Hydrogen-Air Performance and Degradation of Carbon-Supported Pt-alloy Catalyst Measured at High Current Density in Proton Exchange Membrane (PEM) Fuel Cells

Proton exchange membrane (PEM) fuel cell cost targets drive reduction in precious metal loading on anode and cathode. Facile hydrogen oxidation reaction (HOR) enables Pt loading on the anode of 0.05 mg/cm² or less without loss of fuel cell performance. However, the sluggish oxygen reduction reaction (ORR) demands an increase in the intrinsic activity of the catalyst to decrease Pt loading on the cathode. Mass-activity (A/g_Pt) of catalysts for ORR is typically measured in membrane electrode assembly (MEA) using saturated pure oxygen (100% O₂, 100%RH_in) at high voltage i.e. 0.9V_iR-free. In this regard, Pt-alloys supported on carbon (Pt-alloy/C) provide higher catalyst mass-activity for ORR as compared to carbon-supported Pt (Pt/C). However, the size, and hence the cost of fuel cells is determined by performance of the cathode electrode operated under sub-saturated air (21%O₂, <100%RH_in) at high current densities (> 1/Acm²), where proton and oxygen transport-related voltage losses become evident. Cathode electrodes made with Pt-alloy/C catalysts require significant optimization to achieve beginning-of-life (BOL) performance parity under air and at high current densities with cathode electrodes made with Pt/C.  In addition to the high current density BOL air-performance of Pt-alloy/C, we will also compare voltage degradation of Pt-alloy/C to Pt/C cathode as a function of fuel cell operation (voltage cycles, start-stop). We will also discuss correlation of Pt-alloy/C catalyst and carbon support properties to fuel cell performance and degradation.  These results demonstrate the need for further fundamental insight into the high current density air-performance of fuel cell cathodes made with Pt-alloy/C catalysts.