Effect of Metal Composition and Carbon Support on the Durability of the Reversal-Tolerant Anode with IrRu Alloy Catalyst

Abstract

In polymer electrolyte membrane fuel cells (PEMFCs) for fuel cell electric vehicles, cell reversal (CR) at the anode side can occasionally occur-usually when hydrogen supply is interrupted-which results in degradation of the anode. To mitigate this problem, reversal-tolerant anodes (RTAs) using oxygen evolution reaction catalysts have been generally applied. Adding such materials promotes water oxidation and, thus, provides the protons and electrons during CR situation, while minimizing the carbon-oxidation reaction. In this study, we performed a detailed investigation of the sole use of IrxRuy/C catalysts for RTAs in the membrane electrode assembly (MEA)-including the effects of the IrRu alloy composition and the degree of graphitization of the carbon support on the durability under fuel starvation. Supported IrRu alloy catalysts with different Ir/Ru ratios were prepared via a facile impregnation method on carbon supports with differing degrees of graphitization by heat-treatment at a range of high temperatures. X-ray diffraction patterns indicated that the crystal structure of the alloy nanoparticles depended on the alloy composition, showing the development of a hexagonal closely packed structure with increasing Ru content. Raman spectroscopy indicated an increase in the degree of graphitization of carbon with progressively higher processing temperatures. Ir(x)Ru(y)alloys were found to be a suitable replacement for Pt anode from single-cell MEA performance testing. Furthermore, we examined the synergic enhancement of the CR durability of IrRu alloys with different compositions comparing to the Ir and Ru metals by measuring the initial and total voltage change of MEAs under hydrogen starvation. For the same alloy composition, higher CR durability was observed for MEAs with catalysts prepared using a higher degree of graphitization of the carbon support. Based on the results, we concluded that to develop efficient catalysts for RTAs of automotive PEMFCs, it is important to consider both the durability of the carbon support under high voltages and the catalyst composition.