Factors influencing the stability of Pt-based ORR electrocatalysts in HT-PEMFCs: A theoretical investigation

Abstract

Electrocatalyst stability is a key parameter for commercializing high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Here, we used density functional theory (DFT) to investigate the stability of Pt-based electrocatalysts by calculating the binding energy (ΔE_b) of surface Pt atoms under working conditions. Our results show that Pt(1 1 1) is more stable than Pt(1 0 0) and Pt(1 1 0) under vacuum conditions. Stress hurts the stability of Pt(1 1 1), regardless of compressive or tensile stress. Most of the transition metals alloyed with Pt improve the stability of Pt(1 1 1), especially PtV, PtY, and PtTa, which increase the ΔE_b by 0.60–0.70 eV (ΔΔE_b). However, the stability of Pt is significantly destroyed under the working conditions of oxygen reduction reaction (ORR). The specific adsorption of ORR intermediates and electrolyte ions decreases the ΔE_b of Pt(1 1 1) by 0.35–0.95 eV, and the effect of PO₄^3-* is more significant. Furthermore, when the electric field of the electrochemical double layer is coupled with PO₄^3-* specific adsorption, ΔΔE_b further increases to 1.12 eV. Our results highlight the importance of the intrinsic ΔE_b and the working conditions for the stability of Pt-based electrocatalysts. This work provides important guidelines for the design of stable ORR electrocatalysts for HT-PEMFCs.