High/low-index faceted PdNi alloy nanocrystals as highly active and stable electrocatalyst for oxygen reduction

The selective exposure of active surfaces has garnered exceptionally widespread attention in enhancing electrocatalytic performance for oxygen reduction reactions (ORR). Nevertheless, because unmanageable growth thermodynamics and kinetics, the exposure of active surface not only hinders the formation of high-index facets but also induces irreversible reconstruction of low-index facets at high-potential region. Therefore, the controlled synthesis of Pd-based nanocrystals featuring high/low-index facets is highly desirable. In this study, bimetallic PdNi alloys with high/low-index facets were successfully synthesized through crystal structure engineering. Assisted by Ni²⁺, the transition from low-index facets to high-index facets was achieved. These structural features endow PdNi alloy nanocrystals with highest half-wave potential (0.893 V), mass activity (0.127 A mg⁻¹), and specific activity (0.926 mA cm⁻²) in ORR. Additionally, this alloy nanocrystals follow an efficient four-electron reduction pathway and exhibit excellent long-term stability over 10,000 cycles. Density functional theory calculations suggest that the outstanding ORR performance stems from the minimal downhill energy gradient in the rate-determining step, and the reduced oxygen adsorption energy on the PdNi alloy (311) crystal plane. This innovative strategy adds more potentialities for development and commercial application in fuel cells.