Construction of Sheet‐on‐Hollow Cube Cu _2‐ <scp> _<i>x</i> S </scp> / <scp> ZnIn ₂ S ₄ </scp> p‐n Heterojunction for Enhanced Visible‐Light‐Driven Photocatalytic Hydrogen Production

The photocatalytic performance is governed by three critical kinetic processes: photon absorption efficiency, charge carrier separation dynamics, and interfacial reaction kinetics. Strategic engineering through morphological design, elemental doping, heterojunction construction, and vacancy engineering has emerged as effective approaches to enhance these interrelated processes. Herein, we demonstrate a p‐n junction photocatalyst via in‐situ growth of n‐type ZnIn 2 S 4 nanosheets on p‐type Cu 2– x S hollow nanocubes. This hierarchical architecture enables synergistic enhancement of charge separation through built‐in electric field effects, achieving the most suppression of electron–hole recombination compared to pristine ZnIn 2 S 4 . The optimized Cu 2– x S/ZnIn 2 S 4 composite exhibits exceptional visible‐light‐driven hydrogen evolution activity, delivering a production rate of 5.7 mmol h −1 g −1 under broad‐spectrum irradiation (λ ≥ 420 nm), 9.5‐fold higher than bare ZnIn 2 S 4 (0.6 mmol h −1 g −1 ). Notably, an apparent quantum efficiency of 11.4% was achieved at 420 nm monochromatic light, accompanied by remarkable stability over long‐term cyclic tests. Combined X‐ray photoelectron spectroscopy analysis and density functional theory calculations reveal dual enhancement mechanisms: the redistribution of interface charges helps to increase the density of photogenerated electrons and photogenerated holes as well as facilitate efficient carrier migration, while the p‐n junction's band alignment promotes redox reaction kinetics. This work provides fundamental insights into heterojunction engineering for developing cost‐effective photocatalytic systems.