Unmasking Ionomer Degradation in Cathode Catalyst Layers of Polymer Electrolyte Fuel Cells

The widespread deployment of proton exchange membrane fuel cells (PEMFCs) in demanding heavy-duty vehicle applications requires longer system lifetimes necessitating unprecedented durability. While the degradation mechanisms of the bulk perfluorosulfonic acid ionomer membrane are well documented, the susceptibility of the nanometer-thin catalyst layer (CL) ionomer films in electrodes remains a critical unanswered question. Here, we conclusively demonstrate that the current membrane accelerated stress test (AST) does induce CL ionomer degradation through changes in the CL ionomer properties, primarily the CL ionic resistance, when compared to two control tests. The CL ionomer degradation from the AST decreases the PEMFC performance by approximately 90 mV @ 1 A cm–2. Moreover, we demonstrate that this CL ionomer degradation can be eliminated by the incorporation of cerium, a common membrane additive to scavenge radicals.