Efficient Noble-Metal-Free Co-NG/TiO2 Photocatalyst for H-2 Evolution: Synergistic Effect between Single-Atom Co and N-Doped Graphene for Enhanced Photocatalytic Activity

Photocatalytic water splitting for H-2 evolution is appealing for transforming solar energy into clean chemical fuel. This technique generally requires noble metals as H-2 evolution cocatalysts to facilitate efficient cleavage of water. Herein, we report a noble-metal-free TiO2 nanobelts composite photocatalyst, in which TiO2 nanobelts are supported by nitrogen-doped graphene coordinated with a single Co atom (Co-NG). The results show that Co-NG is an efficient cocatalytst for the photocatalytic H-2 production over TiO2. The optimal amount of Co-NG loading is found to be 3.5 wt %, showing a H-2 evolution rate of 677.44 mu mol h(-1) g(-1) under illumination of AM 1.5 G simulated sunlight, which is close to that of platinized TiO2 nanobelts and 2.6 and 31.2 times greater than that of 3.5 wt % NG/TiO2 nanobelts composite and pure TiO2 nanobelts, respectively. The significantly improved photocatalytic activity is ascribed to the remarkable synergistic effect between single-atom Co and N-doped graphene, which serve as effective H+ reduction sites and efficient electron acceptors, respectively. Besides, the Co-NG cocatalyst also effectively retards the recombination of photoinduced charge carriers and leads to a prolonged lifetime of charge pairs. This study reveals that Co-NG is an up-and-coming candidate as cocatalyst for development of cost-effective photocatalysts for efficient solar-driven H-2 evolution.