New factors driving in-plane uneven degradation of Pt in proton exchange membrane fuel cells at high current density

Proton exchange membrane fuel cells (PEMFCs) face persistent challenges in cost, performance, and durability, particularly under high current density (HCD) conditions. While degradation mechanisms under low current density are well-documented, those under HCD remain inadequately understood. This work investigates the in-plane non-uniform degradation behavior of PEMFC over 600 h at 2.0 A/cm², employing in-situ monitoring and numerical simulations. The results reveal that voltage decay rates of 0.069 mV/h, 0.071 mV/h, and 0.098 mV/h at 0.5 A/cm², 1.0 A/cm², and 2.0 A/cm², respectively, indicate accelerated degradation at higher current densities. Importantly, a substantial portion of the voltage losses is reversible, as recovery occurs following shutdown procedures. Furthermore, the cathode catalyst layer is identified as the primary site of degradation, evidenced by a 60.45 % reduction in electrochemical surface area and notable increases in charge transfer and mass transfer resistances. In addition, Platinum particle degradation exhibits spatial non-uniformity, with the particle radius decreasing from 3.35 nm at the cathode inlet to 2.52 nm at the outlet, resulting in an average radius of 2.84 nm—nearly double the initial value of 1.51 nm. The observed spatial heterogeneity is driven by the non-uniform distribution of local current density. These findings indicated the presence of spatially heterogeneous degradation mechanisms in PEMFCs, highlighting the need for mitigating in-plane non-uniformity to improve performance and durability under HCD conditions.