A p-n CuGaS/g-CN heterojunction in S-scheme with escalated charge transport and photothermal effect for solar-driven hydrogen evolution.

The construction of built-in electric field (BIEF) in heterojunction is an effective strategy to enhance solar-driven hydrogen (H) production by minimizing charge carrier recombination and improving transport kinetics. Herein, p-type ternary sulfide CuGaS (CGS) and n-type g-CN nanosheets (CN) are integrated to construct a p-n heterojunction through a simple co-precipitation method for photocatalytic hydrogen evolution reaction (HER). In situ X-ray photoelectron spectroscopy (in situ XPS), in situ electron paramagnetic resonance (EPR) and density functional theory (DFT) calculations revealed that differences in Fermi levels and carrier concentrations between CGS and CN induce charge migration following an S-scheme mechanism, which aligned well with the intrinsic p-n junction field. The escalated BIEF effect enhances interfacial band bending, drives efficient charge separation, and promotes directional charge transfer. As a result, the optimized 20CN/CGS photocatalyst achieves a high H evolution rate of 563 ± 5 μmol g, approximately 3.3 times that of CGS. Additionally, the 20CN/CGS exhibits photothermal properties with further boosted HER rate of 732 ± 6 μmol g at 35 °C, achieving a photothermal conversion efficiency (PCE) of 11 ± 2 %. This indicates its potential for exploitation of thermal heat from solar spectrum. This work provides a promising strategy for designing high-performance p-n heterojunction governed by S-scheme charge transfer to boost solar energy conversion.