Enhancing Oxygen Reduction Activity via Tailoring Microstrain in PdMo Nanoalloy through Repetitive Hydrogen Absorption-Release

The catalytic activities of noble-metal electrocatalysts are heavily correlated to their defective surface structures. However, controllably constructing surface defects on noble-metal nanocrystals remains a great challenge. In this work, an electrochemical method is developed to tailor the surface structure of the PdMo nanoalloy electrocatalyst, involving H absorption followed by its subsequent release near the surface of Pd. The optimized PdMo nanoalloy electrocatalyst exhibits an oxygen reduction reaction (ORR) half-wave potential (E_1/2) of 0.929 V (vs reversible hydrogen electrode, RHE) with a specific activity (SA) as high as 5.09 mA/cm² at 0.9 V (vs RHE) in an alkaline electrolyte, ∼10.6 times that of the state-of-the-art Pt/C electrocatalyst. Density functional theory calculations together with ex situ and in situ electrochemical and structural characterizations unravel that the microstrain generated at the PdMo nanoalloy surface by electrochemically induced H absorption-release can downshift the d-band center of Pd (the ORR active site) in PdMo to decrease oxygen binding and promote *OOH to *O transformation as well as *OH desorption for fast ORR. This work provides a surface defect engineering strategy to develop high-performance noble-metal electrocatalysts for energy applications.