Engineering multi-layered yolk–shell CuO@CuxSn1−xO2 (x = 0, 0.1, 0.2, and 0.3) heterojunction for photocatalytic H2 generation from atmospheric moisture

Abstract

Solar-driven hydrogen (H₂) production is fundamentally constrained by geographic mismatch between regions with high solar irradiance and freshwater availability. Photocatalytic atmospheric moisture splitting (PAMS), which enables hydrogen generation directly from ambient water vapor, has recently emerged as a promising alternative. This research focuses on engineering multi-layered yolk–shell heterojunction by exploiting the synergistic mixed-metal atomic interaction to unlock the intrinsic potential of SnO₂ for practical PAMS-based H₂ production. Herein, a glycerate-mediated metal-alkoxide framework was employed to integrate thermodynamically immiscible Cu ions into the SnO₂ lattice, forming Cu_xSn_x−1O₂ (x = 0, 0.1, 0.2, and 0.3) yolk–shell hollow spheres. The XPS data discovered that the Cu–Sn coordination modulates local electron density around Sn sites, empowering Sn active sites for sustainable H₂ production. The substitution of Sn with Cu induced lattice distortions that create mid-gap defect states near the conduction band, promoting charge transport, suppressing charge recombination, and prolonging carrier lifespan. Additionally, the utilized metal-alkoxide framework offered a hierarchical yolk–shell hollow architecture, enhancing photon trapping, prolonging carrier retention, promoting porosity. Conventional CuO nanoparticles were subsequently encapsulated onto the Cu_xSn_1−xO₂ (x = 0.2) yolk–shell spheres through the isoelectric-mediated annealing technique, providing a multi-layered CuO@Cu_xSn_x−1O₂ (x = 0.2) S-scheme heterojunction with synergistic morphological and electronic compatibility. Under optimized conditions, the CuO@Cu_xSn_x−1O₂ (x = 0.2) heterojunction achieves a H₂ production yield of 1332 µmol g⁻¹ h⁻¹ directly from atmospheric moisture, outperforming Cu-modified Cu_xSn_x−1O₂ (x = 0.2), pristine SnO₂, and CuO by factors of 2.0, 10.9, and 26.6, respectively. The apparent quantum yield (AQE) of 2.2% at 420 nm and solar-to-hydrogen (STH) efficiency of 0.31% further highlight the efficiency of this system. For reliable comparison, H₂ production was further evaluated in a liquid-phase photocatalytic system. The CuO@Cu_xSn_1−xO₂ (x = 0.2) heterojunction exhibited a H₂ production yield of 16.82 mmol g⁻¹ h⁻¹, along with notable AQE of 8.2% at 420 nm and STH efficiency of 0.47%. Stable PAMS performance over successive cycles, together with post-reaction characterizations, confirmed the catalyst's robustness and durability. This work establishes a multi-layered yolk–shell heterojunction for the development of cost-effective and sustainable H₂ generation from ambient moisture.