Enhanced Oxygen Reduction Activity by Selective Anion Adsorption on Non-Precious-Metal Catalysts

Abstract

Non-precious-metal catalysts (NPMC) are promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR), which is the cathode reaction in fuel cells. In this paper, we focus on an iron–nitrogen–carbon (Fe/N/C) catalyst, in comparison to platinum, and investigate how these different types of catalysts behave toward selective anion poisoning. The catalysts are studied with respect to their ORR activity, using the rotating disk electrode (RDE) technique in aqueous HClO4, H2SO4, H3PO4, and HCl electrolytes, and the results are supported by density functional theory (DFT) calculations. We find that the ORR on the Fe/N/C catalyst is less affected by anion poisoning than platinum. Surprisingly, it is seen that phosphoric acid not only does not poison the Fe/N/C catalyst, but instead promotes the ORR; this finding is in sharp contrast to the poisoning effect observed on platinum. This is a highly important finding, as modern high-temperature proton exchange fuel cells (HT-PEMFCs) employ membranes consisting of phosphoric acid that is immobilized into a polybenzimidazole (PBI) matrix.