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1
Stemp, Michael C. "Homogeneous catalysis in alkaline water electrolysis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0019/MQ45844.pdf.
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Engel, Johanna Ph D. Massachusetts Institute of Technology. "Advanced photoanodes for photoassisted water electrolysis." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89856.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
127
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 189-199).
With continuously growing energy demands, alternative, emission-free solar energy solutions become ever more attractive. However, to achieve sustainability, efficient conversion and storage of solar energy is imperative. Photoelectrolysis harnesses solar energy to evolve hydrogen and oxygen from water, thereby enabling energy storage via chemical means. Hematite or [alpha]-Fe₂O₃ has emerged as a highly promising photoanode candidate for photoelectrochemical cells. While significant improvements in its performance have recently been achieved, it remains unclear why the maximum photocurrents still remain well below their theoretical predictions. This study investigates the defect chemistry and conduction mechanism of hematite in order to understand and improve this material's shortcomings. A defect model for donor doped hematite was derived and its predictions conformed by the electrical conductivity of ilmenite hematite solid solution bulk samples as a function of temperature and oxygen partial pressure. The enthalpies of the Schottky defect formation and the reduction reaction for hematite were determined as 13.4 eV and 5.4 eV, respectively. In addition, a temperature independent value for the electron mobility of 0.10 cm2/Vs for 1% Ti donor doped hematite was derived. Furthermore, the electrical conductivity of nanometer scale, epitaxially grown thin films of the ilmenite hematite solid solution system was characterized by electrical impedance spectroscopy. This work reports a detailed correlation between the electrical conductivity of the undoped hematite, the 1 atom% Ti doped hematite and the thin films with higher ilmenite content and the conditions under which they were annealed (20° C=/< T =/< 800° c and 10-4 atm =/< po2 =/< atm). Hematite's room temperature conductivity can be increased from ~10-11 S/cm for undoped hematite films by as much as nine orders of magnitude by doping with the Ti donor. Furthermore, by controlling the non-stoichiometry of Ti-doped hematite, one can tune its conductivity by up to five orders of magnitude. Depending on processing conditions, donor dopants in hematite may be compensated largely by electrons or by ionic defects (Fe vacancies). The electron mobility of the film was determined to be temperature independent at 0.01 cm2/Vs for the < 0001 > epitaxial film containing a Ti donor density of 4.0 x 1020 cm-3. Finally, the photoelectrochemical performance of these materials was tested by cyclic voltammetry and measurements of their quantum efficiencies. The 1% Ti doped hematite thin film exhibited the highest photocurrent density of these dense, thin films at 0.9mA/cm2 with an applied bias of 1.5V vs. RHE. The IPCE of this sample reached 15% at wavelengths between 300nm and 350nm after an annealing treatment at 580° for 36 h. The solid solution containing 33% ilmenite preformed nearly as well as the doped hematite. The performance decreased with higher ilmenite concentrations in the solid solution. For all samples containing any ilmenite, the onset potential shifted to lower values by ~200mV after the annealing treatment. The increase in charge carrier density upon reduction of Ti doped hematite was conformed by a Mott-Schottky analysis of the hematite/electrolyte interface. In contrast, only minor changes in the carrier density were observed when reducing an undoped hematite photoanode. Changes in slope of the Mott-Schottky plots revealed the presence of deep trap states in the hematite films. In-situ UV-vis spectroscopy displayed a pronounced optical signature corresponding to the existence of such deep levels. These results highlight the importance of carefully controlling photoanode processing conditions, even when operating within the material's extrinsic dopant regime, and more generally, provide a model for the electronic properties of semiconducting metal oxide photoanodes.
by Johanna Engel.
Ph. D.
3
Kopecek, Radovan. "Electrolysis of Titanium in Heavy Water." PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/5023.
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The purpose of these studies was to determine if results similar to those of Fleischmann and Pons could be obtained using a titanium cathode instead of palladium in an electrolysis in a heavy water cell. The electrolyte consists of D20 and H2S04• Two experiments have been performed to examine the features of this electrolysis. As titanium shows the same properties to attract hydrogen, it seemed possible that excess heat could be produced. Radiation was monitored, and the surface of the titanium cathode was examined before and after electrolysis for any changes in the morphology and composition, hoping to discover new elements that can be created only by fusion reactions in the cell, i.e. by transmutation. The heat and radiation effects have been evaluated in comparison to a control cell, using the same electrolyte and current. The only difference was the cathode, which was of platinum. It appears that excess heat is produced during electrolyses of heavy water with a titanium cathode. The amount of this excess heat was 750 cal in a one hour period, an energy gain of 44%. No significant emission of any of the products associated with a "classical" deuterium-deuterium fusion was observed during either experiment, i.e. heat but no radiation. Unexpected elements were found in both experiments, i.e. K. Cr, Fe, Ni and Zn. Remarkable is the fact that the new elements always occur very close in the periodic table to an impurity element, i.e. Cu and Zn.
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Zaczek, Christoph. "Electrolysis of Palladium in Heavy Water." PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/5051.
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Following several reports in the past few years about compositional changes on palladium used as a cathode in heavy water electrolysis, the purpose of this research project was to reproduce this results. Two experiments were performed using two cells connected in series, an experimental cell and a control cell. Both experiments used platinum anodes, the experimental cell had a palladium cathode and the control cell had a platinum cathode. The electrolyte was D20 with H2S04. Radiation was monitored during both experiments. Also temperature and voltage were recorded for both experiments, to allow statements about excess heat of the experimental cell in comparison to the control cell. Both experiments had problems with unequal electrolyte loss, so that no statements about excess heat could be made. No significant radiation was detected in either experiment. Also no compositional changes on the palladium cathodes after electrolysis in both experiments could be detected. Impurities in grain-shaped defects on the palladium cathode before the experiment were found in either experiment. These impurities were Si, Ca, 0, and sometimes also Mg, Na and Fe. Localized findings of Au and Pt, in a distance of 1-2μm to each other, were made on the palladium cathode from the second experiment before electrolysis. Spot, grain-shaped and longitudinal defects were found on the original palladium foil used for the cathodes in either experiment No evidence for fusion, or any other nuclear reaction in the crystal lattice of palladium, used as cathode in heavy water electrolysis, was observed.
5
Sathe, Nilesh. "Assessment of coal and graphite electrolysis." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1147975951.
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Rasten, Egil. "Electrocatalysis in water electrolysis with solid polymerelectrolyte." 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-1177.
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Development and optimization of the electrodes in a water electrolysis system using a polymer membrane as electrolyte have been carried out in this work. A cell voltage of 1.59 V (energy consumption of about 3.8 kWh/Nm3 H2) has been obtained at practical operation conditions of the electrolysis cell (10 kA ·m−2, 90 ◦C) using a total noble metal loading of less than 2.4 mg·cm−2 and a Nafion ® -115 membrane. It is further shown that a cell voltage of less than 1.5 V is possible at the same conditions by combination of the best electrodes obtained in this work.
The most important limitation of the electrolysis system using polymer membrane as electrolyte has proven to be the electrical conductivity of the catalysts due to the porous backing/current collector system, which increases the length of the current path and decreases the cross section compared to the apparent one. A careful compromise must therefore be obtained between electrical conductivity and active surface area, which can be taylored by preparation and annealing conditions of the metal oxide catalysts.
Anode catalysts of different properties have been developed. The mixed oxide of Ir-Ta (85 mole% Ir) was found to exhibit highest voltage efficiency at a current density of 10 kA · m−2 or below, whereas the mixed oxide of Ir and Ru (60-80 mole% Ir) was found to give the highest voltage efficiency for current densities of above 10 kA · m−2.
Pt on carbon particles, was found to be less suitable as cathode catalyst in water electrolysis. The large carbon particles introduced an unnecessary porosity into the catalytic layer, which resulted in a high ohmic drop. Much better voltage efficiency was obtained by using Pt-black as cathode catalyst, which showed a far better electrical conductivity.
Ru-oxide as cathode catalyst in water electrolysis systems using a polymer electrolyte was not found to be of particular interest due to insufficient electrochemical activity and too low electrical conductivity.
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Gurrik, Stian. "Performance of supported catalysts for water electrolysis." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18880.
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The most active catalyst for oxygen evolution in PEM water electrolysis is ruthenium oxide. Its major drawback as a commercial catalyst is its poor stability. In a mixed oxide with iridium, ruthenium becomes more stable. However, it would be favorable to find a less expensive substitute to iridium. In this work, the dissolution potential and lifetime of mixed oxides containing ruthenium and tantalum are investigated. In order to effectively determine what effects tantalum and particle size have on stability, only a small amount of tantalum is used, and the catalysts are supported by antimony doped tin oxide, ATO. This leads to a very small particle size, and makes it possible to investigate small amounts of catalyst where little new surface is made available during degradation.Catalysts were prepared with the normal polyol method by reducing RuCl3 and TaCl5 in ethylene glycol, EG, before the metal particles were deposited on the ATO support. The catalysts were investigated electrochemically with cyclic and linear voltammetry. Furthermore, the lifetime of four catalysts were determined by chronoamperometry at 1.455V vs. RHE. The compositions and loading of catalyst on the support were determined by energy dispersive x-ray spectroscopy (EDS) and the particle sizes were measured with transmission electron microscopy (TEM).In one synthesis, the reduction time and temperature were increased from 3 hours at 170◦C to 4 hours at 190◦C in order to increase the reduction rate. While this had no effect on the Ta composition, the catalyst got a fraction of amorphous phase not found in any of the other catalysts. The amorphous Ru0.9Ta0.1O2 particles had the largest particle size and the highest stability of the ones investigated. 10wt% water was added to the synthesis of an ATO-RuO2 catalyst in order to increase the particle size, but no significant effect was observed. Larger RuO2 particles and amorphous Ru0.9Ta0.1O2 particles were obtained by collecting them as unsupported catalysts.The addition of tantalum has a negative effect on the catalytic activity. When Ta is present, the dissolution potential of Ru at around 1.45V is slightly increased, but the degradation rate is increased above 1.49V. A large particle size in RuO2 has a significant positive effect on stability.
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Lumanauw, Daniel. "Hydrogen bubble characterization in alkaline water electrolysis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0017/MQ54129.pdf.
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Iacomini, Christine Schroeder. "Combined carbon dioxide/water solid oxide electrolysis." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/290073.
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Solid oxide electrolysis of a mixture of water and carbon dioxide has many applications in space exploration. It can be implemented in propellant production systems that use Martian resources or in closed-loop life support systems to cleanse the atmosphere of facilities in extraterrestrial bases and of cabin spacecrafts. This work endeavors to quantify the performance of combined water and carbon dioxide electrolysis, referred to as "combined electrolysis", and to understand how it works so that the technology can be best applied. First, to thoroughly motivate the research, system modeling is presented that demonstrates the competitiveness of the technology in terms of electrolysis power requirements and consequential system mass savings. Second, to demonstrate and quantify the performance of the technology, experimental results are presented. Electrolysis cells were constructed with 8% by mol yttria-stabilized zirconia electrolytes, 50/50 by weight platinum/yttria-stabilized zirconia electrodes and chromium-alloy or alumina manifolds and tubing. Performance and gas chromatograph data from electrolysis of many different gas mixtures, including water, carbon dioxide, and a combined mixture of both, are presented. Third, to explain observations made during experiments and theorize about the phenomena governing combined electrolysis, data analyses and thermodynamic modeling are applied. Conclusions are presented regarding the transient response of combined electrolysis, the relative performance of it to that of other mixtures, how its performance depends on the water to carbon dioxide ratio, its effect on cell health, and its preference to water versus carbon dioxide. Procedures are also derived for predicting the composition of combined electrolysis exhaust for a given oxygen production rate, humidity content, and inlet flow rate. The influence of the two cell materials proves to be significant. However, in both cases it is proven that combined electrolysis does not encourage carbon deposition and the makeup of its products is governed by the water gas shift reaction. It is shown that the chromium-alloy system achieves water gas shift reaction equilibrium whereas the alumina system does not. Experimental observations support the argument that chromium oxide inside the chromium alloy cell forces its water gas shift reaction to equilibrium during electrolysis, influencing combined electrolysis performance.
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Ni, Meng, and 倪萌. "Mathematical modeling of solid oxide steam electrolyzer for hydrogen production." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39011409.
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Owe, Lars-Erik. "Characterisation of Iridium Oxides for Acidic Water Electrolysis." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14450.
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Sutherland, Richard Daniel. "Performance of different proton exchange membrane water electrolyser components / cRichard Daniel Sutherland." Thesis, North-West University, 2012. http://hdl.handle.net/10394/9214.
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Water electrolysis is one of the first methods used to generate hydrogen and is thus not considered to be a new technology. With advances in proton exchange membrane technology and the global tendency to implement renewable energy, the technology of water electrolysis by implementation of proton exchange membrane as solid electrolyte has developed into a major field of research over the last decade. To gain an understanding of different components of the electrolyser it is best to conduct a performance analysis based on hydrogen production rates and polarisation curves. The study aim was to compare the technologies of membrane electrode assembly with gas diffusion electrode and the proton exchange membranes of Nafion® and polybenzimidazole in a commercial water electrolyser. To determine which of the components are best suited for the process a laboratory scale electrolyser was to be used to replicate the commercially scaled performance. The effect of feed water contaminants on electrolyser performance was also investigated by introducing iron and magnesium salt solutions and aqueous methanol solutions in the feed reservoir. Components to be tested included different PEM types as well as the base component on which the electrocatalyst layer is applied. The proton exchange membranes compared were standard Nafion® N117 and polybenzimidazole meta-sulfone sulfonated polyphenyl sulfone (PBI-sPSU). A laboratory scale electrolyser from Giner Electrochemical Systems was utilised where different components were tested and compared with one another. Experimental results with commercial membrane electrode assemblies and gas diffusion electrodes demonstrated the influence of temperature on electrolyser performance for the proton exchange membranes, where energy efficiency increased with temperature. The effect of pressure was insignificant over the selected pressure range. Comparison of membrane electrode assembly and gas diffusion electrode technologies showed enhanced performance from MEA technology, this was most likely due to superior electrocatalyst contact with the PEM. Results of synthesised Nafion® N117 and PBI-sPSU MEA showed increased performance for PBI-sPSU, but it was found to be more susceptible to damage under severe conditions. The effect of metal cations in the supply reservoir exhibited reduced energy efficiencies and increased specific energy consumption for the test duration. Treatment with sulphuric acid was found to partially restore membrane electrode assembly performance, though it is believed that permanent damage was inflicted on the membrane electrode assembly electrocatalyst. Use of aqueous methanol solutions were found to increase electrolyser performance. It was also found that aqueous methanol electrolysis occurs at lower current densities, whereas a combination of aqueous methanol and water electrolysis occurred at higher current densities depending on the concentration of methanol.Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.
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Fiorentini, Diego. "Development of a polymeric diaphragm for Alkaline Water Electrolysis." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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The importance of new technologies capable of providing clean energy is one of the most difficult and important challenge that science has to take up. The discovery of new green processes or the development of those already in use are common goals, which can partially solve the current climatic problems. The aim of this thesis is to extend the GVS portfolio with a polymeric separator able to improving the performances of alkaline water electrolysis (AWE) currently in use, as an alternative to separators produced by competitors. The separator consists of a membrane made of a high temperature resistant and chemically inert techno-polymer and an Inorganic filler. Once the new polymer had been studied to see how it affects the properties of the membrane and the basic information had been obtained, the influence of all the parameters in the preparation of the casting solution and the production process were analyzed. In addition, the most appropriate substrate and production method for the separator were investigated and selected in order to produce the best performing membrane possible.
Once the best separator was produced, it was possible to compare it with those produced by competitors, achieving better results in most of the analyses carried out. The prototypes were sent to companies producing cells for the Alkaline Water Electrolysis in order to validate the results obtained internally and carry out stability analyses inside the cells. The next steps after this study will be to industrialize the process developed on a laboratory scale in order to obtain a product that will benefit both the manufacturer and the environment.
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Richardson, Peter. "Oxygen evolution electrocatalysts for proton exchange membrane water electrolysis." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/374786/.
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Proton exchange membrane (PEM) water electrolysers are forecast to become an important intermediary energy storage technology between renewable power sources and energy distribution/usage. This is because they offer a production route to high purity H2 that is both non-polluting and efficient. Energy stored as H2 can be converted back to electricity for use in the national grid, pumped into existing natural gas networks or used as a fuel for hydrogen-powered vehicles. The majority of the energy losses in a PEM water electrolyser are associated with the high overpotential that is required for the electrochemical evolution of O2 that occurs at the anode. The highly oxidising conditions of this reaction coupled to the low pH of the PEM environment restrict electrocatalyst selection to expensive noble metal oxides. Thus to enhance the commercial viability of PEM electrolysers, the goal of electrocatalyst development for the O2 evolution reaction is to (i) increase the catalytic performance, (ii) increase the catalyst stability and (iii) reduce the cost of the catalyst components. In this work a range of iridium-based electrocatalysts with reduced Ir contents have been prepared. Two methods are employed to reduce the Ir content: (i) mixing the Ir with ruthenium to form a binary metal oxide and (ii) dispersing the active Ir phase on an indium tin oxide (ITO) support. Investigation of the electrocatalysts via a combination of different physical and electrochemical characterisation techniques, including a novel in-situ X-ray absorbance experiment, indicates that both approaches produce electrocatalysts with comparable or improved O2 evolution activity compared to the state-of-the-art iridium oxide (IrO2) material. However selection of the most appropriate catalyst for PEM electrolysis may ultimately be a compromise between activity, stability and cost.
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Gojela, Ntombekaya. "Hydrogen economy : MEA manufacturing for PEM electrolysers." Thesis, Nelson Mandela Metropolitan University, 2011. http://hdl.handle.net/10948/1483.
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The electrolysis of water was evaluated as a potentially efficient, as a low cost means of hydrogen production. The theoretical energy, voltage, current, and energy efficiencies of water electrolysis were considered by using various catalyst materials used in the fabrication of membrane electrode assemblies used in low temperature water electrolysis systems. Traditionally, iridium based catalysts have shown to be the most suitable material for its use on electrocatalysis of water to form hydrogen. This study showed that a combination of various elements as a binary and or ternary mixture in the base catalyst that was applied to the anode and cathode by using the Adam’s method had shown to give comparatively good results to that of using iridium oxide on its own. These catalysts were characterized by cyclic voltammetry, at different temperatures (30oC-80oC) with a range of catalyst loading of 0.2-0.5 mg.cm-2 noble metals. The study showed that the Ir40Co40 mixture as an anode catalyst was found to show highest hydrogen efficiency of 73 percent with a relatively low over potential of 0.925V at higher temperature of 80oC. The mixture also showed to give the best electrocatalytic activity with a low Tafel slope of 30.1mV.dec-1. Whereas the Ir50Pt50 showed a comparatively lower hydrogen efficiency of 65 percent with a lower over potential of 0.6V at 50oC. Ternary mixed oxide of Ir20Ru40Co40 showed an even lower over potential of 0.5- 0.6V over a large range of temperatures with a low hydrogen efficiency of 44 percent but gave good electrocatalytic activity in terms of the Tafel slope analysis. On the other hand, mixtures with relatively cheaper material such as Nickel in binary mixture systems such as Pt50Ni50 as cathode catalyst was found to show promising performance of a relatively low over potential that was less than 1.4 V with a low hydrogen efficiency of 62.1 percent Ternary cathode catalyst materials such as Pt33Ni33Co33 exhibited good performance with higher hydrogen efficiency of 65.2 percent at lower over potential of 1.2 V and a higher Tafel slope of 133.9 mV.dec-1 at 80 0C.
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Mangombo, Zelo. "The electrogeneration of hydroxyl radicals for water disinfection." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5745_1190373027.
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This study has shown that OHË radicals can be generated in an Fe/O2 cell from the electrode products via Fenton&rsquo
s reaction and used for water disinfection. The cell system in which the experiments were carried out was open and undivided and contained two electrodes with iron (Fe) as the anode and oxygen (O2) gas diffusion electrode. Typically, 100 ml of Na2SO4.10H2O (0.5M) solution was used as a background electrolyte. OHË radicals were produced in-situ in an acidic solution aqueous by oxidation of iron (II), formed by dissolving of the anode, with hydrogen peroxide (H2O2). The H2O2 was electrogenerated by reduction of oxygen using porous reticulated vitreous carbon (RVC) as a catalyst.
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Petrik, Leslie F. "Pt Nanophase supported catalysts and electrode systems for water electrolysis." Thesis, University of the Western Cape, 2008. http://hdl.handle.net/11394/2743.
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Doctor Scientiae - DScIn this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.
South Africa
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Delgado, Dario. "Electrochemical properties of earth abundant catalysts for efficient water electrolysis." Thesis, Delgado, Dario (2016) Electrochemical properties of earth abundant catalysts for efficient water electrolysis. PhD thesis, Murdoch University, 2016. https://researchrepository.murdoch.edu.au/id/eprint/30718/.
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The hydrogen economy is attracting a great deal of attention from governments and major oil companies. Hydrogen is seen as a solution to the problems arising from the current unsustainable fossil fuel economy. Hydrogen generation can be done thermochemically, electrochemically and biochemically. Of all these options, hydrogen generation using renewable energy inputs to split water electrochemically into hydrogen and oxygen is potentially attractive on a commercial scale. Water electrolysis has two reactions happening simultaneously, the hydrogen and oxygen evolution reactions (i.e. HER and OER) from the cathode and anode respectively. Most of the relevant published work supports the use of platinum group metals for the HER and platinum group oxides for the OER. Platinum group materials are expensive thus a cheap substitute is needed. In this respect, lower cost substitutes (e.g., manganese dioxide, Raney cobalt and Raney nickel) were investigated possessing the following characteristics: (a) stable in the reaction environment; (b) environmentally friendly, (c) good catalytic activity and (d) earth abundant.
The catalytic activity of materials in general can be enhanced by modifying their geometric and electronic factors. In the case of manganese dioxide (MnO2), the electronic factor has been modified by changing its crystalline structure and chemical composition through a range of additives. In the case of nickel and cobalt as raw materials, their geometric factor has been modified by increasing the surface areas with the use of Raney powders. The electrochemical characteristics of the above materials were investigated by subjecting them to linear voltammetry and electrochemical impedance spectroscopy. The materials were also characterized by physical techniques using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) analyses.
The obtained electrochemical results revealed that the best overpotentials found for Raney Ni and Raney Co in alkaline HER were -190 mV and -270 mV (i.e. n100 at 100 mA cm-2) respectively. The presence of Mo, Co and V as additives in the parent y type MnO2 substantially improved the catalytic activity towards acid and alkaline OER. In particular, for acid OER the Co/Mo bimetallic addition to y-MnO2 resulted in 305 mV (at n100) which is competitive to that of commercially available DSA® which is 341 mV (at n100). The physico-chemical characterization of the material before and after electrochemical experiments confirmed the stability in aqueous media. The effectiveness of the modified Watts bath for the deposition of Raney cobalt and Raney nickel, has been established through overpotential curves. The presence of oxide species lowers the efficiency of the electrode which increases the overpotential for the HER on Raney based electrodes. A porous Raney surface type enhances the available area for the hydrogen evolution reaction to occur which increases its energy efficiency (i.e. n100). Recommendations for further developmental work for such catalysts are made.
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Valat, Mathieu Jean. "Elemental and Isotopic Measurements on Palladium After Heavy Water Electrolysis." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/60.
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This study gives the details about several experiments done in Eugene Mallove Laboratory for New Energy Research. Three experiments are presented and discussed in detail with different type of microscopes and mass spectrometry techniques. Also inspired by work done by Rolison and O'Grady [1], the other part of this study presents the variation of isotopic abundance after experiments on palladium cathode immersed in a heavy water electrolyte. This original inspiring paper has been published through proceedings of the first edition of International Conference on Cold Fusion held in Washington D.C. in 1989. In other words, both works provides similar evidence of an isotopic variation before and after low energy nuclear experiments. By measuring the variation in isotopic concentration, before and after electrolysis, these measurements provide insight for how the low energy nuclear phenomenon occurs. Scanning electron microscopes are used in the first part to provide high resolution, high magnification images of the electrodes. They show the morphology the topology of the cathode after experiment. An energy dispersive mass spectrometer is used to provide elemental composition of the cathode and provide a second independent measurement of elemental composition of the cathode. The presented isotopic measurements are made with a secondary ion mass spectrometer. [1]: D. Rolison & W. O'Grady - Mass/Charge Anomalies in Pd after electrochemical loading with deuterium - Section 10 in Proceedings: EPRI-NSF Workshop on Anomalous Effects in Deuterided Metals - (October 16-18, 1989) Washington, D.C.
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Zwaschka, Gregor [Verfasser]. "Shining New Light on Water Electrolysis: Probing Electrolytic Water Splitting on Au and Pt with Micron Spatial and Femtosecond Temporal Resolution / Gregor Zwaschka." Berlin : Freie Universität Berlin, 2021. http://d-nb.info/1224883977/34.
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Siguba, Maxhobandile. "The development of appropriate brine electrolysers for disinfection of rural water supplies." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=init_6284_1180438520.
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A comparative study of electrolysers using different anodic materials for the electrolysis of brine (sodium chloride) for the production of sodium hypochlorite as a source of available chlorine for disinfection of rural water supplies has been undertaken. The electrolyser design used was tubular in form, having two chambers i.e. anode inside and cathode outside, separated by a tubular inorganic ceramic membrane. The anode was made of titanium rod coated with a thin layer of platinum and a further coat of metal oxide. The cathode was made of stainless steel wire. An assessment of these electrolysers was undertaken by studying the effects of some variable parameters i.e.current, voltage and sodium chloride concentration. The cobalt electrolyser has been shown to be superior as compared to the ruthenium dioxide and manganese dioxide electrolysers in terms of hypochlorite generation. Analysis of hydroxyl radicals was undertaken since there were claims that these are produced during brine electrolysis. Hydroxyl radical analysis was not successful, since sodium hypochlorite and hypochlorous acid interfere using the analytical method described in this study.
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Kinney, Chris 1982. "Water modeling the solid oxide membrane electrolysis with rotating cathode process." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32729.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Vita.
Includes bibliographical references (leaf 35).
The Kroll process for refining titanium is an expensive batch process which produces a final product that still requires intensive post processing to create usable titanium. A new process, Solid Oxide Membrane Electrolysis with Rotating Cathode (SOMERC) process is being explored. The SOMERC process is a continuous process that could produce large quantities of high quality titanium at a fraction of the cost of the Kroll process. This paper examines the fluid flow around the ingot in the SOMERC Process. A large shear between the ingot and surrounding fluid will create a fully-dense ingot instead of dendrites, because dendrites are undesirable. Using a camera, a plane of light and titanium dioxide particles, videos and pictures of the water were taken and analyzed to find how to create a large amount of shear between the ingot and the fluid. Out of the speeds tested, a rotation rate of 900Ê»/s for the ingot proved to create the most shear, and therefore the shear between the ingot and fluid increases with increasing rotation rate, making it more likely to suppress the formation of dendrites.
by Chris Kinney.
S.B.
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Smith, Richard. "RuO2 Nanorods as an Electrocatalyst for Proton Exchange Membrane Water Electrolysis." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/527.
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The desire for pure diatomic hydrogen gas, H2(g), has been on the rise since the concept of the hydrogen economy system was proposed back in 1970. The production of hydrogen has been extensively examined over 40 + years as the need to replace current fuel sources, hydrocarbons, has become more prevalent. Currently there are only two practical and renewable production methods of hydrogen; landfill gas and power to gas. This study focuses on the later method; using various renewable energy sources, such as photovoltaics, to provide off-peak energy to perform water electrolysis. Efficient electrolysis takes place in electrochemical cells which maximize performance efficiency with the use of noble metal electrocatalyst. Optimizing these electrocatalyst to be less material dependent, highly durable, and more efficient will support the implementation of power to gas electrolysis into the energy infrastructure.
The main focus of this study is to explore RuO2 nanorods as a possible electrocatalyst for Proton Exchange Membrane (PEM) water electrolysis. A PEM electrolyzer cell has been constructed and fitted with a RuO2 nanorod decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst structure. The current density-voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under water feed operation. The electrocatalytic behavior was compared to that of ribbon mesh anode catalyst structures not decorated with RuO2 nanorods; one coated with a Ir/Ta MMO catalyst, the other was stripped of the MMO coating resulting in a Ti ribbon mesh anode. The results of these experiments show increased activity with the RuO2 nanorod electrocatalyst corresponding to a decrease in electrochemical overpotential. Through the collection of experimental data from various electrolyzer cell configurations, these overpotenials were able to be identified, resulting in categorical attributions of the enhanced catalytic behavior examined.
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Cheng, Yi. "Carbon nanotubes based nanostructured catalysts for water electrolysis and fuel cells." Thesis, Curtin University, 2014. http://hdl.handle.net/20.500.11937/972.
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CNTs composed of 2-7 tubes show significantly better activity for oxygen evolution, and exhibit better ability for hydrogen evolution and oxygen reduction. The better activity of these CNTs is result from the electron transfer pathway through tunneling effect, which makes them favorable materials to develop photo catalysts for water oxidation. Metal-CNTs hybrids with high activity and stability developed here provide new opportunities to develop catalyst with enhanced performance, better durability and low costs.
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Mersch, Dirk. "Wiring of photosystem II to hydrogenase for photoelectrochemical water splitting." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709273.
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Genova-Koleva, Radostina Vasileva. "Electrocatalyst development for PEM water electrolysis and DMFC: towards the methanol economy." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/462861.
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In this thesis, the hydrogen obtained in a PEM water electrolizer (PEMWE) as a reactant to produce methanol when combined with the CO2 captured from the combustion of fossil fuels is proposed. Methanol is easy to manage as a fuel for DMFCs and this would help to recycle the CO2 responsible for the climate change.
PEMWEs have several advantages in comparison with the alkaline electrolysis such as ecological cleanness, low power consumption, small mass, and high purity of the evolved gases. TiO2 nanoparticles and nanotubes as supports for electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were developed. TiO2 and Nb-doped TiO2 with different Nb contents (3-10 at.% Nb vs. Ti) were synthesized via sol-gel method, whereas TiO2 nanotubes (TNT) and Nb-doped TiO2 nanotubes (Nb-TNT) were prepared by the hydrothermal method. The specific surface areas were in the range of 80-100 m2 g-1 for nanoparticles and in the range 150 – 300 m2 g-1 for nanotubes.
XPS measurements showed a local increase of the electron density on Pt when supported onto Nb-TNT, thus indicating a strong metal-support interaction. According to the electrochemical testing, the highest activity towards HER corresponded to Pt supported on 3 at. % Nb-TNT, obtaining better results than those reported in the literature using other materials.
IrO2 and IrRuOx (atomic ratio Ir:Ru equal to 60:40) as OER catalysts were synthesized via the hydrolysis method. From the electrochemical experiments, the highest OER activity of IrO2/Nb-TNT, due to the better dispersion of IrO2 onto the support, was shown. The catalysts supported onto Nb-doped TNT presented the lowest overpotentials for OER.
MEAs 5 cm2 in section were prepared using a new low temperature decal method. IrO2, IrRuOx and 50 wt. % IrO2/Nb-TNT were applied as the anode electrocatalysts with a catalyst loading optimized to 2.0 mgoxide cm-2. Pt loading on the cathode was optimized to 0.5 mgPt cm-2 (Pt black and 20 wt. % Pt/Vulcan XC72 were used). The best performance at 80 °C corresponded to current densities of 0.100 and 0.500 A cm-2 at 1.430 and 1.494 V, respectively, with 50 wt.% IrO2/Nb-TNT on the anode and 20 wt. % Pt/Vulcan XC72 on the cathode. The increase in cost of the MEA with respect to the use of unsupported IrO2 was not significant.
Different solvents (n-butyl acetate (NBA) and 2-propanol (IPA)) having different polarity were used to prepare the catalyst inks of the DMFC electrodes. The catalysts were commercially available Pt and PtRu blacks. The light scattering experiments indicated that the PtRu-Nafion® aggregates in the inks prepared with NBA were larger. The SEM and porosimetry measurements of the catalyst layers showed that the secondary pore volume between the agglomerates was larger for NBA. The linear sweep voltammetry and electrochemical impedance spectroscopy (EIS) results for the methanol electrooxidation in the three-electrode cell denoted the higher active surface area for NBA. The transport limitation was more apparent for IPA because the corresponding size and porosity of the agglomerates formed by the ionomer and the catalyst nanoparticles were smaller than for NBA.
The polarization curves of MEAs in which the anode catalyst layers were formulated with NBA and IPA were recorded in single DMFCs with 2 mol dm-3 CH3OH aqueous solutions at 60 °C. The cathode feed was dry synthetic air at atmospheric pressure. The power density given by the MEA prepared with NBA was about 74 % greater when compared to that prepared with IPA. The interpretation of the EIS results indicated that the proton resistance for NBA was significantly lower than for IPA, thus confirming the greater number of accessible active sites for methanol oxidation in the former.La economía del metanol contempla el uso de dicho alcohol como combustible, obtenido a partir de hidrógeno y CO2 capturado de la combustión de combustibles fósiles, ayudando a mitigar el cambio climático. Para ello se han preparado nanopartículas y nanotubos de TiO2 y de TiO2 dopados con Nb como soportes de catalizadores para electrolizadores de agua PEM. El Nb permitió aumentar la superficie específica de los soportes hasta 300 m2 g-1 (nanotubos). Mediante XPS se demostró un aumento local de la densidad electrónica sobre el Pt soportado sobre TiO2 dopado con Nb, resultando el de contenido del 3 at. % en Nb el de mejores prestaciones para la reducción del hidrógeno, con valores superiores a los descritos en la literatura. Para el desprendimiento de oxígeno se sintetizaron los catalizadores IrO2 e IrRuOx (Ir: Ru de 60:40 at. %), también aplicados sobre nanotubos de TiO2. Se encontró una mejor actividad para IrO2 soportado sobre nanotubos de TiO2 dopados con Nb debido a una mejor dispersión del catalizador sobre el soporte. Se prepararon MEAs con los mejores electrodos para un electrolizador PEM mediante un nuevo método de calcomanía de baja temperatura. El mejor rendimiento correspondió al IrO2 (50 % en peso) soportado sobre nanotubos de TiO2 dopados con Nb en el ánodo, con escaso impacto económico con respecto al uso del IrO2 sin soportar. En cuanto a la pila de combustible DMFC, se prepararon electrodos de PtRu sin soportar, empleando tintas con Nafion y dos disolventes diferentes, con distinta polaridad, acetato de n-butilo (NBA) y 2-propanol (IPA). El tamaño de los agregados y la porosidad fue superior en NBA debido a su menor polaridad, obteniéndose también en este caso una mayor superficie activa. Las curvas de polarización en CH3OH 2 mol dm-3 y aire a 60 °C de los MEAs formulados con NBA, catalizados mediante negro de PtRu y negro de Pt en ánodo y cátodo, respectivamente, indicaron también mejores prestaciones cuando los MEAs se formularon con NBA en el ánodo en lugar de IPA. La densidad de corriente límite con NBA fue unas tres veces mayor y la densidad de potencia un 75% superior.
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Law, Joseph. "The role of vanadium as a homogeneous catalyst in alkaline water electrolysis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0020/MQ54216.pdf.
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Tanaka, Yoshinori. "Studies on dissolution and characteristics of hydrogen bubble generated by water electrolysis." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144556.
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Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第11885号
工博第2578号
新制||工||1361(附属図書館)
23665
UT51-2005-N719
京都大学大学院工学研究科物質エネルギー化学専攻
(主査)教授 小久見 善八, 教授 垣内 隆, 教授 粟倉 泰弘
学位規則第4条第1項該当
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Zhang, Zhihao. "The Development of Three Dimensional Porous Nickel Materials and their Catalytic Performance towards Oxygen Evolution Reaction in Alkaline Media." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40636.
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As the global energy crisis and environmental pollution problem continues, there is an increasing demand for clean and sustainable energy storage and conversion technologies, such as water-splitting electrolysis. Water electrolysis is a process of running an electrical current through water in separating the hydrogen and oxygen. Oxygen evolution reaction (OER) is a key reaction in this electrochemical process, and the electrochemical performance of these systems is usually hindered by the slow OER reaction kinetics. In order to achieve high energy conversion efficiency, the development of efficient OER catalysts is the key. To achieve that, abundant research is done by using noble metal oxides as catalyst, such as IrO2 and RuO2. However, considering their high cost, a cheap earth-abundant material with a high OER catalytic activity is required. Accordingly, this study has been focused on the synthesis of three dimensional porous structured Ni-based OER catalysts. First, a 3D porous Ni meso-foam was developed through a facile high-temperature one-pot synthesis method, and its catalytic activity towards OER was explored. Specifically, the as-synthesized Ni meso-foam material, referred to as raw NMF, has a wire-linked structure and high surface area. A reduction procedure was introduced to obtain reduced Ni meso-foam materials, referred to as NMF-H2. It was also oxidized in air at 600 ℃ to form a semi-hollow NiO crosslinking phase and subsequently reduced in H2 at 300℃, forming a regenerated porous Ni foam material, referred to as NMF-O2/H2. The composition and morphology of all materials were investigated by XRD and SEM, respectively. The SEM image reveals that, in the porous NMF-O2/H2, the cross-linked meso-wire structure was maintained, and the average pore size is between 0.5-5 μm. Electrochemical analysis show that the OER activity of the Ni foam catalysts follows NMF-O2/H2 > NMF-H2 > raw NMF. In addition to the NMF-based materials, a Ni/Ni(OH)2 layer-structured electrocatalyst, referred to as NiDHBT, was also developed using a dynamic hydrogen bubble templating (DHBT) method. First, the 3D-porous micro Ni/Zn nanoplatelets were constructed in a two-step DHBT deposition method. The Ni/Zn foil was used as a scaffold, featured with the open porous structure and high surface area, for the subsequent electrodeposition of Ni(OH)2. Then, the Zn was etched from the as-prepared Ni/Zn/Ni(OH)2 nanocomposite to obtain the NiDHBT. The catalytic performance of the NiDHBT toward OER reaction was evaluated, and the optimal catalysts developed from different electro deposition potentials were determined. On the recognition of the high catalytic activity of NMF-O2/H2 and NiDHBT, porous structured FeOx-Nickel meso-foam, referred to as Fe@NMF-O2/H2, and FeOx- Ni/Ni(OH)2 layered-structure materials, referred to as Fe@NiDHBT, was further developed to explore the benefits of FeOx deposition for its OER catalytic performance. The deposition of FeOx is achieved by physical mixing FeOx colloid with NMF-O2/H2 and NiDHBT, and the electrochemical performance of these materials was examined in 1 M KOH. Among the developed materials, the best performing catalyst is Fe@NiDHBT synthesized by loading FeOx colloid onto the NiDHBT support. The overpotential for Fe@NiDHBT to reach 10 mA·cm-2 is 247mV, and the corresponding Tafel slope is 48.10mV·dec-1. Therefore, it was concluded that the FeOx¬¬ loading modification is an effective strategy to improve the OER activity of Ni foam-based catalysts.
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Eccleston, Kelcey L. "Solid oxide steam electrolysis for high temperature hydrogen production." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/322.
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This study has focused on solid oxide electrolyser cells for high temperature steam electrolysis. Solid oxide electrolysis is the reverse operation of solid oxide fuel cells (SOFC), so many of the same component materials may be used. However, other electrode materials are of interest to improve performance and efficiency. In this work anode materials were investigated for use in solid oxide electrolysers. Perovskite materials of the form L₁₋ｘSrｘMO₃ , where M is Mn, Co, or Fe. LSM is a well understood electrode material for the SOFC. Under electrolysis operation LSM performed well and no interface reactions were observed between the anode and YSZ electrolyte. LSM has a relatively low conductivity and the electrode reaction is limited to the triple phase boundary regions. Mixed ionic-electronic conductors of LSCo and LSF were investigated, with these materials the anode reaction is not limited to triple phase boundaries. The LSCo anode had adherence problems in the electrolysis cells due to the thermal expansion coefficient mismatch with the YSZ electrolyte. The LSCo reacted with the YSZ at the anode/electrolyte interface forming insulating zirconate phases. Due to these issues the LSCo anode cells performed the poorest of the three. The performance of electrolysis cells with LSF anode exceeded both LSM and LSCo, particularly under steam operation, although an interface reaction between the LSF anode and YSZ electrolyte was observed. In addition to the anode material studies this work included the development of solid oxide electrolyser tubes from tape cast precursor materials. Tape casting is a cheap processing method, which allows for co-firing of all ceramic components. The design development resulted in a solid design, which can be fabricated reliably, and balances strength with performance. The design used LSM anode, YSZ electrolyte, and Ni-YSZ cathode materials but could easily be adapted for the use of other component materials. Proper sintering rates, cathode tape formulation, tube length, tape thickness, and electrolyte thickness were factors explored in this work to improve the electrolyser tubes.
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Eccleston, Kelcey Lynne. "Solid oxide steam electrolysis for high temperature hydrogen production /." St Andrews, 2007. http://hdl.handle.net/10023/322.
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Haug, Philipp [Verfasser]. "Experimental and theoretical investigation of gas purity in alkaline water electrolysis / Philipp Haug." München : Verlag Dr. Hut, 2019. http://d-nb.info/1181514061/34.
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Salazar, Gustavo, Wilmer Solis, and Leonardo Vinces. "A Mechanical Development of a Dry Cell to Obtain HHO from Water Electrolysis." Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/653837.
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El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.This article proposes a mechanical development of a dry cell in order to obtain HHO through water electrolysis. Calculations and technical specifications of the materials used for implementation are supported by mathematical, physical and chemical formulas and theories (Faraday´s Law, electrolysis process and mechanical design). The importance of mechanical design is focused on achieving efficient use of the energy provided to the cell that allows the H2 and O2 molecules to be separated without overheating the cell, evaporating the water, loss of current due to the geometry of the electrodes (Foucault Current). Moreover, choosing materials for proper implementation and physical robustness is mandatory. In addition, the mechanical design is not justified in different articles. Nevertheless, the mechanical design of the cell and the efficiency in the production of HHO are related. Therefore, the mechanical design and the calculations were performed, as well as the construction of the dry cell to obtain HHO. The results of the implementation and production were placed and compared with what theoretically the dry cell should produce from the law of Faraday. Finally, the volumetric flow of HHO obtained was 2.70 L per minute. It means a production efficiency of 98.68%. It is higher than the majority of the dry cells.
Revisión por pares
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Mässgård, Hampus, and Arvid Jonsson. "An Industrial Perspective on Ultrapure Water Production for Electrolysis : A techno-economic assessment of membrane distillation for electrolysis - synergies, performance, costs, and value propositions." Thesis, KTH, Industriell ekonomi och organisation (Inst.), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298250.
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Sustainable development is one of the most important issues in todays’ industrial sector, and several markets are now looking for alternatives to fossil fuels. One of these solutions is hydrogen; a clean, easily combustible gas which can be used as fuel in several industrial processes, such as steel production and power generation. However, the production of green hydrogen is limited, and this is where the need for electrolysis emerges. Electrolysis is a way to produce green hydrogen by separating water into hydrogen and oxygen using energy. One crucial aspect is that this process requires extremely pure feedwater, also known as ultrapure water. To produce this water two main systems are investigated; reverse osmosis and membrane distillation, and they are compared from a techno-economic standpoint. Firstly, a literature review was made, which gave theoretical background of core concepts such as different types of electrolysis, water purification, as well as several financial models and theories used in the report. Based on this, calculations were made to analyse the possibility of running membrane distillation entirely on waste heat. From the data gathered the results showed that membrane distillation can be run entirely on waste heat from electrolysis, even with a 25% loss factor included. After the technological calculations, financial calculations were made to directly compare a reverse osmosis-based system with membrane distillation. OPEX and CAPEX for both systems were calculated over a 20-year period and then added together, producing a total price for reverse osmosis at 0,67 €/m3, whereas membrane distillation has a total price of 0,60 €/m3. An assessment of both electrolyser systems and the two water purification systems is made. The electrolyser inquiry ends with the conclusion that two of the electrolysis processes, Proton-Exchange Membrane and Alkaline Water, are suitable to combine with membrane distillation. With the comparative analysis between reverse osmosis and membrane distillation, a longer discussion regarding financial viability is made. The key takeaway here is that membrane distillation is cheaper, both in total and when calculating the net present value. Looking specifically at the membrane distillation market, the conclusion is that it is still in the earlier stages of development, and so customer relationships are crucial. This is reinforced through the value proposition model, which shows that the company should put focus on customer relationships with their product model.Hållbar utveckling är en av de mest kritiska frågorna i dagens industrisektor, och flera aktörer söker alternativ till fossila bränslen. En av dessa lösningar är väte; en ren, lättantändlig gas som kan användas som bränsle i flera industriella processer, såsom stål- och kraftproduktion. Produktionen av hållbart grönt väte är idag småskalig och därav uppstår ett ökat behov av elektrolys. Elektrolys är ett sätt att producera grönt väte genom att separera vattenmolekyler till väte och syre med hjälp av energi. En avgörande aspekt är att denna process kräver extremt rent inmatningsvatten, även känt som ultrarent vatten. För att producera detta vatten undersöks två metoder; omvänd osmos och membrandestillation, och de jämförs ur en tekno-ekonomisk synvinkel. Projektet inleds med en litteraturundersökning, som ger en teoretisk bakgrund av kärnkoncept såsom olika typer av elektrolys, vattenrening, samt flera ekonomiska modeller och teorier som används i rapporten. Baserat på detta görs beräkningar för att konstatera om spillvärmen från elektrolysprocessen räcker för membrandestillationen. Utifrån de insamlade uppgifterna visar resultaten att membrandestillation kan köras helt på spillvärme från elektrolys, även med en 25% förlustfaktor inkluderad. Efter de tekniska beräkningarna gjordes ekonomiska beräkningar för att direkt jämföra ett system baserat på omvänd osmos och membrandestillation. OPEX och CAPEX för båda systemen beräknades över en 20-årsperiod och summerades, vilket gav ett totalpris för omvänd osmos vid 0,67 €/m3, medan membrandestillation har ett totalpris på 0,60 €/m3.Analysen av elektrolysörerna konstaterar att ’Proton-Exchange Membrane’ och ’Alkaline Water’ är två lämpliga metoder att kombinera med membrandestillation. Analysen av omvänd osmos och membrandestillation innehåller en längre diskussion om ekonomisk lönsamhet. I den jämförande analysen mellan omvänd osmos och membrandestillation hålls en längre diskussion om ekonomisk bärkraft. Det viktigaste med detta är att membrandestillation är billigare, både totalt och vid beräkning av nuvärdet. Slutligen görs en fallstudie av ett membrandestillationsföretag. Slutsatsen är att marknaden fortfarande befinner sig i de tidigare utvecklingsstadierna, och därför är kundrelationer avgörande. Detta förstärks genom modellen för värdeerbjudande, som visar att företaget bör fokusera på dessa relationer.
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Ottosson, Anton. "Integration of Hydrogen Production via Water Electrolysis at a CHP Plant : A feasibility study." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-83717.
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Hydrogen gas (H2), that is not produced from fossil oil or natural gas, is expected to become a cornerstone in the energy transition strategy in Europe. The recent years, technological and economic advances in the electrolyzer area, along with political and corporate support, have put H2 at the forefront of many countries’ climate change agenda. Consequently, green H2 is poised to play a large role in the coming energy transition to combat climate change. The possible advantages of integrating H2 production with a combined heat and power plant, or CHP, is investigated in this study. More precisely, the water electrolysis is carried out based on the purified flue gas condensate water and excess heat is recovered as district heating. A comparison of today’s three most common electrolyzer technologies was made, where Proton Exchange Membrane, or PEM, technology was chosen for this project, mainly for its high purity of H2 gas, robust construction, and the ability to run it as a fuel cell. Based on a mass and energy balance, a model including the integration of a PEM with a generic CHP plant was developed. The model was made modifiable, making it possible to change governing parameters, to be able to investigate different possible scenarios. Production flows, losses and other relevant data was calculated from the model. Operational data for the PEM electrolyzer were collected from several manufacturers where a mean value of the data was used as a base-case for the calculations. Based on literature and consulting experts, several assumptions were made, for example the selling price of H2 and the price for electricity. From the base-case were two cases made: a linear and non-linear case. The linear case uses the same input data each year for 20 years, while the non-linear case uses a changing input data each year for 20 years. Calculations were based on an electrolyzer size of 1,4 MW, where auxiliary equipment consumed additional 0,04 MW, resulting in a total energy consumption of 1,44 MW. An operational temperature of 80°C was assumed along with an operational pressure of 5 and 30 bar for the anode and cathode respectively. This resulted in an H2 production flow of 26 kg/h, a process water requirement of 0,2 m3/h, and a possible heat recovery amount of 0,34 MWh with a relevant temperature for the use in district heating. The study shows that the condensate-water at E.ON could provide for ~4000 hours of operation in the wintertime. To enable full operation all year around, a purchase of tap water would be necessary. The economical calculations resulted in an H2 production cost of 53 SEK/kg for the linear case and 58 SEK/kg for the non-linear case. The linear case showed a positive internal rate of return, or IRR, of 1,7%, while the non-linear case resulted in IRR < -25%. A sensitive analysis was made to examine governing parameters. The results of the sensitivity analysis showed that the largest driving variables, that significantly affect the IRR, are the price for electricity and the selling price for H2. The largest OPEX cost was found to be the price of electricity. The results showed that it is feasible to produce H2 at E.ON Örebro in a resource efficient way under certain circumstances, correlated to the electricity and H2 market. With a low electricity price and a selling price of ~50 SEK/kg for H2, good profitability is expected. It is also clear that future work should focus the areas of O2 usage, infrastructure, and market investigation for a more definitive conclusion.
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Dayama, Parth Omprakash. "A Comparative Study of Electrodes and Membranes for Anion Exchange Membrane Water Electrolysis Systems." Thesis, KTH, Tillämpad elektrokemi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-300182.
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Vätgas kan framställas från förnybara energikällor genom vattenelektrolys med anjonbytande membran (AEMWE). AEMWE har vissa fördelar jämfört med traditionell alkalisk vattenelektrolys och elektrolysmed protonledande membran. Till exempel finns det möjlighet att använda alkalisk elektrolyt (även rent vatten) och billiga platinagruppsmetallfria katalysatorer tillsammans med ett anjonbytesmembran. Den största utmaningen med tekniken är att uppnå utmärkt och stabil prestanda för membran och elektroder. AemionTM anjonbytande membran (AEMs) av olika tjocklek, vattenupptag och kapacitet undersöktes i ett AEMWE system med 5 cm2 elektrodarea. Elektrokemisk prestanda hos dessa kommersiella AEM studerades med hjälp av porösa nickel elektroder. Bland de undersökta membranen visade AF2-HWP8-75-X stabil prestanda med en högfrekvent resistans (HFR) på 90 mΩ•cm2 och kunde nå en strömtäthet på 0,8 A/cm2 vid 2,38 V med 1 M KOH vid 60 ˚C. AEMWE med AF2-HWP8-75-X och olika elektrodkombinationer undersöktes under samma driftsförhållanden. En elektrodkombination med Raney-Ni och NiFeO som katod respektive anod visade bäst prestanda under utvärderingen och gav en strömtäthet på 1,06 och 3,08 A/cm2 vid 2,00 respektive 2,32 V. KOH-lösningens temperatur och koncentration sänktes till 45 ˚C respektive 0,1 M för att undersöka effekten av driftsparametrar på flödescellens prestanda. Flödescellen uppvisade god stabilitet under de nya driftsförhållandena, men dess prestanda minskade avsevärt. Den nådde en strömtäthet på 0,8 A/cm2 vid 2,25 V.Hydrogen can be produced from renewable energy sources using a novel anion exchange membrane water electrolysis (AEMWE) system. AEMWE has some benefits over the currently used state-of-the-art alkaline and proton exchange membrane water electrolysis systems. For instance, there is a possibility of using alkaline electrolytes (even pure water) and low-cost platinum-group-metal free catalysts together with an ion exchange membrane. However, the main challenge is that the AEMWE system should show excellent and stable performance, depending on the stability of the membrane and the electrodes. AemionTM anion exchange membranes (AEMs) of different thickness and water uptake capacity were investigated using a 5 cm2 AEMWE system. The electrochemical behaviour of these commercial AEMs was studied using nickel (Ni) felt electrodes. Among the investigated AEMs, the AF2-HWP8-75-X showed stable performance with a high frequency resistance (HFR) of 90 mΩ•cm2 and was able to reach a current density of 0.8 A/cm2 at 2.38 V using 1 M KOH at 60 ˚C. AEMWE systems based on AF2-HWP8-75-X and different electrode combinations were examined under the same operating conditions. An electrode combination with Raney-Ni and NiFeO as cathode and anode, respectively, showed the best performance during the degradation test and provided a current density of 1.06 and 3.08 A/cm2 at 2.00 and 2.32 V, respectively. The operating temperature and concentration of the KOH solution were reduced to 45 ˚C and 0.1 M, respectively, to study the effect of operating parameters on the flow cell performance. The flow cell showed good stability under the new operating conditions, but its performance was reduced significantly. It reached a current density of 0.8 A/cm2 at 2.25 V.
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KNOB, DANIEL. "Geração de hidrogênio por eletrólise da água utilizando energia solar fotovoltaica." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23300.
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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-21T10:10:35Z
No. of bitstreams: 0Made available in DSpace on 2015-01-21T10:10:35Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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McCraven, Elizabeth Kathleen. "Electro-disinfection of Ballast Water." ScholarWorks@UNO, 2009. http://scholarworks.uno.edu/td/1095.
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This research validates electro-disinfection as a potential secondary ballast water treatment technology. Electricity applied to bacteria laden water produced bactericidal effects, reactive oxygen species and chlorine generation which annihilated bacteria. Evaluation of electro-disinfection experiments showed titanium electrodes had the maximum kill efficacy while disinfection with aluminum and stainless steel electrodes had lesser kill efficacy. A continuous flow electro-disinfection reactor was evaluated utilizing artificial brackish and fresh ballast water. Brackish water had a 100% bacteria kill efficiency utilizing titanium electrodes at a current density of 10 mA/cm2. Fresh water was augmented with the addition of salt to increase its electrical conductivity from 232 μS/cm to 873 μS/cm to ascertain 100% bacteria kill efficiency with titanium electrodes and a current density of 9.8 mA/cm2.
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Bollineni, Shilpa. "Hydrogen production via carbon-assisted water electrolysis at room temperature effects of catalyst and carbon type /." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=6025.
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Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains x, 67 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-67).
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Flores, Hernández José Roberto. "Optimization of membrane-electrode assemblies for SPE water electrolysis by means of design of experiments /." Stuttgart : Fraunhofer-IRB-Verl, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014175428&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Goñi, Urtiaga Asier. "Cesium dihydrogen phosphate as electrolyte for intermediate temperature proton exchange membrane water electrolysis (IT-PEMWE)." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2490.
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In this work the potential application of CsH2PO4 as intermediate temperature electrolyte for Proton Exchange Membrane Water Electrolysis (PEMWE) was studied. This material, from the phosphate-based solid acid family, was previously reported as a promising electrolyte for intermediate temperature PEM fuel cells although no study as electrolyte in a PEMWE system had been carried out before. The physico-chemical properties of phosphate-based solid acids in terms of structure and morphology were investigated and their thermal stability evaluated. Proton conductivity at the intermediate temperature range (150 – 300 °C) was measured and the influence of humidity on the stability of CsH2PO4 in terms of dehydration and water solubility determined. Different approaches for the fabrication of CsH2PO4-based membranes are proposed in order to improve the mechanical properties and reduce the thickness and ohmic resistance of the electrolyte. Membrane fabrication techniques including casting of polymer/CsH2PO4 composites, glass-fibre reinforcement, polymer doping or electrospinning were developed and the resulting membranes characterised in terms of structure, proton conductivity and mechanical stability. The compatibility of CsH2PO4 with IrO2 was evaluated and compared to standard acid electrolyte solutions in a three-electrode half-cell in the low temperature range (40 – 80 °C). The performance of IrO2 towards oxygen evolution reaction (OER) in a CsH2PO4 concentrated solution exhibited poor activity, which was attributed to a high kinetic activation caused by the high pH and high phosphate concentration in solution. Finally the performance of CsH2PO4 as solid-state electrolyte in the electrolysis cell was evaluated at intermediate temperatures (235 – 265 °C). Electrodes were optimised in terms of catalyst and ionomer loading for an intimate catalyst/electrolyte contact and characterised by cyclic voltammetry. The electrolysis system was characterised by quasi-steady polarisation curves and electrochemical impedance spectroscopy. The maximum performance obtained by a Pt/CsH2PO4/IrO2 MEA system at 265 °C was 20 mA cm-2 at 1.90 V. This low activity, in good agreement with the results obtained in the half-cell, was mainly attributed to kinetic losses generated in the CsH2PO4/IrO2 interface. The low acidity of the electrolyte is considered to affect the active oxidation state of iridium, Abstract ii creating a non-hydrated oxide layer, which influenced negatively to the performance of the electrolyser. It is therefore concluded that despite the promising results reported for CsH2PO4 as electrolyte in intermediate temperature fuel cells, this material, and presumably the rest phosphate-based solid acids, are not to be considered as potential electrolytes for PEM water electrolysers.
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Jia, Jingshu. "Fabrication of high quality one material anode and cathode for water electrolysis in alkaline solution /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?EVNG%202008%20JIA.
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Svengren, Henrik. "Water splitting by heterogeneous catalysis." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-148181.
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A sustainable solution for meeting the energy demands at our planet is by utilizing wind-, solar-, wave-, thermal-, biomass- and hydroelectric power. These renewable and CO2 emission-free energy sources are highly variable in terms of spatial and temporal availability over the Earth, introducing the need for an appropriate method of storing and carrying energy. Hydrogen has gained significant attention as an energy storage- and carrier media because of the high energy density that is exploited within the ‘power-to-gas’ process chain. A robust way of producing sustainable hydrogen is via electrochemical water splitting. In this work the search for new heterogeneous catalyst materials with the aim of increasing energy efficiency in water splitting has involved methods of both electrochemical water splitting and chemical water oxidation. Some 21 compounds including metal- oxides, oxofluorides, oxochlorides, hydroxide and metals have been evaluated as catalysts. Two of these were synthesized directly onto conductive backbones by hydrothermal methods. Dedicated electrochemical cells were constructed for appropriate analysis of reactions, with one cell simulating an upscale unit accounting for realistic large scale applications; in this cell gaseous products are quantified by use of mass spectrometry. Parameters such as real time faradaic efficiency, production of H2 and O2 in relation to power input or overpotentials, Tafel slopes, exchange current density and electrochemical active surface area as well as turnover numbers and turnover frequencies have been evaluated. Solubility, possible side reactions, the role of the oxidation state of catalytically active elements and the nature of the outermost active surface layer of the catalyst are discussed. It was concluded that metal oxides are less efficient than metal based catalysts, both in terms of energy efficiency and in terms of electrode preparation methods intended for long time operation. The most efficient material was Ni-Fe hydroxide electrodeposited onto Ni metal foam as conductive backbone. Among the other catalysts, Co3Sb4O6F6 was of particular interest because the compound incorporate a metalloid (Sb) and redox inert F and yet show pronounced catalytic performance. In addition, performance of materials in water splitting catalysis has been discussed on the basis of results from electron microscopy, solubility experiments and X-ray diffraction data.
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Bou-Saleh, Ziad. "Nickel-based 3D electrocatalyst layers for production of hydrogen by water electrolysis in an acidic medium." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112559.
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This thesis discusses results on the development of three-dimensional (3D) Ni-based electrocatalytic layers for hydrogen production by water electrolysis in an acidic medium. This is of relevance to the development of polymer-electrolyte-membrane (PEM) hydrogen generators, which are promising hydrogen production systems suitable for both residential and industrial applications.It was demonstrated that patterning of a glassy carbon electrode substrate with a 3D polyaniline (PANI) matrix is a convenient way of increasing the electrocatalytically active surface area of electrodeposited Ni, and hence its apparent electrocatalytic activity. The optimized PANI/Ni electrocatalyst layer showed a significantly higher activity in the hydrogen evolution reaction (HER) then a commercially available Ni-plate surface (control surface).
It was also demonstrated that it is possible to produce a Ni-based HER electrocatalyst layer by synthesizing Ni nanoparticles and supporting them on Vulcan carbon. This electrocatalyst also offered a significantly higher electrocatalytic activity in the HER then the control surface, but lower then the optimized PANI/Ni electrocatalyst.
The electrocatalytic activity of the optimized PANI/Ni layer was also compared to the activity of a 3D catalyst produced by electro-coating a porous reticulated vitreous carbon (RVC) substrate with Ni. This electrocatalyst showed the highest HER electrocatalytic activity among the investigated layers when tested under potentiodynamic polarization conditions. However, under the potentiostatic conditions, the optimized PANI/Ni layer showed the highest electrocatalytic activity.
The mechanisms and kinetics of the HER on the produced electrocatalysts was also investigated, as well as the electrocatalyst layers' surface morphology and crystalline structure.
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Haug, Philipp [Verfasser], and Thomas [Akademischer Betreuer] Turek. "Experimental and theoretical investigation of gas purity in alkaline water electrolysis / Philipp Haug ; Betreuer: Thomas Turek." Clausthal-Zellerfeld : Technische Universität Clausthal, 2019. http://d-nb.info/1231363312/34.
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Ekspong, Joakim. "Hydrogen Fuel from Water - An Advanced Electrocatalyst based on Nitrogen doped Carbon Nanotubes." Thesis, Umeå universitet, Institutionen för fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-105553.
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The production of cost-effective catalysts for the production of hydrogen by electrolysis of water is important for clean energy production. In this work we report on a study of molybdenum disulfide (MoS2) as catalyst for the hydrogen evolution reaction (HER). Nitrogen doped carbon nanotubes (NCNTs) directly synthesized onto carbon paper have been decorated with MoS2. The electrodes utilize the improved conductivity of the NCNTs and the carbon paper for electron transport, combined with the high catalytic activity of MoS2. The NCNTs were successfully decorated with co-axial nano-flakes of MoS2 by a single step solvothermal process using Dimethylformamide (DMF) and ammonium tetrathiomolybdate. MoS2 was also prepared with alternative methods for comparison. The effects of supporting MoS2 on NCNTs were studied by simulations with density functional theory (DFT). The most active adsorption sites for hydrogen on MoS2 were identified and were on the edges. The catalyst showed competitive activity with other earth-abun- dant catalysts with an onset potential of 170 mV and a small Tafel slope of 40 mV/dec. The improved catalytic activity of HER by having NCNTs as support was confirmed by DFT and experimental results.
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Fan, Kaicai. "Development of High Performance Electrocatalyst for Water Splitting Application." Thesis, Griffith University, 2018. http://hdl.handle.net/10072/382229.
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With increasing global demand for energy, rapid depletion of fossil fuels and intensification of environmental concerns, exploring clean and sustainable energy carriers to replace fossil fuel is becoming critical. Among the various alternatives, hydrogen has been intensively regarded as a promising energy carrier to fulfill the increasing energy demand due to its large energy density per unit mass and eco-friendly production possibilities. However, hydrogen does not exist in molecular structure in nature, and it is essential to obtain efficient and sustainable H2 production technologies. Alkaline water electrolysis is an effective, clean and sustainable process to produce high-quality hydrogen. In this process, highly active electrocatalysts for the hydrogen evolution reaction (HER) are required to accelerate the sluggish kinetics and lower the overpotentials (η) for efficient hydrogen evolution. To date, a noble metal, platinum (Pt), is the state-of-art electrocatalyst for HER. However, exploration of alternative electrocatalysts with low cost and excellent electrocatalytic activity is of vital importance to realize large-scale hydrogen production through water electrolysis. Generally, an electrochemically active catalyst should have an optimal hydrogen adsorption free energy to allow efficient catalytic hydrogen adsorption/desorption. In alkaline solution, dissociation of water onto the electrocatalyst determines the overall HER efficiency.
This thesis focuses on rational design and synthesis of different earth-abundant electrocatalysts for electrocatalytic HER in alkaline media. Through facile anion or cation doping strategies, electrocatalysts with abundant accessible active sites, enhanced electronic conductivity and accelerated HER kinetics have been systematically fabricated, characterized and evaluated.
First, an efficient HER electrocatalyst in alkaline media was fabricated by incorporating sulfur atoms into a cobalt (hydro)oxide crystal structure. The resultant catalyst exhibits a remarkably enhanced HER activity with a low-overpotential of 119 mV at 10 mA/cm2 and an excellent durability. The results suggest that cobalt hydroxide benefits water adsorption and cleavage, while the negatively charged sulfur ligands facilitate hydrogen adsorption and desorption on the surface of electrocatalysts, leading to significantly promoted Volmer and Heyrovsky steps for HER in alkaline media.
Second, exploring bifunctional electrocatalysts which can simultaneously accelerate the HER and oxygen evolution reaction (OER) activities plays a key role in alkaline water splitting. Here, sulfur atoms were incorporated into the mixed transition metal hydroxide with high OER performance to render excellent HER activity. The enhanced catalytic activity towards HER was confirmed by a synergistic effect between the retained metal hydroxide host and the incorporated sulfur atoms. In addition, the full water splitting electrolyzer equipped with fabricated bifunctional electrocatalysts as anode and cathode materials exhibited remarkable overall water splitting performance comparable to that with benchmark Pt and RuO2 electrocatalysts.
The S/Se co-doped Co3O4 nanosheets on carbon cloth were fabricated by a facile room temperature chalcogen atom incorporation methodology and were applied as the electrocatalyst for HER in alkaline media. The sulfur and selenium atoms were homogeneously distributed on the surface by forming Co-S or Co-Se bonds which play a key role in the structural change in electrochemical activation. The obtained electrocatalysts demonstrated remarkably improved HER activity compared to that of the original Co3O4.
Finally, molybdenum doped cobalt hydroxide was fabricated with significantly accelerated HER kinetics. The introduced Mo sites not only effectively facilitate water dissociation process and desorption of the OHads intermediates, but also simultaneously optimize the hydrogen adsorption free energy. Therefore, the in situ-generated Mo-doped amorphous cobalt hydroxide exhibited a remarkable HER performance in alkaline media with an overpotential of only -80 mV at a current density of 10 mA/cm2.
This thesis innovatively explores strategies to improve the catalytic activity towards HER of metal (hydro)oxide in alkaline media. The surface foreign atom doping was demonstrated to manipulate the surface structure of catalysts, thus not only improving the water dissociation processes, but also facilitating the hydrogen adsorption/desorption on the catalysts. The demonstrated facile and effective strategies could be adopted for the fabrication of cost-effective and highly active catalysts for other important chemical reactions for energy conversion applications.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Claudel, Fabien. "Vers le développement d’électrocatalyseurs de dégagement d’oxygène actifs et stables." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI052.
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Cette thèse porte sur l’étude et le développement d’électrocatalyseurs à base d’iridium pour la réaction de dégagement de dioxygène (OER) dans les électrolyseurs à membrane échangeuse de protons. En raison de la dégradation marquée des électrocatalyseurs en conditions OER, nous nous sommes particulièrement intéressés à la recherche d’un compromis optimal entre activité catalytique et stabilité. Différents électrocatalyseurs (supportés sur noir de carbone, supportés sur oxydes métalliques dopés et non-supportés) ont été synthétisés et caractérisés par des méthodes électrochimiques et physico-chimiques, notamment par spectroscopie photoélectronique X, microscopie électronique en transmission à localisation identique et spectrométrie de masse à plasma à couplage inductif. Les électrocatalyseurs supportés sont les moins stables en conditions OER, notamment du fait de l’agglomération, la coalescence, la dissolution et le détachement des nanoparticules d’oxyde d’iridium. Ces deux derniers mécanismes de dégradation sont exacerbés par la corrosion des supports carbonés et la dissolution des éléments composant les supports oxydes métalliques dopés. Les électrocatalyseurs non-supportés offrent ainsi le meilleur compromis entre activité et stabilité. Les degrés d’oxydation Ir(III) et Ir(V) ont été identifiés comme les plus actifs pour l’OER en électrolyte acide tandis que l’oxyde Ir(IV) est le plus stable, l’espèce la moins stable étant l’iridium métallique Ir(0). La dégradation des couches catalytiques en cellule d’électrolyse PEM ne semble impacter que très peu les performances globales d’électrolyse par rapport à la dégradation des collecteurs de courantThis thesis focuses on the study and the development of iridium-based electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers. This work investigates in particular electrocatalyst degradation phenomena and aims at reaching an optimal OER activity-stability ratio. Various electrocatalysts (supported on high-surface area carbon, supported on doped-metal oxides and unsupported) have been synthetized and characterized by electrochemical and physico-chemical methods such as X-ray photoelectron spectroscopy, identical-location transmission electron microscopy and inductively coupled plasma mass spectrometry. Supported electrocatalysts feature stability limitations in OER conditions as revealed by agglomeration, coalescence, dissolution, and detachment of iridium oxide nanoparticles, these last two degradation mechanisms being amplified by corrosion of the carbon supports and dissolution of the elements composing the doped metal oxide supports. Unsupported electrocatalysts currently represent the best compromise between OER activity and stability. Ir(III) and Ir(V) oxides were shown to be the most active towards the OER while Ir(IV) oxide is the most stable, the least stable species being metallic iridium Ir(0). In real PEM water electrolyzers, the global electrolysis performance seems to be less impacted by the degradation of catalytic layers than the degradation of current collectors
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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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Pan, Hsiao-yung, and 潘孝勇. "Waste Water Treatment by Electrolysis." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/91226453036104617171.
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碩士國立臺灣大學
生物產業機電工程學研究所
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The aim of this study is to apply electrolysis in waste water treatment focusing on removal of total suspended non-metal solids(TSS). Relations among applied voltage, current, area of electrodes and distance between electrodes were quantified. Two experimental tanks including water re-circulating type and fixed batch type were set up and amount of waste water were both 100 liter. Electrodes were made from stainless steel. 6 plates of 1.4m x 1cm x 1mm and 4 plates of 60cm x 1cm x 1mm were used in the re-circulating and fixed batch tanks, respectively. The removal rate at the first 10 minutes for the waste water at 500μS/cm EC and initial TSS of 200-500 ppm in the re-circulating tank was about 30-40 %. For the waste water at 250-750μS/cm EC and initial TSS of 500 ppm, the highest removal rate at the first 10 minutes was 56.7 %. The TSS removal rates in direct relation to the EC values of the waste water. The removal rate at the first 10 minutes for the waste water at initial TSS of 200-500 ppm and 2 mS/cm EC in the fixed batch tank was 40-50 %. Compare both systems using waste water at 750μS/cm EC and initial TSS of 500 ppm, the removal rate for the fixed batch type at the first 20 minutes was less than the re-circulating type. However, the situation reverse after 1 hour of treatment. The final TSS for the fixed batch type and re-circulating type treatments were 40 and 100 ppm, respectively.