Stability of Atomically Dispersed Fe-N-C ORR Catalyst in Polymer Electrolyte Fuel Cell Environment

We have investigated the durability of a platinum group metal (PGM-)free Fe-N-C catalyst in which the Fe sites are atomically dispersed (AD), and found it to be quite stable in standard accelerated stress test (AST) cycles normally used for low-PGM catalysts: a square wave with 0.6 V lower potential limit (LPL) - 0.95 V upper potential limit (UPL) with 3-s holds at UPL and LPL in H2/N2, at 1.5 atm, 80 C and 100% RH. Considering the metrics normally employed to characterize the durability of the low-PGM catalysts after 30,000 AST cycles, this PGM-free catalyst lost <50% catalyst activity, <50% H2/air performance at 0.8 V, and 40 mV at 1.5 A cm-2. However, it is less stable in H2/air, losing ∼50% catalyst activity after just 7.5 h of polarization measurements (load cycles). In combined cycles, the majority of the loss in catalyst activity occurred during the load cycles in H2/air rather than AST cycles in H2/N2. We have concluded that, unlike low-PGM catalysts that lose electrochemically active surface area (ECSA) through potential cycling-induced processes, (AD)Fe-N-C catalysts degrade by processes associated with the presence of oxygen.