Boosting the Role of Ir in Mitigating Corrosion of Carbon Support by Alloying with Pt

Abstract

Corrosion of carbon support is one of the most crucial causes of the degradation of polymer electrolyte membrane fuel cells (PEMFCs) utilizing carbon-supported platinum nanoparticles (Pt/C) as a catalyst. To mitigate carbon corrosion, Pt is alloyed with iridium (Ir), which is catalytically active for the oxygen evolution reaction (OER), with various compositions of PtxIry. The carbon-supported PtxIry alloy catalysts (PtxIry/C) show slightly lower initial activity for the oxygen reduction reaction (ORR) than Pt/C. However, the ORR activities of the PtxIry/C catalysts increase with repeating potential cycles from 1.0 to 1.5 V-RHE, while Pt/C exhibits a rapid decay in the ORR activity and a mixture of Pt/C and Ir/C (Pt/C + Ir/C, Pt-to-Ir ratio of 85:15) maintains its initial activity. After 5k potential cycles, the mass activity of Pt85Ir15 was 0.071 A mg(PGM)(-1), which is significantly higher than that of Pt/C (0.017 A mg(PGM)(-1)) and Pt/C + Ir/C (0.039 A mg(PGM)(-1)). These results can be attributed to the atomically distributed Ir in Pt85Ir15. Clearly, carbon corrosion occurs in Pt/C and in Pt-rich regions of Pt/C + Ir/C, whereas the carbon support in Pt85Ir15/C is effectively protected from corrosion. As a result, the greatest amount of CO2 emission is detected as coming from Pt/C, followed by Pt/C + Ir/C and Pt85Ir15/C. During the potential cycles, high-index Pt facets are formed on the surface of Pt85Ir15/C, leading to an increase in the ORR activity. When employed as cathode catalysts of a PEMFC, Pt85Ir15/C exhibits improved durability compared to Pt/C and Pt/C + Ir/C under high-voltage cycles to 1.5 V (5k cycles). This work demonstrates that the atomic distribution of Ir in Pt is an effective strategy for mitigating corrosion of the carbon support and to enhance the durability of PEMFCs exposed to high potentials.