Rapid Joule heating synthesis of Ni doped into porous honeycomb C3N4 with greatly improved photocatalytic H2 production

Abstract

Photocatalytic water splitting is one of the sustainable and environmentally-friendly methods for producing hydrogen. Bulk C₃N₄ shows promise in the photocatalytic production of H₂, but its activity is greatly limited by low number of reactive sites. Herein, Ni-doped porous honeycomb C₃N₄ (Ni/HCN-V_N) was prepared for photocatalytic hydrogen production using a morphology modulation method followed by rapid Joule heating treatment. The porous honeycomb structure could expose more reactive sites and improve light utilization. Compared to the traditional calcination method, the Joule heating method well retained the honeycomb structure, which gave Ni/HCN-V_N a higher specific surface area (33.2 m² g⁻¹), approximately 3.2 times higher than that of bulk C₃N₄ (10.3 m² g⁻¹). Moreover, the introduction of Ni along with the generated nitrogen vacancies (during the Joule heating treatment) provided more reactive sites, further improving the photocatalytic activity. Experimental and theoretical calculations indicated that fast charge transfer between the metal (Ni) and the substrate (C₃N₄) occured, and the dual active sites (Ni and nitrogen vacancies) would strengthen the adsorption of H₂O and desorption of H₂. Overall, as-prepared Ni/HCN-V_N exhibited a high photocatalytic H₂ production rate (420.02 μmol g⁻¹ h⁻¹). This work provides a rapid synthesis strategy for the preparation of porous honeycomb C₃N₄ with rich defective sites and metal doping, and will make an important contribution to the structural design and modulation of photocatalytic properties.