CO2 TOLERANCE AND DEGRADATION OF AFC ELECTRODES

Abstract

Alkaline fuel cells may become an important element in pollution free energy conversion. In the literature most papers in the field of low temperature fuel cells are concerned with polymer electrolyte fuel cells. However, there are still a lot of research groups and companies working on alkaline fuel cells. The advantages and disadvantages of AFC are presented. The DLR procedure for CO2 tolerant rolled gas diffusion electrodes are shown and the carried out degradation experiments. The used electrodes are examined with porosity, surface analyze measurement and electrochemical investigation methods. Investigation on CO2 poisoning shows the advantages of new rolled AFC electrodes. There is no significant degradation effect on CO2 within the first 3500 hours of operation with 150 times elevated concentration of carbon dioxide. The investigation of degradation mechanisms on these electrode shows that the mechanisms are known. Two different degradation mechanisms are observed: the first depends on charge transfer and the second on time of operation. Investigation using XPS measurements show a decomposition of PTFE during long term operation. The lifetime is over 5000 hours and comparable with life times of PEFC electrodes. It can be concluded, due to the work at DLR, that carbon dioxide poisoning of electrodes from rolled DLR electrodes does not take place. These investigations demonstrate that AFCs are highly efficient cells for portable and stationary applications.