Activity and Durability of Pt/Ir Catalysts for Oxygen Reduction as a Function of Different Platinum Shells

We performed a systematic experimental and theoretical analysis of the oxygen reduction reaction (ORR) activity and durability of Pt/Ir catalysts featuring different platinum shells. Four Pt/Ir catalysts with different platinum monolayers (ML) on an iridium core were synthesized. The nanostructure and composition of the catalysts were studied using scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. ORR activity and catalyst durability were studied using cyclic voltammetry with rotating disk electrode. Density functional theory calculations were performed to estimate the ORR activity of Pt(111) and nML Pt/Ir(111) surfaces (n = 0, 1, 2). Although the specific ORR activities of the synthesized Pt/Ir catalysts were lower or comparable to those of 50%Pt/C, the mass activities were higher due to the enhanced utilization of platinum. Accelerated stress tests (ASTs) revealed that the durability of 1 ML Pt/Ir surpassed that of the other studied catalysts. The factors influencing the trends in specific and mass activities, durability, and the feasibility of implementing a Pt/Ir system in practical proton exchange membrane fuel cells (PEMFCs) are discussed.