Materials Engineering toward Durable Electrocatalysts for Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have penetrated many commercial markets, especially in the automotive market as Toyota has launched the first commercially mass-produced fuel cell vehicle, the Mirai in 2014. Electrocatalysts play an irreplaceable role in determining the PEMFCs, performance and account for half of the total cost. Despite substantial progress in exploiting highly active platinum group metal (PGM) and PGM-free electrocatalysts, current electrocatalysts are faced with significant durability challenges, i.e., high-performance electrocatalysts usually suffer from rapid degradation during PEMFC operation. The lifetime of the reported electrocatalysts is far from the requirement of performing steadily over the 8000 h of operation in commercialized PEMFCs. To this end, addressing the durability issues of oxygen reduction reaction (ORR) electrocatalysts is imperative for their practical employment in PEMFCs. Herein, the state-of-the-art advances in understanding the durability issues of PGM and PGM-free catalysts for ORR under fuel cell conditions and the materials engineering strategies to tackle these issues are summarized. The insights into the durability issues, involving the degradation mechanisms and the impact of operation conditions are reviewed. Establishing strategies to mitigate catalyst degradation through rational design of stable PGM and PGM-free catalysts is highlighted.