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

Abstract 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 TiO 2 supports are synthesized, achieving significantly enhanced photocatalytic hydrogen production. Compared to Pd@Pt/TiO 2 , Pd@Pt 0.4 Pd 0.15 Ir 0.15 Ru 0.15 Rh 0.15 core–shell nanocubes/TiO 2 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 0.4 Pd 0.15 Ir 0.15 Ru 0.15 Rh 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 TiO 2 ; (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.