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1
Weaver, Eric P. "Low voltage electrochemical hydrogen production." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001849.
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Cloutier, Caroline R. "Advanced electrochemical reforming of methanol for hydrogen production." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39857.
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The issue of efficient, low-cost, sustainable hydrogen (H₂) production is one of the barriers to the adoption of a H₂ economy. In this thesis, the electrochemical production of H₂ from liquid methanol (CH₃OH) in acidic aqueous media was studied in a proton exchange membrane (PEM) electrolyser in the static mode at low temperatures. A baseline study showing the influence of CH₃OH concentration, catalyst, catalyst support, operating temperature and operating mode was established. A theoretical thermodynamic analysis of the system was carried out as a function of temperature, and the limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined. The effect of electrochemical promotion (EP) was investigated to see if it can increase the efficiency and performance of H₂ production through electrochemical processes.
The electrochemical promotion of electrocatalysis (EPOE) was investigated by carrying out the electrolysis in triode and tetrode operation. It was shown to improve the PEM electrolysis in the galvanostatic and potentiostatic modes. A decrease in electrolysis voltage or an increase in electrolysis current proportional to the current or potential imposed in the auxiliary circuit was observed when the auxiliary current or potential was opposite to the electrolyser circuit current or potential. The effect was observed using catalytic and non-catalytic non-precious electrolyser electrode materials. It was postulated that triode and tetrode operation enhanced the electro-oxidation rate through electrochemical pumping and spillover of protons. With this novel electrolysis configuration, electrolysis cost reduction may be achieved through the use of non-precious electrolyser anode materials and/or improving electrolyser performance.
The electrochemical promotion of catalysis (EPOC) was also investigated for the catalytic reforming of CH₃OH at low temperature with Pt-Ru/C and Pt-Ru/TiO₂. The synthesized Pt-Ru/TiO₂ was characterized physico-chemically and electrochemically. Powder catalytic CH₃OH reforming tests showed that both catalysts can be used to generate H₂. EPOC experiments were conducted on gas diffusion electrodes (GDEs) in galvanostatic control. Under the experimental conditions, only supplying H⁺ to the catalyst working electrode surface resulted only in a Faradaic enhancement of the catalytic activity for the low temperature reforming of CH₃OH, which appears to be a purely electrophilic behaviour.
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Fatollahi-Fard, Farzin. "Production of Titanium Metal by an Electrochemical Molten Salt Process." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/893.
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Titanium production is a long and complicated process. What we often consider to be the standard method of primary titanium production (the Kroll process), involves many complex steps both before and after to make a useful product from titanium ore. Thus new methods of titanium production, especially electrochemical processes, which can utilize less-processed feedstocks have the potential to be both cheaper and less energy intensive than current titanium production processes. This project is investigating the use of lower-grade titanium ores with the electrochemical MER process for making titanium via a molten salt process. The experimental work carried out has investigated making the MER process feedstock (titanium oxycarbide) with natural titanium ores|such as rutile and ilmenite|and new ways of using the MER electrochemical reactor to \upgrade" titanium ores or the titanium oxycarbide feedstock. It is feasible to use the existing MER electrochemical reactor to both purify the titanium oxycarbide feedstock and produce titanium metal.
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Landon, James R. "Electrochemical Oxygen Production: Catalyst Development to Meet the World’s Oxygen Demands." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/557.
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Ghahremani, Raziyeh. "Electrochemical Oxidation of Lignin for the Production of Value-added Chemicals." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1603983239429615.
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Wang, Huizhi, and 王慧至. "Electrochemical conversion of aluminum energy: energy efficiency, co-production concept and systemcharacteristics." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B4697040X.
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Lyu, Xiang. "Furfural and Hydrogen Production from Raw Biomass Integrating Chemical and Electrochemical Methods." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1605089185418469.
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Paschkewitz, Timothy Michael. "Ammonia Production at Ambient Temperature and Pressure: An Electrochemical and Biological Approach." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/4893.
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The majority of power generated worldwide is from combustion of fossil fuels. The sustainability and environmental impacts of this non renewable process are severe. Alternative fuels and power generation systems are needed, however, to cope with increasing energy demands. Ammonia shows promise for use in power generation, however it is costly to produce and very few methods of using it as a fuel are developed. To address the need for alternative methods of ammonia synthesis, this research designed and tested a bioelectrochemical device that generates NH3 through electrode induced enzyme catalysis. The ammonia generating device consists of an electrode modified with a polymer that contains whole cell Anabaena variabilis, a photosynthetic cyanobacterium. A. variabilis contains nitrogenase and nitrate/nitrite reductase, catalysts for the production of ammonia. In this system, the electrode supplies driving force and generates a reductive microenvironment near cells to facilitate enzymatic production of NH3 at ambient temperatures and pressures.
Farm animal wastes contain significant amounts of NO2- and NO3-, which can leech into groundwater sources and contaminate them. The system described here recycles NO2- and NO3- to NH4sup+ by the nitrate/nitrite reductase enzyme. Unlike nitrogen fixation by the nitrogenase enzyme whose substrate is atmospheric N2, the substrates for nitrate/nitrite reductase are NO2- and NO3-. The ammonia produced by this system shows great potential as a crop fertilizer.
While the substrates and enzymatic basis for ammonia production by nitrogenase and nitrate/nitrite reductase are very different, there is utility in the comparison of commercially produced ammonia by the Haber Bosch synthesis and by the bioelectrocatalytic device described here. In one day, the Haber Bosch process produces 1800 tons of NH3 at an energetic cost of $500/ton. Per ton of ammonia, the Haber Bosch process consumes 28 GJ of energy. The bioelectrocatalytic device produces 1 ton of NH3 for $10/ton, consuming only 0.04 GJ energy, which can be obtained by sunlight via installation of a photovoltaic device. Thus, the system presented here demonstrates ammonia production with significant impact to the economy.
NH3 production by the bioelectrocatalytic is dependent upon A. var. cell density and electrode polarization. The faradaic current response from cyclic voltammetry is linearly related to cell density and ammonia production. Without electrode polarization, immobilized A. var. do not produce ammonia above the basal level of 2.8 ± 0.4 ΜM. Ten minutes after cycled potential is applied across the electrode, average ammonia output increases to 22 ± 8 ΜM depending on the mediator and substrate chemicals present. Ammonia is produced by this system at 25 °℃ and 1 atm. The electrochemical basis for enhanced NH3 by immobilized cyanobacteria is complex with multiple levels of feedback.
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Lowe, Sean E. "Electrochemical Approaches for the Production of Functional Graphene and its Niche Applications." Thesis, Griffith University, 2019. http://hdl.handle.net/10072/389548.
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Graphene has inspired the intrigue of researchers and industry for its potential to improve the performance of existing materials and create entirely new materials and devices. Although graphene has numerous proposed applications, it has not seen widespread adoption in the marketplace. This is partly due to the limitations of existing graphene synthesis routes, which can be costly, hazardous, low yield, or difficult to scale. Electrochemical approaches to graphene synthesis, however, may allow us to address these challenges.
In this thesis, an electrochemical route to graphene is developed and its applications explored. Specifically, a packed bed electrochemical reactor capable of producing electrochemically-derived graphene oxide (EGO) from graphite is introduced. The developed method has several distinguishing features which make it promising for certain applications and larger-scale implementation. In contrast to most existing electrochemical approaches, the current method can use as its input natural flake graphite with no binder, compression, or extensive preprocessing. Low, constant current anodic charging in a dilute sulfuric acid electrolyte produces graphite oxide which can be readily dispersed in polar solvents to predominantly single- to few-layer EGO. The graphite electrode making up the packed bed can be scaled along all of its dimensions for larger scale implementations. The product can be thermally treated in air at 200 °C to increase its conductivity beyond what is possible with conventional, chemically-derived graphene oxide.
Throughout the thesis, several key synthesis parameters are explored to improve our fundamental understanding of graphite oxidation and produce a variety of EGO products. It was found that using boron-doped diamond as the conductive interface between the graphite and power source dramatically improved the yield. The dispersibility and degree of oxidation could be increased by using expanded graphite as precursor. Poor electrolyte diffusion throughout the packed bed was overcome by implementing bulk solution diffusion channels inside the bed itself.
A systematic study found several relationships between the electrolyte acid concentration and the product. Dilute sulfuric acids (less than or equal to 7.1 M) produced EGO with a less crystalline and less oxidised structure, relative to the more concentrated acid. It was found that 11.6 M sulfuric acid produced optimally oxidised graphene, while 7.1 M acid produced less oxidised, but more conductive material.
Two different graphene applications were considered. The utility of EGO as a conductive nanofiller in lithium ion battery cathodes was demonstrated. A thorough investigation also explored EGO as a conductive nanofiller in flexible, wearable tactile sensors. Here, EGO can be readily mixed with aqueous surfactantwrapped polydimethylsiloxane (PDMS), 3D printed, then thermally deoxygenated in situ. The 3D printed sensors have exceptional feature resolution and performance.
Ultimately, the current thesis represents a significant step forward for EGO synthesis and application. The experiments demonstrate the utility of electrochemical reactor engineering for producing new processes and unique types of graphene. This type of work will be critical for the eventual larger-scale production of electrochemically-derived graphene.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Zhao, Ge. "Effects of surface microstructure and nanostructure on osteoblast-like mg63 cell number, differentiation and local factor production." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/36532.
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Surface roughness affects bone formation around orthopaedic implants in vivo and osteoblast functions in vitro. Osteoblast-like MG63 cells cultured on rough surfaces exhibited decreased cell number, increased differentiation and increased local factor production when compared to cells grow on smooth surfaces. In these experiments, roughness was characterized as average peak to valley height (Ra) which is not equal throughout the surface. Other features of roughness, including peak and valley area distributions and curvature of the valleys, will affect cell functions. In this study, novel titanium surfaces were prepared by photolithography to produce well designed microstructure and nanostructure. Smooth disks were made by producing craters of 10 micrometer, 30 micrometer and 100 micrometer diameters on titanium disks with constant curvatures. Craters were placed sparsely (10/1, 30/1, 100/1) or compactly (10/6, 30/6, 100/6). Smooth disks were also acid etched to make an overall roughness of Ra 0.7 micrometer or anodized to produce volcano-like nanostructure of Ra 0.4 micrometer. The results revealed the distinguishing contributions of microcrater size, crater spacing and nanostructures to surface effect on cell number, differentiation (alkaline phosphatase; osteocalcin) and local factor levels (TGF-beta1; PGE2). Cell attachment depends on crater spacing; cell growth and aggregation depend on crater dimension and cell morphology depends on the presence of nanostructural features. Cell differentiation and local factor production are modulated by acid etched roughness in concert with microstructure, and active TGF-beta1 level depends on nanoscale roughness.
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Goldet, Gabrielle. "Electrochemical investigations of H2-producing enzymes." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:696e5b9d-a80f-493e-85d4-0954be499b72.
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Hydrogenases are a family of enzyme that catalyses the bidirectional interconversion of H+ and H2. There are two major classes of hydrogenases: the [NiFe(Se)]- and [FeFe]-hydrogenases. Both of these benefit from characteristics which would be advantageous to their use in technological devices for H2 evolution and the generation of energy. These features are explored in detail in this thesis, with a particular emphasis placed on defining the conditions that limit the activity of hydrogenases when reducing H+ to produce H2. Electrochemistry can be used as a direct measure of enzymatic activity; thus, Protein Film Electrochemistry, in which the protein is adsorbed directly onto the electrode, has been employed to probe catalysis by hydrogenases. Various characteristics of hydrogenases were probed. The catalytic bias for H2 production was interrogated and the inhibition of H2 evolution by H2 itself (a major drawback to the use of some hydrogenases in technological devices to produce H2) was quantified for a number of different hydrogenase. Aerobic inactivation of hydrogenases is also a substantial technological limitation; thus, inactivation of both H2 production and H2 oxidation by O2 was studied in detail. This was compared to inhibition of hydrogenases by CO so as to elucidate the mechanism of binding of diatomic molecules and determine the factors limiting inactivation. This allows for a preliminary proposal for the genetic redesigning of hydrogenases for biotechnological purposes to be made. Finally, preliminary investigation of the binding of formaldehyde, potentially at a site integral to proton transfer, opens the field for further research into proton transfer pathways, the structural implications thereof and their importance in catalysis.
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Benson, Lyndsey. "Production and development of titanium alloys derived from synthetic rutile using electrochemical deoxidation." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18922/.
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Kirkaldy, Niall. "Exploring organic, redox-active materials for electrolytic hydrogen production and electrochemical energy storage." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/30842/.
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Proton exchange membrane electrolysers (PEMEs) constitute the state-of-the-art in electrolytic water splitting, capable of producing H2 at high current density and efficiency. However, when operating at low current or under increased pressure, H2 and O2 can cross through the membrane which separates the electrodes, creating a potentially explosive gas mixture and reducing the efficiency. Electron-coupled proton buffers (ECPBs) provide a solution to the issues of gas crossover in electrolytic water splitting, by breaking up the oxygen and hydrogen evolution reactions (OER and HER) into two separate steps. This provides benefits to gas purity and improves the operational safety of the electrolyser. Initially, ECPBs were limited to polyoxometalate (POM) compounds, which contain expensive transition metals and have high molecular weights. The use of a cheap organic species as an ECPB was later introduced using hydroquinone sulfonate (HQS); however, this compound was found to be unstable under extended redox cycling, making it unsuitable for practical applications. This thesis details the examination of a host of organic molecules for use as ECPBs, and their development into practical PEME systems. In the first section of work, several classes of organic compounds were investigated to determine their suitability for different modes of ECPB operation. This included anthraquinone-2,7-disulfonic acid (AQDS), which was found to be exceptionally stable under extended redox cycling, providing a lifetime 17 times greater than the previously published HQS. Biphenyl tetrasulfonic acid (BPTS) was found to have a redox potential of 1.037 V vs. the standard hydrogen electrode (SHE), and was subsequently used in a photoelectrochemical cell (PEC). This PEC was able to operate at currents of 0.9 mA∙cm−2 under 1 Sun illumination with zero applied external bias, and the removal of H2 production from the cell eliminates the possibility of explosive gas combinations forming. A sulfonated viologen molecule ((SPr)2V), was found to have a redox potential of −0.392 V vs. SHE, making it capable, in theory, of evolving H2 spontaneously from the reduced solution. Unfortunately, this was not possible due to the chemical stability of the compound. Organic molecules with high pKa functional groups were then investigated at high pH, in the hope of identifying the first ECPB for alkaline water splitting. Although no suitable molecule was identified in the course of this research, the work detailed here provides a solid foundation for future studies. In the second section of work, an ECPB-mediated PEME cell was developed for the first time. This system utilised the AQDS molecule identified in the first section, implementing it into a dual cell PEME which produced H2 and O2 in separate locations. This electrolyser was shown to operate at a similar level to a conventional PEME (in excess of 1.5 A∙cm−2), while producing H2 at higher purity and without cross contamination of the product gases. Through operating the cells independently of one another, H2 was able to be produced at current densities of up to 3.71 A∙cm−2 at 2.0 V. In the third section, similar systems were constructed using the polyoxometalate ECPBs, phosphomolybdic acid (PMA) and silicotungstic acid (STA). These systems were developed to a similar level as the AQDS electrolyser, before being directly compared in terms of performance and cost. Although the conventional PEME was found to have the highest voltage efficiency of the four systems (78.65% at 1 A∙cm−2), it was also found to have the lowest Faradaic efficiency (92.82%), and was the only system examined where crossover of the product gases was observed. Of the three ECPB-based systems, the AQDS PEME was found to have the highest voltage efficiency (54.70% at 1 A∙cm−2) and Faradaic efficiency (>99%), as well as being able to operate at the highest current densities. A mole-for-mole cost-comparison of the different ECPBs revealed AQDS to be just 2.11% and 1.02% of the cost of PMA and STA, respectively. In the final results section, the AQDS PEME was adapted so that the AQDS oxidation cell provided an energy output instead of producing H2, thereby moving away from water splitting and towards electrochemical energy storage. The system developed here is a hybrid between redox flow battery and fuel cell technology, utilising a rechargeable liquid electrolyte alongside the H2O/O2 redox couple. Charging the device proceeded in the same manner as O2 evolution in the AQDS PEME, but the subsequent oxidation of AQDS was then coupled to O2 reduction (forming H2O) instead of proton reduction (forming H2). The system was developed to produce a maximum power density of 124 mW∙cm−2, with a great deal of scope for further improvements.
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Richardson, Caleb 1792?-1820. "Production of phosphorus alloys through thermal reactions and electrochemical reduction of molten apatite." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/131003.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, May, 2020Cataloged from the official PDF version of thesis.
Includes bibliographical references (pages 32-34).
A process for extracting phosphorus from fluorapatite through high temperature electrochemical means. Theoretical modelling and calculations show that P-alloys can be manufactured directly from decomposed molten fluorapatite. Nickel-phosphide is chosen as an examplary alloy both for its incredible thermodynamic stability and for its mechanical properties. Molten hydroxyapatite decomposes as it melts into two solid phosphorus rich phases, tricalcium phosphate and tetracalcium phosphate. Fluourapatite behaves in a similar manner, albeit at a higher temperature. These two calcium phosphates can be reduced to calcium oxide and oxygen in the presence of nickel, forming Ni₃P. Included in this paper is an in-depth overview of current and past phosphorus reduction methods and a discussion of their improvement.
by Caleb Richardson.
S.B.
S.B. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Rodene, Dylan D. "Engineering of Earth-Abundant Electrochemical Catalysts." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6106.
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Alternative energy research into hydrogen production via water electrolysis addresses environmental and sustainability concerns associated with fossil fuel use. Renewable-powered electrolyzers are foreseen to produce hydrogen if energy and cost requirements are achieved. Electrocatalysts reduce the energy requirements of operating electrolyzers by lowering the reaction kinetics at the electrodes. Platinum group metals (PGMs) tend to be utilized as electrocatalysts but are not readily available and are expensive. Ni1-xMox alloys, as low-cost and earth-abundant transition metal nanoparticles (NPs), are emerging as promising electrocatalyst candidates to replace expensive PGM catalysts in alkaline media. Pure-phase cubic and hexagonal Ni1-xMox alloy NPs with increasing Mo content (0–11.4%) were synthesized as electrocatalysts for the hydrogen evolution reaction (HER). In general, an increase in HER activity was observed with increasing Mo content. The cubic alloys were found to exhibit significantly higher HER activity in comparison to the hexagonal alloys, attributed to the higher Mo content in the cubic alloys. However, the compositions with similar Mo content still favored the cubic phase for higher activity. To produce a current density of -10 mA/cm2, the cubic and hexagonal alloy NPs require over-potentials ranging from -62 to -177 mV and -162 to -242 mV, respectively. The cubic alloys exhibited over-potentials that rival commercial Pt-based electrocatalysts (-68 to -129 mV at -10 mA/cm2). The cubic Ni0.934Mo0.066 alloy NPs showed the highest alkaline HER activity of the electrocatalysts studied and therefore a patent application was submitted.
Bulk Ni–Mo phases have been known as electrocatalysts for the HER for decades, while recently transition metal phosphides (TMPs) have emerged as stable and efficient PGM alternatives. Specifically, Ni2P has demonstrated good HER activity and improved stability for both alkaline and acidic media. However, Ni2P electrocatalysts are a compromise between earth-abundance, performance (lower than Ni–Mo and PGMs) and stability. For the first time Ni–Mo–P electrocatalysts were synthesized with varying atomic ratios of Mo as electrocatalysts for alkaline HER. Specific phases, compositions and morphologies were studied to understand the intrinsic properties of TMPs leading to high HER activity. The Ni1.87Mo0.13P and Ni10.83Mo1.17P5 NPs were shown to be stable for 10 h at –10 mA cm-2 with over-potentials of –96 and –82 mV in alkaline media, respectively. The Ni1.87Mo0.13P and Ni10.83Mo1.17P5 NPs exhibited an improved performance over the synthesized Ni2P sample (–126 mV at –10 mA cm-2), likely a result of the overall phosphorous content and hetero-structured morphologies. A strong correlation between phase dependence and the influence of Mo on HER activity needs to be further investigated.
Furthermore, understanding the intrinsic properties of electrocatalysts leading to high water splitting performance and stability can apply electrocatalysts in other research applications, such as photoelectrochemical (PEC) water splitting, water remediation and sustainable chemical processing applications. Contributions to photocatalytic water remediation and electrochemical chlorinated generation to halogenate pyridone-based molecules are reported. Electrochemical techniques were developed and reported herein to aid in understanding electrochemical performance, chemical mechanisms and the stability of electrocatalysts at the electrode-electrolyte interfaces.
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Wiencke, Jan-Christian. "Analysis of the electrochemical processes during the production of liquid iron by Molten Oxide Electrolysis." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0329.
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L'électrolyse en milieu oxydes fondus (MOE) peut être envisagée comme une nouvelle technologie de l’industrie sidérurgique pour la production de fer liquide sans émission de CO2. Dans ce concept, l'électrolyse est utilisée pour produire de l’oxygène gazeux et du fer liquide à des températures supérieures à 1810 K. Dans cette étude sont présentées les principales réactions électrochimiques lors de l’électrolyse en milieu fondu (MgO-Al2O3-SiO2). Une quantité importante de fer liquide a été produite lors d'électrolyses conduites pendant plusieurs heures. L'analyse MEB-EDS du dépôt a révélé un alliage de fer métallique quasi pur, uniquement contaminé par le matériau cathodique. Ce résultat traduit une sélectivité élevée du procédé électrolytique. L'étude de la réponse de l'électrolyte en fonction de la tension électrique et de la concentration de fer a révélé une limitation par la diffusion lors de l’électrolyse de bains de faibles concentrations en oxyde de fer, et à des potentiels inférieurs à 1,5 V. La demi-réaction de la cathode a été identifiée comme la réduction du fer ferreux en fer métallique. L’extrapolation des droites de Tafel sur les courbes courant-tension corrigées de la chute ohmique a conduit à des coefficients de transfert (de la réaction cathodique) proches à 0,6. L’ordre de réaction de réduction de FeII en Fe0 a été évalué autour de 1. L'analyse de la demi-réaction anodique dans les oxydes fondus à faible teneur en fer a montré que les premières espèces éctroactives sont les anions oxydes libres. Pour des tensions électriques croissantes, le transport des anions O2- libres devient limité et le transfert de charge est partiellement attribué à l’oxydation du fer ferreux. Au contraire, dans des mélanges d’oxydes fondus à concentrations élevées en fer, le transfert de charge est réalisé dans toute la gamme de tension par l'oxydation du fer ferreux. C’est seulement à haute tension, que l’oxydation des anions oxyde contribue au transfert des charges. Dans l'ensemble des compositions testées, aucune limitation du courant n’a été observée sur la réaction anodiqueMolten oxide electrolysis (MOE) is an ambitious technique for the production of liquid iron by the use of renewable energies and thus lower CO2 emissions in the steel industry. In this concept, electrolysis is used to produce gaseous O2 and liquid iron metal at temperatures above 1810 K. In the experimental study presented here the key-parameters of the electrochemical reactions in a magnesio-aluminosilicate electrolyte and at the electrodes during MOE are investigated. A significant amount of liquid iron metal was produced during experiments of several hours. SEM-EDS analysis of the deposit revealed an alloy of iron metal and of the cathode material, which thereby indicates high process selectivity. Investigation of the electrolyte’s response in dependence of cell voltage and iron concentration inferred a diffusional limitation at low iron oxide concentrations at potentials below 1.5 V. The cathode half-reaction was identified as the reduction of ferrous iron to liquid iron metal. Using Tafel interpretation reaction-transfer coefficients close to 0.6 and an order of reaction around 1 were determined. The analysis of the anode half-reaction showed that in low iron bearing molten oxides, oxide anions were firstly oxidized into O2 gas. At high iron concentrations the charge transfer is conducted in the entire cell voltage range by the oxidation of ferrous iron. The participation of oxide anions in the charge transfer was only witnessed at high cell voltages. In the entire compositional range a limitation of the measured current due to the anode half reaction was not observed
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Bauer, Ralph Aaron. "Inorganic membranes for power generation and oxygen production." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556889103215598.
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Skar, Rolf Alexander. "Chemical and Electrochemical Characterisation of Oxide/Hydroxide Impurities in the Electrolyte for Magnesium Production." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-104.
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This work is part of a research program where the aim is to develop an
electroanalytical technique to determine the amount of dissolved oxide and hydroxide in industrial Mg electrolytes. The systems studied were mixtures of MgCl2 and NaCl, ranging from pure MgCl2 to melts containing 10 mole % MgCl2 / 90 mole % NaCl. To these melts, additions of MgO and MgOHCl were done at temperatures ranging from 475 to 850°C. Voltammetric measurements were performed before and after addition of MgO or MgOHCl and melt samples were taken for analysis. The quenched melt samples wereanalysed by carbothermal reduction analysis and the acid consumption method to obtain the O2- and OH- contents in the samples. Linear sweep voltammetry was performed with a sweep rate of 200 mV/sec in two potential regions to detect the concentration of dissolved MgOHCl and MgO. The experiments were performed inside a glove box having water and oxygen contents of, respectively, <1 ppm and <2 ppm. The results indicate that the rate of decomposition of MgOHCl increases with increasing temperature, as expected. In melts with high content of NaCl the underpotential deposition of sodium has a large influence on the uncertainty in the reading of the current density of MgOHCl reduction. Linear relations between MgO and MgOHCl concentrations and the peak current densities for the electrochemical reactions of the dissolved MgO and MgOHCl species in the melt, respectively, were observed. The diffusion coefficients of MgO and MgOHCl in the different melts were calculated. The diffusion coefficients decrease with increasing content of MgCl2. For MgOHCl the diffusion coefficient decreases from 5.6*10-5 cm2/sec in 20 mole % MgCl2 / 80 mole % NaCl to 2.1*10-5 cm2/sec in pure MgCl2, both measurements done at 800°C. For MgO the diffusion coefficient decreases from 6*10-5 cm2/sec in 41.5 mole % MgCl2 / 58.5 mole % NaCl to 0.8*10-5 cm2/sec in pure MgCl2, both measurements done at 730°C. The results show that it is possible to use cyclic voltammetry for quantitative analysis of MgOHCl in MgCl2 based melts.
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Jeong, Yeon Uk. "Solution-based chemical synthesis of electrode materials for electrochemical power sources /." Digital version:, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p9992829.
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Rautenbach, Daniel. "The development of an electrochemical process for the production of para-substituted di-hydroxy benzenes." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/159.
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The project was concerned with the investigation of the electrochemical oxidation of various phenols, and to develop a viable reaction system for the production of the respective hydroquinones. Current production routes utilizing phenol as starting material have the limitations of using large amounts of acids, having to be stopped at low conversions and producing a mixture of the hydroquinones and catechols. Of the possible routes to the respective hydroquinones from the various phenols, the electrochemical oxidation of these phenols offers commercial and environmental advantages and hence formed the theme of the investigation. The synthetic possibilities proved to be more prevalent in a system when the electrochemical oxidation of these phenols was performed in an aqueous medium utilizing an organic co-solvent. Results obtained during this investigation made it possible to make certain predications about the mechanism taking place. This was found to depend on the anode material used for the oxidation. The results showed that the process developed for the electrochemical oxidation of these phenols, yields mainly the para-isomers of the respective hydroquinones and benzoquinones in good yields and selectivities, with fair current efficiencies and good mass balances at high conversions. For example: * Phenol (batch) 8 F: 345% current efficiency, 70% hydroquinone, 6% catechol, 9% benzoquinone, 9% phenol and 94 mass balance. * 2-Tert-butylphenol (flow) 10 F: 37% current efficiency, 65% hydroquinone, 33% benzoquinone, 2% phenol and 100% mass balance. * 2,6-Di-tert-butylphenol (flow) 11 F: 23% current efficiency, 92 % hydroquinone, 6% benzoquinone, 1% phenol and 99% mass balance. The developed electrochemical oxidation system offers the following advantages over previous and current methods: simplified isolation and extraction procedures, smaller amounts of acid usage, reasonably selective synthesis of the para-isomer and a less corrosive system all at high conversions.
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Byrne, C. S. C. "The modelling of a reaction and reactor for the electrochemical production of geraniol and nerol." Thesis, University of Newcastle Upon Tyne, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371252.
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Eskandari, Azin. "A preliminary theoretical and experimental study of a photo-electrochemical cell for solar hydrogen production." Thesis, Université Clermont Auvergne (2017-2020), 2019. http://www.theses.fr/2019CLFAC104.
Full textAbstract:
Afin de relever le défi énergétique et climatique du 21ième siècle qui s’annonce, une solution consiste, pour valoriser la ressource solaire, à mettre au point des procédés de production de vecteurs énergétiques stockables par photosynthèse artificielle permettant la synthèse de carburants solaires, en particulier l’hydrogène. La compréhension de ses procédés et l’obtention de performances cinétiques et énergétiques élevées nécessitent le développement de modèles de connaissance génériques, robustes et prédictifs considérant le transfert de rayonnement comme processus physique contrôlant le procédé à plusieurs échelles mais aussi les différents autres phénomènes intervenant dans la structure ou la réification du modèle.Dans le cadre de ce travail de doctorat, le procédé photo-réactif au cœur de l’étude était la cellule photo-électrochimique. D’un fonctionnement plus complexe que le simple photoréacteur, avec une photo-anode et une (photo)cathode, la cellule photo-électrochimique dissocie spatialement les étapes d’oxydation et de réduction. En se basant à la fois sur la littérature existante (essentiellement dans le domaine de l’électrochimie) et en déployant les outils développés par l’équipe de recherche sur le transfert de rayonnement et la formulation du couplage thermocinétique, il a été possible d’établir des indicateurs de performance des cellules photo-électrochimiques.En parallèle de l’établissement de ce modèle, une démarche expérimentale a été entreprise en se basant tout d’abord sur une cellule commerciale de type Grätzel (DS-PEC) indiquant les tendances générales de tels convertisseurs de l’énergie des photons avec en particulier une chute de l’efficacité énergétique en fonction de la densité incidente de flux de photons. Un dispositif expérimental modulable (Minucell) a aussi été développé et validé afin de caractériser des photo-anodes de différentes compositions comme des électrodes de TiO2 imprégnées de chromophore pour un fonctionnement en cellule de Grätzel ou bien des électrodes d’hématite Fe2O3 (SC-PEC) où le semiconducteur joue à la fois les fonctions d’absorption des photons et de conduction des porteurs de charges. Surtout, le dispositif Minucell a permis de tester, caractériser et modéliser le comportement d’une cellule photo-électrochimique de type bio-inspiré pour la production d’H2 utilisant à la photo-anode un catalyseur moléculaire Ru-RuCat (développé par ICMMO Orsay/CEA Saclay) et à la cathode un catalyseur CoTAA (développé par LCEMCA Brest). Minucell a été utilisé pour caractériser chaque élément constitutif d’une cellule photo-électrochimique puis la cellule dans son ensemble, confirmant les tendances et observations obtenues sur les efficacités énergétiques.Ce travail préliminaire ouvre de très nombreuses perspectives de recherche, il pose des bases communes entre électrochimie et génie des systèmes photo-réactifs et donne des pistes quant à la conception et l’optimisation cinétique et énergétique des cellules photo-électrochimiques pour la production d’hydrogène et de carburants solairesIn order to meet the energy and climate challenge of the coming 21st century, one solution consists of developing processes for producing storable energy carriers by artificial photosynthesis to synthesize solar fuels, in particular hydrogen, in order to valorize the solar resource. The understanding of these processes and the achievement of high kinetic and energetic performances require the development of generic, robust and predictive knowledge models considering radiative transfer as a physical process controlling the process at several scales but also including the various other phenomena involved in the structure or reification of the model.In this PhD work, the photo-reactive process at the heart of the study was the photo-electrochemical cell. More complex than the simple photoreactor, with a photo-anode and a (photo)cathode, the photo-electrochemical cell spatially dissociates the oxidation and reduction steps. Based both on the existing literature (mainly in the field of electrochemistry) and by deploying the tools developed by the research team on radiative transfer and thermokinetic coupling formulation, it was possible to establish performance indicators of photo-electrochemical cells.In parallel to the establishment of this model, an experimental approach was undertaken based first on a commercial Grätzel-type cell (DS-PEC) indicating the general trends of such photon energy converters with in particular a drop in energy efficiency as a function of the incident photon flux density. A modular experimental device (Minucell) has also been developed and validated in order to characterize photo-anodes of different compositions such as chromophore impregnated TiO2 electrodes for operation in Grätzel cells or Fe2O3 hematite electrodes (SC-PEC) where the semiconductor plays both the functions of photon absorption and charge carrier conduction. Above all, the Minucell device allowed to test, characterize and model the behavior of a bio-inspired photo-electrochemical cell for H2 production using at the photo-anode a Ru-RuCat molecular catalyst (developed by ICMMO Orsay/CEA Saclay) and at the cathode a CoTAA catalyst (developed by LCEMCA Brest). Minucell was used to characterize each constituent element of a photo-electrochemical cell and then the cell as a whole confirming the trends and observations obtained on energy efficiencies.This preliminary work opens up a wide range of research prospects, lays common ground between electrochemistry and photo-reactive systems engineering, and provides insights into the design and kinetic and energy optimization of photo-electrochemical cells for the production of hydrogen and solar fuels
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Zhang, Yubai. "Electrochemical synthesis of 2D materials and their applications in energy storage." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/410071.
Full textAbstract:
2D materials have inspired the intrigue of researchers and industries for its potential to improve the performance of existing materials in energy storage field. However, wide application of 2D material such as graphene and transition metal dichalcogenides in batteries is not implemented since the tremendous challenges and issues, the quality, quantity, and cost concerns impede its commercialization. Electrochemical approach performs as a controllable and scalable method for exfoliating, expanding, and functionalizing the pristine bulk materials on-demand. Sodium ion batteries, a promising candidate for lithium ion batteries, and aqueous zinc ion batteries, a safe energy storage system have received considerable attention in recent decades. The research herein focuses on the electrochemical exfoliation of graphite for its application in sodium ion battery anode, adopting the electrochemical graphene oxide (EGO) as functional agent combining with vanadium oxide for aqueous zinc ion battery cathode, and electrochemical production of molybdenum disulfide in a packed bed reactor.
The PhD thesis generally is composed of three parts. In the first part, graphite is exfoliated and oxidized in a packed bed reactor. The effects of boron doping and oxidation on the graphene-based material were studied for high performance sodium ion battery anode respectively in Chapter 2 and Chapter 3. The electrochemical route from natural graphite to graphene oxide is investigated in terms of concentration of acid electrolyte (sulfuric acid). It was found that 12 M sulfuric acid reacted graphene oxide could deliver higher capacity of sodium ion battery than other concentrations. Boron doped graphene was synthesized by a twostep reaction, electrochemical fabrication of the tetraborate anions intercalated graphite oxide followed by reduction by annealing at 900 °C for 3 h under Ar gas. It was found that the boron doped graphene containing 0.21 at. % of boron was highly defective delivers a good capacity of 129.59 mAh g-1 at the current density of 100 mA g-1 and a long-term cyclic stability under current density of 500 mA g-1 retaining 100.20 mA g-1 after 800 cycles. The battery performance of boron doped graphene is better than that without boron doping.
To further improve the sodium ion battery anode performance, mildly reduced graphite oxide with layered structure was synthesized by a simple electrochemical oxidation of expanded graphite followed by mildly heating reduction as reported in Chapter 3. The irrigated pipe in the expanded graphite packed bed assists with diffusion of electrolyte. A fast thermal reduction at 150 °C for 20 min on the electrochemical graphite oxide achieves a controlled deoxygenation and maintaining of the large interlayer gap of the product for high sodium storage capacity. The thermally processed electrochemically produced graphite oxide could deliver a high reversible capacity of 268 mAh g-1 at a current density of 100 mA g-1, and 163 mAh g-1 at a high current density of 500 mA g-1 and a good capacity retaining capability (in average 0.0198% loss per cycle) over 2000 cycles.
In the second part, the EGO was integrated with vanadium oxide as cathode material for aqueous zinc ion battery. A simple spray dry method is applied to generate electrode materials, which is catering to industrial production. The aqueous mixture for spray drying is formed by quenching the molten V2O5. The products received after spray drying is vanadium oxide hydrate of amorphous structure. The zinc ion storage performance is investigated in terms of content of graphene oxide in the composite. The fabricated amorphous V2O5-EGO composite xerogel with 2D heterostructure possesses high zinc ion storage capability, high rate performance and stable cycling stability due to the functionality of graphene embedded in the composite material.
In the third part, inspired by the common intercalation electrochemistry of graphite and transition metal dichalcogenide, exfoliation for 2D MoS2 from its bulk crystal powder is investigated by using the packed bed set up. Organic solvent is found to be a critical factor in the electrochemical activation and the mechanical exfoliation process. The MoS2 bulk crystal can be exfoliated to few-layer nanosheets with stable solution dispersibility. This finding further broadens the horizon of electrochemical production of transition metal dichalcogenides through a scalable approach of electrochemical reaction in packed bed.
To sum up, this PhD thesis represents a huge step forward for EGO applications in sodium ion battery anode and aqueous zinc ion battery cathode. In addition, it develops a scalable production of vanadium oxide/graphene material by the spray dry method. The utility of the packed bed electrochemical reactor is extended to transition metal dichalcogenide MoS2. This work will be a valuable guidance for adoption of graphene, vanadium oxide, and MoS2 in the market of energy storage materials.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Science
Science, Environment, Engineering and Technology
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Taheri, Najafabadi Amin. "High-yield production of graphene sheets by graphite electro-exfoliation for application in electrochemical power sources." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/59330.
Full textAbstract:
This thesis first aims at developing an electrochemical approach for low temperature, simple, and cost-effective synthesis of graphene microsheets (GNs) using graphitic electrodes in ionic liquid (IL) medium. The second major focus involves the products application as cathode-modifying microporous layers (MPLs) in proton exchange membrane fuel cells (PEMFCs) as well as anode-modifying materials in microbial fuel cells (MFCs). For the electrochemical exfoliation, a novel IL/acetonitrile electrolyte is introduced, and investigated with low concentration of ionic liquids. Using iso-molded graphite rod as the anode, up to 86% of exfoliation was achieved with the majority of the products as graphene flakes in addition to smaller quantities of carbonaceous particles and rolled sheets. Moreover, the simultaneous anodic and cathodic GN production was developed here with a synergistic exfoliation effect. When graphitic anode and cathode were subjected to a constant cell potential, up to 3 times higher exfoliation yields were generated compared to single-electrode studies on each side (~6-fold improvement in total). Thorough materials characterization confirmed the production of ultrathin GNs (< 5 layers) on both electrodes, with cathodic sheets being relatively larger and less functionalized. On the application side, the successful integration of GNs in MPLs resulted in enhanced PEMFC performance over a wide range of operating conditions. GN-based MPLs improved performance in the kinetic and ohmic regions of the polarization curve, while the addition of carbon black (CB), particularly Vulcan XC72, to form a composite GN+CB MPL, further extended the improvement to the mass transport limiting region. This was reflected by an approximate 30% and 70% increase in peak power densities compared to CB and GN MPLs, respectively, at the relative humidity (RH) of 100%. Despite the presence of CB, GN+CB MPLs also retained their superior performance at a much lower RH of 20%, thereby widening the peak power gap with CB MPLs to 80%. On the other side, the functionalized GN-modified carbon cloth anodes integrated within single-chamber MFCs generated an over four-fold improvement in peak power density compared to the plain carbon cloth (2.85 W m-² vs 0.66 W m-², respectively), exceeding the previously reported values with graphene anodes.Applied Science, Faculty of
Graduate
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Nota, Monica. "Electrochemical oxidation of Kraft lignin for the production of value-added chemicals on Ni and Co electrocatalysts." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21706/.
Full textAbstract:
La vanillina è un’aldeide aromatica importante da un punto di vista industriale, in quanto viene ampiamente utilizzata dall’industria alimentare, cosmetica e farmaceutica. Attualmente, la vanillina da biomasse viene ottenuta attraverso l’ossidazione catalitica della lignina. Un’alternativa è rappresentata dall’ossidazione elettro-catalitica, un processo che sta riscuotendo un notevole interesse, perché permette di lavorare in condizioni blande. L’obiettivo di questo lavoro è stato quello di sintetizzare elettro-catalizzatori che favoriscano la depolimerizzazione della lignina Kraft per ottenere selettivamente vanillina. Sono state utilizzate schiume di Ni a cella aperta, tal quali e elettro-depositate con idrossidi di Ni-Co e Co. La formazione degli osso-idrossidi dei metalli, sulla superficie delle schiume, e la OER contribuiscono all’elettro-ossidazione della lignina, mentre la resa di vanillina dipende sia dal catalizzatore che dalle condizioni di reazione (potenziale applicato e tempo di reazione). La resa maggiore di vanillina è stata ottenuta applicando 0.6 V vs SCE con un tempo di reazione di un’ora e utilizzando la schiuma di Ni bare come catalizzatore. Indipendentemente dal tipo di catalizzatore usato, aumentando il tempo di reazione la resa di vanillina diminuisce, probabilmente a causa delle reazioni di ri-condensazione e ossidazione successiva dei prodotti che coinvolgono la vanillina stessa. La presenza di idrossidi di Ni-Co e Co sulla schiuma di Ni non ne migliora l’attività catalitica. La schiuma Co/Ni esibisce un’elevata carica accumulata e un’alta conversione, probabilmente dovuto alle reazioni parassite che sfavoriscono l’accumulo di vanillina. Le schiume Ni-Co/Ni invece, presentando sia una resa in vanillina intermedia tra le altre due ma associata ad una carica accumulata molto bassa. Un risultato incoraggiante per possibili sviluppi futuri.
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Das, Gupta R. "The electrochemical production of filled carbon nanotubes and their use as anode materials in lithium-ion batteries." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598289.
Full textAbstract:
This thesis examines the electrochemical production of filled carbon nanotubes and their application in lithium-ion batteries. Tin filled carbon nanotubes were produced via an electrolysis process in mixed LiCl/SnCl2 electrolytes with graphite electrodes at 775°C. The reaction mechanism of the production process was investigated, in addition to the relationship between the physical and chemical properties of the post-electrolysis product and the experimental method/conditions used. The link between the post-electrolysis product’s composition and morphology and their electrochemical performance in lithium-ion batteries was also analysed in detail. A variety of experimental setups and electrolytic processes were compared. The electrolytic production processes examined included constant current electrolysis, constant voltage electrolysis with respect to a molybdenum pseudo reference and a switching electrolysis with respect to the molybdenum reference using two identical electrodes where the polarity was changed after a set time. The novel switching electrolysis method was examined in most detail due to the superior product and consistency results achieved. An optimised switching electrolysis procedure was developed. To assess their potential use as a lithium-ion battery anode material, the post-electrolysis material containing tin filled carbon nanotubes were examined as the active material in half-cells. The cells were composed of lithium metal foil as the counter electrode and a mixture containing a majority of post electrolysis material along with carbon black, binder and in the case of some cells, graphite, as the working electrode. The post-electrolysis material displayed promising characteristics, with high capacity and stable cycling performance. The post-cycled electrode material was characterised by SEM and HRTEM to assess changes to the morphology of the electrode material resulting from the cycling environment.
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Gmitter, Andrew J. "The influence of inert anode material and electrolyte composition on the electrochemical production of oxygen from molten oxides." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44211.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 109-116).
Shifts in global and political climates have led industries worldwide to search for more environmentally sound processes that are still economically viable. The steel industry is studying the feasibility of molten oxide electrolysis, a novel process by which molten iron and gaseous oxygen are the products; no carbon dioxide is produced at the site of the electrolysis cell. The research presented in this thesis focuses on the anodic reaction and the preliminary development of an inert anode, as well as investigations into the mechanism of the oxygen evolution reaction. Various elements have been considered with the platinum group metals possessing the best combination of physical properties to serve as the inert anode. Cyclic voltammetry at 1575°C was used to compare the candidates. Iridium yielded the highest current density at a given overpotential followed by rhodium and platinum regardless of the composition of the electrolyte. Speculation as to metal oxide intermediate phases formed and mechanisms for the oxygen evolution reaction are discussed. Notably, the basicity of the molten aluminosilicate electrolyte was found to greatly influence the rate of oxygen gas evolution as evidenced by the linear dependence of the current density on optical basicity. This is crucial for the design of a full-scale electrolysis cell as improved kinetics of the anodic reaction will yield higher throughput and/or enhanced power efficiency. Combining our finding of the relationship between current density and basicity with previous authors' contributions on the effect of partial pressure of oxygen, we argue that to a first approximation, the magnitude of the current density is governed by the concentration of free oxide ions and by the partial pressure of oxygen in the headspace above the melt.
(cont.) Lastly, to, in part, address the disparate natures of the interests of steelmakers, glassmakers, geochemists, and electrochemists, the difficulties in performing electrochemical measurements at extremely high temperatures (~1600°C), and the absence of a comprehensive review of the last sixty years of work on oxygen evolution from molten silicates, this thesis is intended to serve as an essential guide for future work in this field.
by Andrew J. Gmitter.
S.M.
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Molefe, Lerato Yvonne. "Polyacrylic acid and polyvinylpyrrolidone stabilised ternary nanoalloys of platinum group metals for the electrochemical production of hydrogen from ammonia." University of the Western Cape, 2016. http://hdl.handle.net/11394/5317.
Full textAbstract:
Masters of ScienceThe electrochemical oxidation of ammonia has attracted much attention as an efficient green method for application in direct ammonia fuel cells (DAFCs) and the production of high purity hydrogen. However, the insufficient performance and high costs of platinum has hindered the large scale application of ammonia (NH₃) electro-oxidation technologies. Therefore, there is a need for the fabrication of efficient electrocatalysts for NH₃ electrooxidation with improved activity and lower Pt loading. Owing to their unique catalytic properties, nanoalloys of platinum group metals (PGMs) are being designated as possible electrocatalysts for NH₃ oxidation. This study presents for the first time a chemical synthesis of unsupported ternary PGM based nanoalloys such as Cu@Pt@Ir with multi-shell structures and Cu-Pt-Ir mixed nanoalloys for electro-catalysis of NH3 oxidation. The nanoalloys were stabilised with polyvinylpyrrolidone (PVP) as the capping agent. The structural properties of the nanoalloys were studied using ultraviolet-visible (UV-Vis) and fourier transform infra-red (FTIR) spectroscopic techniques. The elemental composition, average particle size and morphology of the materials were evaluated by high resolution transmission electron microscopy (HRTEM) coupled to energy dispersive X-ray (EDX) spectroscopy. High resolution scanning electron microscopy (HRSEM) was used for morphological characterisation. Additionally, scanning auger nanoprobe microscopy (NanoSAM) was employed to provide high performance auger (AES) spectral analysis and auger imaging of complex multi-layered Cu@Pt@Ir nanoalloy surface. X-ray diffraction (XRD) spectroscopy was used to investigate the crystallinity of the nanoalloys. The electrochemistry of the nanoalloy materials was interrogated with cyclic voltammetry (CV) and square wave voltammetry (SWV). The electrocatalytic activity of novel Cu-Pt-Ir trimetallic nanoalloys for the oxidation of ammonia was tested using CV. UV-Vis spectroscopy confirmed the complete reduction of the metal precursors to the respective nanoparticles. FTIR spectroscopy confirmed the presence of the PVP polymer as well as formation of a bond between the polymer (PVP) chains and the metal surface for all nanoparticles (NPs). Furthermore, HRTEM confirmed that the small irregular interconnected PVP stabilised Cu@Pt@Ir NPs were about 5 nm in size. The elemental composition of the alloy nanoparticles measured using EDX also confirmed the presence of Cu, Pt and Ir. Cyclic voltammetry indicated that both the GCE|Cu-Pt-Ir NPs and GCE|Cu@Pt@Ir NPs are active electrocatalysts for NH3 oxidation as witnessed by the formation of a well-defined anodic peak around -0.298 V (vs. Ag/AgCl). Thus the GCE|Cu-Pt-Ir NPs was found to be a suitable electrocatalyst that enhances the kinetics of oxidation of ammonia at reduced overpotential and high peak current in comparison with GCE|Cu@Pt@Ir NPs, GCE|Pt NPs, GCE|Ir NPs and GCE|Cu NPs electrocatalysts. The presence of the crystalline phases in each sample was confirmed by XRD analysis. The surface analysis of Cu@Pt@Ir nanoalloy with AES surveys revealed the presence of Pt, Ir and Cu elements in all probed spots suggesting some mixing between the layers of the nanoalloy. Yet, analysis of nanoalloys by CV and XRD confirmed the presence of Cu-Pt and Pt-Ir solid solutions in the Cu-Pt-Ir and Cu@Pt@Ir nanoalloys respectively.
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Duda, Royce D. "Genetic Manipulation and Culturing of Azotobacter vinelandii for the Production of Nitrogenase for Use in Protein-Engineered Electrochemical Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1530282333596752.
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Wilson, Aaron Doyle. "Electrochemical catalysts for the production and oxidation of hydrogen featuring nickel complexes containing cyclic diphosphine ligands with positioned pendant amines." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3207761.
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Mejia, Rodriguez Ma del Rosario. "Ligand effects on bioinspired iron complexes." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2504.
Full textAbstract:
The synthesis of diiron thiolate complexes was carried out using two ligands
that were expected to furnish improved catalytic activity, solubility in water, and
stability to the metal complexes. The water-soluble phosphine 1,3,5-triaza-7-
phosphaadamantane, PTA, coordinates to the Fe centers forming the disubstituted
complex (m-pdt)[Fe(CO)2PTA]2, which presents one PTA in each iron in a transoid
arrangement. Substitution of one CO ligand in the (m-pdt)[Fe(CO)3]2 parent complex
forms the asymmetric (m-pdt)[Fe(CO)3][Fe(CO)2PTA]. Enhanced water solubility was
achieved through reactions with electrophiles, H+ and CH3
+, which reacted with the N
on the PTA ligand forming the protonated and methylated derivatives, respectively.
The 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IMes, was reacted with
(m-pdt)[Fe(CO)3]2 yielding the asymmetric (m-pdt)[Fe(CO)3][Fe(CO)2IMes], an
electron rich, air stable complex that does not show reactivity with H+.
Electrocatalytic production of hydrogen was studied for the all-CO, bis-PMe3,
mono- and di-PTA FeIFeI complexes, as well as the PTA-protonated and -methylated
derivatives. The all-CO species produce H2, in the presence of the weak HOAc, at their second reduction event, FeIFe0 ?? Fe0Fe0, that occurs at ca. ??1.9 V, through an
EECC mechanism. The mono- and di-substituted phosphine complexes present
electrocatalytic production of H2 from the Fe0FeI redox state; this reduction takes place
at ??1.54 V for (m-pdt)[Fe(CO)3][Fe(CO)2PTA], and at ca. ??1.8 for the disubstituted
PMe3 and PTA derivatives. A positive charge on the starting complex does not have
an effect on the production of H2. It was found that the protonated and methylated
derivatives are not the catalytic species for H2 production. At their first reduction event
the neutral precursor forms, and catalysis occurs from the FeIFeI complex in all cases.
The possibility of enhanced catalytic activity in the presence of H2 O was
explored by conducting electrochemical experiments in the mixed CH3CN:H2O solvent
system for the PTA-substituted complexes. The reduction potential of the catalytic
peak is shifted to more positive values by the presence of H2 O. The cyclic
voltammogram of {(m-pdt)[Fe(CO)2(PTA?? H)]2}2+ in CH3CN:H2O 3:1 shows the
reduction of a more easily reduced species in the return scan. This curve-crossing
event provides evidence for the (h2-H2)FeII intermediate proposed in the ECCE
mechanism.
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Вороніна, Олена Володимирівна. "Електродні процеси на сплавах та сполуках ванадію в водневій енергетиці." Thesis, НТУ "ХПІ", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/38323.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.03 – технічна електрохімія. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2018 р.
Дисертація присвячена розробці технологічного процесу виробництва водню з використанням нових електродних матеріалів на основі ванадієвих сплавів і алюмінієвих сплавів. Матеріал електрода на основі ванадію виключає утворення феритів при лужному електролізі. Алюмінієві сплави виключають виділення кисню на анодах через корозійний процес з деполяризацією водню. Тому на обох електродах можна виділяти водень на електролізерах без мембрани при електролізі лужної води. Досліджені основні показники анодних процесів на сплаві алюмінію АМЦ в лужних розчинах з домішками хлоридів. В інтервалах густин струму 1-5 А/дм² та температурах 18-20 ⁰С розчинення сплаву забезпечується негативними потенціалами. При збільшенні швидкості розчинення в умовах анодної поляризації потенціал аноду зміщується в позитивну область на 150-200 мВ. Керування гальваностатичним режимом електролізу в досліджуваних розчинах дозволяє збільшити швидкість виділення водню при розчиненні сплаву за рахунок прискорення дифузійних процесів в анодному просторі та забезпечення відведення продуктів електролізу в прианодному шарі. Визначено кінетичні залежності і механізми виділення водню на алюмінієвих сплавах, що призводить до зменшення перенапруги реакції виділення водню на катодах і утворення водню на анодах шляхом розчинення алюмінію. Наведено дослідно-промислові випробування безкисневого електросинтезу на вдосконалених електролізерах при напругах електролізу 0,3-1 В. Це дозволяє знизити матеріальні та енергетичні витрати на електроліз.Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.17.03 – Technical Electrochemistry. – National Technical University "Kharkiv Polytechnical Institute", Kharkiv, 2018. The thesis deals with the development of the technological process of hydrogen production using new electrode materials based on vanadium alloys and aluminum alloys. The vanadium based electrode material exclude the formation of ferrites in alkaline electrolysis. Aluminum alloys exclude the oxygen evolution on the anodes due to the corrosion process with hydrogen depolarization. Therefore it is possible to produce hydrogen on both electrodes in electrolyzers without membrane in alkaline water electrolysis. The kinetic dependences and mechanisms of hydrogen evolution on aluminum alloys have been determined, which leads to the reduce of overvoltage of hydrogen evolution reaction on cathodes and produce hydrogen on anodes by aluminum dissolving. Experimental-industrial tests of oxygen-free hydrogen production in developed electrolyzers at cell voltages of 0.3-1 V are presented. This allows to reduce the material and energy costs of electrolysis.
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Вороніна, Олена Володимирівна. "Електродні процеси на сплавах та сполуках ванадію в водневій енергетиці." Thesis, НТУ "ХПІ", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/38316.
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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.03 – технічна електрохімія. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2018 р.
Дисертація присвячена розробці технологічного процесу виробництва водню з використанням нових електродних матеріалів на основі ванадієвих сплавів і алюмінієвих сплавів. Матеріал електрода на основі ванадію виключає утворення феритів при лужному електролізі. Алюмінієві сплави виключають виділення кисню на анодах через корозійний процес з деполяризацією водню. Тому на обох електродах можна виділяти водень на електролізерах без мембрани при електролізі лужної води. Досліджені основні показники анодних процесів на сплаві алюмінію АМЦ в лужних розчинах з домішками хлоридів. В інтервалах густин струму 1-5 А/дм² та температурах 18-20 ⁰С розчинення сплаву забезпечується негативними потенціалами. При збільшенні швидкості розчинення в умовах анодної поляризації потенціал аноду зміщується в позитивну область на 150-200 мВ. Керування гальваностатичним режимом електролізу в досліджуваних розчинах дозволяє збільшити швидкість виділення водню при розчиненні сплаву за рахунок прискорення дифузійних процесів в анодному просторі та забезпечення відведення продуктів електролізу в прианодному шарі. Визначено кінетичні залежності і механізми виділення водню на алюмінієвих сплавах, що призводить до зменшення перенапруги реакції виділення водню на катодах і утворення водню на анодах шляхом розчинення алюмінію. Наведено дослідно-промислові випробування безкисневого електросинтезу на вдосконалених електролізерах при напругах електролізу 0,3-1 В. Це дозволяє знизити матеріальні та
енергетичні витрати на електроліз.Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.17.03 – Technical Electrochemistry. – National Technical University "Kharkiv Polytechnical Institute", Kharkiv, 2018. The thesis deals with the development of the technological process of hydrogen production using new electrode materials based on vanadium alloys and aluminum alloys. The vanadium based electrode material exclude the formation of ferrites in alkaline electrolysis. Aluminum alloys exclude the oxygen evolution on the anodes due to the corrosion process with hydrogen depolarization. Therefore it is possible to produce hydrogen on both electrodes in electrolyzers without membrane in alkaline water electrolysis. The kinetic dependences and mechanisms of hydrogen evolution on aluminum alloys have been determined, which leads to the reduce of overvoltage of hydrogen evolution reaction on cathodes and produce hydrogen on anodes by aluminum dissolving. Experimental-industrial tests of oxygen-free hydrogen production in developed electrolyzers at cell voltages of 0.3-1 V are presented. This allows to reduce the material and energy costs of electrolysis.
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Naderinasrabadi, Mahtab. "A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight Aromatic Compounds and Cogeneration of Hydrogen." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1584622583669502.
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Witkowska, Malgorzata Danuta. "Interrogation of the manufacturing route of aluminium AA 1050 used in lithographic application." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/interogation-of-the-manufacturing-route-of-aluminium-aa-1050-used-in-lithographic-application(57658930-cb45-470e-b6ab-626781f1c8a2).html.
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The aluminium AA1050 alloy, known as commercially pure aluminium, contains 99.5% Al, together with Fe and Si as major alloying elements. During fabrication of aluminium substrates for lithographic printing plates in Bridgnorth Aluminium Ltd, the AA 1050 aluminium alloy proceeds through various stages of thermomechanical processing, with the conditions at each processing stage influencing the microstructure of the final coil. Because of its specific gravity, tensile strength, surface performance and coating adhesion behaviour, the AA 1050 aluminium alloy is one of the preferred materials for offset printing, which has been the dominant printing process for years. During manufacturing of the offset plate, the AA 1050 alloy is subjected to alkaline etching, electrograining and anodizing. Reactivity of the material to those chemical and electrochemical processes depends on various alloy properties, the thickness and composition of oxide film over the macroscopic alloy surface, cold work applied and the presence of second phase particles, which influence properties and quality of the final product.During the project, the main objectives were to understand the process in the production of the final product from slab to coil as well as to investigate some microstructural changes during the following stages of the production process and, finally, the performance behaviour of the final product.The set of experiments, including microstructural observation and electrochemical tests, has been developed to investigate the AA 1050 aluminium sheet in accordance with the objective of this study. Four homogenisation trials in the industry environment were performed to enable sample collection from the real production line; also, samples from each processing stage were examined with the special attention paid to those collected during the plant experimental homogenisation trials. It was found that the microstructure of the aluminium changed throughout the different production stages and influences the material response in the alkaline solution used for etching. Furthermore, the conditions of homogenisation (time and temperature) have impact on the properties like the electrochemical behaviour in alkaline and acid solutions, as well as the microstructure of the final aluminium sheet. Differentiation between the behaviour of final gauge samples was possible in terms of characterisation of the second phase particles characterisation (distribution and composition) present in the resultant alloy product.
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Yu, Wenchao. "Development of nanostructured materials based on manganese oxides and produced by an electrochemical method for water electrolysis." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066383/document.
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Le mécanisme élémentaire de l'électrodépôt de films de MnO2 fût étudié sur des électrodes de Pt massif dans des électrolytes aqueux. Il se révèle être une réaction multi-étapes sensible au pH et à la force ionique. La chronoampérométrie couplée à des électrolytes neutres peu concentrés favorise l'électrodépôt de films stables de MnO2. Le FTO est un meilleur substrat que l'ITO parce qu'il présente une activité électrochimique plus élevée et favorise la stabilité mécanique de films électrodéposés de MnO2. De plus, le potentiel d'électrodépôt influence à la fois la structure et la morphologie des films de MnO2. Les films amorphes de MnO2 obtenus à potentiel élevé possèdent une activité électrocatalytique et une stabilité plus élevées que la birnessite. Un traitement thermique peut améliorer amplement leur activité électrocatalytique et leur stabilité mécanique. Une transition de phase des films de MnO2 apparaît à 500 °C. Leur morphologie change de façon dramatique après chauffage au-delà de cette température. Les échantillons chauffés à 500 °C ont la meilleure activité électrocatalytique pour l'OER. Les cations Na+, K+, Ca2+ and Mg2+ sont insérés en petites quantités dans la structure des films de MnO2 au cours de la démarche d'électrodépôt, mais ils influencent néanmoins la structure et la morphologie des films. Finalement, les films de birnessite ou amorphes apparaissent comme des candidats prometteurs en tant que catalyseurs pour la dissociation photoélectrochimique de la dissociation de l'eau, puisqu'ils génèrent des photocourants considérables sous lumière solaire. Pour cela, des films de MnO2 épais, amorphes et recuits à 500 °C produisent les meilleures performancesThe basic electrodeposition mechanism of MnO2 films was studied first on bulk Pt electrodes in various aqueous electrolytes. It was revealed that MnO2 electrodeposition is a multi-step reaction that is sensitive to pH and ionic strength. Chronoamperometry coupled to low concentration neutral aqueous solutions favors the electrodeposition of stable MnO2 films. FTO was found to be a better substrate than ITO, because it has a higher electrochemical activity and could enhance the mechanical stability of electrodeposited MnO2 films. Moreover, the potential used for electrodeposition has great influence on both the structure and the morphology of MnO2 films. Amorphous MnO2 films obtained at high potential possess higher electrocatalytic activity and stability than the birnessite-type MnO2 variety. The heat treatment can greatly enhance the electrocatalytic activity and mechanical stability. A phase transition of MnO2 films appears at 500 °C. The morphology changes dramatically after heating above this temperature. Samples heated at 500 °C are found to have the best electrocatalytic activity towards OER. Na+, K+, Ca2+ and Mg2+ cations were found to be inserted in small amounts into the structure of MnO2 films during the electrodeposition procedure but they influence the structure and morphology of the films. Finally, birnessite type and amorphous MnO2 films appear to be promising candidates as catalysts for photoelectrochemical water splitting, as they are able to generate considerable photocurrents under solar light illumination. In this purpose, thick and amorphous films with 500 °C heat treatment are supposed to produce the best performances
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Sikorskytė, Aušra. "Auginimo technologijų įtaka 'Elise' obuolių kokybei." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2007. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2007~D_20070816_153932-61327.
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Sikorskytė A. Auginimo technologijų įtaka 'Elise' obuolių kokybei: Ekologijos specialybės agroekologijos specializacijos magistro darbas / Vadovė V. Rutkovienė; LŽŪU. – K., 2007 – 54 p.: 16 pav., 15 lentelių, 2 priedai. Bibliogr.: 63 pav.
SANTRAUKA
Magistratūros studijų baigiamajame darbe tiriama auginimo technologijų įtaka Elise obuolių kokybei.
Darbo objektas – Malus genties augalo vienos Elise veislės vaisiai, brandinami obelų, kurios auga Kauno kolegijos Kraštotvarkos fakulteto mokomajame – pomologiniame sode (Mastaičiai, Kauno r.). Minėtos veislės obelys auginamos ekologinėmis ir įprastinėmis sąlygomis.
Darbo tikslas – įvertinti auginimo technologijų įtaką Elise obuolių kokybei.
Darbo metodai – eksperimentinis, atlikti elektrocheminiai ir cheminiai kokybės tyrimai, mokslinės literatūros ir tyrimo duomenų analizė.
Darbo rezultatai. Įprastinėmis ir ekologinėmis sąlygomis augintų obuolių kokybė vertinta pagal elektrocheminius, fizinius ir cheminius parametrus. Nustatyta, kad gausesnį derlių subrandino įprastinėmis sąlygomis augančios obelys.
Nustatyti koreliaciniai ryšiai tarp elektrocheminių ir fizinių parametrų: stiprūs atvirkštiniai ryšiai yra tarp vaisiaus skersmens (r =-0,88), masės (r =-0,77) ir elektrinio laidžio; atvirkštiniai koreliaciniai ryšiai tarp vaisiaus skersmens ir P vertės (r = -0,85) bei vidutinio stiprumo atvirkštiniai koreliaciniai ryšiai tarp vaisiaus masės ir P vertės (r = -0,67).
Esminiai skirtumai nustatyti tarp cheminės sudėties (bendrojo... [toliau žr. visą tekstą]Sikorskytė A. Growing technologies influence on quality of apple ‘Elise’: the final work of Master’s Degree Studies of Agro ecology specialisation of Ecology speciality/ Supervisor V. Rutkovienė; LŽŪU. – K., 2007 – 54 pages: 16 pictures, 15 tables, 2 annexes, 63 literature sources. SUMMARY The final work of Master Degree Studies is based on the research of influence of growing technologies on quality of apple variety Elise. The object of the final work – As an object of the research fruits of one variety Elise of genus Malus plants were selected. Following plants are growing in the educational – phomological garden of Landscape faculty of college of Kaunas (Mastaičiai, Kaunas district). Apple trees of variety Elise are grown under organic and conventional conditions. The aim of the final work – to evaluate the influence of growing technologies on the quality of apple fruits Elise. Methods of the final work – experimental; electrochemical and chemical research of quality has been made; the analysis of science literature and data of research. Result of the final work. The quality of organic farming and conventionally grown apple fruits has been evaluated according to electrochemical, physical and chemical characteristics. Judging by the results obtained the yield from conventional apple trees has been bigger then those grown by the organic farming. The correlation between electrochemical and physical results has been obtained as follows: strong converse relations are among... [to full text]
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Cooper, Matthew E. "Energy Production from Coal Syngas Containing H2S via Solid Oxide Fuel Cells Utilizing Lanthanum Strontium Vanadate Anodes." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1219867679.
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Gallagher, Kevin Gregory. "Challenges in low-temperature fuel cells." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/37264.
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Low-temperature fuel cells (LTFC) such as phosphoric acid fuel cells (PAFC) and proton exchange membrane fuel cells (PEMFC) are a promising electrochemical energy system for the conversion of hydrogen to electricity. Many challenges must be overcome before commercialization is possible. This dissertation focuses on the degradation of carbon catalyst supports and PEMFC water management. Kinetic studies are presented on the structure-reactivity relationship including an in-depth study of commercially available and model carbons. A mechanism and numerical model of the electrochemical oxidation of graphene-based carbon is proposed to explain longstanding questions. Three mechanisms are concluded to contribute to the current decay commonly observed during electrochemical oxidation: mass loss, reversible passive oxide formation, and irreversible oxide formation. Water uptake and electro-osmosis are investigated to improve the understanding and aid modeling of water transport in PEMFCs below 0 °C. The implication of an electro-osmotic drag coefficient less than unity is discussed in terms of proton transport mechanisms. Capillary pressure saturation relations are presented for carbon fiber paper which can both be used as gas-diffusion layers in PEMFCs. Boundary and scanning curves for imbibition and drainage are measured to further understanding of the hysteresis observed during PEMFC operation.
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Bateni, Fazel. "Development of Non-precious Metal and Metal Oxide Electrocatalysts for an Alkaline Lignin Electrolysis Process." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1562674707447307.
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Mensah, Joel B. [Verfasser], Regina Akademischer Betreuer] Palkovits, and Lars Mathias [Akademischer Betreuer] [Blank. "Chemo-catalytic and electrochemical deoxygenation of bio-derivable 3-hydroxydecanoic acid : production of drop-in fuels and fine chemicals / Joel Boakye Mensah ; Regina Palkovits, Lars M. Blank." Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/1226303811/34.
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Gueneau, de Mussy Jean Paul. "Production and study of a Ti/Ti02/Noble metal anode." Doctoral thesis, Universite Libre de Bruxelles, 2002. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211348.
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Plusieurs métaux de notre vie courante sont obtenus industriellement au moyen de procédés électrolytiques. Un des procédés les plus communs est l’électro-obtention de cuivre, dans lequel le métal est déposé à la cathode tandis que l'oxygène se dégage à l'anode. Généralement, en usine, plusieurs anodes et cathodes, ayant une surface de 1 m2 et séparées par plus ou moins 10 cm sont alternées dans une cellule contenant une solution d'acide sulfurique riche en sulfate de cuivre. En fonction des conditions d'utilisation, les cathodes sont remplacées, après un certain temps, par des nouvelles de façon à récupérer le cuivre déposé. De ce fait, les anodes doivent être capables de résister sans se corroder, se déformer ou perdre leurs propriétés électrocatalytiques pendant de longues périodes. Au début, des alliages en Pb (pb-Ag, Pb-Ca-Sn,) ont été utilisés comme anodes. Malheureusement, malgré leur faible prix, ces anodes présentent des surtensions élevées et une faible résistance à la corrosion et au fluage. Par conséquent, une alternative aux anodes traditionnelles en 1 développée. Ce nouveau type d'anode, connu sous le nom d’anode dimensionnellement stable (DSA) est fabriquée à partir d'une tôle en Ti recouverte par un mélange d'oxydes de métaux nobles catalysant la réaction de dégagement d'oxygène. Différentes techniques peuvent être utilisées pour préparer la couche d'oxyde. La technique la plus souvent employée consiste à décomposer thermiquement une solution de chlorures contenant un ou plusieurs nobles. Malheureusement, ce type d'anode est cher et a tendance à perdre son activité électrocatalytique avec le temps.
Dans le but de produire une DSA à faible prix, pouvant résister de longues périodes sans se passiver, un nouveau type de DSA a été développé dans le présent travail. Cette anode est produite par électrodépôt d'un métal noble dans les pores d'un substrat microporeux en Ti/TiO2.
Ce travail a permis de démontrer qu'une DSA avec une concentration en métal noble peut être obtenue par la voie proposée. Il a été montré que les propriétés électriques et électrochimiques de ces DSAs sont directement liées aux caractéristiques morphologiques et structurales du en Ti/TiO2. Lorsque la couche barrière existant au fond des pores est suffisamment fine et que le film présente des défauts, la résistance me l'interface Ti/métal noble est faible. Ceci abouti à des DSAs possédant d'excellentes propriétés électrocatalytiques. Les DSAs optimales sont capables de résister à des conditions similaires à celles employées en industrie avec des surtensions de ~ 0.4 V, ce qui représente un gain de 50% par rapport aux surtensions normalement atteintes par les anodes traditionnelles en Pb.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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Tatin, Arnaud. "Electrochemical CO2 splitting into CO and O2 in neutral water using earth-abundant materials : from molecular catalysts to a whole electrolyzer." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC164/document.
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L'énergie électrique (de préférence d’origine renouvelable) peut être stockée dans des liaisons chimiques grâce à un électrolyseur approprié. Les réactions typiques comprennent la production d'hydrogène, la production d'hydrocarbures et la synthèse d'ammoniac. Ces électrocarburants permettent de faciliter l'intégration de sources d'énergie renouvelables dans le mix de production électrique. Ils sont compatibles avec l'infrastructure industrielle actuelle et la chaîne d'approvisionnement et peuvent être stockés facilement. En outre, ce procédé est à la fois un moyen de stocker l'électricité dans des liaisons chimiques (vecteurs énergétiques) et une technique de synthèse de composés chimiques à partir de matières premières comme le CO2 plutôt que de ressources fossiles.La thèse s’intéresse au développement de nouveaux catalyseurs moléculaires pour la conversion sélective du CO2 en CO en utilisant uniquement des matériaux abondants sur Terre, comme les porphyrines de Fer. Tout d'abord, les tentatives pour obtenir de nouveaux catalyseurs avec divers substituants sont détaillées. Une fois qu'un catalyseur hydrosoluble actif est identifié, une évaluation des performances est réalisée en utilisant des techniques électrochimiques telles que la voltammétrie cycliqueElectrical energy (preferably issued from renewable sources) can be stored in chemical bonds thanks to an appropriate electrolyzer. Typical reactions include hydrogen generation, the production of hydrocarbons and oxygenates, and ammonia synthesis. Such electrofuels supplement the integration of renewable energy sources in the electrical production mix; they are compatible with the current industrial infrastructure and supply chain, while they can be stored easily. Besides, they may be used either as a means to store the electricity in the chemical bonds of high-energy-content molecules or as various feedstocks to manufacture high value compounds.The thesis focused on the development of new molecular catalysts for the selective CO2-to-CO conversion in water using only earth-abundant materials, namely iron-based porphyrin derivatives. First, successful and unsuccessful attempts to derive new catalysts with various substituents are reviewed. Once an active water-soluble catalyst is identified, a performance assessment is completed using electrochemical techniques such as cyclic voltammetry investigations.Then, the immobilization of said catalysts onto the electrode surface is discussed. Once a robust integration in the catalytic film is secured, the coupling with a heterogeneous water-oxidation catalyst can be considered. The subsequent assembly of a whole electrolysis cell is reported, where a cobalt-based film was picked for the anode. Finally, economic perspectives provide a clear, rational basis for future optimization of the device
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Gross, Pierre-Alexandre. "Modification de nanotubes de TiO2 pour la production d’hydrogène par photodissociation de l’eau sous lumière solaire." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAF053.
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Ce travail de thèse traite de la production d’hydrogène par le procédé de photoélectrocatalyse en utilisant une photoanode à base de nanotubes de TiO2 verticalement alignés. L’utilisation du TiO2 étant limité pour des applications solaires en raison de son large gap, il est nécessaire de le modifier. Deux approches sont proposées pour modifier les nanotubes de TiO2 et leur permettre d’absorber la lumière visible. La première est une modification chimique du TiO2 par co-dopage cationique-anionique (Ta-N) ou (Nb-N). Les cations sont insérés durant la croissance des nanotubes grâce à une approche inédite, et l’azote est inséré durant le traitement thermique. Ceci a pour effet la formation d’orbitales hybrides qui entraîne une réduction du gap et une activité sous lumière visible, tout en permettant une stabilité de la structure. La seconde approche consiste à déposer des nanoparticules d’Ag sur la surface des nanotubes de TiO2. Grâce au contrôle de la morphologie des nanoparticules d’Ag, leur résonnance plasmonique permet de stimuler l’absorption du TiO2 et ainsi d’augmenter son rendement à la fois sous lumière UV et sous lumière visibleThis work is about the production of hydrogen by photoelectrocatalysis using a vertically aligned TiO2 nanotubes based photoanode. Utilization of TiO2 for solar applications is limited due to its large band gap, it has to be modified. Two approaches are proposed for the modification of the TiO2 nanotubes to make them absorb visible light. The first one is the chemical modification of the TiO2 by (Ta-N) or (Nb-N) cationic-anionic co-doping. Cations are inserted during the growth of the nanotubes by a novel approach, and nitrogen is inserted during heat treatment. This leads to the formation of hybrid orbitals resulting in a band gap reduction and of activity under visible light. The second approach consists of the deposition of Ag nanoparticles on the surface of the TiO2 nanotubes. Thanks to the control of the morphology of the Ag nanoparticles, their plasmonic resonance can enhance the absorption of TiO2 and thus increase its activity both under UV and visible light
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Nechache, Aziz. "Mise en place et développement d'un outil de diagnostic in situ basé sur la spectroscopie d'impédance électrochimique pour l'étude des électrolyseurs haute température à oxyde solide." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066137.
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Un outil de diagnostic in situ pour l'étude des électrolyseurs à oxyde solide, fondé sur la spectroscopie d'impédance électrochimique, a été mis en place à travers une analyse systématique de l'influence de plusieurs paramètres (densité de courant, température, composition et débit des gaz) sur les performances et le comportement d'une monocellule commerciale dans une configuration à 2 électrodes. Les principaux phénomènes régissant le fonctionnement de la cellule ont été identifiés. Une analyse de son comportement après apparition et évolution dans le temps d'une dégradation prématurée, suite à une modification sur le banc d'essai, a été réalisée. Un mécanisme expliquant l'origine et les conséquences de cette dégradation prématurée a été proposé. Une étude sur l'influence de l'épaisseur d'une des deux électrodes de la cellule a par ailleurs permis de distinguer deux des phénomènes principaux liés à la diffusion de H2O à l'électrode Ni-YSZ. Enfin, l'étude du comportement de la cellule après dégradation par conduction électronique de l'électrolyte YSZ a mis en évidence la formation de porosités entrainant notamment des délaminations à l'interface YSZ/YDC. Un état de dégradation plus avancé que pour les tests précédents a été observé pour les couches YDC et Ni-YSZ. Ce phénomène se manifeste par un déplacement en fréquence de l'ensemble du diagramme d'impédance mesuré vers les plus basses fréquences, formant une boucle négative. Rp finit par disparaitre, le courant circulant alors majoritairement via la conduction électronique de l'électrolyte YSZAn in situ diagnosis tool, based on electrochemical impedance spectroscopy, for the study of solid oxide electrolyzer cells was established through the analysis of the influence of several parameters (current density, temperature, gas composition and gas flow rate) on the performances and the behavior of a commercial single cell studied in a two-electrode configuration. The main phenomena governing the cell were identified. An analysis of its behavior after appearance and evolution with time of a premature degradation was carried out. A mechanism explaining the origin and the consequences of such degradation was suggested. Furthermore, studying the influence of the cathode thickness allowed distinguishing two of the main phenomena associated to H2O diffusion at the Ni-YSZ electrode. In addition, a study of the cell behavior after degradation by electronic conduction of the YSZ electrolyte showed formation of numerous porosities leading to delaminations at the YSZ/YDC interface. This phenomenon was characterized by a shift of the overall impedance diagram to the lowest frequencies, with appearance of a negative loop which finally leads to the disappearance of Rp as the current circulates mostly via electronic conduction of the YSZ electrolyte
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Lapinsonnière, Laure. "Contribution à l'évaluation et à l'optimisation des application des systèmes microbio-électrochimiques : traitement des eaux, production d'électricité, bioélectrosynthèse." Phd thesis, Université Rennes 1, 2013. http://tel.archives-ouvertes.fr/tel-01002645.
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Les systèmes microbioélectrochimiques exploitent le métabolisme de microorganismes particuliers afin de catalyser des réactions d'oxydoréduction. Ces microorganismes organisés en biofilms à l'anode ou à la cathode sont en général des bactéries dites électroactives et peuvent être exploités dans une multitude d'applications. Une revue bibliographique des aspects fondamentaux et applicatifs de ce domaine est présentée. La génération d'électricité couplée à l'épuration d'eaux usées à l'anode de piles à combustible microbiologiques a été étudiée. Des bioanodes développées à partir d'acétate (substrat non fermentescible) sont capables de s'adapter et de dégrader le glucose et le lactose (substrats fermentescibles). Leur adaptation et leurs performances dépendent de la maturité du biofilm, du substrat et du renouvellement régulier de l'anolyte. Les propriétés physico-chimiques de la surface des électrodes ont été modulées afin de promouvoir la connexion de biofilms. A l'anode, nous avons étudié le greffage covalent d'acides phényle boroniques susceptibles de se complexer avec des glucides de la membrane externe des bactéries. Cette fonctionnalisation permet de réduire le temps de formation des biofilms et d'en améliorer les performances électriques sur graphite et sur nanotubes de carbone à parois multiples. A la cathode, les modifications de surface connues sur les bioanodes n'ont pas démontré d'influence sur les performances des biocathodes. Les différentes phases du développement de biocathodes catalysant la réduction du dioxygène à haut potentiel ont été étudiées. Le suivi de biocathodes réduisant le CO2 en acides organiques montre une production séquentielle d'acides organiques à chaîne aliphatique de plus en plus longue.
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Allanore, Antoine. "Étude expérimentale de la production de fer électrolytique en milieu alcalin : mécanisme de réduction des oxydes et développement d'une cellule." Thesis, Vandoeuvre-les-Nancy, INPL, 2007. http://www.theses.fr/2007INPL109N/document.
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Le fer est l'un des rares métaux qui ne soit pas produit industriellement par électrolyse. Pour aider au développement d'un tel procédé pour l'acier, l'électrolyse des oxydes de fer en milieu sodique est examinée, selon deux approches. La première démarche consiste en l'étude expérimentale du mécanisme réactionnel. L'électrochimie des ions indique qu'il est possible de produire du métal par électrodéposition en milieu alcalin. Parallèlement, l'étude de la réduction d'une particule d'oxyde hématite révèle qu'elle subit, lors de sa conversion en fer métallique, une transformation macroscopique en phase solide. Les analyses démontrent la formation de magnétite comme intermédiaire réactionnel. La seconde démarche est dédiée à la production du fer métallique, par électrolyse d'une suspension de particules d'oxyde dans diverses configurations de cellules. L'incidence des paramètres de procédé a été établie et permet de proposer des éléments de conception d'une cellule industrielleIron is one of the few metals which is not industrially produced by electrolysis. The electrowinning of iron metal from its oxides in alkaline solution has been studied to develop such an ironmaking route. Two approaches have been adopted. The first one concerns the evaluation of the reaction mechanism. The study of iron ions electrochemistry in alkaline media shows that the electrodeposition of iron metal is possible. The study of a single iron oxide particle reduction reveals that a reaction of the hematite solid phase is possible. The analysis of a partially converted particle proves that magnetite is formed as an intermediate. The second field of study is dedicated to the production of iron metal in various electrochemical cells, using a suspension electrolysis process. The influence of the key operating parameters is established to assess the possible scale-up. All these elements are gathered to propose the main features of an industrial cell dedicated to the reaction
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Chauveau, Florent. "Synthèse et caractérisations électrochimiques de nouveaux matériaux pour anodes d'électrolyseurs à haute température." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13944/document.
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L’électrolyse de la vapeur d’eau à haute température (EHT) est une voie permettant de produire de l’hydrogène d’une grande pureté et avec un fort rendement, ceci sans émission de CO2. Un des verrous actuels de cette technologie est la forte surtension associée à la réaction d’oxydation des ions O2- qui se déroule à l’électrode à oxygène (anode). L’objectif de ce travail était de concevoir de nouveaux matériaux d’anode possédant des propriétés de conductivité mixte (i.e. électronique et ionique), dans le but d’obtenir des surfaces de réaction plus importantes afin de diminuer cette surtension. A cet effet, une étude comparative a été réalisée sur huit oxydes (ferrites et nickelates de terres rares). Après synthèse et mise en forme, ces matériaux ont fait l’objet de caractérisations physico-chimiques puis électrochimiques en demi-cellules symétriques sous atmosphère unique afin de déterminer ceux présentant les meilleures propriétés sous courant nul et sous polarisation anodique. Quatre composés de structure dérivée de type K2NiF4 ont ainsi été sélectionnés pour être caractérisés de façon plus approfondie en cellules complètes à électrolyte support en conditions EHT (750 - 850°C). Il a ainsi été possible d’obtenir, pour une tension de cellule de 1,3 V une densité de courant de 0,9 A/cm² à 850°C, soit près de deux fois plus qu’avec une cellule identique comportant comme matériau d’anode un composite commercial optimisé à base de LaMnO3 substitué au strontiumHigh temperature steam electrolysis (HTSE) is a way to produce hydrogen with a high purity, with noteworthy efficiency and without CO2 emission. Nowadays, a blocking point concerning this technology is the high overvoltage related to the oxidation of the O2- ions occurring at the oxygen electrode (anode). The aim of this work was to design new anode materials with mixed conducting properties (i.e. electronic and ionic), in order to obtain larger reaction areas and to lessen this overvoltage. In this aim, eight compounds (ferrites and rare earth nickelates) were investigated. After synthesis and shaping, these compounds were characterized using physical, chemical and electrochemical analyses in symmetrical half cells, under single atmosphere, in order to determine which ones have the best properties under zero current and under anodic polarization. Four compounds of structure derived from K2NiF4-type were then selected to be more accurately characterized in complete electrolyte supported cells, under HTSE conditions (750 - 850°C). It was then possible to obtain, for a 1.3 V cell voltage, a current density of 0.9 A/cm² at 850°C, which is nearly two times larger than the one obtained with a same cell including a commercial composite material based on strontium substituted LaMnO3 as anode
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Gueret, Robin. "Systèmes moléculaires pour la production d'hydrogène photo-induite dans l'eau associant des catalyseurs de cobalt à un photosensibilisateur de ruthénium ou un colorant organique." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAV074/document.
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Les travaux de cette thèse sont centrés sur le développement de systèmes moléculaires en solution homogène pour la production photocatalytique de dihydrogène dans l'eau utilisant des catalyseurs de cobalt à ligands pentadentate tétrapyridinique ou tétra- et pentaaza macrocycliques. Associés au photosensibilisateur et à l’ascorbate comme donneur d’électron sacrificiel, les complexes à ligands macrocycliques présentent d’excellentes performances pour la production d’H2, bien supérieures à celles des complexes à ligands polypyridiniques en termes d’efficacité et de stabilité, en raison de la grande stabilité de leur état réduit «Co(I)». Enfin, [Ru(bpy)3]2+ a pu être substitué par un colorant organique très robuste du type triazatriangulénium conduisant à un système photocatalytique encore plus performant. Ces résultats démontrent que les colorants organiques sont une alternative viable aux photosensibilisateurs à base de métaux nobles, même en milieu aqueux acideThe work of this manuscript is focused on the design of molecular systems in homogeneous solution for photocatalytic production of molecular hydrogen in water using cobalt catalysts with pentadentate tetrapyridinic and tetra- and pentaza macrocyclic ligands. In association with [Ru(bpy)3]2+ as photosensitizer and sodium ascorbate as sacrificial electron donor, the macrocycle based catalysts display high performances for H2 production, far exceeding those of the polypyridine based catalysts, both in terms of activity and stability, because of the stability of their reduced state «Co(I)». Finally, [Ru(bpy)3]2+ was successfully substituted with a robust organic dye belonging to the triazatriangulenium family, leading to an even more efficient photocatalytic system. These results demonstrate well that organic dyes are a truly efficient alternative to noble metal based photosensitizers, even in acidic aqueous medium
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Smith, Elliott Ryan. "Electrochemical, Spectroscopic, and Theoretical Studies on the Effects of Exchanging Se for S in the 2FeE (E= S or Se) Butterfly Core and Modifications to the µ-E to µ-E Linkers in [FeFe]-Hydrogenase Inspired Electrocatalysts for H₂ Production." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/312561.
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Molecular hydrogen has been proposed as an energy store to help meet the world's ever increasing demand for clean energy because the oxidation product (produced by either combustion or in a fuel cell) results in the formation of water. To realize this goal, energy efficient catalysts comprised of earth abundant elements must be used. The work in this dissertation describes investigations of diiron dichalcogen catalysts used for proton reduction. These complexes are inspired by the active site of the [FeFe]-hydrogenase enzyme. Catalysts were extensively studied with cyclic voltammetry in conjunction with photoelectron spectroscopy and density functional theory calculations in order to determine the effects that bridging ligands and 2Fe2E (E = S or Se) core substitutions have on the electronic structure and catalytic ability of these complexes. The complex µ-(pyrazine-2,3-dithiolato)diironhexacarbonyl (pyrazine-cat) was prepared and found to catalyze proton reduction at a -0.49 V overpotential, which represents a 16% decrease over the previously studied complex µ-(benzene-1,2-dithiolato)diironhexacarbonyl (benz-cat). Electrochemical investigations in conjunction with DFT calculations indicated the possibility of two mechanisms for proton reduction, both of the ECEC type. The first mechanism is Fe-based and analogous to the mechanism reported for benz-cat. The second is a nitrogen-based mechanism which occurs at more negative potentials than the Fe-based mechanism. Overall, pyrazine-cat maintained the ability to mediate successive redox states similar to benz-cat and the electron withdrawing nature of the pyrazine caused the initial reduction to occur at a lower potential than benz-cat. Ultimately this results in the decreased overpotential for catalytic proton reduction by pyrazine-cat. Investigations of the electronic structure and catalytic ability of complexes of the type (µ-ECH₂XCH₂E-µ)Fe₂(CO)₆ where E = S or Se and X = CH₂, S or Se were also carried out. All complexes were found to catalyze H₂ production from acetic acid in acetonitrile. DFT calculations indicate that when X = S or Se the HOMO changes character from predominatly metal based (X = CH2) to containing significant chalcogen lone pair character. The presence of the chalcogen lone pair character helps to facilitate a rotated structure in either the oxidized or reduced forms of these complexes. Through computations it was found that oxidation of the X = S or Se complexes results in a CO ligand rotating into a semi-bridging position, which opens a vacant site on one of the Fe-centers. The bridgehead bends toward this vacant site donating electron density greatly stabilizing the cation and more interestingly forming a structure which strongly resembles the active site of the [FeFe]-hydorgenase. Complexes which contain a chalcogen in the bridgehead undergo potential inversion, leading to a two-electron initial reduction. This is in part due to electron-electron repulsion between chalcogen lone pair electrons and the reduced Fe-centers, which leads to the formation of a rotated dianion.Complexes with the general structure (µ-E (CH₂)nE-µ)Fe₂ (CO)₆ where E = S or Se and n = 3, 4, or 5 were investigated using cyclic voltammetry, photoelectron spectroscopy, and DFT calculations. Substitution of Se in the 2Fe2E core for S resulted in a lengthening of the FeFe bond. As the linker length increased from n =3 to 5, one of the apical CO's is pushed down due to a steric interaction creating a more obtuse Fe-Fe-C angle. Larger effects of the linker length were seen in the oxidation and reduction chemistry. CV and UPS show that linker length has little effect on the oxidation potential or onset ionization energy. Computations predict that the oxidized structure is rotated, and as the linker length increases there is an agostic interaction which forms between a methylene proton and the vacant site on the rotated Fe-center. Reduction potentials for these complexes are found to decrease with increasing linker length, which was attributed to the steric interaction between the alkane linker and the apical CO helping to facilitate rotation of the anion. Interestingly catalytic potentials were found to depend almost entirely on chalcogen character in the 2Fe2E core, with S-containing catalysts having a lower catalytic potential than Se-containing catalysts. The long known complex [η⁵-CpFe(CO)SMe]₂ was investigated as both a proton reduction and H₂ oxidation catalyst. Reduction of [η⁵-CpFe(CO)SMe]₂ revealed that the complex undergoes a two electron irreversible reduction and the reduced species precipitates onto the glassy carbon electrode surface. The new species on the electrode surface facilitates proton reduction at a -0.3 V overpotential, which is significantly lower (0.9 V) than the most similar complex Fp₂. Unlike previous catalysts of this type, [η⁵-CpFe(CO)SMe]₂ catalytic current does not decrease as overpotential decreases. [η⁵-CpFe(CO)SMe]₂ was also shown to undergo two one-electron oxidations, and in the presence of H₂ and the dication, appears to oxidize H₂. The ability of [η⁵-CpFe(CO)SMe]₂ to both oxidize H₂ and reduce protons to H₂ addresses a known deficiency for catalysts mimicking the function of the active site of the [FeFe]-hydrogenase.