Dual electric-field synergy in C3N4/C3N5/CoP homojunction-Schottky junction: Boosting directional charge separation for efficient photocatalytic H2 evolution

Inefficiency in photogenerated charge separation, especially within the in-plane heptazine units of widely used carbon nitride semiconductors, severely restricts photocatalytic H 2 evolution. Herein, a dual electric field was constructed in a novel C 3 N 4 /C 3 N 5 /CoP (CNHJ- X /CoP) composite via the synergistic integration of a C 3 N 4 /C 3 N 5 homojunction and a C 3 N 5 /CoP Schottky junction. The optimized CNHJ-5/CoP exhibits a photocurrent density 7.5 times higher than that of pure C 3 N 5 , along with a hydrogen evolution rate of 1878 μmol·g −1 ·h −1 (apparent quantum efficiency = 14.1% at 400 nm), which is 24.5% higher than that of C 3 N 5 /CoP binary composite. X-ray photoelectron spectroscopy, density functional theory calculations, and charge dynamics characterization collectively confirm that the dual electric field enhances the in-plane charge separation efficiency within the C 3 N 5 heptazine units and facilitates the directional transfer of photoelectrons from C 3 N 5 to both C 3 N 4 and CoP. Specifically, the homojunction promotes the retention of more holes in C 3 N 5 for reaction with triethanolamine, while the Schottky junction accelerates electron transfer to CoP for H 2 evolution, thereby driving the forward reaction. This work provides new insights into the design of advanced dual-electric-field systems for enhancing charge separation in two-dimensional nanosheets, thereby boosting photocatalytic H 2 evolution.