Single-atomic Co-N4-O site boosting exciton dissociation and hole extraction for improved photocatalytic hydrogen evolution in crystalline carbon nitride

Single atom co-catalyst loading has been demonstrated to be an effective strategy for achieving efficient photocatalytic water splitting. Unfortunately, the origins of the high activity of the single atom sites remain unrevealed owing to the lack of deep insight on their coordination environment. Herein, single-atom Co was loaded on crystalline g-C3N4 (CCN) nanorod in the form of five-coordination (Co-N4-O) at the heptazine cavities. Both experimental and theoretical evidences revealed that single-atomic Co-N4-O sites in CCN-Co played a key role in exciton dissociation and photogenerated charge carrier separation as well as subsequent hole extraction and transfer. Under visible light irradiation, the photogenerated holes in CCN directionally transferred to Co-N4-O sites and were rapidly extracted by hole sacrificial agent. As a result, the obtained CCN-Co sample with 0.32 wt. % Co and 1.0 wt. % Pt exhibited significantly improved photocatalytic hydrogen production rate of 32.1 mmol g−1 h−1, nearly 4 times and 38 times higher than that of CCN and bulk g-C3N4, respectively. The apparent quantum yield as high as 49.5 % was achieved at 420 nm. This work opens new insights for understanding the effect of single-atom active sites in promoting photocatalytic hydrogen production.