Hollow Cu _2– <i> _x </i> S@CuCo ₂ S ₄ Core–Shell S-Scheme Heterojunction Nanoreactors with Multiple Internal Reflections for Boosted Photocatalytic Hydrogen Evolution

The integration of S-scheme heterojunctions with hollow nanostructures offers an effective strategy to suppress charge recombination and enhance light utilization in photocatalytic hydrogen evolution. Herein, hollow Cu2–xS@CuCo2S4 core–shell nanoreactors were fabricated through sequential acidic etching and hydrothermal sulfurization. The distinctive hollow architecture enables multiple internal light reflections, significantly improving solar harvesting efficiency. In situ X-ray photoelectron spectroscopy (XPS) measurements and DFT calculations confirm the formation of an S-scheme heterojunction featuring a built-in electric field that promotes directional electron transfer from Cu2–xS to CuCo2S4, effectively inhibiting recombination while preserving strong redox potentials. As a result, the optimized Cu2–xS@CuCo2S4 nanoreactors achieve a remarkable visible light-driven H2 evolution rate of 3.494 μmol·mg–1·h–1, which is 8.96 and 2.27 times higher than those of pristine Cu2–xS and CuCo2S4, respectively. This work provides a promising approach for designing multifunctional hollow S-scheme heterojunctions for efficient solar-to-hydrogen conversion.