Dissertations / Theses on the topic 'Morphology of electrojet'

The demand for alternative secondary batteries to lithium-ion batteries (LIBs) grows. Sodium-ion batteries (SIBs) have been studied for many years and could replace LIBsfor some application. Metallic anodes for both LIBs and SIBs are interesting due totheir high energy densities. Several aspects such as reactivity, stability and depositionmorphology must be properly addressed before metallic Na could be considered apossible anode material. This study aims to evaluate deposition of Na on Alelectrodes using fundamental electrochemical theories. Na deposition was studiedusing pouch cells and sodium triflate (NaOTf) in dimethyl glycol ether (diglyme) aselectrolyte. Galvanostatic deposition using different current densities, electrolyteconcentrations and potential pulses prior to galvanostatic deposition were tested. Theelectrochemical methods used in this study were galvanostatic deposition andchronoamperometry. The morphology of deposited Na was analyzed with ex-situscanning electron microscopy (SEM). A decrease of the size of deposited Na islandswas observed for both increasing current density and decreasing electrolyteconcentration. Fluctuations and poor stability in the deposition potential wereobtained when decreasing the electrolyte concentration under 0.5 M and also whenincreasing the current density over 1 mA cm-2. The most homogeneous depositionwas obtained with a 1030 ms potential pulse amplitude (-3 V vs. Na+/Na) prior togalvanostatic deposition (1 mA cm-2, 0.5 mAh cm-2) using 0.1 M NaOTf in diglyme aselectrolyte. Reproducibility was a major issue in this study and further investigation ofseveral parameters is needed.

For the Li1+xV1-xO2 materials, the amount of excess Li does not change the average crystal structure; however, it alters the cycling performance greatly. This suggests that the local structure governs the electrochemical behaviour. This motivated us to employ the pair distribution function (PDF) technique to probe the local structure. The analyses show the displacements of V3+ form trimers. A structure model for the stoichiometric LiVO2 incorporating the V3+ distortion was constructed and refined, to assist in the assignment of the Li sites revealed by the 6Li nuclear magnetic resonance (NMR) results. For the TiO2-B materials, previous investigations of nanostructured phases suggested the Li insertion mechanism of these materials has a morphological dependence. However, the morphology of the nanoparticles, which to date shows the best cycling performance among all the TiO2 phases with various morphologies, has not been well studied due to the technical challenges which arise from the nature of the diffraction technique and the limited particle sizes. We therefore employed techniques including small-angle X-ray scattering (SAXS) and PDF analyses, to provide an accurate description of the morphology for these nanoparticles. Combining advanced structure modelling, we demonstrated that the nanoparticles adopt an oblate shape with the minor-axis along the b-axis. For the CuF2 conversion material, which theoretically has an exceptionally high specific energy density, behaves differently in practice when compared with other fluorides, such as FeF2 and NiF2. The mechanism underlying its unique electrochemical performance and poor reversibility were investigated via a variety of characterization methods, including cyclic voltammetry (CV), X-ray absorption near edge structure (XANES), PDF and NMR spectroscopy. We demonstrated that Cu dissolution takes place upon charge, associated with the consumption of the LiF phase via the formation of a Cu1+ intermediate. Such side reaction prevents Cu from transforming back to CuF2, leading to negligible capacities in subsequent cycles and making this material challenging to use in a rechargeable battery.

In der vorliegenden Arbeit wird erstmals systematisch der Einfluss von gasförmigen und festen Verunreinigungen auf das O2, Pt│YSZ- Elektrodensystem am praxisnahen Beispiel der Lambdasonde untersucht. Dazu wurden Festelektrolyt- und Elektrodenmaterialien unterschiedlicher Zusammensetzung und Morphologie den realen Abgasbedingungen nachempfundenen, chemischen und physikalischen Einflüssen ausgesetzt und in Bezug auf Langzeitstabilität, Sensitivität und Wirkmechanismen untersucht. Im Einzelnen lag der Fokus der Untersuchungen auf zwei Ausführungsformen von Elektroden, die sich vor allem durch mikro- bzw. nanoskalige Partikelgrößenverteilungen sowie der Platin/YSZ-Zusammensetzung unterschieden und als Mikro- bzw. Nano-Elektrode bezeichnet wurden. Der Einfluss von Siliciumdioxid als gezielt dem Festelektrolyten beigemischte intrinsische Vergiftung sollte in Wechselwirkung zu den extrinsischen Verunreinigungen wie Natriumionen, Wasserdampf und Phosphorpentoxid untersucht werden. Im Unterschied zu den in der Literatur betrachteten, vereinfachten Modellsystemen konnten damit erstmals Wechselwirkungen beschrieben werden, die zu einem tieferen Verständnis des realen Sensorverhaltens, vor allem der Degradation beitragen. Insbesondere ist es gelungen, ein Modell für die Sauerstoffreaktion an geschädigten Elektroden aufzustellen. Neben der bekannten elektrochemischen Reduktion von Sauerstoff spielen die Transportvorgänge an der Elektrodenoberfläche eine entscheidende Rolle, über die in der Literatur bisher nur wenig bekannt war.

The topic of this thesis is the degradation of fuel cell electrodes in proton exchange membrane fuel cells (PEMFCs). In particular, the degradation associated with localized fuel starvation, which is often encountered during start-ups and shut-downs (SUs/SDs) of PEMFCs. At SU/SD, O2 and H2 usually coexist in the anode compartment. This situation forces the opposite electrode, i.e. the cathode, to very high potentials, resulting in the corrosion of the carbon supporting the catalyst, referred to as carbon corrosion. The aim of this thesis has been to develop methods, materials and strategies to address the issues associated to carbon corrosion in PEMFC.The extent of catalyst degradation is commonly evaluated determining the electrochemically active surface area (ECSA) of fuel cell electrode. Therefore, it was considered important to study the effect of RH, temperature and type of accelerated degradation test (ADT) on the ECSA. Low RH decreases the ECSA of the electrode, attributed to re-structuring the ionomer and loss of contact with the catalyst.In the search for more durable supports, we evaluated different accelerated degradation tests (ADTs) for carbon corrosion. Potentiostatic holds at 1.2 V vs. RHE were found to be too mild. Potentiostatic holds at 1.4 V vs. RHE were found to induce a large degree of reversibility, also attributed to ionomer re-structuring. Triangle-wave potential cycling was found to irreversibly degrade the electrode within a reasonable amount of time, closely simulating SU/SD conditions.Corrosion of carbon-based supports not only degrades the catalyst by lowering the ECSA, but also has a profound effect on the electrode morphology. Decreased electrode porosity, increased agglomerate size and ionomer enrichment all contribute to the degradation of the mass-transport properties of the cathode. Graphitized carbon fibers were found to be 5 times more corrosion resistant than conventional carbons, primarily attributed to their lower surface area. Furthermore, fibers were found to better maintain the integrity of the electrode morphology, generally showing less degradation of the mass-transport losses. Different system strategies for shut-down were evaluated. Not doing anything to the fuel cell during shut-downs is detrimental for the fuel cell. O2 consumption with a load and H2 purge of the cathode were found to give around 100 times lower degradation rates compared to not doing anything and almost 10 times lower degradation rate than a simple air purge of the anode. Finally, in-situ measurements of contact resistance showed that the contact resistance between GDL and BPP is highly dynamic and changes with operating conditions.
Denna doktorsavhandling behandlar degraderingen av polymerelektrolytbränslecellselektroder. polymerelektrolytbränslecellselektroder. Den handlar särskilt om nedbrytningen av elektroden kopplad till en degraderingsmekanism som heter ”localized fuel starvation” oftast närvarande vid uppstart och nedstängning av bränslecellen. Vid start och stopp kan syrgas och vätgas förekomma samtidigt i anoden. Detta leder till väldigt höga elektrodpotentialer i katoden. Resultatet av detta är att kolbaserade katalysatorbärare korroderar och att bränslecellens livslängd förkortas. Målet med avhandlingen har varit att utveckla metoder, material och strategier för att både öka förståelsen av denna degraderingsmekanism och för att maximera katalysatorbärarens livslängd.Ett vanligt tillvägagångsätt för att bestämma graden av katalysatorns degradering är genom mätning av den elektrokemiskt aktiva ytan hos bränslecellselektroderna. I denna avhandling har dessutom effekten av temperatur och relativ fukthalt studerats. Låga fukthalter minskar den aktiva ytan hos elektroden, vilket sannolikt orsakas av en omstrukturering av jonomeren och av kontaktförlust mellan jonomer och katalysator.Olika accelererade degraderingstester för kolkorrosion har använts. Potentiostatiska tester vid 1.2 V mot RHE visade sig vara för milda. Potentiostatiska tester vid 1.4 V mot RHE visade sig däremot medföra en hög grad av reversibilitet, som också den tros vara orsakad av en omstrukturering av jonomeren. Cykling av elektrodpotentialen degraderade istället elektroden irreversibelt, inom rimlig tid och kunde väldigt nära simulera förhållandena vid uppstart och nedstängning.Korrosionen av katalysatorbäraren medför degradering av katalysatorn och har också en stor inverkan på elektrodens morfologi. En minskad elektrodporositet, en ökad agglomeratstorlek och en anrikning av jonomeren gör att elektrodens masstransportegenskaper försämras. Grafitiska kolfibrer visade sig vara mer resistenta mot kolkorrosion än konventionella kol, främst p.g.a. deras låga ytarea. Grafitiska kolfibrer visade också en förmåga att bättre bibehålla elektrodens morfologi efter accelererade tester, vilket resulterade i lägre masstransportförluster.Olika systemstrategier för nedstängning jämfördes. Att inte göra något under nedstängning är mycket skadligt för bränslecellen. Förbrukning av syre med en last och spolning av katoden med vätgas visade 100 gånger lägre degraderingshastighet av bränslecellsprestanda jämfört med att inte göra något alls och 10 gånger lägre degraderingshastighet jämfört med spolning av anoden med luft. In-situ kontaktresistansmätningar visade att kontaktresistansen mellan bipolära plattor och GDL är dynamisk och kan ändras beroende på driftförhållandena.

QC 20131104

碩士
國立中山大學
化學系研究所
104
We report a novel approach to study the electrochemical performance of nitroxide radical polymer brushes for thin-film electrodes, in association with the in-situ surface morphology characteristics. In this thesis, we synthesized non-cross-linked nitroxide radical polymer brushes as the positive electrode material for thin-film electrodes via surface-initiated atom transfer radical polymerization (SI-ATRP), which is an effective method to produce smoothly surfaced organic radical polymer brushes with different grafting densities. After SI-ATRP, the covalent bonds between the nitroxide polymers and the conducting substrate are formed, which not only prevent the organic polymer from dissolving into organic electrolyte solution but also improve the cycle life performance of batteries. To understand the correlation between the density of surface-initiator and the amount of polymer chains via calculations of grafting density, we examined the electrochemical performance and the morphology of nitroxide radical polymers by varying their grafting densities. The polymer brushes with different grafting densities are characterized by water contact angle goniometer, atomic force microscope (AFM) and electron spectroscopy for chemical analysis (ESCA), along with electrochemistry techniques such as cyclic voltammetry (CV) and chronopotentiometry (CP). For further study of the mechanism in the polymer layer during electrochemical reactions within designated voltage ranges, in-situ measurements are performed by combining AFM and chronoamperometry (CA). The experimental results show that at 1% initiator composition polymer brushes exhibit better electrochemical performance, and the swelling effect in this electrolyte is also more obvious, implying an enhanced motion of polymer chains. Moreover, the space between ionic channels is enlarged by lowing the grafting density, which leads to a faster ionic diffusion rate. Through in-situ measurements, we found that polymer brushes at 1% initiator composition possess larger variation in thickness than at 100% initiator composition, and the value of apparent diffusion coefficients of polymer brushes reaches its maximum at 1% initiator composition as well, which are both in agreement with the molecular dynamic stimulation results. This study provides direct evidence showing that polymer brushes at 1% initiator composition have larger ionic-channel space, allowing more rapid passage of the anions.

碩士
國立雲林科技大學
化學工程與材料工程系
104
The aim of this study is to investigate the different morphology control and preparation procedure for the preparation of polypyrrole (PPy)/reduced graphene oxide (RGO) nanocomposite electrode materials applied on the impact of supercapacitor electrode. By means of various synthesis parameters (the oxidant, the dopant, pathways) and other fixed parameters (reaction time, temperature, auxiliary doping acid concentration, etc.) prepared of PPy and PPy/GO of three different morphology, namely, nanowires, nanoclips, and nanospheres. The morphology can be observed by SEM images. Further reduced the GO to RGO, prepared PPy / RGO nanocomposite. By the cyclic voltammetry, three different morphology of polypyrrole (PPy) of the electrochemically active area and specific capacitance values are significantly different, order nanowires (PPy-W)> nanoclips (PPy-C)> nanospheres (PPy-S). Followed by the same parameters, GO and pyrrole monomer with a composite weight ratio of 7: 3 was synthesized by three kinds of different morphology material named PPy7GO3, and compare the electrochemically active area and specific capacitance values are significantly different, order nanowires(PPy7GO3-W)> nanoclips (PPy7GO3-C)> nanospheres (PPy7GO3-S). Because of poor conductivity of graphene oxide, RGO active surface area significantly higher than the GO. After prepared PPy7GO3, We are further chemical reduction method will reduce the GO into RGO, and re-doping, the synthesis method is called three-step synthesis method. Cyclic voltammetry showed that the electrochemically active area and specific capacitance values not as expected to enhance the effect of specific capacitance, but dropped significantly. Due to two-step synthesis method instead of three-step synthesis method, two-step synthesis method reduced the GO to RGO and then synthesis with Py monomer to PPy7RGO3. By the cyclic voltammetry, two-step synthesis method compared with three-step synthesis method has a higher specific capacitance values. Then, this study synthesized PPy7RGO3 nanocomposite by a novel one-step synthesis method. The one-step synthesis method used hydroiodic acid and Acetic acid not only as a oxidant but as a dopant, simultaneously GO reduced and polymerization with pyrrole monomers in an acidic environment. Comparison of three kinds of preparation procedure by the cyclic voltammetry, the electrochemically active area and specific capacitance values are significantly different, order PPy7RGO3 (HI, 1-step) > PPy7RGO3 (HI, 2-step) > PPy7RGO3 (SB, 3-step). Its showed PPy7RGO3 (HI, 1-step) has better specific capacitance values, PPy7RGO3 (HI, 1-step) have a higher specific capacitance values (543 F/g) than others at 5 mV/s scan rate. In order to compared with most of the studies in the literature, increased the ratio of GO and pyrrole monomer with a composite to 95:5 was synthesized material named PPy95RGO5(HI, 1-step). It’s specific capacitance up to 748 F/g at 5 mV/s scan rate. Followed by electrochemical impedance spectroscopy (EIS), showed PPy95RGO5(HI, 1-step) has the lowest charge transfer impedance, so that its electrochemical properties of composite materials are preferred. From the above study, through control morphology and the preparation of procedures, to the best performance of PPy / RGO nanocomposite as supercapacitor electrode.

碩士
逢甲大學
電子工程學系
105
The resistive random access memory is the most promising for novel nonvolatile memory, which has attracted much attention because of its advantages such as low power consumption, high operating speed, simple structure and good scalability. This paper is research for the electrochemical metallization (ECM) type ReRAM, and discussing electric properties for operation electric field, memory window (On/Off ratio), data retention and endurance. The ECM-type ReRAM uses active metal (Cu, Ag) for anode oxidation, cathode reduction reaction to form the conduction path in the resistive switching layer. In addition, Cu metal is often used in the back-end technique and Cu-based ReRAM is compatible with semiconductor processes. However, Cu metal has not yet been resolved for dry etching, so our laboratory developed Cu chemical displacement technique (CDT) which can displace material to Cu in a specific area and successfully applied CDT in ReRAM. In this thesis, different surface morphology electrodes were formed by Cu CDT, then spin-coated zinc oxide thin film as resistive switching layer for Al / ZnO / Cu structure ReRAM. And the interface roughness of electrode and resistive switching layer was varied by Cu chemical displacement technique. The interface roughness increase thus enhanced local electric field. Therefore the samples exhibited stable operation electric field, large memory window (>105) and excellent endurance. Finally, the impact of Cu grain size and surface roughness for resistive switching properties has been compared.

Part I. Novel composite polyelectrolyte materials were developed that exhibit desirable charge propagation and ion-retention properties. The morphology of electrode coatings cast from these materials was shown to be more important for its electrochemical behavior than its chemical composition.

Part II. The Wilhelmy plate technique for measuring dynamic surface tension was extended to electrified liquid-liquid interphases. The dynamical response of the aqueous NaF-mercury electrified interphase was examined by concomitant measurement of surface tension, current, and applied electrostatic potential. Observations of the surface tension response to linear sweep voltammetry and to step function perturbations in the applied electrostatic potential (e.g., chronotensiometry) provided strong evidence that relaxation processes proceed for time-periods that are at least an order of magnitude longer than the time periods necessary to establish diffusion equilibrium. The dynamical response of the surface tension is analyzed within the context of non-equilibrium thermodynamics and a kinetic model that requires three simultaneous first order processes.

碩士
國立雲林科技大學
化學工程與材料工程系
102
The aim of this study is to investigate the effect of a supercapacitor performance of different of polyaniline (PA) / graphene oxide (GO) composite electrode materials. By means of various synthesis parameters (the aniline monomer concentration, pH,temperature,reaction time), preparation of polyaniline / graphene oxide of three different forms, namely, nanotubes, nano fiber arrays, and nanospheres. We also tried to synthesize polyaniline / graphene oxide (PA / GO) in three different forms of the condition, try the graphene oxide-free environment separately prepared polyaniline (PA). Although not necessarily and morphology of polyaniline / graphene oxide composite material is the same, but substantially similar, can be observed by SEM images.By the cyclic voltammetry,three different forms of polyaniline (PA) of the electrochemically active area and specific capacitance values are significantly different,order nanofiber(PA-FA)>nanosphere(PA-S)>nanotube(PA-T). By the cyclic voltammetry (CV), founding that different forms of polyaniline / graphene oxide (PA / GO) composite electrochemical active surface area is not the same, which PA7GO3-S has the largest active area, PA5GO5-FA active area of the smallest .Because of poor conductivity of graphene oxide, RGO active surface area significantly higher than the GO [47], after prepared PA7GO3-S. Be further chemical reduction method will reduce the GO into RGO, and re-doping, the synthesis method is called three-step synthesis method [58]. Cyclic voltammetry showed that the current density, electrochemically active area and specific capacitance values improved significantly. Most of the studies in the literature will be reduce graphene oxide into graphene, and then modified, or graphene (RGO) directly to the platform as aniline monomer is polymerized to prepared PANI / GNS composites, called two-step synthesis method [43]. In this thesis uses three-step synthesis method (in-situ polymerization-reduction/dedoping-redoping) to avoid reduction of graphene oxide (RGO) may cause the aggregation, and the impact of the in situ polymerization of polyaniline composite effect. First aniline monomer on graphene oxide polymerization, then the PA / GO reduction, re-doping prepared PA7RGO3-S. This study comparing two different processes investigate the effect of electrical capacity. The results showed that compared to the two-step synthesis method using a three-step synthesis method of the preferred method has a capacitance value. Literature [57, 58] taken with the preparation of the thesis PA / RGO composite program is very similar. The results show that the composite material of the thesis prepared PA7RGO3-S, the capacitance value has advantages. The reason is that although the process is similar, but in the aniline polymerization stage compared with stirring conditions (mechanical stirring or ultrasonic) significantly different. If mechanical stirring way, aniline polymerization, precipitation or aggregation-prone situation occurs, but the polymerization was allowed to stand, or ultrasonic assisted mode, can be uniformly dispersed in the solution. These two ways will directly affect the polymerization capacitance value. Finally, this research continues to explore the effects of added carboxylic content of carbon nanotubes on the performance of the capacitor electrode material. In order to maintain the original shape, so that the physical blending add the carbon nanotubes, can be prepared PA7RGO3-S-CNT ternary composites. Adding carboxylic content of carbon nanotubes for the best optimized to 5 wt%, adding 5 wt% CNT ternary composite PA7RGO3-S-CNT5 at 200 mV s-1 long cycle test, the retention ratio of 96 % to maintain and improve the binary materials PA7RGO3-S. Keywords:Supercapacitor、Polyaniline/ graphene oxide

碩士
國立成功大學
材料科學及工程學系
103
In this research, we aim to understand the influence of nanostructures and surface charge on the detection of dopamine. We synthesize several functionalized poly(3,4-ethylenedioxythiophene) (PEDOT), including carboxylic acid, ethylene glycol, and phosphocholine functional groups. The results showed the nanostructured PEDOT with carboxylic acid groups provides best detection limit mainly contributed by electrostatic interaction between carboxylic acid and dopamine. Furthermore, we evaluate the performance of our electrodes in the presence of proteins. The electrodes are immersed into solutions containing BSA, lysozyme and fibrinogen for 6 hours before test. The results show the non-specific binding of protein lower the detection sensitivity. However the electrode presents a similar detection ability from 1 to 50 μM of domamine concentration, and achieves a lower detection limit about 1 μM. These show the electropolymerized functionalized PEDOT having the properties of light stability, consistency under protein influence and mass production.

博士
國立清華大學
材料科學工程學系
104
In this thesis, I focused on development of morphology control and device structure engineering of solution-processed organic solar cells (OSCs) and solution-processed MoOx (s-MoOx) treated silver nanowire (AgNWs) transparent conducting electrodes (TCE). In the first part of this thesis, we reviewed the development of solution-processed OSCs, followed by the theory and working mechanism of silver nanowire transparent conducting electrodes. In chapter 2, we systematically studied the devices performance, surface morphology, crystallinity and external quantum efficiency (E.Q.E.) of P3HT:PC61BM organic solar cells fabricated by rapid-drying blade-coating and spin-coating methods with (w/) and without (w/o) solvent annealing. In chapter 3, we studied the optical constants of PC61BM, PC71BM and C70, and device performance of solution-processed small molecule OSCs utilizing these three acceptors and the donor-acceptor-acceptor push-pull donor molecules. In chapter 4, we investigated the atomic force microscopy, scanning electron microscopy, transmission electron microscopy (TEM), cross-sectional TEM images, photoluminance quenching measurement and device performance of inverted quasi-bilayer OSCs fabricated using halogen-free solvent. In chapter 5, we reported s-MoOx-treated AgNW TCEs utilizing low-temperature processes. Notably, this s-MoOx-treated AgNW TCEs exhibit multi-characteristics, such as high transmission, low sheet resistance, low haze value, better mechanical properties against bending and adhesion tests, and preferable gap states for efficient hole injection in optoelectronic applications.