Spectroscopic and Theoretical Insights Into High‐Entropy‐Alloy Surfaces and Their Interfaces with Semiconductors for Enhanced Photocatalytic Hydrogen Production

Recently, high-entropy alloy (HEA) nanocatalysts have shown outstanding catalytic performance. However, their integration with semiconductors for photocatalytic reactions remains largely unexplored. Here, Pd@HEA core-shell nanocrystals with controlled compositions and facets on TiO₂ supports are synthesized, achieving significantly enhanced photocatalytic hydrogen production. Compared to Pd@Pt/TiO₂, Pd@Pt_0.4Pd_0.15Ir_0.15Ru_0.15Rh_0.15 core-shell nanocubes/TiO₂ exhibit superior photoactivity, driven by optimized Schottky junctions and synergistic multimetallic interactions that enhance photocatalysis. UV photoelectron spectroscopy reveals a high work function of 4.81 eV for Pd@Pt_0.4Pd_0.15Ir_0.15Ru_0.15Rh_0.15, enabling efficient charge separation between Pd@HEA and TiO₂. Meanwhile, transient absorption spectroscopy confirms a significantly prolonged carrier lifetime of 4 ms, far surpassing that of pure TiO₂; (65 µs). In addition, in situ X-ray photoelectron spectroscopy confirms that photo-induced electrons preferentially accumulate on Ir and Pt sites, increasing their electron density and identifying them as primary adsorption sites. Furthermore, density functional theory calculations further reveal that Pt-based bridge sites exhibit a more optimal hydrogen binding free energy than Ir-based sites, suggesting that Pt serves as the dominant active site in photocatalysis. This study establishes a framework for the rational design of HEA-semiconductor photocatalysts, providing fundamental insights for solar-driven hydrogen production.