Understanding the Dual Role of Ionomer Content in PEMFC Catalyst Layers: Trade-Offs Between Performance and Durability

Electrochemical reactions in proton exchange membrane fuel cells (PEMFCs) predominantly occur within the membrane electrode assembly (MEA), dictating power output and lifetime. As a key functional component of the catalyst layer (CL), ionomer plays a decisive role in establishing effective three-phase boundaries, maintaining proton-conducting networks. While the impact of ionomer-to-carbon (I/C) ratio on MEA performance has been recognized, its coupled effect on durability remains underexplored. Herein, MEAs with I/C ratios ranging from 0.4 to 1.2 were fabricated, and the influence of ionomer content on performance and durability was systematically investigated through microstructural characterization, electrochemical measurement, and accelerated stress testing. Results reveal distinct trade-offs: insufficient ionomer impairs proton transport and durability, while excess ionomer hinders mass transport and electrochemical performance but helps maintain CL stability. Specifically, an I/C ratio of 1.2 exhibits the highest durability but the lowest performance. An I/C ratio of 0.8 achieves the optimal peak power density (1156 mW cm–2) while maintaining good durability, superior to lower I/C ratios. Balancing performance and durability, an I/C ratio of 0.8 emerges as the optimal choice. This work provides both experimental evidence and mechanistic insights into the influence of ionomer content in CL, offering guidance for the design of high-performance and durable PEMFCs.