Enhancing light and dark photocatalytic hydrogen production via graphene conductive networks in carbon nitride composites

Abstract

The development of photocatalysts capable of operating under both light and dark conditions is critical for sustainable solar energy utilization. This study presents a graphene-enhanced cyano-functionalized carbon nitride composite, fabricated via a simple electrostatic assembly method, to achieve efficient photocatalytic hydrogen evolution during day–night cycles. The introduction of graphene does not alter the structure of ^NCNCN. Graphene functions as an electron-conductive network, significantly improving charge separation and storage capabilities. Under visible light (λ ≥ 400 nm), the optimal composite with 0.5 wt% graphene exhibited a hydrogen production rate of 3156 µmol h⁻¹ g⁻¹, 35% higher than that of pure ^NCNCN. Remarkably, under dark conditions, it achieved a hydrogen yield of 3.8 µmol, representing a 65% enhancement. Photoelectrochemical analyses validated the reduced recombination of electron–hole pairs and enhanced conductivity. The proposed mechanism highlights the role of graphene in facilitating electron transfer to Pt co-catalysts and storing electrons via cyanide-K⁺ pairs for delayed hydrogen production in the dark. This work demonstrates the potential of graphene-based composites as efficient all-weather photocatalysts for sustainable energy applications.