Langzeitstabilität der Polymerelektrolyt-Wasserelektrolyse bei reduziertem Iridiumgehalt

For the CO2-free generation of hydrogen, the use of energy from weather dependent and therefore fluctuating renewable power sources is required. A promising technique for hydrogen production is the polymer electrolyte membrane (PEM) water electrolysis, due to its capability to adjust quickly to fluctuating input power. However, the currently high iridium loading of the anode and the poor understanding of occurring degradation phenomena under varying input power profiles are important challenges to be overcome for the widespread use of PEM water electrolysis for hydrogen production. The present thesis aims to reduce the use of iridium in PEM water electrolysis and investigate the consequences thereof regarding cell performance and its long-term stability. Two approaches are being followed to reduce the iridium loading. On the one hand, a new type of catalyst system with reduced iridium content is used. On the other hand, a reduced loading of benchmark catalyst is employed. For this second approach, the effect of loading reduction on long-term stability is investigated and referenced to stability data of cells with standard electrodes. For this purpose, the influences of the input power profile and cell setup on the long-term stability are investigated. The occurring degradation phenomena are analyzed based on electrochemical, physico-chemical and material-analytical measurements. The contributions of the individual phenomena are separated from one another to identify the critical components for performance degradation. Important tools used for this separation comprise, amongst others, the analyses of polarization curves and an improved way of setting up the cell. A new type of supported catalyst system was identified (iridium, supported on antimony doped tin oxide) that shows three times the mass specific activity as the benchmark material. Electrodes with reduced iridium loading were found to show higher degradation rates with respect to cells with standard electrodes. In summary, mainly the anodic porous transport layer and anode catalyst layer contribute to the degradation of cell performance. Regarding the employed power profiles for the standard cell setup, improved performance stability was demonstrated under dynamic power profiles with respect to constant operation. Furthermore, both operation modes led to similarly low degradation rates using an optimized cell setup, indicating the ability of PEM water electrolysis to operate in a stable manner under the fluctuating power profiles used