrrega de dipòsit de FeNiOOH i la temperatura de post-sinterització dels nanofils de ITO/Fe2O3/Fe2TiO5/FeNiOOH com a fotoànodes per la dissociació de l’aigua en electrolits alcalins. Els detalls de l’estructura s’han investigat principalment mitjançant TEM i STEM-EELS, mentre que la transferència de càrrega i els mecanismes de la dinàmica de reacció han estat investigats sistemàticament per PEIS. Al Capítol 5 hem optimitzat les condicions del bany químic per sintetitzar CoFe PBA suportat sobre fotoànodes basats en nanofils de Fe2O3/Fe2TiO5 per la dissociació de l’aigua en electròlits àcids. Els detalls de l’estructura han estat investigats principalment per TEM i STEM-EELS mentre que la transferència de càrrega i els mecanismes de la dinàmica de reacció han sigut investigats sistemàticament per PEIS. Al Capítol 6, ens hem centrat en la caracterització de defectes estructurals, transmissió de fase, vacants en materials 2D per HER per la dissociació de l’aigua amb un STEM dedicat amb correcció d’aberracions, incloent HAADF, ABF, EELS-STEM, GPA i simulacions d’HAADF. Finalment, al Capítol 7 es resumeixen les conclusions generals d’aquest treball, juntament amb les projeccions futures d’aquests.
The energy originated from fossil fuels has enabled the remarkable advancement of civilization over the past century. However, fossil fuels are not infinite in supply and they are a source of increasing atmospheric carbon dioxide and the associated abominable environmental effects. Improving the efficiency of the energy storage devices and conversion of solar energy into hydrogen energy via water splitting are key technologies to tackle the serious energy and environmental problems. Earth-abundant, environmental-friendly semiconductors for supercapacitor and water splitting applications have received great attention due to their specific characteristics. It is well established that the capacitive properties of semiconductors are greatly affected by their nanostructure and poor conductivity, leading to a limited energy and power densities. Thus, understanding and manipulating the hierarchical structure at the nanoscale is essential to design composite materials for energy storage with enhanced charge transfer and electrolyte ions transportation abilities. On one hand, in photoelectrochemical water splitting (PEC), the electron-hole recombination in the bulk interfaces plays a determinative role in the catalytic performance. The investigation about modulation of the charge transfer kinetics as well as the energy level and density of surface state upon the modification of a second semiconductor or oxygen evolution catalysts (OEC) could be of great interest. On the other hand, for hydrogen evolution catalysts (HEC), as the identification of structural defects, phase transmission and vacancies presented in the 2D materials play a vital role in optimizing the catalyst for hydrogen evolution reaction (HER) in water splitting. This dissertation is divided into 7 chapters: Chapter 1 is the introduction part, which includes the background of supercapacitors and water splitting and reviews the limited factors affecting the electrochemical properties of semiconductors for supercapacitor and water splitting applications. In Chapter 2 summarizes the applied methodologies in this dissertation. This chapter includes the details about the TEM, STEM, EELS experimental setups, data processing, simulations and general introductions to the electrochemical techniques, such as cyclic voltammetry, electrochemical impedance spectrum as well the electrical circuit model for illustrating the surface states. Specific synthesis procedures and experimental results for every one of the studied nanosystems are presented in Chapters 3-6. Chapter 3 deals with the fabrication of core-branch Fe2O3/PPy nanocomposites as negative electrode for supercapacitor applications as well as the investigation of PPy nanoleaves growth mechanism onto the hematite nanoflakes. In Chapter 4, we have optimized the synthesis conditions, including the ITO thickness, TiO2 thickness, FeNiOOH deposition charge and the post-sintering temperature of ITO/Fe2O3/Fe2TiO5/FeNiOOH nanowire-based photoanodes for water splitting in alkaline electrolyte. The detailed structure has been mainly investigated by TEM and STEM-EELS, while, the charge transfer and reaction kinetic mechanisms were systematically investigated by PEIS. In Chapter 5, we have optimized the chemical bath conditions for synthesising CoFe PBA supported onto Fe2O3/Fe2TiO5 nanowire-based photoanodes for water splitting in acidic electrolyte. The detailed structure has been mainly investigated by TEM and STEM-EELS, while, the charge transfer and reaction kinetic mechanisms were investigated by PEIS. In Chapter 6, we moved the characterization of structural defects, phase transmission, vacancies in 2D materials for HER in water splitting with advanced aberration-corrected dedicated STEM, including HAADF, ABF, EELS-STEM, GPA and HAADF simulation. Finally, Chapter 7 summarizes the general conclusions of this dissertation, along with a brief outlook.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.
Includes bibliographical references (p. 143-154).
The Nanostructured (TM) 3D Fabrication and Assembly Process was developed as a novel method of creating three-dimensional (3D) nanostructured devices using two- dimensional micro- and nanopatterning tools and techniques. The origami method of fabrication is a two-part process in which two-dimensional (2D) membranes are first patterned and then folded into the desired 3D configuration. This thesis presents an origami fabrication method based on the use of SU-8 membranes and elastic gold hinges. Magnetic actuation, stress-induced folding, vertical spacing, and lateral alignment of the membranes are discussed. This thesis also reports on the used of the Nanostructured OrigamiTM process to create a functional electrochemical energy storage device. An electrochemical capacitor, or a supercapacitor, is selected because its performance can be readily improved by the addition of 3D geometry and nanoarchitecture. In addition to improved performance, the origami fabrication method allows such devices to be integrated into preexisting MEMS and IC processes, thus enabling the fabrication of complete micro- and nanosystems with an integrated power supply. The supercapacitors were created by selectively depositing carbon-based electrode materials on the SU-8 membrane and then folding the structure so that oppositely-charged electrode regions face each other in a 3D arrangement. The fabrication process, electrochemical testing procedure, and analysis of the results are presented.
by Hyun Jin In.
S.M.

Electrochemical energy storage has been widely used in various areas, including new energy sources, auto industry, and information technology. However, the performance of current electrochemical energy storage devices does not meet the requirements of these areas that include both high energy and power density, fast recharge time, and long lifetime. One solution to meet consumer demands is to discover new materials that can substantially enhance the performance of electrochemical energy storage devices. In this dissertation we report four transition metal materials systems with potential applications in electrochemical energy storage. Nanoscale and nanostructured materials are expected to play important roles in energy storage devices because of their enhanced and sometimes unique physical and chemical properties. Studied here is the comparative electrochemical cation insertion into a nanostructured vanadium oxide, a promising electrode material candidate, for the alkali metal ions Li+, Na+ and K+ and the organic ammonium ion, in aqueous electrolyte solutions. Observed are the distinctive insertion processes of the different ions, which yield a correlation between physical degradation of the material and a reduction of the calculated specific charge. The results reveal the potential of this nanostructured vanadium oxide material for energy storage. Vanadium based electrochemical systems are of general interest, and as models for vanadium based solid-state electrochemical processes, the solution state and the solid-state electrochemical properties of two cryolite-type compounds, (NH4)3VxGa1-xF6, and Na3VF6, are studied. The electrochemical behavior of (NH4)3VxGa1-xF6 explored the possibility of using this material as an electrolyte for solid state energy storage systems. Zeolite-like materials have large surface to volume ratios, with ions and neutral species located in the nanometer sized pores of the 3-dimensional framework, potentially yielding high energy density storage capabilities. Yet the insulating nature of known zeolite-like materials has limited their use for electrical energy storage. Studied here are two vanadium based zeolite-like structures, the oxo-vanadium arsenate [(As6V15O51)-9]∞, and the oxo-vanadium phosphate [(P6V15O51)-9]∞, where the former shows electronic conduction in the 3-dimensional framework. Mixed electronic and ionic conductivity, from the framework and from the cations located within the framework, respectively, is measured in the oxo-vanadium arsenate, and allows the use of this material in electrochemical double-layer capacitor configuration for energy storage. By contrast, the oxo-vanadium phosphate shows ionic conduction only. Lastly, a new strontium manganese vanadate with a layered structure exhibiting mixed protonic and electronic conductivity is studied. The various transition metal compounds and materials systems experimentally studied in this thesis showcase the importance of novel materials in future energy storage schemes.
Ph. D.

Fluctuation in the demand for electrical power and the intermittent nature of the supply of energy from renewable sources like solar and wind have made the need for energy storage a dire necessity. Current storage technologies like batteries and supercapacitors fall short either in terms of power output or in their ability to store sufficient energy. Pseudocapacitors combine features of both and offer an alternative to stabilize the power supply. They possess high rates of charge and discharge and are capable of storing much more energy in comparison to a supercapacitor. In the quest for solutions that are economical and feasible, we have investigated Prussian Blue in aqueous electrolytes for its use as a pseudocapacitor. Two different active materials based on Prussian Blue were prepared; one that has just Prussian Blue and the other that contains a mixture of Prussian Blue and carbon nanotubes (CNTs). Four electrolytes differing in the valence of the cation were employed for the study. Cyclic voltammetry and galvanostatic charge-discharge were used to characterize the electrodes. Our experiments have shown specific capacitances of Prussian Blue electrodes in the range of 140-720 F/g and that of Prussian Blue-CNT electrodes in the range of ~52 F/g. The remarkable capacity of charge storage in Prussian Blue electrodes is attributed to its electrochemical activity ensuring surface redox and its tunnel-like structure allowing ease of entry and exit for ions like Potassium. Simple methods of synthesis have yielded specific capacitances of the order of hundreds of Farads per gram showing that Prussian Blue has promise as an electrode material for applications needing high rates of charge-discharge.

Heterogeneous nanostructures such as coaxial nanotubes, nanowires and nanorods have been of growing interest due to their potential for high energy-conversion efficiencies and charge/discharge rates in solar cell, energy storage and fuel cell applications. Their superior properties at nanoscale as well as their high surface area, fast charge transport along large interfacial contact areas, and short charge diffusion lengths have made them attractive components for next generation high efficiency energy-conversion devices. The primary focus of this work was to understand the doping mechanism of TiO2 nanotube exclusively with strontium as an alkaline earth metal to shine light on the relation between the observed enhancement in photocatalytic properties of doped TiO2 nanotubes and its structural and electronic characteristics. The mechanism of Sr incorporation into the TiO2 nanotube structure with the hypothesis of possibility of phase segregation has been explored in low concentrations as a dopant and in very high concentrations by processing of SrTiO3 nanotube arrays. Detailed experimental examination of the bulk and surface of the Sr-doped nanotubes has been performed to understand the effect of dopant on electronic structure and optical properties of the TiO2 nanotubes. Moreover, in order to minimize the polarizations associated with the ionic/electronic charge transport in the electrolyte and anode of solid oxide fuel cells (SOFCs), a new platform is developed using vertically oriented metal oxide nanotube arrays. This novel platform, which is made of coaxial oxide nanotubes on silicon substrates, has the potential to simultaneously lower the operating temperature and production cost leading to significant enhancement in the performance of micro-SOFCs.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 182-200).
Establishing catalytic structure-function relationships enables optimization of the catalyst structure for enhanced activity, selectivity, and durability against reaction conditions and prolonged catalysis. One class of catalysts that could benefit from systematic optimization is non-platinum group metal (non-PGM) electrocatalysts for the O₂ reduction reaction (ORR) to water (4e⁻ reduction) and / or hydrogen peroxide (2e⁻ reduction). The electrically conductive metal-organic frameworks (MOFs) M₃(HXTP)₂ (HXTP = 2,3,6,7,10,11-hexaimino or hexahydroxytriphenylene (HITP or HHTP, respectively)) feature a crystalline structure that contains homogeneously distributed, square planar transition metal sites reminiscent of those doped into carbonaceous media for ORR catalysis. Ni₃(HITP)2 functions as an active and stable ORR electrocatalyst in alkaline medium.
Experimental and computational techniques enabled elucidation of the kinetics, mechanism, and active site for ORR with Ni₃(HITP)₂, as well as understanding the essential nature of the extended MOF structure in providing catalytic activity. Varying the metal and ligand combinations within this class of MOFs afforded two distinct phases. Probing the stability, catalytic activity, product distribution, and electronic properties of the two phases of MOFs identified phase-dependent catalytic activity, regardless of the metal or chelating atom identity. Since the birth of the first rechargeable battery in 1860, emerging battery technologies have both provided answers to energy demands as well as additional obstacles to navigate.
Recent works have explored using MOFs as ionically conductive solid-state electrolytes which would eliminate the need for volatile organic liquids and potentially offer a wider electrolyte potential window and means of controlling the plating of alkali metals during charging. This work has taken advantage of the modular charge found in a Cu-azolate MOF, wherein guest Cl⁻ ions coordinated to Cu₄-lined clusters can be washed out of the structure, and stoichiometric loadings of anions varying in size can be reconstituted into the MOF when soaking the MOF in solutions containing alkali or alkaline earth metal salts. The anions are held in place through coordination to the Cu²⁺ centers, thus enabling the charge-balancing metal cations to achieve high transference numbers within this solid electrolyte. Further, the versatility regarding the identity of the guest metal salt provides a handle for modulating the cation transport activation energy and ionic conductivity.
by Elise Marie Miner.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry

This project focuses on the computational design of novel catalyst for artificial synthesis: converting sunlight into fuels. With the atomic-scale insight of catalysts obtained by theoretical calculations, many efficient and optimum catalysts for these processes have been designed and engineered. The outcomes of this thesis are expected to provide theoretical solutions for current global energy and environmental challenges.

This research focuses on the synthesis and development of new functional nanomaterials with tailored morphology for high performance supercapacitors and hydrogen generation through electrolysis of water splitting in order to alleviate the energy crisis and environmental problems. A series of nickel based nanomaterials have been synthesized and their electrochemical properties were thoroughly studied. Ultrafine amorphous barium nickel phosphate nanofibers, and Ni-Co and NiCu layered double hydroxide (LDH) nanosheet arrays directly grown on carbon fibre clothes (CFC) demonstrated excellent performance for supercapacitors while NiCoFe LDH nanosheet arrays on CFC showed high catalytic activity for oxygen evolution reaction for water splitting.

Template-assisted electrodeposition is a powerful technique for fabricating complex nanostructured electrodes. Through the use of pulsed-electrodeposition nanostructured electrodes of Al, Cu and Sn have been realised and subsequently coated electrochemically with V2O5, MnxO, Li, Cu2O and a polymer electrolyte. Nanorods with a multi-layered Cu2O/Cu structure have likewise been produced through electrodeposition. Nanostructured electrodes are ideal for studying electrochemical energy storage and have as such been used to investigate the electrochemistry of conversion and alloying reactions in detail. Key properties of the Cu2O conversion reaction were found to be dependent on the particle size. Prolonged cycling was seen to induce an electrochemical milling process which reduced the particle size. This process was found to improve the cell capacity retention due to improved accessibility of the material. The redox potential at which the particles react was found to be size dependent as smaller particles reacted at lower potentials. The Li-alloying reaction was also investigated by analysing several different alloy-forming materials. All materials exhibited a decline in capacity during cell cycling. This decline was observed to be time dependent and could as such be explained by a diffusion limited process. Moreover, the capacity losses were found to occur during partial lithiation of the electrode material leading to Li trapping in the electrode material. Li trapping was also observed for commonly used anode current collectors as the metals have some solubility for Li. Conducting boron-doped diamond electrodes were however seen to be resistant to Li diffusion and are therefore recommended as viable current collectors for anodes handling metallic lithium (i.e. Li-alloys and Li metal).

This thesis presents work relating to the fabrication of novel thin film electrodes for energy storage applications, with a focus on low cost, nanostructured transition metal oxides, and electrode manufacture by atomised spray deposition. Iron oxide (FeO_x) nanowires were synthesised hydrothermally and combined with multi-walled carbon nanotubes (MWNT) in sprayed electrodes, which provided the necessary conductivity enhancement for effective energy storage. The spray processing technique allowed for facile control over the relative fraction of MWNTs in the sprayed electrodes. Optimised electrodes were investigated in a range of aqueous electrolytes, and the best energy storage behaviour occurred in Na₂SO₃ with a maximum capacitance from cyclic voltammetry of 312 Fg^-1 at a scan rate of 2 mVs^-1. The FeO_x/MWNT electrodes were investigated for their suitability as lithium-ion battery anodes and showed reasonable energy storage behaviour. Nickel oxide (NiO) electrodes were manufactured by hydrothermal synthesis and annealing followed atomised spray deposition. The performance of the NiO electrodes was enhanced though combination with aqueous graphene suspensions, produced in-house by ultrasonic exfoliation of graphite. The processing route used to combine the nanomaterials was considered and a co-synthesis route resulted in the best performing electrodes. Different substrates were investigated, as the most commonly used Ni-foam substrate reacted with the basic electrolytes necessary for electrochemical activity of NiO. NiO/graphene electrodes showed charge/discharge capacitances of up to 571 Fg^-1 at a current density of 10 Ag^-1, which was maintained at over 300 F/g at a very high current density of 100 Ag^-1. Asymmetric supercapacitor devices were constructed using various combinations of FeO_x, NiO, and commercial carbon black electrodes to extend the operating potential window beyond the ~1.23 V limit of symmetric aqueous-electrolyte devices. Power densities of over 20 kWkg^-1 were achieved for an FeO_x/MWNT-carbon device, which was comparable with current commercial carbon-only supercapacitors.