Thesis (M. Tech. - (Engineering: Electrical, Department: Electronic Engineering, Faculty of Engineering and Technology)) -- Vaal University of Technology, 2011. / “Never before in peacetime have we faced such serious and widespread shortage of energy” according to John Emerson, an economist and power expert for Chase Manhattan Bank. Many analysts believe that the problem will be temporary, but others believe the energy gap will limit economic growth for years to come. A possible solution to this problem can be fuel cell technology. Fuel cells (FCs) are energy conversion devices that generate electricity from a fuel like hydrogen. The FC however, could also be used in the reverse or regenerative mode to produce hydrogen. The reversible fuel cell (RFC) can produce hydrogen and oxygen by introducing water to the anode electrode chamber, and applying a potential across the anode and cathode. This will cause the decomposition of the water to produce oxygen at the anode side and hydrogen at the cathode side. In order to make this process as efficient as possible several aspects need to be optimised, for example, the operation temperature of the RFC, water management inside the RFC and supply voltage to the RFC. A three cell RFC and its components were constructed. The three cell RFC was chosen owing to technical reasons. The design factors that were taken into consideration were the different types of membranes, electrocatalysts, bipolar plates and flow topologies. A water trap was also designed and constructed to eliminate the water from the hydrogen water mixture due to water crossover within the MEA. In order to optimise the operation of the RFC a number of experiments were done on the RFC. These experiments included the optimal operating voltage, the effect that the temperature has on the production rate of hydrogen, and the effect that the water flow through the RFC has on the production rate of hydrogen. It was found that there is no need to control the water flow through the RFC because it had no effect on the production rate of hydrogen. The results also showed that if the operating temperature of the RFC were increased, the energy it consumes to warm the RFC significantly decreases the efficiency of the whole system. Thus the RFC need not be heated because it consumes significantly more energy to heat the RFC compared to the energy available from the hydrogen produced for later use. The optimised operating voltage for the three cell RFC was found to be 5.05 V. If the voltage were to be increased or decreased the RFC efficiency would decrease.

La durabilité des piles à combustible à membrane échangeuse de proton (PEMFC) est un des verrous technologiques majeurs qui freinent leurs implantations sur le marché. Ces travaux de thèse s’inscrivent dans ce contexte en proposant l’élaboration de matériaux en carbure de niobium comme support de catalyseur pour remplacer les supports carbonés actuellement utilisés dans les cathodes de PEMFC. Notre démarche est d’associer cette composition à différentes morphologies contrôlées pour développer des matériaux conducteurs, présentant une porosité adaptée et chimiquement plus stable que le carbone qui se corrode dans les conditions de fonctionnement des PEMFC. Ainsi trois voies de synthèse basées sur des techniques variées (filage électrostatique, synthèse hydrothermal avec agent structurant) ont été étudiées aboutissant à trois types de morphologie : des poudres nanostructurées, des tissus nanofibreux et des nanotubes aux parois poreuses. Après leurs caractérisations structurales et morphologiques approfondies, ces supports ont été catalysés avec des nanoparticules de platine synthétisées par une méthode polyol assisté par micro-onde. La finalité de ce projet est d’évaluer les performances électrochimiques relatives à la réaction de réduction de l’oxygène de ces supports catalysés pour mettre en avant leurs exceptionnelles stabilités comparées à un support catalysé de référence (Pt/C) sans perte significative d’activité catalytique. / One pivotal issue to be overcome for the widespread adoption of Proton exchange membrane fuel cells (PEMFC) is the stability overtime. In this context, This PhD project focuses on the elaboration of niobium carbide based electrocatalyst supports for the PEMFC cathode to replace the conventional carbon based supports that notoriously suffer from corrosion in fuel cell operating conditions. The approach is to associate this alternative chemical composition with controlled morphologies in order to design electronically conductive and chemically stable materials with the appropriate porosity. Three different syntheses involving hydrothermal template synthesis or electrospinning have been developed leading to three different morphologies: nanostructured powders with high surface area, self-standing nanofibrous mats, and nanotubes with porous walls. These various supports have been catalysed by deposition of platinum nanoparticles synthesised by a microwave-assisted polyol method, and they have been characterised for their chemical and structural composition, morphology, and electrochemical properties. This work demonstrates that the Pt loaded NbC supports feature a greater electrochemical stability than a commercial Pt/C reference and similar electrocatalytic activities towards the oxygen reduction reaction.