Increasing fuel cell durability during prolonged and intermittent fuel starvation using supported IrOx

Abstract

Addition of an oxygen evolution reaction (OER) catalyst is a materials approach to mitigate the impacts of potential reversal caused by fuel starvation. In this study Iridium oxide (IrOx) supported on graphitized Vulcan (GV) black (56 wt% Ir) was added as an OER catalyst into the anode of a membrane electrode assembly (MEA) (0.1 mgIr/cm2). When exposed to intermittent 5-, 10- and 30- minutes of starvation, with 10 min recovery periods, the reversed cell potential was clamped at −0.8 V, mitigating severe carbon degradation. The intermittently starved MEAs regained >95% of their initial performance. After the first event, the performance loss was significant at 4% (0.2 A/cm2) with increases in ohmic resistance, thereafter the performance remained relatively stable. Using SEM and EIS, the increased ohmic resistance was attributed to deformation and contraction of the membrane and ionomer reconfiguration which impacted proton conductive pathways. Thinning of the anode was unavoidable, contributing to contact resistance and decreased performance. The Pt and IrOx/GV catalyst remained relatively stable when subjected to multiple short periods of fuel starvation. The IrOx/GV MEA was reversal tolerant and provided insight into the degradation processes which occur during periodic and prolonged fuel starvation.