Electrochemical and surface science analysis investigations on DMFC cells

Kurzfassung

For the optimization of membrane-electrode-assemblies (MEAs) and of the operation pro¬cedure a detailed understanding of the processes inside the fuel cells are necessary. Electrochemical impedance spectroscopy is a powerful tool to investigate the individual processes inside an operating fuel cell. In an operating fuel cell the transport processes can be a dominating factor limiting the performance of the cell. It is possible to elucidate the transport process inside the cell as a function of the operating conditions in the test station. For this purpose impedance spectra were measured at various flow rates, cell temperatures and methanol concentrations in a DMFC single cell. In addition to the effect of the various operation conditions the effect of the alteration of the transport processes due to the degradation of the DMFC MEAs with the operating time is investigated. The oxygen reduction reaction (OOR) at the cathode has an important influence on the performance of DMFC. To improve the performance of the cathode catalysts several alternative catalysts were investigated and compared to commercially available supported electro catalysts. Beside the characterization by U-I characteristics and EIS as electrochemical methods, surface science analysis such as XPS, SEM, EDX and chemisorption were applied to provide important insight into the structural and chemical properties of the electrodes The results of combined investigations of different cathode catalysts for low temperature fuel cell electrodes will be presented.