Regulating electron-hole pairs of g-C₃N₄ efficiently separated and fully utilized for photosynthesis of H₂O₂ under visible light

Photocatalytic synthesis of hydrogen peroxide (H₂O₂) over graphitic carbon nitride (g-C₃N₄) has gained increasing attention due to green, economy, sustainability and safety. However, its activity is impeded by the low oxidizing ability of photoexcited holes, sluggish oxygen reduction reaction (ORR) kinetics, and fast recombination of photoexcited charge carriers. Here, we show an Ohmic heterojunction of NiS₂/g-C₃N₄ for photosynthesis of H₂O₂ from water and air under visible light illumination without sacrificial agents. In this photosynthesis system, NiS₂ regulated the valence band of g-C₃N₄ and improved the oxidation capacity of photogenerated holes, which can directly oxidize H₂O to produce H₂O₂. Additionally, NiS₂ and g-C₃N₄ form a reverse barrier layer (the internal electric field force and the band bending produce forces in the same direction upon the photogenerated electron transfer), which is conducive to the separation and migration of photogenerated charge carriers. More importantly, the separated electrons and holes are fully utilized, respectively reducing O₂ and oxidizing H₂O to produce H₂O₂. The activity of H₂O₂ production by NiS₂/g-C₃N₄ was therefore significantly improved (approximately 4.5-fold activity enhancement in contrast to g-C₃N₄) when the two pathways were carried out simultaneously. This study sheds light on the reverse barrier layer photocatalyst with multiple functions for efficient H₂O₂ photosynthesis and relevant solar energy utilization.