Construction of Co Doping Graphitic Carbon Nitride With Regulation of Nitrogen Vacancy Concentration for Enhancing Photocatalytic CO ₂ Reduction Performance

In recent years, graphitic carbon nitride (g‐C 3 N 4 ) containing nitrogen vacancies has been widely used as a photocatalyst in CO 2 reduction reactions. The introduction of transition metals into this system helps to improve its photocatalytic performance, but regulating the synergistic effect of nitrogen vacancies and metal sites has always been a challenge. In this work, we synthesized a composite material featuring metal Co species anchored on g‐C 3 N 4 with nitrogen vacancies (Co/Nv‐WCN) through the molten salt method combined with the simple chemical reduction method, achieving a sea urchin‐like morphology. The experimental results reveal that the concentration of nitrogen vacancies in the composites was successfully controlled by trace H 2 O during the molten salt synthesis system. The as‐prepared Co 10 /Nv‐WCN‐L sample (by trace‐H 2 O‐derived) with optimal nitrogen vacancies achieves a CO production rate (252.2 μmol g −1 h −1 ), demonstrating one‐fold activity as much as that of Co 10 /Nv‐WCN‐M with excessive vacancies (by free‐H 2 O‐derived, 132.2 μmol g −1 h −1 ), and surpassing the performance of the corresponding reference materials. The excellent photocatalytic activity is attributed to the synergistic effect between the appropriate concentration of nitrogen vacancies and Co species, which is also proved by the photoelectrochemical characterization. This study provides new insights for designing efficient, low‐cost, and durable CO 2 reduction photocatalysts.