(Invited) Understanding and Tuning the Cell Reversal Tolerance of PEM Fuel Cell Anodes: Application-Relevant Design Parameters for Precious Metals Catalysts

Abstract

The shared vision of a hydrogen economy, in which sustainable hydrogen covers a substantial fraction of a nation’s energy demand, unites supporters from science, industry, and politics to engage in cooperative exchange and collaborative work. Several publicly and privately funded initiatives support research and innovation activities on renewable hydrogen production, distribution and storage, as well as fuel cell technologies for transportation and stationary applications with the goal of achieving set climate neutrality goals and limit the impact of human-driven climate change [1].In this context, proton exchange membrane (PEM) fuel cells are considered to play a pivotal role in the decarbonization of the mobility sector, as they allow a simple power scaling through a modular stack design, offer a refueling time and range comparable to conventional combustors, but in contrast, are pollutant- and emission-free when green hydrogen is used [2]. In applications with high lifetime requirements, the management of challenging operating conditions is of key importance. Recently, particular attention was paid to cell reversal events triggered by hydrogen starvation, which – without proper countermeasures – lead to a sharp decline in performance within seconds as the carbon-supported catalyst significantly corrodes at the anode [3].Among other remedies, the incorporation of a co-catalyst, like iridium oxide [4], that favors the harmless oxygen evolution reaction (OER) of water over the destructive carbon oxidation reaction (COR) is broadly employed to improve the intrinsic stability of Pt/C-based anode catalysts. However, the scarcity of platinum and especially iridium makes sophisticated catalyst and electrode concepts indispensable to serve the stability requirements in a resource-saving way. Based on the latest findings and developments, we derived a wide range of material requirements and material adjustments, which in combination enhance the tolerance against hydrogen starvation induced degradation. Incremental improvements of the Pt/C-based anode catalyst form the foundation [5], which is further extended by a broad screening of several iridium-based co-catalysts under application-relevant conditions [6]. As will be emphasized, a careful selection of the anode catalyst system properties not only results in a significant increase in the initial cell reversal tolerance but is also crucial to maintaining this stability after operation under reductive H2 conditions.