DFT approach for predicting the pH-potential-dependent durabilities of Pt-skinned Pt-M (M = Ni, Co, and Ir) alloys for fuel cell cathodes

Abstract

Pt-skinned Pt-M (M = Ni, Co, and Ir) alloy catalysts have been reported as cathode catalysts for polymer electrolyte membrane fuel cells (PEMFCs) that are durable and highly efficient toward the oxygen reduction reaction (ORR). While density functional theory (DFT) studies have confirmed that these catalysts are efficient, they did not clearly demonstrate the superior durability imparted by the Pt-skin layer. Herein, we introduce an atomic segregation model based on density functional theory calculated (DFT-calculated) vacancy formation energies that overcomes these limitations. Solvation-corrected segregation energies reveal that the Pt/PtNi(111), Pt/PtCo(111), and Pt/PtIr(111) surfaces, which can contain very low amounts of Pt, are highly resistant to atomic segregation from the alloy catalyst. The influence of the Pt-skin layer of the examined Pt/PtM catalysts was closely investigated by considering the PEMFC operating conditions, including solvation, the oxygen-rich environment of the cathode, the electrical double-layer, pH, potential, and temperature. As a result, we demonstrated that the Pt/PtCo catalyst exhibits superior durability with a high vacancy formation energy for the Pt-skin layer.