Biochar doped carbon nitride to enhance the photocatalytic hydrogen evolution through synergy of nitrogen vacancies and bridging carbon structure: Nanoarchitectonics and first-principles calculation

Enhancing the separation and transfer of photogenerated carries is vital for improving the efficiency of photocatalytic hydrogen evolution reaction (HER) of graphitic carbon nitride (g-C3N4). Herein, a carbon-rich g-C3N4 with nitrogen vacancies (CCN4) was constructed by incorporating the biochar into g-C3N4 during a thermal polymerization in N2 atmosphere. The doped carbon atoms replaced the bridged nitrogen and increased the delocalization pi states. The synergy of the enhanced pi states and nitrogen vacancy favored narrowing the bandgap and accelerating the charge separation and migration in catalyst. Meanwhile, the CCN4 catalyst had favorable kinetics for HER, with simpler steps and a lower energy barrier than the PCN sample, in which H2 production from *H is prior to OH generation. The CCN4 catalyst exhibited excellent HER activity with a hydrogen evolution rate of 3342.4 mu mol center dot g- 1 center dot h-1 with 0.5 wt% cocatalyst Pt, which was 5.1 times higher than that of pristine g-C3N4 (PCN). Additionally, CCN4 exhibited good resistance to salt with the concentration near that of natural seawater, showing the further improved hydrogen evolution rate of 3808.8 mu mol center dot g- 1 center dot h-1. The findings reported in this work shed light on a biochar-tailored protocol to control the defects of g-C3N4 and optimize its intrinsic electronic properties and photocatalytic HER.