Deconvolution of ECSA Loss and Transition Metal Leaching upon Voltage Cycling Induced Aging of Pt-Alloy Cathode Catalysts in a PEM Fuel Cell

The durability of Pt-alloy cathode catalysts for proton exchange membrane fuel cells (PEMFCs) is limited by the loss of electrochemically active surface area (ECSA) and the leaching of the alloyed transition metal. In this study, we separately quantify the ECSA loss and the Co leaching of a commercial Pt _2.5 Co/C cathode catalyst over voltage cycling accelerated stress tests (ASTs) in 5 cm ² single-cells, varying several voltage cycling parameters, namely the upper potential limit (0.95 V vs 0.85 V), the hold time at the upper potential limit (1 s vs 5 s), and the voltage ramp rate (∼9 V s ⁻¹ vs 0.7 V s ⁻¹ ). The analysis shows that a higher UPL and a longer hold time at the UPL both accelerate ECSA loss and Co leaching, whereas the voltage ramp rate has no measurable effect. Reducing the upper potential limit from 0.95 V to 0.85 V changes the ratio of Co leaching and ECSA loss, i.e., the degradation path of the catalyst: The lower UPL leads to more Co leaching at the same normalized ECSA loss. The results question the validity of harsh AST protocols for Pt-alloy cathode catalysts that might systematically underestimate the amount of Co leaching over the catalyst lifetime.