Characterization of the three-phase boundary in differently-synthesized membrane-electrode assemblies
Final Report Abstract
One main aim in fuel cell research is to significantly improve the performance of direct methanol fuel cells in order to meet the standards set for example by the U.S. Department of Energy for future energy development. In this respect, we found it not sufficient to increase the electrocatalytic activity of the used catalysts, e.g. by using tailored nanoparticles and improved membranes. In our now completed project, the additional problems related to the electrode structure in the membrane-electrode assembly (MEA) have been investigated in detail. The main objective in structuring the MEA electrodes must be to provide an environment to the catalyst particles, which allows to use a maximum of the noble metal employed preserving as much of the catalytic activity as possible. Consequently, mass transfer in the catalyst layer and connection of the catalyst to the ion and the electron conducting phase (commonly termed three-phase boundary) belong to the major issues in recent research efforts. One step towards this direction has been presented in this Sino-German project. Structural and electrochemical investigation techniques were combined by both German partners in order to unravel correlations between the MEA structure and its performance. The MEA structure was modified using novel catalyst support materials. These were specifically designed and synthesized by the Chinese partner to meet particular problems of the three-phase boundary, e.g. mass transport or contact to the proton conducting phase or both. New support geometries were employed to facilitate mass transport in liquid feed operation as well as the connection to the ionomer. Another class of catalysts using hydrous ruthenium oxides as support materials was applied to provide enhanced surface proton conductivity improving the connection to the ionomer. Finally, these two approaches were combined in a carbon nanotube (CNT) catalyst support coated with a thin layer of RuOOHx and decorated with platinum nanoparticles. This system should provide both an open porous structure as well as intrinsic proton conductivity needed for the efficient utilization of the platinum employed.
Publications
- L. Cao, F. Scheiba, C. Roth, F. Schweiger, C. Cremers, U. Summing, X. Qiu, 'Novel nano-composite Pt/RuO2*xH2O/CNT catalysts for DMFC', Angew. Chem. Int. Ed., 45, 5315, (2006).
- F. Scheiba, M. Scholz, C. Lin, C. Roth, C. Cremers, X. Qiu, U. Slimming, H. Fuess, 'On the suitability of hydrous ruthenium oxide supports to enhance intrinisic proton conductivity in direct methanol anodes', Fuel Cells, 6, 439, (2006).
