Impact of Ionomer Mobility on Transport and Structural Properties of the Cathodic Catalyst Layer in a PEMFC Durability Test

Kurzfassung

Over the last decades, catalysts and ionomers have been developed to increase the efficiency and lower the platinum group metal (PGM) content in polymer electrolyte membrane fuel cells (PEMFCs). This reduction of PGM electrode loadings has a significant impact on performance and degradation due to local transport challenges near the catalyst surface, which is often only attributed to oxygen diffusion limitations. But up to the present date, it is not proven that this limitation is not also caused by oxygen convection or proton and water transport. Thus, the origin and importance of different transport limitations are still under discussion. Furthermore, the impact of the different limitations might be influenced by degradation processes. In the presented study, a 500 h dynamic degradation test was applied using a low Pt-loaded MEA to analyze the impact of the applied load cycling on the transport and structural properties of the cathodic catalyst layer. This includes electrochemical analysis of the catalyst layer properties and identification of reasons for the appearing performance losses and changes in the transport limitations. Additionally, local AFM measurements are applied to evaluate structural changes in different positions of the cell and to improve the understanding of ionomer/catalyst interaction in the catalyst layer and the resulting changes during load cycling. This analysis revealed that the mobility of the ionomer can result in structural changes of the electrode and thus influence the different transport mechanisms and limitations. The combination of different techniques enabled the detailed understanding of the degradation mechanisms causing the performance decay and can provide useful guidelines to design future PEMFC electrodes with significantly improved performance and durability. The project FURTHER-FC has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No 875025. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.