Model catalyst studies on hydrogen and ethanol oxidation for fuel cells

Fuel cells are considered a possible option for future automotive applications. They chemically convert a multitude of different energy carriers to electricity and are not limited by the Carnot-efficiency. This review investigates the ethanol oxidation reaction which takes place at the anode of a direct ethanol fuel cell (DEFC). Reaction pathways under different conditions, in acid and alkaline media, are reported. Special focus lies on the CO2 current efficiency (CCE) which is important for the overall efficiency of the fuel cell. The present CC bond is the biggest challenge for achieving a total oxidation from ethanol to CO2. Reported results are promising, with CCEs higher than 80%. In order to further enhance reaction kinetics the DEFC can be operated at higher temperatures, e.g. 200–400 °C. This requires a new and more temperature resilient membrane. Ammonium polyphosphate composites are suitable materials which show good conductivity and high thermal stability up to approximately 250 °C. As a benchmark system for catalyst research this review discusses achievements of model catalyst studies on nanostructured surfaces for hydrogen related reactions. By carefully designing support and catalyst nanoparticles specific exchange current densities more than four orders of magnitude higher than for bulk platinum were realized. For ethanol oxidation model catalyst studies were performed too. Studies aiming at understanding the influence of coordination, particle size, substrate, composition and alloying of catalyst particles on the ethanol oxidation are presented. Catalysts at elevated temperatures are also within the scope of this review.