Nicotinamide cofactors in their reduced and oxidised forms are important redox agents in biology. Of about 3000 dehydrogenases available to date, many require these cofactors for their activity. Dehydrogenases are of interest to chemists as they offer asymmetric catalysis to yield chiral products. The requirement of dehydrogenases for nicotinamide cofactors necessitates research into finding the best way of recycling the oxidised or reduced forms of these cofactors. Electrocatalytic NAD(P)H oxidation and NAD(P)⁺ reduction on standard electrodes is problematic due to unwanted side reactions and high overpotential requirements, but in Nature efficient enzyme catalysts are available to facilitate these reactions. The focus of this Thesis, the Soluble Hydrogenase of R. eutropha (SH) is a multimeric bidirectional hydrogenase that couples H2 oxidation to the reduction of NAD⁺ to NADH. Protein Film Electrochemistry (PFE) has been employed to study NAD⁺-reducing catalytic moieties of the SH for the first time. It is shown that SH subunits on an electrode are able to catalyse NADH oxidation and NAD⁺ reduction efficiently with minimal overpotential, which is significant because in vivo, NAD(H) cycling is coupled to 2H⁺/H₂ cycling and these reactions are closely spaced in potential. Substrate affinities and inhibition constants for the SH, determined using PFE are discussed in the context of the SH function and the related catalytic domains of respiratory Complex I. A range of molecules that are known to inhibit the related Complex I have been investigated for their ability to inhibit the SH moieties: the similarity between inhibition constants is consistent with structural and functional similarity between the SH and Complex I. The ability of the SH moieties to sustain NAD(H) catalysis in the presence of O₂ is also demonstrated and is consistent with the requirement for the SH to function under aerobic conditions and to reactivate the inactivated hydrogenase moiety by supplying low potential electrons from NADH. Engineered variants of the SH, designed to enhance the affinity towards NADP⁺, were investigated for the first time, using PFE. Electrochemical characterisation of the variants is presented and results are discussed alongside findings on the wild type SH. The variants are shown to exhibit NADP⁺ reduction, and to have higher affinity towards NADP⁺ than the wild type SH. The first efficient NADP⁺ reduction and NADPH oxidation is observed for one of the variants on a graphite electrode and the best variant showed a K_M of 1.7 mM for NADP⁺. This Thesis also provides evidence for the ability of moieties of the SH to be used in cofactor regeneration systems. Two novel systems are demonstrated. The first involves H₂ driven NADH recycling based on the NAD⁺-reducing moiety of the SH immobilised on graphite particles together with a hydrogenase or platinum, with electrons from H₂ passed from the hydrogenase through the graphite to the NAD⁺-reducing moiety. The second involves an electrode modified with the NAD⁺-reducing moiety of the SH, and is demonstrated as an electrochemical NADH recycling system coupled with NADH-dependent pyruvate reduction to lactate by lactate dehydrogenase. The ability of variants of the SH to catalyse NADP⁺ reduction suggests that it may also be possible to use these systems for recycling NADPH for catalysis of important biotransformation reactions by NADPH-dependent dehydrogenases.

The desire for pure diatomic hydrogen gas, H2(g), has been on the rise since the concept of the hydrogen economy system was proposed back in 1970. The production of hydrogen has been extensively examined over 40 + years as the need to replace current fuel sources, hydrocarbons, has become more prevalent. Currently there are only two practical and renewable production methods of hydrogen; landfill gas and power to gas. This study focuses on the later method; using various renewable energy sources, such as photovoltaics, to provide off-peak energy to perform water electrolysis. Efficient electrolysis takes place in electrochemical cells which maximize performance efficiency with the use of noble metal electrocatalyst. Optimizing these electrocatalyst to be less material dependent, highly durable, and more efficient will support the implementation of power to gas electrolysis into the energy infrastructure. The main focus of this study is to explore RuO2 nanorods as a possible electrocatalyst for Proton Exchange Membrane (PEM) water electrolysis. A PEM electrolyzer cell has been constructed and fitted with a RuO2 nanorod decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst structure. The current density-voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under water feed operation. The electrocatalytic behavior was compared to that of ribbon mesh anode catalyst structures not decorated with RuO2 nanorods; one coated with a Ir/Ta MMO catalyst, the other was stripped of the MMO coating resulting in a Ti ribbon mesh anode. The results of these experiments show increased activity with the RuO2 nanorod electrocatalyst corresponding to a decrease in electrochemical overpotential. Through the collection of experimental data from various electrolyzer cell configurations, these overpotenials were able to be identified, resulting in categorical attributions of the enhanced catalytic behavior examined.

L'examen de la filière EVHT (Electrolyse de Vapeur d'eau à Haute Température) montre qu'elle est en train de passer de la phase de recherche à la phase de développement. Il devient maintenant nécessaire de prouver et si possible d'améliorer la compétitivité de cette technologie. Pour cela nous avons fait ressortir le besoin de posséder un outil capable de faire le lien entre les producteurs d'hydrogène, propriétaires d'usine, et les fabricants d'empilements de cellules d'électrolyse. Pour répondre à cet objectif principal, deux contraintes fortes sont identifiées : être insérable dans un schéma usine (logiciel de simulation de procédé), et être représentatif de la technologie de cellule et du stack utilisée. La modélisation d'un objet dans un logiciel de simulation de procédé implique généralement une représentation très simplifiée de celui-ci. Pour pouvoir satisfaire ces contraintes, nous avons bâti une chaîne de modèles partant des modèles d'électrodes et aboutissant finalement à une modélisation de procédé représentative de la technologie EVHT utilisée. Le travail et la valeur ajoutée de cette thèse sont focalisés sur cette démarche d'optimisation énergétique globale et locale, qui permet, à chaque échelle, une analyse adaptée des phénomènes principaux se déroulant dans chaque objet et le chiffrage de l'impact énergétique et économique de la technologie utilisée. Cette démarche permet d'aboutir à un outil capable de réaliser une optimisation technico-économique poussée sur une unité de production EVHT / HTSE field (High Temperature Steam Electrolysis) is moving from the research phase to development phase. It?s now necessary to prove and to possibly improve the technology competitiveness. Therefore we need a tool able to allow communication between hydrogen producers and electrolysis cell stack designers. Designers seek where their efforts have to focus, for example by searching what are the operating best conditions for HTSE (voltage, temperature). On the contrary, the producer wants to choose the most suitable stack for its needs and under the best conditions: hydrogen has to be produced at the lowest price. Two main constraints have been identified to reach this objective: the tool has to be inserted into a process simulation software and needs to be representative of the cell and stack used technology. These constraints are antagonistic. Making an object model in a process simulation usually involves a highly simplified representation of it. To meet these constraints, we have built a model chain starting from the electrode models and leading to a representative model of the HTSE technology used process. Work and added value of this thesis mainly concern a global and local energy optimization approach. Our model allows at each scale an appropriate analysis of the main phenomena occurring in each object and a quantification of the energy and economic impacts of the technology used. This approach leads to a tool able to achieve the technical and economic optimization of a HTSE production unit.

This research validates electro-disinfection as a potential secondary ballast water treatment technology. Electricity applied to bacteria laden water produced bactericidal effects, reactive oxygen species and chlorine generation which annihilated bacteria. Evaluation of electro-disinfection experiments showed titanium electrodes had the maximum kill efficacy while disinfection with aluminum and stainless steel electrodes had lesser kill efficacy. A continuous flow electro-disinfection reactor was evaluated utilizing artificial brackish and fresh ballast water. Brackish water had a 100% bacteria kill efficiency utilizing titanium electrodes at a current density of 10 mA/cm2. Fresh water was augmented with the addition of salt to increase its electrical conductivity from 232 μS/cm to 873 μS/cm to ascertain 100% bacteria kill efficiency with titanium electrodes and a current density of 9.8 mA/cm2.

Le but de ces travaux était de développer des membranes conductrices protoniques de type phosphonique par PECVD radio-fréquence en décharges continue et pulsée à partir du mono-précurseur diméthyl allylphosphonate. De telles membranes sont pressenties comme pouvant avantageusement remplacer la membrane Nafion® ou les membranes conventionnelles de type sulfonique ou phosphonique classiquement utilisées dans les dispositifs piles à combustible ou électrolyseur de type PEM. Ainsi, une étude paramétrique visant à établir des corrélations entre les propriétés des films et les paramètres de dépôt a été menée. Il ressort de cette étude paramétrique que l’utilisation d’une décharge pulsée est favorable à une vitesse de croissance plus élevée et une densité des films plus faible que le mode de décharge continue, favorisant ainsi la conduction protonique. Nous avons également démontré que les dépôts réalisés en mode de décharge pulsée présentent de meilleures capacités de sorption et de rétention d’eau, ce qui est bénéfique pour l’application visée qui est la (photo-)électrolyse de l’eau. Par ailleurs toutes les membranes phosphoniques plasma préparées sont stables d’un point de vue rétention d’eau et réseau covalent jusqu’à au moins 250 °C, ce qui garantit leur utilisation dans des systèmes pouvant fonctionner jusqu’à 120 °C. Par la suite les membranes phosphoniques plasma ont été intégrées en cellule d’électrolyse de l’eau, associées au Nafion® en tant qu’électrolyte. Les caractérisations électrochimiques en cellule ont montré que les membranes phosphoniques plasma sont suffisamment compétitives pour être envisagées dans le futur comme électrolytes solides à part entière dans des AME « tout solide ». / The purpose of this work was to develop phosphonic-type proton conductive membranes by radio-frequency PECVD in a continuous or pulsed discharge from the single precursor dimethyl allylphosphonate. Such membranes could advantageously replace the Nafion® membrane or conventional sulfonic-type or phosphonic acid-type membranes, more classically used in PEM fuel cells and electrolysis devices. A parametric study was carried out in order to establish correlations between the properties of the films and the deposition parameters. It appears that the use of a pulsed discharge promotes better films properties, namely higher growth rate and lower density, than the continuous discharge, thus promoting proton conduction. It was also noticed that the deposits prepared in a pulsed discharge have the highest sorption and water retention capacities, which is particularly beneficial for the intended application i.e. the (photo-) electrolysis of water. Furthermore, all the plasma phosphonic membranes prepared are stable in terms of water retention and covalent network up to at least 250 °C, which ensures their use in systems able to operate up to 120 °C. Subsequently the plasma phosphonic membranes, deposited on the Nafion® as mechanical support, were integrated as electrolyte membrane into a water electrolysis cell. It turns out that plasma phosphonic membranes are competitive enough to be envisaged in the future as integral solid electrolytes in solid membrane-electrodes assemblies.

Este trabalho contém um estudo experimental para a obtenção e a validação de um combustível à base de água, obtido através da eletrolise desta e denominado de HHO (Gás de Brown), a ser utilizado como auxiliar na queima de hidrocarbonetos dos demais combustíveis fósseis e de fontes renováveis como o álcool hidratado (etanol). Para a realização deste trabalho foi utilizado um eletrolisador composto por placas de aço inox 316L e eletrólito à base de hidróxido de potássio, conjunto este de eletrólito em sua concentração ideal, material de construção do eletrolisador determinado através de estudo prévio em bibliografia. Posto o sistema em funcionamento, realizado a análise exergética da composição e do gás gerado, onde se verificou a existência de energia disponível para gerar trabalho útil e que o maior desperdício se encontrava na potência elétrica utilizada para a produção do gás. Após esta validação o gás foi submetido a testes em dinamômetro de desempenho e emissões com motores de combustão interna com deslocamento de 1,6 litros, porém com configurações diferentes de alimentação. Para que os dados refletissem a utilização de maior demanda de combustível, como no trânsito urbano, foram escolhidas as rotações de 1500rpm, 2500rpm e 3500rpm, com aberturas de borboleta em dois estágios, total 100% e abertura parcial a 40%. As variáveis controladas foram a potência, o torque, o consumo instantâneo de combustível, o fator lambda (λ) e a emissão dos gases CO, CO2 e HC. Em ambos os testes, aberturas total e parcial, com suas respectivas particularidades de no sistema de alimentação, foram apresentadas tendências de melhora em desempenho e reduções de emissões, devido aos valores obtidos estarem dentro das incertezas de medição no caso do sistema de alimentação por carburador e combustível principal o álcool hidratado, contudo no caso do sistema de alimentação por injeção eletrônica programável à gasolina comercial, com injeção de gás individualizada os resultados apresentados ficaram moderadamente acima das incertezas de medição. Entretanto, o sistema utilizado no experimento com gasolina + HHO e injeção programável, apresentou uma redução de emissões de CO em 26,4% (abertura parcial) e 18,6% (abertura total), reduzindo as emissões de HC em 16% (abertura parcial) e 14,5% (abertura total) e, por sua vez, o consumo de combustível reduziu em 29,6%. / This work contains an experimental study to obtain and validate a water-based fuel obtained through the electrolysis of this one and denominated HHO (Brown Gas), to be used as an auxiliary in the hydrocarbon burning of other fossil fuels and renewable sources such as hydrated alcohol (ethanol). For this work, an electrolyzer composed of 316L stainless steel plates and electrolyte based on potassium hydroxide was used, this electrolyte assembly in its ideal concentration, electrolyte construction material determined through a previous bibliography study. After the system was in operation, the exergy analysis of the composition and generated gas was performed, where the existence of available energy to generate useful work was verified and that the greatest waste was in the electric power used for the production. After this validation the gas was submitted to dynamometer tests of performance and emissions with engines of internal combustion with displacement of 1.6 liters, but with different feeding configurations. For the data to reflect the use of higher fuel demand, such as in urban traffic, the revolutions of 1500rpm, 2500rpm and 3500rpm were chosen, with twostage butterfly apertures, total 100% and partial opening at 40%. The variables controlled were power, torque, instantaneous fuel consumption, lambda factor (λ) and emission of CO, CO2 and HC gases. In both tests, total and partial openings, with their respective peculiarities of the feed system, presented trends of improvement in performance and emission reductions, due to the values obtained being within the uncertainties of measurement in the case of the carburetor feed system and the main fuel is the hydrated alcohol, however in the case of the commercial gasoline programmable electronic fuel injection system with individualized gas injection the presented results were moderately above the measurement uncertainties. However, the system used in the experiment with gasoline + HHO and programmable injection showed a reduction of CO emissions by 26.4% (partial opening) and 18.6% (total opening), reducing HC emissions by 16% ( partial opening) and 14.5% (total opening) and, in turn, fuel consumption decreased by 29.6%.

Tendo em vista a Economia do Hidrogênio e sua infinidade de possibilidades, este trabalho estuda a geração de hidrogênio utilizando a energia solar fotovoltaica. Tendo em vista o consumo mundial de energia crescente, novos métodos de produção energética tem que ser levados em consideração, como o fato do hidrogênio ser um vetor energético de baixo impacto ambiental. Por outro lado, as reservas de combustíveis fósseis não serão capazes de satisfazer essa demanda em longo prazo e seu uso contínuo produz efeitos colaterais, como a poluição que ameaça a saúde humana e os gases de efeito estufa associados à mudança climática. No contexto do Brasil, a eletrólise da água combinada com as energias renováveis e células a combustível seriam uma boa base para melhorar o fornecimento de energia distribuída. Propõe-se, no presente trabalho, produzir hidrogênio por energia renovável, especificamente pelo acoplamento direto de um gerador fotovoltaico a um eletrolisador alcalino de água experimental, concebido localmente. Busca-se entender as características inerentes da interação desses dispositivos, encontrar as eficiências de cada etapa do sistema montado, assim como a eficiência global, adquirindo uma noção mais precisa e prática do uso da energia solar fotovoltaica na alimentação de um eletrolisador. Os resultados experimentais evidenciaram que a transferência da energia do gerador fotovoltaico ao eletrolisador depende fortemente das condições instantâneas climáticas e do modo como estes estão conectados. A interdependência entre variáveis foi reproduzida pelas investigações com destaque para: densidade de corrente no eletrolisador, potencial elétrico, irradiância solar, concentração do eletrólito, área do eletrodo e dimensões da célula eletrolítica. A eficiência do eletrolisador alcançada foi de 21%. A eficiência global (irradiância solar - hidrogênio) foi de 2%. O presente estudo dá subsídios para que seja dimensionado o acoplamento do sistema eletrolisador - gerador FV a partir de uma célula eletrolítica buscando-se minimizar perdas. / In view of the Hydrogen Economy and its endless possibilities, this work studies the hydrogen production using solar photovoltaic energy. With increasing global energy consumption, new methods of energy production have got to be taken into consideration, as hydrogen that it is an energy carrier with low environmental impact. On the other hand, fossil fuel reserves will not be able to meet this demand in the long term and its continuous use produces side effects such as pollution that threatens human health and greenhouse gases which are associated with climate change. For Brazilian energy context, electrolysis combined with renewable power source and fuel cell power generation would be a good basis to improve the distributed energy supply. It is proposed in this paper, to produce hydrogen by a direct coupling of a PV array with an experimental alkaline electrolyzer designed locally. It seeks to understand the inherent characteristics of the interaction of these energy forms, find the efficiencies of each step of the assembled system, as well as the global efficiency, acquiring a more precise notion and practice of the use of solar photovoltaic coupled with an electrolyzer. The experimental results showed that the transfer of energy from the PV array to the electrolyzer depends heavily on instant climatic conditions and how they are connected. The interdependence between variables was reproduced by the investigations, considering especially: current density, electric potential, solar irradiance, concentration of electrolyte, the electrode area and size of the electrolytic cell. The electrolyzer achieved an efficiency of 21%, approximately one-third of a commercial electrolyser efficiency. The overall efficiency (sol-hydrogen) was 2%. The present study gives subsidies to design an electrolyser PV generator system based on a given electrolytic cell seeking low losses.

Tendo em vista a Economia do Hidrogênio e sua infinidade de possibilidades, este trabalho estuda a geração de hidrogênio utilizando a energia solar fotovoltaica. Tendo em vista o consumo mundial de energia crescente, novos métodos de produção energética tem que ser levados em consideração, como o fato do hidrogênio ser um vetor energético de baixo impacto ambiental. Por outro lado, as reservas de combustíveis fósseis não serão capazes de satisfazer essa demanda em longo prazo e seu uso contínuo produz efeitos colaterais, como a poluição que ameaça a saúde humana e os gases de efeito estufa associados à mudança climática. No contexto do Brasil, a eletrólise da água combinada com as energias renováveis e células a combustível seriam uma boa base para melhorar o fornecimento de energia distribuída. Propõe-se, no presente trabalho, produzir hidrogênio por energia renovável, especificamente pelo acoplamento direto de um gerador fotovoltaico a um eletrolisador alcalino de água experimental, concebido localmente. Busca-se entender as características inerentes da interação desses dispositivos, encontrar as eficiências de cada etapa do sistema montado, assim como a eficiência global, adquirindo uma noção mais precisa e prática do uso da energia solar fotovoltaica na alimentação de um eletrolisador. Os resultados experimentais evidenciaram que a transferência da energia do gerador fotovoltaico ao eletrolisador depende fortemente das condições instantâneas climáticas e do modo como estes estão conectados. A interdependência entre variáveis foi reproduzida pelas investigações com destaque para: densidade de corrente no eletrolisador, potencial elétrico, irradiância solar, concentração do eletrólito, área do eletrodo e dimensões da célula eletrolítica. A eficiência do eletrolisador alcançada foi de 21%. A eficiência global (irradiância solar - hidrogênio) foi de 2%. O presente estudo dá subsídios para que seja dimensionado o acoplamento do sistema eletrolisador - gerador FV a partir de uma célula eletrolítica buscando-se minimizar perdas. / In view of the Hydrogen Economy and its endless possibilities, this work studies the hydrogen production using solar photovoltaic energy. With increasing global energy consumption, new methods of energy production have got to be taken into consideration, as hydrogen that it is an energy carrier with low environmental impact. On the other hand, fossil fuel reserves will not be able to meet this demand in the long term and its continuous use produces side effects such as pollution that threatens human health and greenhouse gases which are associated with climate change. For Brazilian energy context, electrolysis combined with renewable power source and fuel cell power generation would be a good basis to improve the distributed energy supply. It is proposed in this paper, to produce hydrogen by a direct coupling of a PV array with an experimental alkaline electrolyzer designed locally. It seeks to understand the inherent characteristics of the interaction of these energy forms, find the efficiencies of each step of the assembled system, as well as the global efficiency, acquiring a more precise notion and practice of the use of solar photovoltaic coupled with an electrolyzer. The experimental results showed that the transfer of energy from the PV array to the electrolyzer depends heavily on instant climatic conditions and how they are connected. The interdependence between variables was reproduced by the investigations, considering especially: current density, electric potential, solar irradiance, concentration of electrolyte, the electrode area and size of the electrolytic cell. The electrolyzer achieved an efficiency of 21%, approximately one-third of a commercial electrolyser efficiency. The overall efficiency (sol-hydrogen) was 2%. The present study gives subsidies to design an electrolyser PV generator system based on a given electrolytic cell seeking low losses.

Intermittent renewable energy sources, such as solar and wind, will only be viable if the electrical energy can be stored efficiently. It is possible to store electrical energy cleanly by splitting the water into oxygen (a clean byproduct) and hydrogen (an energy dense fuel) via water electrolysis. The efficiency of hydrogen production is limited, in part, by the high kinetic overpotential of the oxygen evolution reaction (OER). OER catalysts have been extensively studied for the last several decades. However, no new highly active catalyst has been developed in decades. One reason that breakthroughs in this research are limited is because there have been many conflicting activity trends. Without a clear understanding of intrinsic catalyst activity it is difficult to identify what makes catalysts active and design accordingly. To find commercially viable catalysts it is imperative that electrochemical activity studies consider and define the catalyst’s morphology, loading, conductivity, composition, and structure. The research goal of this dissertation is twofold and encompasses 1) fundamentally understanding how catalysis is occurring and 2) designing and developing a highly active, abundant, and stable OER catalyst to increase the efficiency of the OER. Specifically, this dissertation focuses on developing methods to compare catalyst materials (Chapter II), understanding the structure-compositional relationships that make Co-Fe (oxy)hydroxide materials active (Chapter III), re-defining activity trends of first row transition metal (oxy)hydroxide materials (Chapter IV), and studying the role of local geometric structure on active sites in Ni-Fe (oxy)hydroxides (Chapter V). As part of a collaboration with Proton OnSite, the catalysts studied are to be integrated into an anion exchange membrane water electrolyzer in the future. This dissertation includes previously published and unpublished co-authored material. / 10000-01-01

Metal oxides and (oxy)hydroxides, particularly those containing two or more metals have many uses as electronic materials and catalyst, especially in energy applications. In this dissertation, the structure-property relationships of these mixed-metal materials are explored in order to understand how these materials work and to guide design of materials with even higher efficiency for a given application. Chapter I introduces the materials and studies undertaken. Chapter II presents a fundamental analysis of the electronic and local atomic properties of mixed-transition-metal aluminum oxide thin films. The final three chapters focus on water electrolysis for hydrogen production, which is limited in part by the slow kinetics of the oxygen evolution reaction (OER). Nickel-iron and cobalt-iron (oxy)hydroxides have been shown to be the most active in alkaline conditions. Although it is evident that Fe is essential for high activity, its role is still unclear. Chapter III investigates the role of Fe in NiOOH by comparing the effects of Ti, Mn, La, and Ce incorporation on the OER activity of NiOOH in base. Chapter IV evaluates the OER activity and Tafel behavior of Fe3+ impurities on different noble metal substrates. Chapter V describes the results of in situ and in operando X-ray spectroscopy experiments, which shows that the local structure around Fe atoms in Co(Fe)OOH changes during OER while that of Co stays the same. This work adds to the growing body of literature that suggests Fe is essential to the catalytic active site for the OER on transition-metal (oxy)hydroxides. This dissertation contains previously published and un-published coauthored material. / 2020-01-11