Дисертації: "Electrolysi"

1

Melane, Xolani. "Visualisation of electrolyte flow fields in an electrolysis cell." Diss., University of Pretoria, 2015. http://hdl.handle.net/2263/57492.

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The performance and efficiency of an electrochemical system with gas evolution can be related to the mass transfer effects which are influenced by the resulting two-phase flow. The aim of this investigation was to develop a better understanding in the effects of current density, anode height and inter-electrode spacing on the electrolyte flow patterns and to validate Computational Fluid Dynamic (CFD) model predictions of the electrolyte flow patterns. The CFD model was developed in a previous study and was applied to the experimental rig developed for this study, in which the electrolysis of copper sulphate was studied. A direct flow visualisation technique was used as the method of investigation in the experimental work. To facilitate the visual observation of the electrolyte flow patterns, O2 gas bubbles evolved on the anode surface were used as the flow followers to track the electrolyte flow patterns. At the bottom of the anode where there was no gas evolution, polyamide seeding particles (PSP) were used as the flow followers. A Photron FASTCAM SA4 high speed camera with a capability of recording up to 5000 fps was used to record the electrolyte flow patterns and circulation. The Photron FASTCAM Viewer (PFV) camera software was used for the post analysis of the recordings and for measuring bubble size, bubble speed and the speed of the PSP tracking particles. The experimental results were then compared with the results obtained from the CFD model simulation in order to validate the CFD model. The electrolysis cell was approximated by a simplified planar two-dimensional domain. The fluid flow patterns were assumed to be affected only by the change in momentum of the two fluids. To simplify the model, other physical, chemical and electro-magnetic phenomena were not modelled in the simulation. The Eulerian multiphase flow model was used to model the multiphase flow problem investigated. The flow fields observed in the experiments and predicted by the model were similar in some of the positions of interest. The gas bubble flow field patterns obtained in the experiment and model were similar to each other in Position A (the top front of the anode), C (the area at the bottom of the cell below the anode), and D (the gap between the anode and the diaphragm), with the only exception being Position B (slightly above the anode top back). The experimental results showed an accumulation of the smaller gas bubbles in Position B with a resulting circulation loop across that region. On the other hand, the model predictions did not show this gas bubble accumulation and circulation in Position B. All the flow patterns predicted for the electrolyte flow illustrated similar flow patterns to the ones observed in the experimental results, including the circulation loop in Position B. The bubble speeds measured at Position A in the experimental work had a reasonable agreement with the bubble speeds predicted by the model. The error between the two results ranged from 6% to 29% for the various cases which were tested. An increase in the current density generated more gas bubbles which resulted in an increase in the bubble speed. Increasing the anode height increased the amount of gas bubbles generated as well as bubble speed while the bubble speed was decreased with an increasing inter-electrode distance.
Dissertation (MEng)--University of Pretoria, 2015.
tm2016
Chemical Engineering
MEng
Unrestricted

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2

Klose, Carolin [Verfasser], Stefan [Akademischer Betreuer] Glunz, and Simon [Akademischer Betreuer] Thiele. "Novel polymer electrolyte membrane compositions for electrolysis and fuel cell systems." Freiburg : Universität, 2020. http://d-nb.info/1208148036/34.

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3

Sathe, Nilesh. "Assessment of coal and graphite electrolysis." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1147975951.

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4

Sahar, Abdallah. "Etude par analyse spectrale de processus aux electrodes fortement aleatoires." Paris 6, 1988. http://www.theses.fr/1988PA066522.

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Le but de ce travail a consiste a etudier deux processus electrochimiques a comportement fortement aleatoire, a savoir le degagement de bulles gazeuses sur une electrode et l'electrolyse en lit fluidise

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5

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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6

SIRACUSANO, STEFANIA. "Development and characterization of catalysts for electrolytic hydrogen production and chlor–alkali electrolysis cells." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1337.

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Gli argomenti di questa tesi hanno riguardato l’elettrolisi cloro-soda e l’elettrolisi dell’acqua mediante sistemi basati su membrane a scambio protonico (PEM). • Elettrolisi cloro-soda. Il cloro è oggi essenzialmente ottenuto mediante i processi industriali di elettrolisi di cloro-soda ed, in minore quantità, dall’elettrolisi dell’acido cloridrico. Il principale problema di questi processi è l’elevato consumo di energia elettrica che, solitamente, rappresenta una parte sostanziale del costo totale di produzione. Per l’ottimizzare di tale processo è necessario, quindi, ridurre il consumo energetico. La sostituzione del tradizionale catodo ad evoluzione di idrogeno, con un elettrodo a diffusione gassosa ad ossigeno, comporta una nuova reazione che riduce il potenziale termodinamico di cella e questo si traduce in un risparmio energetico del 30-40%. L’attività di ricerca è stata indirizzata verso lo studio di elettrodi a diffusione gassosa per la reazione di riduzione di ossigeno con particolare attenzione all’analisi superficiale e morfologica degli elettrocatalizzatori. In particolare l’attenzione è stata focalizzata sui fenomeni di deattivazione che coinvolgono questo tipo di elettrodi. Test di durata sono stati condotti sugli elettrodi in cella cloro-soda. Analisi di tipo comparativo sugli stessi sono state condotte, prima e dopo il loro funzionamento, nelle condizioni operative di interesse. La superficie degli elettrodi è stata analizzata mediante microscopio elettronico a scansione e spettroscopia fotoelettronica a raggi X. Analisi di bulk sono state effettuate mediante diffrattometria a raggi X ed analisi termogravimetrica. • Elettrolisi dell’acqua (PEM). L’idrogeno può essere prodotto a partire da sorgenti energetiche rinnovabili come fotovoltaico, eolico mediante l’elettrolisi dell’acqua. In particolare, l’elettrolisi, mediante l’utilizzo di un elettrolita polimerico (PEM), è considerata una promettente metodologia per la produzione di idrogeno, alternativa al convenzionale processo di elettrolisi il cui elettrolita è un liquido alcalino, altamente tossico e corrosivo. Un elettrolizzatore PEM possiede certamente dei vantaggi confrontato con il classico processo alcalino in termini di semplicità, sicurezza ed alta efficienza energetica. Questo sistema utilizza la già affermata tecnologia delle celle a combustibile ad elettrolita polimerico. Sfortunatamente il processo di scissione elettrochimica dell’acqua è associata ad un elevato consumo energetico, principalmente dovuto agli alti sovrapotenziali nella reazione anodica di evoluzione di ossigeno. Risulta quindi di fondamentale importanza trovare elettrocatalizzatori per l’evoluzione di ossigeno ottimali in modo da minimizzare le perdite. Il platino è utilizzato al catodo per la reazione di evoluzione di idrogeno (HER) e gli ossidi di iridio o rutenio sono usati all’anodo per la reazione di evoluzione di ossigeno (OER). Questi ossidi metallici sono richiesti perché, confrontati al platino metallico, offrono alta attività catalitica, una migliore stabilità a lungo termine ed una minore perdita di efficienza dovuta alla corrosione o all’inquinamento. Il lavoro è stato principalmente indirizzato verso: 1) la sintesi e caratterizzazione di anodi a base di RuO2 e IrO2; 2) la sintesi di supporti conduttori a base di subossidi di titanio con alta area superficiale. 1) Catalizzatori nanostrutturati a base di RuO2 e IrO2 sono stati preparati mediante un processo colloidale a 100°C; gli idrossidi così ottenuti sono stati calcinati a differenti temperature. L’attenzione è stata focalizzata sugli effetti che il trattamento termico produce sulla struttura cristallografica e sulla dimensione delle particelle di questi catalizzatori e come queste proprietà possono influenzare le performance degli elettrodi per la reazione di evoluzione di ossigeno. Caratterizzazioni elettrochimiche sono state fatte mediante curve di polarizzazioni, spettroscopia d’impedenza, e misure di crono-amperometria. 2) Una nuova metodologia di sintesi per la preparazione dei subossidi di titanio con fase Magneli (TinO2n-1) è stata sviluppata. Le caratteristiche di questi materiali sono state valutate sotto condizioni operative, in elettrolizzatori di tipo SPE, e confrontate con la polvere commerciale Ebonex. La stessa fase attiva a base di IrO2 è stata usata, come elettrocatalizzatore, per entrambi i sistemi.
The topics of this PhD thesis are concerning with Chlor alkali electrolysis and PEM water electrolysis. • Chlor alkali electrolysis. The industrial production of chlorine is today essentially achieved through sodium chloride electrolysis, with only a minor quantity coming from hydrochloric acid electrolysis. The main problem of all these processes is the high electric energy consumption which usually represents a substantial part of the total production cost. Therefore, in order to improve the process, it is necessary to reduce the power consumption. The substitution of the traditional hydrogen-evolving cathodes with an oxygen-consuming gas diffusion electrode (GDE) involves a new reaction that reduces the thermodynamic cell voltage and leads to an energy savings of 30-40%. My research activity was addressed to the investigation of the oxygen reduction at gas-diffusion electrodes as well as to the surface and morphology analysis of the electrocatalysts. Specific attention was focused on deactivation phenomena involving this type of GDE configuration. The catalysts used in this study were based on a mixture of micronized silver particles and PTFE binder. In this study, fresh gas diffusion electrodes were compared with electrodes tested at different times in a chlor-alkali cell. Electrode stability was investigated by life-time tests. The surface of the gas diffusion electrodes was analyzed for both fresh and used cathodes by scanning electron microscopy and X-ray photoelectron spectroscopy. The bulk of gas diffusion electrodes was investigated by X-ray diffraction and thermogravimetric analysis. • PEM water electrolysis. Water electrolysis is one of the few processes where hydrogen can be produced from renewable energy sources such as photovoltaic or wind energy without evolution of CO2. In particular, an SPE electrolyser is considered as a promising methodology for producing hydrogen as an alternative to the conventional alkaline water electrolysis. A PEM electrolyser possesses certain advantages compared with the classical alkaline process in terms of simplicity, high energy efficiency and specific production capacity. This system utilizes the well know technology of fuel cells based on proton conducting solid electrolytes. Unfortunately, electrochemical water splitting is associated with substantial energy loss, mainly due to the high over-potentials at the oxygen-evolving anode. It is therefore important to find the optimal oxygen-evolving electro-catalyst in order to minimize the energy loss. Typically, platinum is used at the cathode for the hydrogen evolution reaction (HER) and Ir or Ru oxides are used at the anode for the oxygen evolution reaction (OER). These metal oxides are required, compared to the metallic platinum, because they offer a high activity, a better long-term stability and less efficiency losses due to corrosion or poisoning. My work was mainly addressed to a) the synthesis and characterisation of IrO2 and RuO2 anodes; b) conducting Ti-suboxides support based on a high surface area. a) Nanosized IrO2 and RuO2 catalysts were prepared by using a colloidal process at 100°C; the resulting hydroxides were then calcined at various temperatures. The attention was focused on the effect of thermal treatments on the crystallographic structure and particle size of these catalysts and how these properties may influence the performance of oxygen evolution electrode. Electrochemical characterizations were carried out by polarization curves, impedance spectroscopy and chrono-amperometric measurements. b) A novel chemical route for the preparation of titanium suboxides (TinO2n−1) with Magneli phase was developed. The relevant characteristics of the materials were evaluated under operating conditions, in a solid polymer electrolyte (SPE) electrolyser, and compared to those of the commercial Ebonex®. The same IrO2 active phase was used in both systems as electrocatalyst.

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7

Owais, Ashour A. [Verfasser]. "Packed Bed Electrolysis for Production of Electrolytic Copper Powder from Electronic Scrap / Ashour A Owais." Aachen : Shaker, 2003. http://d-nb.info/1181600782/34.

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8

Soundiramourty, Anuradha. "Towards the low temperature reduction of carbon dioxide using a polymer electrolyte membrane electrolysis cell." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112174.

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L’objectif principal de ce travail de thèse était d’évaluer les propriétés électro catalytiques de différents composés moléculaires vis-à-vis de la réduction électrochimique basse température du dioxyde de carbone, en vue d’applications dans des cellules d’électrolyse à électrolyte polymère solide. Après avoir mesuré les performances de métaux modèles (cuivre et nickel) servant de référence, nous avons testé les performances de quelques composés moléculaires à base de nickel. Le rôle catalytique de ces différents composés a été mis en évidence en mesurant les courbes intensité-potentiel dans différents milieux. Nous avons évalué l’importance de la source en hydrogène dans le mécanisme réactionnel. Les produits de réduction du dioxyde de carbone formés dans le mélange réactionnel ont été analysés par chromatographie en phase gazeuse. Nous avons ensuite abordé la possibilité de développer des cellules d’électrolyse à électrolyte polymère solide. Nous avons testé des cellules utilisant soit des anodes à eau liquide pour le dégagement d’oxygène, soit des anodes à hydrogène gazeux. L’utilisation de complexes moléculaires à base de nickel à la cathode a permis d’abaisser le potentiel de la cathode et de réduire le CO₂ mais la réaction de dégagement d’hydrogène reste prédominante
The main objective of this research work was to put into evidence the electrocatalytic activity of various molecular compounds with regard to the electrochemical reduction of carbon dioxide, at low temperature, in view of potential application in PEM cells. First, reference values have been measured on copper and nickel metals. Then the performances of some molecular compounds have been measured. The electrochemical activity of these different compounds has been put into evidence by recording the current-potential relationships in various media. The role of a hydrogen source for the reduction processes has been evaluated. The formation of reduction products has been put into evidence and analyzed by gas phase chromatography. Then, a PEM cell has been developed and preliminary tests have been performed. PEM cells with either an oxygen-evolving anode or a hydrogen-consuming anode have been tested. Using nickel molecular complexes, it has been possible to lower the potential of the cathode and to reduce CO₂ but the parasite hydrogen evolution reaction was found to remain predominant

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9

Owais, Ashour [Verfasser]. "Packed Bed Electrolysis for Production of Electrolytic Copper Powder from Electronic Scrap / Ashour A Owais." Aachen : Shaker, 2003. http://d-nb.info/1181600782/34.

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10

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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11

Soleimany, Mehranjani Alireza. "Tape casting of ceramic GDC/YSZ bi-layer electrolyte supports for high temperature co-electrolysis." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/17600/.

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High temperature co-electrolysis of carbon dioxide and steam may provide an efficient, cost effective, and environmentally friendly production of syngas from curtailed wind energy. To achieve cost competitive high performance (e.g. with minimum internal resistance) electrolysis cells, it is critical to develop materials and cell configuration optimal for coelectrolysis. In addition, a cost-effective fabrication procedure is important in allowing broader commercialisation of Solid Oxide Electrolysis Cells (SOECs). The initial part of this work emphasises on the feasibility of SOECs plant for converting curtailed wind energy to syngas to enhance the grid flexibility. We first obtained operating parameters for the conversion plant based on the most recent literature data on the performance of high temperature co-electrolysis for syngas production. In addition, an evaluation of the interaction between variable generation and typical electricity demand patterns was presented; and, limitations in the flexibility of traditional electric generators were considered. Furthermore, in a projection of wind generation made for 2020, we estimated the maximum power value of the curtailment wind profile to be 23.9 GW. It was remarked that the cost increase for constraining wind in future could make SOEC conversion technology more commercially attractive. An estimation of the total investment costs for grid connected electrolysis system was made by considering the share of operating cost. The share of electricity price in the total cost of syngas production was estimated to be 61%. It was shown that using cost effective electricity could significantly reduce the syngas production price. The total investment costs for grid connected electrolysers were projected to be 0.38 M£/MW in 2020. It was highlighted that the scope of electrochemical conversion of CO2 to fuel offers flexible demand that is not yet sufficiently understood. There are still technical barriers that need to be addressed in the field of manufacturing processes, grid integration and system operation. A key factor in operating solid oxide electrolysis cells (SOECs) is the ability to provide a sufficiently high level of oxide ion conduction through the electrolyte in the cell. Commonly, high performance cells use Y-stabilised ZrO2 (YSZ) or Gd-doped CeO2 (GDC10). Whilst GDC10 has higher oxide ion conductivity than YSZ, it suffers from electronic conduction due to the partial reduction of Ce4+ to Ce3+ during operation at high temperature and low oxygen partial pressure environment. Here we describe the fabrication of a bilayer GDC10/8YSZ electrolyte support using tape casting and single step co-sintering. A cost effective fabrication procedure is important in allowing broader commercialisation of Solid Oxide Cells for fuel cell/electrolysis applications. A bi-layer 8YSZ/GDC electrolyte is suggested as an effective solution to avoid ceria reduction in a fuel (reducing) environment, thereby preventing current leakage across the electrolyte, while maintaining high oxide ion conduction. Bilayer zirconia/ceria processing has proven problematic due to thermochemical instability at high sintering temperatures. We first prepared and optimised the slip formulations for tape casting process, this was necessary to achieve high green density and uniform tapes. Furthermore, the shrinkage profile of the two bulk materials in bilayer electrolyte were matched using a Fe2O3 sintering additive. Additions of 5 mol% of Fe2O3 in the GDC layer and 2 mol% of Fe2O3 in the YSZ layer prevents delamination during co-sintering. The addition of Fe2O3 promotes densification behaviour, enabling achievement of a dense bilayer (~90%) at a reduced sintering temperature of 1300 °C; ~ 150 °C below conventional sintering temperatures. Bilayer 8YSZ/GDC10 electrolytes with relative thickness of 73/154 μm was successfully fabricated by tape casting and low-temperature co-sintering at 1300 °C. No significant microstructural defects or delamination were observed after co-firing The effect of the Fe2O3 sintering aid on the crystal structure of two bulk materials used in bilayer electrolyte were investigated by X-ray diffraction. Results showed that, both materials with Fe2O3 additions maintain their fluorite structure. The analysis revealed a reduction in unit cell volume for both Fe2O3-doped samples. While using Fe2O3 sintering aid was found to improve the sinterability of the two bulk materials, increasing the dopant concentration above the solubility limit leads to the formation of an iron rich phase, which was subsequently analysed by energy-dispersive X-ray spectroscopy. Elemental analysis at YSZ/GDC interface revealed asymmetric elemental diffusion behaviour when using Fe2O3 to co-sinter YSZ/GDC bilayers, with lower diffusivity of Zr and Y ions in the GDC layer compared to that of Ce and Gd ions detected in the YSZ layer, showing the positive effect of Fe2O3 on limiting the interdiffusion behaviour. Electrochemical impedance measurements in air revealed the total conductivity of the Fe2O3 containing bilayer electrolytes increased by an order of magnitude compared to Fe2O3-free bilayers. This was attributed to two factors; first, by limiting the overall elemental interdiffusion length from ~15 to ~5μm and, second, by achieving better contact between the YSZ and GDC layers and higher sintered density when using a Fe2O3 additive as a sintering aid. The cost-effective low-temperature processing technique presented in this study is expected to help widen the material selection and resolve the thermochemical issues associated with high-temperature co-sintering allowing a broader commercialisation of SOECs.

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12

Lou, Ning. "A Study on Electrolyte Optimization by Adopting Additives in Electrolytic In-Process Dressing (ELID)." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1271452998.

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13

Watkins, Luke. "Development of non-noble catalysts for hydrogen and oxygen evolution in alkaline polymer electrolyte membrane electrolysis." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2296.

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Hydrogen is seen as the ‘energy carrier of the future’ due to the element’s relative abundance, the formation of water as opposed to the green house gases when utilised as a fuel in fuel cells, and the ability to be produced by electrolysers powered from renewable energy sources such as wind, water and sunlight. The development of hydrogen production through electrolysis is hindered by the high costs associated with the technology, specifically the ion exchange membranes and electrocatalysts that are employed in the membrane electrode assemblies used in polymer electrolyte electrolysers. This research focused on the development of non-noble catalysts suitable for hydrogen and oxygen evolution in alkaline electrolysis. Synthesis of NiO was achieved through thermal decomposition, chemical bath deposition and solution growth techniques. A mixed metal oxide, NiCo2O4, was synthesized through thermal decomposition of metal nitrate salts. Cyclic voltammetry and steady state electrochemical experiments on the electrodes were conducted in an electrochemical half cell electrolyser. A thin film of pure NiO was formed onto a titanium substrate through chemical bath deposition followed by thermal decomposition. The performance of the electrode at 1.73 V, relative to the mass of the catalyst loading, produced 0.25 A cm-2 mg-1 in 1 M NaOH at 25°C (IrO2 produced 0.44 A cm-2 mg-1 in the same electrolyser). The electrode’s performance is attributed to the nanoporous structure of the catalyst film (20 – 200 nm pore diameters), which was formed from the chemical bath deposition method used to prepare the catalyst films. Unfortunately this procedure has a limited film thicknesses so higher loadings could not be achieved. Higher loadings of other non-noble electrocatalysts were made possible with addition of a PVDF binder to the catalyst film. Physical analysis through XRD was performed on the most promising catalysts for the oxygen evolution reaction to confirm their composition. A blend of α-Ni(OH)2 and 4Ni(OH)2•NiOOH•xH2O formed through the chemical bath deposition technique produced higher current densities (104 mA cm-2 at 0.8 V vs. Hg/HgO) than another non-noble metal catalyst, NiCo2O4 (97 mA cm-2) II in 1 M NaOH at 25°C. An alkaline polymer electrolyser free from noble metals was developed with a membrane electrode assembly that utilised a partially fluorinated membrane, a PVBC/PVC ionomer in the catalyst layers, 1.0 mg NiMoO4 cm-2 in the cathode and 0.7 mg NiCo2O4 cm-2 in the anode. It produced 0.4 A cm-2 in 1 M KOH at 25° at a potential of 1.9 V.

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14

Dunleavy, Christopher Squire. "Development of quantitative techniques for the study of discharge events during plasma electrolytic oxidation processes." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/228637.

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Plasma electrolytic oxidation, or PEO, is a surface modification process for the production of ceramic oxide coatings upon substrates of metals such as aluminium, magnesium and titanium. Two methodologies for the quantitative study of electrical breakdown (discharge) events observed during plasma electrolytic oxidation processes were developed and are described in this work. One method presented involves direct measurement of electrical breakdowns during production of an oxide coating within an industrial scale PEO processing arrangement. The second methodology involves the generation and measurement of electrical breakdown events through coatings pre-deposited using full scale PEO processing equipment. The power supply used in the second technique is generally of much lower power output than the system used to initially generate the sample coatings. The application of these techniques was demonstrated with regard to PEO coating generation on aluminium substrates. Measurements of the probability distributions of discharge event characteristics are presented for the discharge initiation voltage; discharge peak current; event total duration; peak instantaneous power; charge transferred by the event and the energy dissipated by the discharge. Discharge events are shown to increase in scale with the voltage applied during the breakdown, and correlations between discharge characteristics such as peak discharge current and event duration are also detailed. Evidence was obtained which indicated a probabilistic dependence of the voltage required to initiate discharge events. Through the scaling behaviour observed for the discharge events, correspondence between the two measurement techniques is demonstrated. The complementary nature of the datasets obtainable from different techniques for measurement of PEO discharge event electrical characteristics is discussed with regards to the effects of interactions between concurrently active discharge events during large scale PEO processing.

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15

Karakurkchi, A. V., N. D. Sakhnenko, M. V. Ved, and A. S. Gorohivskiy. "Nanostructured catalytic cobalt containing PEO-coatings on alloy AL25." Thesis, Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/22609.

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16

Fawcett, Lydia. "Electrochemical performance and compatibility of La2NiO4+δ electrode material with La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte for solid oxide electrolysis". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24667.

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La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) is an oxygen ion conducting electrolyte material widely used in solid oxide fuel cells (SOFC). La2NiO4+δ (LNO) is a mixed ionic-electronic conducting layered perovskite with K2NiF4 type structure which conducts oxygen ions via oxygen interstitials. LNO has shown promising results as an SOFC electrode in the literature. In this work the compatibility and performance of LNO electrodes on the LSGM electrolyte material for solid oxide electrolysis cell (SOEC) is investigated. The materials were characterised as SOEC/SOFC cells by symmetrical and three electrode electrochemical measurements using Electrochemical Impedance Spectroscopy (EIS). Conductivity and ASR values were obtained in the temperature range 300-800°C with varying atmospheres of pH2O and pO2. The cells were also subjected to varied potential bias, mimicking fuel cell or electrolysis use. Enhancement of LNO performance was observed with the application of potential bias in both anodic and cathodic mode of operation in all atmospheres with the exception of cathodic bias in pO2 = 6.5x10-3 atm. In ambient air at 800°C LNO ASRs were 2.82Ω.cm2, 1.83Ω.cm2 and 1.37Ω.cm2 in OCV, +1000mV bias and -1000mV bias respectively. In low pO2 at 800°C LNO ASRs were 9.17Ω.cm2, 1.74Ω.cm2 and 456.9Ω.cm2 in OCV, +1000mV bias and -1000mV bias respectively. The increase in ASR with negative potential bias in low pO2 is believed to be caused by an increase in mass transport and charge transfer impedance responses. Material stability was confirmed using X-Ray Diffraction (XRD), in-situ high temperature pH2O and pO2 XRD. In-situ XRD displayed single phase materials with no observable reactivity in the conditions tested. Scanning Electron Microscopy images of cells tested by EIS in all atmospheres displayed no microstructure degradation except for those cells tested in a humid atmosphere which display a regular pattern of degradation on the LNO surface attributed to reaction with the Pt mesh current collector.

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Dumortier, Mikaël. "Modélisation numérique des transferts de matière, de chaleur et électrochimiques au sein d'un électrolyseur haute température." Thesis, Montpellier 2, 2013. http://www.theses.fr/2012MON20127/document.

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L'électrolyse haute température de l'eau à l'aide de membranes en céramique conductrice de protons est un processus intéressant pour la production d'hydrogène. Ce processus, qui peut être effectué sans catalyseurs nobles, produit de l'hydrogène pur et nécessite moins d'électricité que l'électrolyse classique à basse température. Le développement futur de ces réacteurs à membrane nécessite des efforts accrus sur la simulation numérique afin d'optimiser la chaleur et les transferts de masse ainsi que la conception de cellules d'électrolyse. Ce travail présente un ensemble d'équations sélectionnées dans la littérature et des démonstrations mathématiques rigoureuses permettant la description des phénomènes de transport dans la cellule et en particulier dans les électrodes qui sont composées de cermets. A partir de ce modèle, une étude paramétrique est conduite de façon à caractériser l'influence des différents paramètres opératoires sur ces phénomènes. Les différentes observations de cette étude permettent de dresser un ensemble d'hypothèses pour le développement de méthodes destinées à la simplification du modèle et à la réduction du temps de résolution. Ces modèles simplifiés permettent la détermination analytique des grandeurs dans l'électrode et ont conduit à la construction de nombres adimensionnels et de longueur caractéristiques du dispositif
High temperature electrolysis of water by using proton conducting ceramic membranes is an interesting process for producing hydrogen. This process can be carried out without noble catalysts and produces pure hydrogen and requires less electricity than classical low temperature electrolysis. The future development of such membrane reactors requires increasing efforts on numerical simulation in order to optimize the heat and mass transfers as well as the design of electrolysis cells. This work presents a set of equations selected from the literature and rigorously demonstrated for the description of transport phenomena in the cell and particularly in the electrodes which are made of cermets. From this model, a parametric study is conducted in order to characterize the influence of various operating parameters on these phenomena. The different findings of this study provide a set of assumptions for the development of methods for simplifying the model and reducing the time of resolution. These simplified models allow analytical determination of quantities in the electrode and leads to the establishment of dimensionless numbers and characteristics length of the device

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Verdin, Baptiste. "Etude d'électrodes grande surface d'électrolyseurs PEM : inhomogénéités de fonctionnement et intégration de catalyseurs innovants." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS036/document.

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La production d’hydrogène par électrolyse de l’eau PEM prendra une place importante dans le paysage énergétique pour le stockage des EnR. Le changement d’échelle nécessaire ne peut s’envisager que par une augmentation significative de la puissance nominale, passant essentiellement par l’accroissement de leur taille et de la densité de courant. Dans ces conditions, un fonctionnement optimal et une durée de vie suffisante ne pourront être obtenus que par l’homogénéisation de la répartition du courant à la surface des électrodes. Au cours de cette thèse, nous avons utilisé pour la première fois un outil de cartographie des distributions de courant et de température à la surface d’AME grande surface, issus d’un design industriel. Une carte de mesure S++® conçue sur mesure et adaptée à l’utilisation envisagée a été intégrée à une monocellule PEM de 250cm². Une caractérisation électro-mécanique de la cellule a mis en évidence le lien existant entre le champ de forces de compression mécanique et de la densité de courant. Nous montrons qu’une compression mécanique optimale n’est pas suffisante pour homogénéiser la distribution de courant : le design de cellule, et plus particulièrement la distribution des fluides, joue un rôle majeur dans l’inhomogénéité de la distribution de courant, récurrente entre le centre et la périphérie de la cellule. Nous soulignons la concentration des lignes de courant vers le centre de l’AME lors de tests dynamiques, conséquence d’un vieillissement spatialement différencié. Nous avons également développé une structure d’électrode permettant de ré-homogénéiser globalement la distribution de courant, ce qui permet un meilleur maintien des performances dans le temps. Nous avons également développé un modèle numérique de la couche catalytique permettant de mieux comprendre la répartition des lignes de courant en fonction des caractéristiques géométriques des collecteurs poreux. Nous mettons en lumière le rôle majeur des surtensions dans le pouvoir répartiteur de la couche active, qui est particulièrement faible côté cathodique. Nous préconisons de densifier la couche catalytique pour une meilleure répartition du courant et pour limiter les différenciations locales de vieillissement. L’ensemble des observations en mono cellule a été confirmé par des essais sur un stack commercial
Hydrogen production from PEM water electrolysis will take a great place in the energy landscape for RES storage. This scale shift requires a significant increase of the nominal power, and therefore an increase in size and a gain in the current density. Optimal operation (in terms of efficiency and lifetime) can be obtained only if the distribution of current lines over the electrode surface is adequately homogeneous. In this thesis, we have used for the first time a specific tool for the in-situ mapping of current and temperature in a large surface area PEM single cell. A customized S++® measuring plate, adapted to our application, has been implemented in a 250cm² PEM single cell. Electromechanical characterization of the cell has put into evidence the link between the field of clamping force and the local current density. We have shown that an optimal mechanical compression is not sufficient to homogenize current distribution. We have demonstrated that the cell design, in particular the fluid distribution, plays a major role in current distribution inhomogeneities, which recurrently form between the center and the periphery of the cell. We have also shown that during dynamic operation, current lines tend to concentrate at the center of the cell as a consequence of spatially differentiated ageing. We have developed an electrode structure that facilitates the global re-homogenization of current lines and additionally shows an increased durability. In parallel, we have developed a numerical model to calculate the distribution of current lines within the thickness of catalytic layers as a function of the geometry of the PTL. We have found that overvoltages play a major role in current distribution, and that the cathode is prone to more heterogeneities. We propose to densify the catalyst layers for a better current repartition and a lesser differentiated ageing. Key findings from single cell tests have been confirmed on a commercial stack

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Schalenbach, Maximilian Verfasser], Detlef [Akademischer Betreuer] [Stolten, and Eckhard [Akademischer Betreuer] Spohr. "Proton conduction and gas permeation through polymer electrolyte membranes during water electrolysis / Maximilian Schalenbach ; Detlef Stolten, Eckhard Spohr." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/118606921X/34.

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Liu, Chang Verfasser], Werner [Akademischer Betreuer] [Lehnert, and Lorenz [Akademischer Betreuer] Singheiser. "Noble metal coated porous transport layers for polymer electrolyte membrane water electrolysis / Chang Liu ; Werner Lehnert, Lorenz Singheiser." Aachen : Universitätsbibliothek der RWTH Aachen, 2021. http://d-nb.info/124069119X/34.

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21

Schalenbach, Maximilian [Verfasser], Detlef [Akademischer Betreuer] Stolten, and Eckhard [Akademischer Betreuer] Spohr. "Proton conduction and gas permeation through polymer electrolyte membranes during water electrolysis / Maximilian Schalenbach ; Detlef Stolten, Eckhard Spohr." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://nbn-resolving.de/urn:nbn:de:101:1-2019051406021643509245.

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22

Rozain, Caroline. "Développement de nouveaux matériaux d’électrodes pour la production d’hydrogène par électrolyse de l’eau." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112177/document.

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La production d’hydrogène et de dioxygène par électrolyse PEM (PEM « Proton Exchange Membrane ») de l’eau s’effectue grâce à la présence de métaux nobles dans les couches catalytiques: à la cathode, le platine supporté sur du carbone est généralement utilisé (les chargements en métaux nobles sont faibles de l’ordre de 0,5 mg/cm²) ; à l’anode, la production d’oxygène s’effectue à des potentiels élevés (> 1,6 V vs. ESH). Les oxydes de métaux nobles sont utilisés seuls dans la couche active anodique et servent à la fois de catalyseurs et de conducteurs électroniques. Comme ils sont parmi les métaux les plus denses, pour obtenir une continuité électrique de la couche anodique, les chargements doivent être très élevés, de l’ordre de 2-3 mg/cm².Cette thèse propose ainsi de développer de nouveaux matériaux supports stables électrochimiquement et bons conducteurs électroniques pour séparer les fonctions de catalyse et de conduction électronique. Pour cela, des assemblages membrane électrodes intégrant des particules de titane comme support de catalyseur anodique ont été préparés dans notre laboratoire. Testés en mono-cellule de 25 cm², leurs principales caractéristiques ont été déterminées par voltampérométrie cyclique, spectroscopie d’impédance et grâce à des courbes de polarisations à différentes températures. La comparaison des résultats obtenus entre ces anodes « innovantes » et celles à base de catalyseur seul a permis de mettre en évidence la présence d’un chargement anodique seuil de 0,5 mg/cm² en dessous duquel la présence d’un support de catalyseur est nécessaire pour assurer la percolation électrique. Grâce à l’utilisation de ce support de catalyseur bon marché, les chargements anodiques ont pu être réduits jusqu’à des valeurs aussi faibles que 0,1 mg/cm² IrO2, soit une réduction de dix fois au minimum par rapport aux taux généralement employés dans la littérature, tout en maintenant des performances identiques
It is expected that PEM water electrolysis will play a significant role in the hydrogen society as a key process for producing hydrogen from renewable energy sources but before this, substantial cost reductions are still required. Because of the high acidity of membrane materials used in PEM water electrolysers, expensive noble-metals or their oxides are required as electrocatalysts (platinum for hydrogen evolution and iridium for oxygen evolution). As the oxygen evolution reaction takes place with a large overpotential (anodic potential > 1.6 V) only few materials can be used to avoid corrosion. In state-of-the-art, noble metal oxides are generally used alone in the active layer with typical loadings of 2-3 mg/cm² and act as both catalyst and electronic conductor.In order to reduce the noble metal loadings and keep a good electronic conductivity of the catalytic layer, iridium can be supported onto a conductive and electrochemical stable material support. To gain more insights, several MEAs with anodes made of pure iridium oxide or 50 wt % IrO2/Ti anodes have been prepared and characterized using cyclic voltammetry and impedance spectroscopy, and by measuring polarization curves at different operating temperatures. Without the catalyst support, anodic loadings can be reduced down to 0,5 mg/cm² without any degradation in the electrochemical performances. By using anodes made of iridium oxide and titanium particles, further reductions of anodic loading can be made down to 0.1 mg/cm² with performances similar to those obtained with conventional loadings of several mg cm-2

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Karakurkchi, A. V., M. V. Ved, N. D. Sakhnenko, I. Yu Yermolenko, and S. I. Zyubanova. "Electroplating and functional properties of amorphous Fe-Mo(W) and Fe-Mo-W coatings." Thesis, Институт химии растворов им. Г. А. Крестова РАН, 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/22618.

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24

González, Martínez Isaí [Verfasser], and Kai [Akademischer Betreuer] Sundmacher. "Hydrogen chloride electrolysis in a polymer-electrolyte-membrane reactor with oxygen-depolarized cathode / Isaí González Martínez. Betreuer: Kai Sundmacher." Magdeburg : Universitätsbibliothek, 2015. http://d-nb.info/1080560793/34.

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25

Wauters, Cary N. "Electrolytic membrane recovery of bromine from waste gas-phase hydrogen bromide streams using a molten salt electrolyte." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/10131.

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26

Kunovjánek, Miroslav. "Elektrolyzér pro výrobu vodíku." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217696.

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The work is concerned with a production of hydrogen and oxygen through by the help of electrolytic process in a device called electrolyzer. The basis of the work is assurance of the best efficiency of this process by testing a variety of materials and surfaces of electrodes, and testing different types of alkalic electrolytes.

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27

Allanore, Antoine. "Étude expérimentale de la production de fer électrolytique en milieu alcalin : mécanisme de réduction des oxydes et développement d'une cellule." Thesis, Vandoeuvre-les-Nancy, INPL, 2007. http://www.theses.fr/2007INPL109N/document.

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Le fer est l'un des rares métaux qui ne soit pas produit industriellement par électrolyse. Pour aider au développement d'un tel procédé pour l'acier, l'électrolyse des oxydes de fer en milieu sodique est examinée, selon deux approches. La première démarche consiste en l'étude expérimentale du mécanisme réactionnel. L'électrochimie des ions indique qu'il est possible de produire du métal par électrodéposition en milieu alcalin. Parallèlement, l'étude de la réduction d'une particule d'oxyde hématite révèle qu'elle subit, lors de sa conversion en fer métallique, une transformation macroscopique en phase solide. Les analyses démontrent la formation de magnétite comme intermédiaire réactionnel. La seconde démarche est dédiée à la production du fer métallique, par électrolyse d'une suspension de particules d'oxyde dans diverses configurations de cellules. L'incidence des paramètres de procédé a été établie et permet de proposer des éléments de conception d'une cellule industrielle
Iron is one of the few metals which is not industrially produced by electrolysis. The electrowinning of iron metal from its oxides in alkaline solution has been studied to develop such an ironmaking route. Two approaches have been adopted. The first one concerns the evaluation of the reaction mechanism. The study of iron ions electrochemistry in alkaline media shows that the electrodeposition of iron metal is possible. The study of a single iron oxide particle reduction reveals that a reaction of the hematite solid phase is possible. The analysis of a partially converted particle proves that magnetite is formed as an intermediate. The second field of study is dedicated to the production of iron metal in various electrochemical cells, using a suspension electrolysis process. The influence of the key operating parameters is established to assess the possible scale-up. All these elements are gathered to propose the main features of an industrial cell dedicated to the reaction

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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 courant
This 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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Williams, Mario. "Characterization of platinum-group metal nanophase electrocatalysts employed in the direct methanol fuel cell and solid-polymer electrolyte electrolyser." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&amp.

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King, Rebecca Lynne. "Investigation of Anode Catalysts and Alternative Electrolytes for Stable Hydrogen Production from Urea Solutions." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1275514221.

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31

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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Yang, Xuedi. "Cathode development for solid oxide electrolysis cells for high temperature hydrogen production." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/979.

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This study has been mainly focused on high temperature solid oxide electrolysis cells (HT-SOECs) for steam electrolysis. The compositions, microstructures and metal catalysts for SOEC cathodes based on (La₀.₇₅Sr₀.₂₅)₀.₉₅Mn₀.₅Cr₀.₅O₃ (LSCM) have been investigated. Hydrogen production amounts from SOECs with LSCM cathodes have been detected and current-to-hydrogen efficiencies have been calculated. The effect of humidity on electrochemical performances from SOECs with cathodes based on LSCM has also been studied. LSCM has been applied as the main composite in HT-SOEC cathodes in this study. Cells were measured at temperatures up to 920°C with 3%steam/Ar/4%H₂ or 3%steam/Ar supplied to the steam/hydrogen electrode. SOECs with LSCM cathodes presented better stability and electrochemical performances in both atmospheres compared to cells with traditional Ni cermet cathodes. By mixing materials with higher ionic conductivity such as YSZ(Y₂O₃-stabilized ZrO₂ ) and CGO(Ce₀.₉Gd₀.₁O₁.₉₅ ) into LSCM cathodes, the cell performances have been improved due to the enlarged triple phase boundary (TPB). Metal catalysts such as Pd, Fe, Rh, Ni have been impregnated to LSCM/CGO cathodes in order to improve cell performances. Cells were measured at 900°C using 3%steam/Ar/4%H₂ or 3%steam/Ar and AC impedance data and I-V curves were collected. The addition of metal catalysts has successfully improved electrochemical performances from cells with LSCM/CGO cathodes. Improving SOEC microstructures is an alternative to improve cell performances. Cells with thinner electrolytes and/or better electrode microstructures were fabricated using techniques such as cutting, polishing, tape casting, impregnation, co-pressing and screen printing. Thinner electrolytes gave reduced ohmic resistances, while better electrode microstructures were observed to facilitate electrode processes. Hydrogen production amounts under external potentials from SOECs with LSCM/CGO cathodes were detected by gas chromatograph and current-to-hydrogen efficiencies were calculated according to the law of conservation of charge. Current-to-hydrogen efficiencies from these cells at 900°C were up to 80% in 3%steam/Ar and were close to 100% in 3%steam/Ar/4%H₂. The effect of humidity on SOEC performances with LSCM/CGO cathodes has been studied by testing the cell in cathode atmospheres with different steam contents (3%, 10%, 20% and 50% steam). There was no large influence on cell performances when steam content was increased, indicating that steam diffusion to cathode was not the main limiting process.

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Vukasin, Julien. "Modélisation des transferts de masse et de chaleur dans une cellule d'électrolyse de production de fluor." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT132.

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Анотація:

Modélisation des transferts de masse et de chaleur dans une cellule d'électrolyse de production de fluor. La production de fluor par électrolyse est une étape clé de la conversion de l’uranium dans l’industrie nucléaire. Afin d’optimiser ce procédé, les travaux de thèse décrits dans ce manuscrit se sont concentrés sur deux axes : le développement d’un modèle numérique de l’électrolyseur et l’étude du phénomène d’hyperpolarisation cathodique néfaste pour le bon fonctionnement de la cellule. Un modèle couplant plusieurs physiques (thermique avec solidification, diphasique, électrocinétique) a été développé et des essais expérimentaux ont été menés afin d’acquérir, d’une part, certaines propriétés physiques de l’électrolyte nécessaires aux simulations (conductivité thermique et capacité thermique à pression constante) et, d’autre part, des données expérimentales permettant de qualifier le modèle obtenu. Ce travail de modélisation a abouti à l’obtention d’un modèle 3D fiable couplant les physiques citées précédemment, ceci à l’échelle d’un pilote R&D semi-industriel. L’impact de la solidification de l’électrolyte sur le transfert de chaleur a également pu être simulé pour la première fois. Ces essais ont également permis de fournir des premières explications sur le phénomène d’hyperpolarisation cathodique en dressant des tendances claires quant à l’influence de certains paramètres de contrôle de l’électrolyseur comme le titre HF et la température de consigne
Computer modeling of heat transfer and mass transfer in an electrolytic cell for production of fluorineElectrolytic production of fluorine is a key step in uranium conversion for the nuclear industry. In order to improve this process, the work described in this dissertation aims at two main objectives: to build a numerical simulation of the electrolysis cell and to understand the cathodic hyperpolarization effect which lowers the productivity of the cell. A model coupling several physics (heat transfer with solidification, two-phase flow, electrokinetics) has been developed and experiments were made in order to evaluate unknown physical properties of the electrolyte (thermal conductivity and heat capacity at constant pressure). Experimental data were also acquired in order to assess the capacity of the model to simulate various phenomena occurring inside the cell. Eventually, a reliable 3D model of a semi-industrial R&D cell coupling the physics above mentioned has been obtained. The negative impact of the solidification of the electrolyte on the cooling system was simulated for the first time. Thanks to these experiments, it was also possible to determine the major trends which drive the cathodic hyperpolarization effect. The influence of HF mass fraction and temperature on this phenomenon was clearly shown

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34

Palaniappan, Ramasamy. "Improving The Efficiency Of Ammonia Electrolysis For Hydrogen Production." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1386341476.

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35

Nemeth, Regina. "Electrolysis of chalcopyrite." Thesis, Luleå tekniska universitet, Industriell miljö- och processteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70590.

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Copper is one of the most important metals globally, due to its wide application range and excellent chemical properties. Today it is commonly produced from chalcopyrite concentrates by the pyrometallurgical route with high emissions of greenhouse gasses. Tougher restrictions from authorities and governments on the industry give rise to research on other production routes for metals. Research has proven that copper production from chalcopyrite concentrates by the electrochemical route is possible. The project purposes were to produce copper from a chalcopyrite concentrate by removing sulfur during molten salt electrolysis and determine how the trace elements arsenic and antimony distributed. The chalcopyrite concentrate used in the trials was clean with low amount of impurities, therefore a dirty pyrite concentrate with higher content of impurities was used for determining the distribution of As and Sb. The electrolysis would roughly process 80 g of raw concentrate. The experimental set-up consisted of a pit-furnace with a stainless-steel crucible filled with 43.9 wt% NaCl and 56.1 wt% KCl.. The working electrode was composed of baskets made of molybdenum mesh containing either 2 or 4 briquettes of 20 g. The counter electrode was composed of a graphite block and the atmosphere was kept inert with nitrogen gas. The equimolar salt mixture was heated to 770 ° and a constant cell voltage at 2.5 V was applied until the current had decreased and stabilized. It was concluded that the time-current curve for reduction of chalcopyrite followed a similar trend to that reported in the literature. The up-scaling of electrolysis of sulfuric concentrates was proven to be successful. Iron was captured on the inside of the sample holder and copper from the outside, separating the two elements into two fractions. This indicated that the separation of copper and iron occurred spontaneously, probably due to the magnetization of the reduced iron particles under the influence of the electromagnetic field induced by the electrolysis current. Analyses by XRD, SEM, LECO and XRF proved that sulfur was reduced to < 0.2 wt% in the two product fractions. Most of the sulfuric compounds in the raw concentrates ended up as pure elements (As, Sb, Pd and Zn) in the copper product followed by the loss of the corresponding metallic elements in the exhaust gas due to evaporation of these elements. Much knowledge of electrolysis of chalcopyrite was gained. To reach the original objectives further trials with an improved basket holder functioning as the cathode must be made. The results indicated that the electrochemical approach is suitable for copper production from chalcopyrite concentrates and further studies are recommended.

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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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37

Laveissière, Marie. "Elaboration et caractérisations de revêtements élaborés par oxydation micro-arcs sur alliage de titane TA6V." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30351.

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Анотація:

Les traitements de surface sont souvent nécessaires pour améliorer les performances des matériaux métalliques et élargir les spectres de leurs applications. L'alliage de titane TA6V (ou grade 5) est ainsi utilisé dans de nombreux domaines (du biomédical à l'aéronautique) car il est léger et possède de bonnes propriétés en anticorrosion et de résistance à la température. Cependant, son comportement tribologique est en fait médiocre et doit donc être amélioré à l'aide d'un revêtement. L'objectif de ces travaux a été d'élaborer par Oxydation Micro-Arcs (OMA), des revêtements sur substrat TA6V, afin d'en améliorer les propriétés tribologiques. L'OMA est un procédé d'oxydation électrochimique innovant et récent, pour lequel restent à clarifier les mécanismes de croissance des revêtements et l'influence exacte de certains paramètres opératoires, en particulier la composition de l'électrolyte ou le signal électrique imposé. L'étude systématique de différents électrolytes a tout d'abord permis d'élaborer des revêtements adhérents, avec des épaisseurs comprises entre 5 et 60 µm. Ces revêtements résultent de la conversion électrochimique du substrat et de l'incorporation d'espèces depuis l'électrolyte. Ils sont composés d'une phase amorphe, dont la proportion dépend directement de la quantité de silicates dans le bain, et de phases cristallisées formées suite à l'élévation importante de la température surfacique lors du traitement. La compréhension des corrélations entre électrolyte et revêtement a notamment permis de limiter la formation de la phase amorphe molle et de favoriser celle de structures cristallines dures, menant au final à un électrolyte optimisé. L'étude des paramètres électriques, tels que la fréquence ou le temps de traitement, a mis en évidence par ailleurs leur influence importante sur la composition et la morphologie des revêtements. La modification du rapport cyclique a ainsi permis de modifier la composition chimique du revêtement, en favorisant la formation d'alumine cristallisée au sein de celui-ci. Enfin, ces revêtements ont été caractérisés du point de vue mécanique. La présence de phases cristallisées dans le revêtement a permis d'en augmenter la dureté, en comparaison du substrat de TA6V. Toutefois, à cause de la rugosité élevée des revêtements élaborés par OMA, il est apparu indispensable d'effectuer un post-traitement de polissage mécanique pour réduire le coefficient de frottement et le volume de matière usée. Au final, la compréhension des corrélations entre paramètres opératoires et propriétés du revêtement a permis d'élaborer avec succès un revêtement aux propriétés tribologiques très prometteuses, c.-à-d. un coefficient de frottement inférieur à 0,3 et un volume usé inférieur à 0,01 mm3 après 100 000 cycles, démontrant une amélioration significative des propriétés mécaniques surfaciques du substrat TA6V
Surface treatments are often needed for metallic materials in order to improve their performances and broaden their scope of applications. TA6V (or grade 5) titanium alloy is used in many fields (going from biomedical to aeronautical parts) because it is light and possesses good anticorrosion and thermal properties. Nevertheless its tribological behavior needs substantial improvements that a coating may provide. The aim of this work was to prepare, using Plasma Electrolytic Oxidation (PEO), coatings on TA6V in order to improve its tribological properties. PEO is a recent and innovative electrochemical oxidation process for which growth mechanisms and accurate influence of operating parameters such as electrolyte composition or applied electrical signal, still need clarification. Systematic study of several electrolytes led to the preparation of adherent coatings with thicknesses between 5 and 60 µm. These coatings result from both electrochemical conversion of the substrate and incorporation of compounds from the electrolyte. They are composed of an amorphous phase, its proportion depending directly on the silicates quantity in the bath, and crystalline phases formed after the important rise of surface temperature during treatment. The understanding of correlations between electrolyte and coatings have limited the formation of the soft amorphous phase and favored hard crystalline structures, leading to an optimized electrolyte. The study of electrical parameters, such as frequency or treatment time, highlighted their strong influence on the coatings composition and morphology. The duty cycle influenced the chemical composition of the coatings, promoting the formation of crystalline alumina. Finally coatings prepared with PEO were mechanically tested. The presence of crystalline phases allowed the increase of the coatings Vickers hardness compared to the bare TA6V. Nevertheless, due to the PEO coatings roughness, a step of mechanical polishing post-treatment appeared necessary in order to reduce the friction coefficient and wear loss. Finally, the understanding of correlations between process parameters and coatings properties, has successfully led to the preparation of a coating with promising tribological properties, namely a friction coefficient below 0.3 and a wear loss inferior to 0.01 mm3 after 100,000 cycles, demonstrating a significant improvement in surface mechanical properties of the TA6V substrate

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38

Wang, Yijun. "Advances in electroanalytical chemistry." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:90a0e93a-7c48-4b32-9788-5806b9f85acc.

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This thesis concerns several advances in electroanalytical chemistry which are separated into four parts: the electrochemical investigation of diffusional behaviour, the mechanistic and kinetic study of electrochemistry with room temperature ionic liquids (RTILs), the study of weakly-supported electrochemistry and a comparison of the Butler-Volmer and Marcus-Hush kinetic theories of electron transfer. A study of the diffusional behaviour of electroactive species is essential for further studies, especially in the case when electrochemistry is complicated through ion-pairing interactions between the electroactive species and other electrolytes. In Part II of this thesis, the possibility of the ferricenium ion-paired with perchlorate and hexauorophosphate in acetonitrile was discussed firstly employing chronoamperometric technique. Afterwards, the hexaammineruthenium III/II couple supported by chloride, nitrate and sulfate respectively was studied by a similar method. In order to avoid unwanted ion-pairing effects, room temperature ionic liquids can be applied as solvent, which provide high conductivity by their own ionic nature so that experiments can be conducted without adding additional supporting ions. Because of RTILs have distinctive properties, for example, high viscosity, high conductivity and ionic nature, electrochemistry could be greatly changed compared to those in conventional solvents. Part III of this thesis gives a detailed description of this topic. First, a study of the reduction of 1,4-benzonquinone in 1-ethyl-3-methylimidazolium bis(triuoromethanesulfonyl)imide is presented to show the new mechanistic insight into comproportionation in a electrochemical process. Second, a discussion of the oxidation of hydroquinone in the same RTIL is introduced to suggest a possible ECE scheme which was never reported before. The interest of weakly supported electrochemistry is also well-established, which not only provides another alternative strategy to avert ion-pairings but also offers more physical insights into electrochemical processes. Quantitative methods analysing voltammetries without an excess amount of supporting electrolyte are developed by introducing a migration term into the mass transport equation. In Part IV, new mechanistic insights into the reduction of 2-nitrobromobenzene and the dimerisation of 2,6-diphenylpyrylium in acetonitrile were provide by using weakly-supported cyclic voltammetry. Also, pulse techniques was also adopted to investigate the reduction of cobaltocenium and cobalt(III) sepulchrate, giving an alternative way for electrochemical analysis. A major application of electroanalytical chemistry is investigating electrochemical kinetics. Two kinetic models mostly concerned by electrochemists are Butler-Volmer and Marcus-Hush formalisms. The classic phenomenological model, Butler-Volmer formalism successfully describes most common electron transfer kinetics but shows little reference with nature of the involved species, solution and electrode material, while a more physically insightful theory, the Marcus-Hush formalism, takes species natural properties, for instance, a change of distances or geometry in the solvation or coordination shells of the redox, into account although it requires more complex formulations. Comparative studies of these two theories are presented in Part V in order to improve our understanding of the electron transfer kinetics under different circumstances. First, comparison of cyclic voltammograms of the reduction of europium(III) and 2-methyl-2-nitropropane at mercury microhemispherical electrodes was carried out. Second, square wave and differential pulse voltammetric techniques were also employed to further discriminate the two kinetic models. These studies all find that the symetric Marcus-Hush theory assuming the reactants and products have identical force constant dose not satisfactorily agree with the experimental results. Hence, the introduction of asymmetric Marcus-Hush theory was presented considering different oxidative and reductive reorganization energies, which gives reasonable agreement with experiments and makes this theory more insightful.

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Rahil, Abdulla. "Dispatchable operation of multiple electrolysers for demand side response and the production of hydrogen fuel : Libyan case study." Thesis, De Montfort University, 2018. http://hdl.handle.net/2086/17439.

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Concerns over both environmental issues and about the depletion of fossil fuels have acted as twin driving forces to the development of renewable energy and its integration into existing electricity grids. The variable nature of RE generators assessment affects the ability to balance supply and demand across electricity networks; however, the use of energy storage and demand-side response techniques is expected to help relieve this situation. One possibility in this regard might be the use of water electrolysis to produce hydrogen while producing industrial-scale DSR services. This would be facilitated by the use of tariff structures that incentive the operation of electrolysers as dispatchable loads. This research has been carried out to answer the following question: What is the feasibility of using electrolysers to provide industrial-scale of Demand-side Response for grid balancing while producing hydrogen at a competitive price? The hydrogen thus produced can then be used, and indeed sold, as a clean automotive fuel. To these ends, two common types of electrolyser, alkaline and PEM, are examined in considerable detail. In particular, two cost scenarios for system components are considered, namely those for 2015 and 2030. The coastal city of Darnah in Libya was chosen as the basis for this case study, where renewable energy can be produced via wind turbines and photovoltaics (PVs), and where there are currently six petrol stations serving the city that can be converted to hydrogen refuelling stations (HRSs). In 2015 all scenarios for both PEM and alkaline electrolysers were considered and were found to be able to partly meet the project aims but with high cost of hydrogen due to the high cost of system capital costs, low price of social carbon cost and less government support. However, by 2030 the price of hydrogen price will make it a good option as energy storage and clean fuel for many reasons such as the expected drop in capital cost, improvement in the efficiency of the equipment, and the expectation of high price of social carbon cost. Penetration of hydrogen into the energy sector requires strong governmental support by either establishing or modifying policies and energy laws to increasingly support renewable energy usage. Government support could effectively bring forward the date at which hydrogen becomes techno-economically viable (i.e. sooner than 2030).

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Treptow, Florian. "Polyaniline as electrolyte in polymer electrolyte membrane fuel cells." Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/11086.

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The applications of polyaniline (PAni) for use as electrolyte in Polymer-Electrolyte-Membrane Fuel Cells (PEMFC) were investigated. P Ani was dissolved in N-methyl pyrrolidone (NMP), cast as Emeraldine Base membranes (EB) and then doped with halide acids. The proton conductivity was measured according to Hittorf. The chloride ion distribution within the membrane was evaluated using energy-dispersive-X-ray analysis (EDX) and photometric analysers and the diffusion coefficient was calculated. The specific resistance was determined using conventional 4-point measurement. Halide doped membranes were found to be proton conducting, however, during cell operation halide removal occurred causing a rapid decline in the cell performance. The maximum power density achieved was O.3m W·cm-2 for a 70J.1m thick membrane saturate with chloride between 3,5 and 4,5mgchloride per gPAni. Composite membranes with phosphotungstic acid (PWA), antimonic acid (AA) and zirconium phosphate (ZP) were developed and also tested in a standard measuring fuel cell. While membranes produced via ion exchange (ZP) showed the same result like halide doped ones, AA composite membranes showed a stable voltage and current results. The highest measured outcome of 373.3mW·cm-2 was found with a PWA membrane, produced through dispersing 3g of phosphotungstic acid in 300ml of a 1% polyanilinelNMP solution. It was also observed, that the higher power density was obtained from the fuel cell which uses the lower-loaded membrane. It is clear that a positive effect on the cell performance is given by the addition of phosphotungstic acid to the polyaniline membrane. Therefore, the saturation of PW A have to be taken into account to not lower the power density.

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Pierra, Mélanie. "Couplage de la fermentation sombre et de l’électrolyse microbienne pour la production d’hydrogène : formation et maintenance du biofilm électro-actif." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20150/document.

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L'hydrogène, qui constitue une solution alternative et durable à l’usage d’énergies fossiles, est produit essentiellement par reformage de combustibles fossiles (95%). Des filières de production plus soucieuses de l'environnement sont envisagées. Deux familles de technologies sont explorées: 1) par décomposition thermochimique ou électrochimique de l'eau et 2) à partir de différentes sources de biomasse. Parmi celles-ci, les cellules d'électrolyse microbienne ou «Microbial electrolysis cell (MEC)» permettent de produire de l'hydrogène par électrolyse de la matière organique. Une MEC consiste en une cathode classique qui assure la production d'hydrogène par la réduction électrochimique de l'eau, associée à une bioanode qui oxyde des substrats organiques en dioxyde de carbone. Ce processus d'oxydation n'est possible que grâce au développement sur l'anode d'un biofilm microbien électroactif qui joue le rôle d'électro-catalyseur. Par rapport aux procédés courants d'électrolyse de l'eau, une MEC requière un apport énergétique 5 à 10 fois plus faibles. En outre, les procédés « classiques » de production de bio-hydrogène par voie fermentaire en cultures mixtes convertissent des sucres avec des rendements limités à 2-3 moles d'hydrogène par mole d'hexose tout en coproduisant des acides organiques. Alimenté par de l'acétate, une MEC produit au maximum 3 moles d'hydrogène/mole d'acétate. Le couplage de la fermentation à un procédé d'électrolyse microbienne pourrait donc produire de 8 à 9 moles d'hydrogène/mole d'hexose, soit un grand pas vers la limite théorique de 12 moles d'hydrogène/mole d'hexose. L'objectif de cette thèse est d'analyser les liens entre la structure des communautés microbiennes dans les biofilms électroactifs et en fermentation, les individus qui les composent et les fonctions macroscopiques (électroactivité du biofilm, production d'hydrogène) qui leur sont associées dans des conditions permettant de réaliser le couplage des deux procédés. L'originalité de cette étude a été de travailler en milieu salin (30-35 gNaCl/L), favorable au transport de charges dans l'électrolyte de la MEC. Dans un premier temps, la faisabilité de la fermentation en conditions salines (3-75 gNaCl/L) a été démontrée en lien avec l'inhibition de la consommation de l'hydrogène produit et une forte prédominance d'une nouvelle souche de Vibrionaceae à des concentrations en sel supérieures à 58 gNaCl/L. D'autre part, la mise en œuvre de biofilms électroactifs dans des conditions compatibles avec la fermentation sombre a permis la sélection d'espèces dominantes dans les biofilms anodiques et présentant des propriétés électroactives très prometteuses (Geoalkalibacter subterraneus et Desulfuromonas acetoxidans) jusqu'à 8,5 A/m². En parallèle, la sélection microbienne opérée lors d'une méthode d'enrichissement utilisée pour sélectionner ces espèces à partir d'une source d'inoculum naturelle sur leur capacité à transférer leurs électrons à des oxydes de Fer(III) a été étudiée. Une baisse des performances électroactives du biofilm liée à une divergence de sélection microbienne dans ces deux techniques de sélection mène à limiter le nombre de cycle d'enrichissement sur Fer(III). Cependant, l'enrichissement sur Fer(III) reste une alternative efficace de pré-selection d'espèces électroactives qui permet une augmentation de rendement faradique de 30±4% à 99±8% par rapport au biofilm obtenu avec un inoculum non pré-acclimaté. Enfin, l'ajout d'espèces exogènes issues de la fermentation sombre sur le biofilm électroactif a révélé une baisse de l'électroactivité du biofilm se traduisant par une diminution de la densité de courant maximale produite. Cette baisse pourrait s'expliquer par à une diminution de la vitesse de transfert du substrat due à un épaississement apparent du biofilm. Cependant, un maintien de sa composition microbienne et de la quantité de biomasse laisse supposer une production d'exopolymères (EPS) dans le biofilm en situation de couplage
Nowadays, alternative and sustainable solutions are proposed to avoid the use of fossil fuel. Hydrogen, which constitutes a promising energy vector, is essentially produced by fossil fuel reforming (95%). Environmentally friendly production systems have to be studied. Two main families of technologies are explored to produce hydrogen: 1) by thermochemical and electrochemical decomposition of water and 2) from different biomass sources. Among those last ones, microbial electrolysis cells (MEC) allow to produce hydrogen by electrolysis of organic matter. A MEC consists in a classical cathode, which provides hydrogen production by electrochemical reduction of water, associated to a bio-anode that oxidizes organic substrates into carbon dioxide. This process is only possible because of the anodic development of an electroactive microbial biofilm which constitutes an electrocatalyst. In comparison to classical water electrolysis process, a MEC requires 5 to 10 times less electrical energy and therefore reduces the energetic cost of produced hydrogen. Furthermore, classical process of dark fermentation in mixed cultures converts sugars (saccharose, glucose) to hydrogen with a limited yield of 2-3 moles of hydrogen per mole of hexose because of the coproduction of organic acids (mainly acetic and butyric acids). Fed with acetate, a MEC can produce up-to 3 moles of hydrogen per mole of acetate. Therefore, the association of these two processes could permit to produce 8 to 9 moles of hydrogen per mole of hexose, which represents a major step toward the theoretical limit of 12 moles of hydrogen per mole of hexose.Therefore, this work aims at analyzing the relationship between microbial community structures and compositions and the associated macroscopic functions (biofilm electroactive properties, hydrogen production potential) in electroactive biofilms and in dark fermentation in conditions allowing the coupling of the two processes. The originality of this study is to work in saline conditions (30-35 gNaCl/L), which favors the charges transfer in the MEC electrolyte.First of all, feasibility of dark fermentation in saline conditions (3-75 gNaCl/L) has been shown. This was linked to an inhibition of produced hydrogen consumption and the predominance of a new Vibrionaceae species at salt concentrations higher than 58 gNaCl/L. Secondly, electroactive biofilm growth in conditions compatibles to dark fermentation (pH 5.5-7 and fed with different organic acids) allowed to select dominant microbial species in anodic biofilms that present promising electroactive properties (Geoalkalibacter subterraneus and Desulfuromonas acetoxidans) with maximum current densities up to 8.5 A/m². In parallel, the microbial selection occurring during iron-reducing enrichment method used to select species from a natural inoculum source and based on their capacity to transfer electrons to iron oxydes (Fe(III)) has been studied. A decrease of electroactive performances of the biofilm linked to the divergence of microbial selection led to a limitation of the number of iron-enrichment steps. However, enrichment on Fe(III) presents an efficient alternative to pre-select electroactive species with an increase of coulombic efficiency from 30±4% to 99±8% in comparison with a biofilm obtained with a non-acclimated inoculum. Finally, the addition of exogenous bacteria from a dark fermenter on the electroactive biofilm revealed a decrease of electroactivity with a decrease of maximum current density produced. This diminution could be explained by a lower substrate transfer due to an apparent thickening of the biofilm. Nevertheless, the stability of microbial composition and of bacterial quantity on the anode suggests that a production of exopolymers (EPS) occurred

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42

Giancola, Stefano. "Membranes ionomères renforcées par des nanofibres obtenues par électrofilage pour piles à combustible et l'électrolyseur." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT218.

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Анотація:

La production de membranes échangeuses de protons (PEM) robustes et présentant une conductivité élevée est essentielle pour le développement à grande échelle de dispositifs de stockage et de conversion de l’énergie tels que les piles à combustible (PEMFC) et les électrolyseurs (PEMWE). Ces travaux de thèse portent sur la préparation et la caractérisation de membranes composites préparées à partir d’acide perfluorosulfonique, à chaine latérale courte (SSC-PFSA), de type Aquivion®, et de fibres de polymères obtenues par filage électrostatique. Cette dernière technique permet de préparer des matériaux fibreux à porosité élevée, caractérisés par la présence de fibres de diamètres sub-micrométriques, et pouvant être utilisés comme renfort mécanique des membranes ionomères. Le polysulfone a été retenu comme constituant des fibres étant donné ses stabilités mécanique et chimique élevées d’une part et pour la possibilité de modifier ses propriétés physico-chimiques par fonctionnalisation, d’autre part. Ces membranes comportant une distribution homogène des nanofibres dans toute leur épaisseur ont été préparées à partir d’un procédé d’imprégnation Des membranes renforcées, Aquivion®-PSU, basées sur un PFSA dont le poids équivalent (EW) varie entre 700 et 870 g.mol-1 et dont la concentration massique de fibres varie entre 5 et 18 %, ont été préparées. Les membranes renforcées sont caractérisées par des faibles gonflements volumique et surfacique et par une rigidité plus élevée en comparaison des membranes non renforcées de même EW. La perméabilité a l’hydrogène a engluement été réduite. Les améliorations en terme de propriétés mécaniques et dimensionnelles n’ont pas amené à une diminution significatif de la conductivité protonique, qui été maintenue aux mêmes valeurs des membranes non renforcée. Les assemblage membrane-électrode (AME) préparés à partir de ces membranes composites ont montré des caractéristiques i/V intéressantes et prometteuses (1.76 V à 2 A/cm²).Des Polysulfones fonctionnalisés avec le 1,2,3 triazole portant des groupements alkyle ou aryle ont été préparés par une voie de synthèse rapide et a haute rendement assistée par micro-ondes. Les nanofibres electrofilées de PSU fonctionnalisé avec le 4-ethyl-1,2,3-triazole (PSUT), avec un degré de fonctionnalisation en espèce triazole de 0.3 et 0.9 par unité répétitive de PSUT ont été intégrées à une matrice Aquivion®. L’objectif de ces travaux est d’améliorer la stabilité mécanique des membranes composites à partir des interactions acido-basiques PFSA-PSUT (réticulation ionique). Les membranes Aquivion®-PSUT sont caractérisées par une rigidité, une dureté et une ductilité plus élevées en comparaison des membranes Aquivion® renforcées par les fibres de PSU non fonctionnalisées. Une diminution du gonflement volumique et surfacique a également été observée sans perte de la conductivité jusqu’à une concentration massique de fibres de 12 %. Les AME préparés à partir de membranes renforcées Aquivion®-PSUT (12%) sont caractérisés par les mêmes propriétés courant/tension, en monocellule de pile à combustible fonctionnant à 80 °C et 100 % d’humidité relative, que ceux préparés à partir d’Aquivion®
The preparation of highly proton conducting and durable proton exchange membranes (PEM) for low temperature fuel cells (PEMFC) and electrolysers (PEMWE) is crucial for the large scale application of these energy conversion/storage devices. This PhD thesis focuses on the preparation and characterisation of composite membranes based on highly conducting Aquivion® short side chain perfluorosulfonic acid (PFSA) and polymer fibres obtained by electrospinning. This technique allows the preparation of highly porous mats of fibres with sub-micrometric diameters that can act as an efficient mechanical reinforcement for ionomer membranes. The chosen polymer is the mechanically robust and chemically stable polysulfone (PSU), which can also been functionalised to modify its physico-chemical properties. Reinforced PEM with fibres homogeneously dispersed through the entire membrane cross-section have been realised by a fast and efficient impregnation process.Aquivion®-PSU reinforced membranes based on PFSA with equivalent weight (EW) ranging from 700 to 870 g mol-1 and fibre loading ranging from 5 to 18 wt% have been prepared. They showed reduced volume and area swelling and higher stiffness with respect to non-reinforced membranes with the same EW. The hydrogen crossover was also reduced. The improvement in mechanical and dimensional properties was not detrimental for the in-plane proton conductivity that was kept at the same value of non-reinforced membranes. Membrane-electrode assemblies (MEA) based on these composite PEM show promising i/V characteristics in PEMWE (1.76 V at 2 A cm-2).Polysulfones functionalised with 1,2,3-triazole bearing alkyl and aryl ring substituents have been synthesized by a fast and high-yield chemical route involving the azide-alkyne cycloaddition reaction assisted by microwaves as last step. Electrospun nanofibers of polysulfone functionalised with 4-epthyl-1,2,3-triazole (PSUT) with a degree of functionalisation of 0.3 and 0.9 triazole moiety per PSUT repeat unit have been embedded into the Aquivion® matrix. The aim of this study was to further improve the mechanical properties of the membrane by PFSA-PSUT acid-base interactions (ionic crosslinking). Aquivion®-PSUT membranes showed enhanced mechanical stiffness, toughness and ductility with respect to Aquivion® membranes reinforced with the non-functionalised polymer with the same EW and fibre loading. Reduced volume and area swelling have also been observed with no drop of proton conductivity until a fibre loading of (12 wt%). MEA based on Aquivion®-PSUT reinforced membrane with 12 wt% fibre loading showed identical fuel cell polarisation curve with respect to a MEA based on Aquivion® at 80 °C and 100 % of relative humidity (RH)

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43

Limon, Petersen Juan Gualberto. "Weakly supported voltammetry." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:c14f972c-8653-41c2-b2d1-b080e691e4dc.

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This thesis is concerned with dynamic electrochemical experiments with different concentrations of supporting electrolyte. Normally supporting electrolyte is added to a solution in order to avoid undesirable effects as migration and potential drop in solution. However, in the present thesis we focus on the study and understanding of such effects as the concentration of supporting electrolyte decreases. First a theoretical treatment is proposed, based on numerical simulation using the Nernst-Planck- Poisson system of equations. The theoretical treatment is compared with previous works as electroneutrality, the differences between both models are explained. The model is also compared with theoretical results to validate the theoretical treatment. Experimental results of chronoamperometry and cyclic voltammograms are compared with theoretical results obtaining remarkable agreement. Is noteworthy that to the best of the author’s knowledge this is the first time that experimental dynamic voltammetry under weakly supported conditions has been successfully modeled by a theoretical treatment. The electrochemical reaction of a non-charged electroactive species is presented for the system ferrocene/ferrocenium in acetonitrile in which the oxidized and reduced species are soluble in solution, the reaction is studied at different concentrations of supporting electrolyte. Comparison is presented between theoretical simulations and experimental results, for which potential drop in solution is studied. Then systems involving charged electroactive species are treated, in these cases the decrease of supporting electrolyte influence the mass transport of the electroactive species due to migration, comparison between different experimental systems as hexaammineruthenium (III)/(II), cobaltoceniun/cobaltocene and hexacyanoferrate (III)/(II) are presented in comparison with theoretical simulations. More complex mechanistic paths are also investigated, such as deposition and stripping, in which it is established that the level of support required to achieve ‘diffusion only’ voltammetry is on dependence of the concentration of amalgamated electroactive species prior to the stripping step. Comparison between theoretical simulation and experimental results of the deposition and stripping of thallium at a mercury hemisphere are presented, and found to be in good agreement for either chronoamperometry and cyclic voltammetry Simulations are also presented showing the necessary required amount of supporting electrolyte required to achieve ‘diffusion only’ cyclic voltammetry. This is obtained by comparison between diffusion only software and the simulation described in the present thesis. The required amount of supporting electrolyte is shown to depend on the concentration of the electroactive species and supporting electrolyte in the media, the electrode radius, the diffusion coefficient of species and the scan rate. Finally, the cyclic voltammetry in weakly supporting media is used to obtain mechanistic information, by using the migration of electroactive species to differentiate the mass transport of electroactive species to the electrode. The two single electron reductions of anthraquinone in acetonitrile is presented, and the comproportionation mechanistic path is observed in weakly supported media, diffusion only voltammetry is normally unable to present whether this mechanism path takes place, due to the similarity in diffusion coefficients of the electroactive species. In contrast in weakly support conditions the diffusion controlled comproportionation mechanistic path is observed experimentally and constraints for the rate constant are discussed.

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44

Radel, Jason. "Electrolytic capacitive display." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/35594.

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This thesis describes the novel use of an electrolytic capacitor to controllably modulate the optical properties of a surface. The electrically-controlled modulation is achieved using electrodes comprised of carbon nanofoam, a new allotrope of carbon that has an extremely high surface to volume ratio, resulting in a very high capacitance per unit volume which enables the material to attract a significant amount of electrostatic charge, an amount that is much greater than would be the case if the electrodes were not so highly porous. In the display described here, a diffusely reflective porous material, positioned above an interdigital array formed by two carbon nanofoam electrodes, was immersed in an electrolyte solution in which light-absorbing dye ions had been dissolved. When an electrical potential was applied across the electrodes, the capacitor charged and the dye ions were drawn into the pores of the electrodes and therefore drawn out of the bulk solution and porous material, causing the material to become reflective rather than colored. When the applied voltage was removed, the dye ions were able to diffuse out of the nanofoam and redistribute throughout the bulk solution and into the material, causing it to return to its original colored appearance. This effect was shown to be reproducible over many cycles and various experiments were conducted to develop a better understanding of the interaction of the dye ions with the carbon nanofoam electrodes and to understand how these interactions affect the time-course of the response. Potential applications of this technology include low power, high-contrast reflective image display devices, particularly in applications where the visual appearance of ink on paper is required. These so-called “electronic paper” displays are becoming more common in devices such as e-book readers, but the displays that are currently used in these devices are limited in terms of brightness and switching speed. The results of this research indicate that this approach using high capacitance porous electrodes may have application in high contrast reflective display devices.

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45

Udagawa, Jun. "Hydrogen production through steam electrolysis : model-based evaluation of an intermediate temperature solid oxide electrolysis cell." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/8310.

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Steam electrolysis using a solid oxide electrolysis cell at elevated temperatures might offer a solution to high electrical energy consumption associated with conventional water electrolysers through a combination of favourable thermodynamics and kinetics. Although the solid oxide electrolysis cell has not. received significant attention over the past several decades and is yet to be commercialised, there has been an increased interest towards such a technology in recent years, aimed at reducing the cost of electrolytic hydrogen. Here, a one-dimensional dynamic model of a planar cathode-supported intermediate temperature solid oxide electrolysis cell stack has' been developed to investigate the potential for hydrogen production using such an electrolyser. Steady state simulations have indicated that the electrical energy consumption of the modelled stack is significantly lower than those of water electrolysers commercially available today. However, the dependence of stack temperature on the operating point has suggested that there is a need for temperature control. Analysis of a possible temperature control strategy by variation of the air flow rate through the stack has shown that the resulting changes in the convective heat transfer between the air flow and stack can alter the stack temperature. Furthermore, simulated transient responses indicated that manipulation of such an air flow rate can reduce stack temperature excursions during dynamic operation, suggesting that the p,oposed control strategy. has a good potential to prevent issues related to the stack temperature fluctuations.

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46

BARDET, JEAN-PAUL. "Contribution a l'etude de l'effet d'anode dans les electrolytes fondus tel le melange equimoleculaire licl-kcl fondu." Paris 6, 1986. http://www.theses.fr/1986PA066585.

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Le calcul des profils theoriques de la raie semi-degeneree li (i) 4f4d4p->2p, incluant une correction tenant compte de l'effet dynamique des ions permet de preciser les principaux parametres du plasma duodique obtenu par electrolyse du melange equimoleculaire fondu licl-kcl. Methode de calcul systematique des elements matriciels de l'operateur omega (t) intervenant dans le formalisme de magnus, pour tout alcalin, pour des collisions electroniques faibles et fortes. Les resultats donnes, appliques aux niveaux n = 4, permettent de confirmer les valeurs numeriques des parametres du plasma (t::(e),n::(e)) et de verifier que les conditions de la limite d'impact sont atteintes

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47

Roubaud, Emma. "Technologie électro-microbienne pour le traitement des eaux usées couplé à la récupération d'hydrogène." Thesis, Toulouse, INPT, 2019. http://www.theses.fr/2019INPT0091.

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Une cellule d’électrolyse microbienne (CEM) alimentée en eau usée permet simultanément la production d’hydrogène à plus faible cout énergétique que l’électrolyse conventionnelle et la diminution de la charge polluante de l’eau. La thèse a eu pour objectif d’identifier les verrous freinant la montée en échelle de l’électrolyse microbienne adaptée au traitement de l’eau usée domestique et de proposer des solutions d’optimisation concernant les divers composants d’une CEM. L’installation d’une membrane échangeuse de cations entre les compartiments anodique et cathodique a notamment permis l’utilisation d’une solution de KHCO3 concentrée comme catholyte. Pour une densité de courant de 10 A/m², l’activité électro-catalytique des ions HCO3 a permis de diminuer la surtension cathodique de 380 mV par rapport à l’eau usée domestique. Un graphite industriel a été sélectionné comme le matériau le plus adapté à la formation de bioanodes de taille industrielle, notamment pour sa résistance mécanique permettant de l’usiner et de créer ainsi des bioanode 3D. Un traitement de surface électrochimique appliqué sur les électrodes en graphite a permis d’augmenter de 56% les densités de courant produites par les bioanodes formées à partir de ce graphite traité. Enfin, un prototype de CEM à l’échelle laboratoire a été conçu sur la base des résultats expérimentaux obtenus auparavant pendant la thèse et de travaux de modélisation numérique. Une production moyenne d’hydrogène de 3,8 L/La/j a été atteinte, soit 1,5 fois plus que la production la plus élevée rapportée dans la littérature concernant les CEM alimentées en eau usée domestique
A microbial electrolysis cell (MEC) supplied with wastewater simultaneously produces hydrogen with a lower energy cost than conventional electrolysis and reduces the wastewater polluting. This thesis aimed to identify the barriers hampering to the up-scaling of microbial electrolysis applied to domestic wastewater treatment and to propose optimization solutions for the various components of an MEC. The installation of a cation exchange membrane between the anode and cathode compartments made it possible to use a concentrated KHCO3 solution as the catholyte. For a current density of 10 A/m², the electro-catalytic activity of the HCO3 ions allowed reducing the cathode overpotential by 380 mV compared to domestic wastewater. A grade of industrial graphite has been selected as the most suitable material for the formation of industrial-scale bioanodes, especially for its mechanical resistance which is adapted to machining and thus creating 3D bioanodes. An electrochemical surface treatment applied to the graphite electrodes increased by 56% the current densities produced by the bioanodes formed from this treated graphite. Finally, a laboratory scale MEC prototype was designed on the basis of experimental results obtained previously during the thesis and numerical modelling work. An average hydrogen production of 3.8 L/La/j was achieved, which is 1.5 times higher than the highest production reported in the literature for MECs supplied with domestic wastewater

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48

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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49

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.

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50

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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