Durability screening of Pt ternary alloy (111) surfaces for oxygen reduction reaction using Density Functional Theory

Abstract

Degradation of Oxygen Reduction Reaction (ORR) catalytic activity in acidic environments is one of the biggest challenges in developing cost-effective Proton Exchange Membrane Fuel Cells (PEMFCs). In this work, we screened the durability of 138 Pt ternary alloy (111) surfaces by calculating the surface Pt vacancy formation energy, and surface segregation energy using a Density Functional Theory (DFT). Specifically, we investigated Pt ternary systems showing improved durability over corresponding Pt binary systems. Our results identify Pt-Cu-Pd as the most promising candidate. We analyzed the reason for the improved durability using a Density Derived Electrostatic and Chemical (DDEC) method. The improved durability is attributed to the strong resistance to oxygen-induced surface segregation of Cu and Pd, attractive interactions between corresponding bonds (Pt-Cu, Pt-Pd, Cu-Pd). We also show that the ORR activity of the Pt-Cu-Pd(111) is higher than that of Pt(111). We studied the effect of Pd on the ORR activity, and we found that the subsurface Pd slightly strengthen the bonding between surface Pt and adsorbates but its effect is negligible when the overall Pt content is 75 at%, while the effect is noticeable when Pt content is ~50 at%. Although Pt-Cu-Pd catalysts were previously synthesized and tested, our comprehensive screening of Pt ternary alloy (111) surfaces provides an explanation of why Pt-Cu-Pd is the most durable ORR catalysts in an acidic environment.