Different Conditions, Different Composition: Reactive Environment-Induced Surface Composition Dynamics in Pt-Based Bimetallic Alloys.

Due to their unique properties, bimetallic platinum-based alloys often exhibit superior activity compared to their parent counterparts for many catalytic reactions. Nevertheless, as multimetallic systems, they often undergo compositional and structural changes under reactive conditions, potentially compromising performance. Elucidating the dynamic behavior of alloy surfaces under reactive environments is thus essential for predictive catalyst design. In this study, we utilize Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) to monitor in real time the redox-driven surface restructuring of model Pt-M alloys (M = Co, Ni, Cu) with systematically tailored compositions. Samples underwent sequential oxidative (5 mbar O2) and reductive (5 mbar H2) treatments across a temperature range from room temperature to 300 °C for real-time tracking of surface composition, oxidation states, and electronic structure as functions of reactive environment, temperature, alloy type, and stoichiometry. Results reveal that exposure to reactive gas atmospheres induces substantial surface dynamics. Overall, in oxidative atmospheres, the less noble component preferentially oxidizes and segregates to the surface, triggering dealloying, while in subsequent reductive atmospheres, its reduction induces partial realloying with Pt. The extent and reversibility of these processes are discussed depending on alloy type and composition, providing insights into redox-driven surface dynamics and offering a basis for the rational design of durable, high-performance Pt-based multimetallic catalysts.