Mechanism insights and system-level operation analysis of cathode recirculation for durability enhancement in automotive PEMFC

Cathode recirculation (CR) has emerged as a promising strategy to mitigate accelerated degradation in proton exchange membrane fuel cells (PEMFCs) under low-load conditions. While previous studies have primarily focused on CR's external performance impacts, the fundamental mechanisms underlying its durability enhancement and operational characteristics in high-power self-humidifying systems remain insufficiently understood. This study firstly systematically investigates CR-enhanced durability mechanisms through rigorously controlled single-cell tests. Macroscopic analyses demonstrate that CR significantly mitigates polarization curve degradation, with maximum attenuation reduction reaching 58.4 % at 0.3 A/cm2. Microscopic characterization reveals CR primarily alleviates the increases in both charge transfer and diffusion resistance, slowing electrochemical surface area (ECSA) loss by 62.7 % compared to non-recirculation (NCR) mode and reducing cathode catalyst layer (CCL) crack propagation rate by 2.4 percentage points. Following the mechanistic insights obtained at the single-cell level, system-level validation is conducted in a high-power automotive self-humidifying fuel cell system. The results show that optimal CR operation requires progressively higher pump speeds with increasing current density to maintain equivalent voltage reduction, governed by competing oxygen dilution and humidification effects. Additionally, CR demonstrated the capability to reduce idle power output while maintaining protective voltage levels, resulting in reduced energy management pressure. Overall, the presented framework bridges single-cell mechanistic understanding with system-level optimization strategies, advancing durable automotive fuel cell development.