Work-function-mediated unidirectional charge flow enables 139-fold enhanced photocatalytic hydrogen evolution on g-C3N4

Abstract

Suppressing photogenerated carrier recombination remains a pivotal challenge in photocatalyst design. In this work, we strategically integrate Co₃O₄ as a hole-extracting layer and Ni as an electron-trapping cocatalyst onto graphitic carbon nitride (g-C₃N₄), establishing a work-function-gradient-driven charge transport pathway along the Co₃O₄ → g-C₃N₄ → Ni directional cascade, resulting enhanced carrier concentration and charge migration kinetics. The optimized 1.5 %Ni-1 %Co₃O₄-C₃N₄ achieves a remarkable photocatalytic hydrogen evolution rate of 16.71 μmol h⁻¹, surpassing 1 %Co₃O₄-C₃N₄ (5.17 μmol h⁻¹), 1.5 %Ni-C₃N₄ (1.64 μmol h⁻¹) and g-C₃N₄ (0.12 μmol h⁻¹) by 3.2, 10.2 and 139.2 times, with robust stability over multiple cycles. Photoelectric characterizations confirm accelerated charge separation via synergistic electron transfer by Ni electron sinks and Co₃O₄ hole extractor. Density functional theory reveals work function gradient of Co₃O₄, g-C₃N₄, and Ni driving unidirectional electron flow from Co₃O₄ to Ni active sites via g-C₃N₄ as bridge, while an upward-shifted Ni d-band center and optimized hydrogen adsorption energy (ΔG_*H) of 1.5 %Ni-1 %Co₃O₄-C₃N₄ enhance *H reduction kinetics. This work establishes a work-function-gradient based strategy for advancing solar-to-hydrogen conversion technologies.