Spin Polarization and Interface Engineering Modulated Carrier Dynamics in NiO/Ni2+-Doped Cd0.5Zn0.5S Z-Scheme Heterojunctions for Enhanced Solar-Driven Hydrogen Evolution

Developing efficient Z-scheme photocatalysts with rapid interfacial charge transfer is critical yet challenging for solar-driven hydrogen production. This study proposes a bifunctional nickel engineering strategy that synergizes bulk doping and interfacial modulation in NiO/Ni²⁺-doped Cd_0.5Zn_0.5S (NiO/Ni-CZS) Z-scheme heterojunctions. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses confirm the formation of Ni–S covalent bonds between NiO and Ni-CZS, as well as the existence of Ni³⁺/Ni²⁺ redox centers in the heterojunction. Lattice-doped Ni²⁺ induces lattice distortion in CZS, which generates the spin-polarized electric field to drive the directional migration of photogenerated electrons and holes, thereby enhancing bulk charge separation efficiency. Moreover, the synergistic effect of the interfacial Ni–S covalent bonds and Ni³⁺/Ni²⁺ redox centers establishes a dual channel of charge transfer, facilitating interfacial charge transport in the Z-scheme heterojunction. The optimized NiO/Ni-CZS exhibits an exceptional hydrogen evolution rate (5436.68 μmol·g^–1·h^–1), which is 3.0, 2.2, 1.9, and 200.5-fold higher than that of the pristine CZS, Ni-CZS, NiO/CZS, and NiO, respectively. Mott–Schottky and electron paramagnetic resonance (EPR) analysis reveal an efficient Z-scheme charge transfer pathway. This study provides a new idea for the rational design of high-efficiency Z-scheme heterojunction photocatalysts and reveals the crucial role of spin polarization and interface engineering in governing carrier separation at heterojunctions.