Cobalt-Doped NiO/GDY S-Scheme Heterojunction Enables Ultrafast Charge Separation for Enhanced Photocatalytic Hydrogen...

Constructing efficient charge separation pathways remains a critical challenge for enhancing photocatalytic hydrogen evolution performance. In this study, a cobalt doping strategy was employed to precisely modulate the band structure of NiO, leading to the formation of an S-scheme GDY/Co_0.10Ni_0.90O heterojunction. UV-Vis diffuse reflectance spectroscopy and Mott-Schottky analyses confirmed that cobalt doping not only broadens the light absorption range but, more importantly, induces a fundamental transition of the heterojunction type from Type-I (GDY/NiO) to S-scheme (GDY/Co_0.10Ni_0.90O). The optimized CGCN35 sample achieves a hydrogen evolution rate of 2.03 mmol/g/h, which is 10 times higher than that of pristine NiO. In situ X-ray photoelectron spectroscopy, density functional theory calculations, electron paramagnetic resonance testing, and Kelvin Probe Force Microscopy further reveal the built-in electric field and band bending characteristics at the S-scheme heterojunction interface. This elucidates the synergistic mechanism that promotes spatial charge separation while preserving strong redox capabilities. This work demonstrates that precise doping engineering enables the controllable modulation of heterojunction band alignment, offering a new strategy to overcome the trade-off between charge separation and redox capability in conventional heterojunctions, thereby providing both theoretical foundation and practical paradigm for designing highly efficient photocatalysts.