Nils Rieger, Kemisk fysik

With the progressing climate change and its increasingly tangible impacts, the urgent need for a substantial global reduction in greenhouse gas emissions has become evident. Among the emissions, carbon dioxide is considered the primary driver of climate change, making the decarbonization of high-emission sectors essential. One such sector is transportation, which accounts for significant annual greenhouse gas emissions. Among various approaches to decarbonize transportation, fuel cells operated with hydrogen are regarded as a promising technology, as they emit only water. The high energy density of hydrogen combined with the compact design of fuel cells, particularly polymer electrolyte fuel cells, makes them highly attractive for mobile applications. However, challenges remain, including the reliance on expensive catalyst materials and limited lifetime due to electrode corrosion and catalyst deactivation. Addressing these issues requires both improving efficiency through novel catalysts or optimized utilization and developing strategies to mitigate electrode degradation. Achieving these goals demands a detailed mechanistic understanding of electrode component interactions under dynamic operating conditions.
This thesis investigates ionomer interactions within proton exchange membrane fuel cell (PEMFC) electrodes using electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). Measurements on platinum, carbon, and gold electrodes with and without a thin Nafion layer reveal potential-dependent changes in viscoelastic properties linked to ionomer hydration, while being strongly correlated with the oxidation state of the metal/support surface. Similar behavior observed with a spray-coated PEMFC catalyst layer with carbon supported platinum catalyst during EQCM-D measurements underscores the practical relevance of these findings. Furthermore, the thesis explores degradation suppression in palladium-based anion exchange membrane fuel cell (AEMFC) electrodes via a protective TiO₂-shell, confirmed by identical-location transmission electron microscopy (TEM) imaging and accelerated durability tests. At the same time, enhanced hydrogen oxidation reaction activity is demonstrated for this electrode architecture. Collectively, these studies advance the mechanistic understanding of electrode processes and propose strategies to improve performance and durability of polymer electrolyte hydrogen fuel cells.