Viologen doping induced charge storage in carbon nitride for enhanced photocatalytic hydrogen production

Abstract

The rapid recombination of photogenerated charges is the primary bottleneck hindering photocatalytic hydrogen generation with graphitic carbon nitride (g-C₃N₄). Herein, by introducing methyl viologen (MV) into the carbon nitride framework, CN-MV-x with enhanced photoinduced charge carrier separation is fabricated. The surface chemistry and photoelectrochemical properties of CN-MV-x samples are greatly enhanced. Owing to the increased charge separation with electron extraction by doped MV, the highest hydrogen evolution rate of 1.65 mmol g⁻¹ h⁻¹ is achieved by the CN-MV-x photocatalyst doped with 10 mmol MV (CN-MV-10). More impressively, CN-MV-10 also shows an extraordinary electron storage ability, which powers time-delayed hydrogen production in the dark after light illumination. Further analysis indicates that this time-delayed hydrogen evolution ability is ascribed to electron accumulation in the conduction band of carbon nitride. This study provides a new route to improve photoinduced charge separation by introducing redox species.