Defect and Electronic Structure Engineering Graphitic Carbon Nitride with Dual-Gas-Phase Reaction for Visible-Light-Driven Hydrogen Evolution

Abstract

The intrinsic high charge recombination and narrow light absorption seriously affect the performance of g-C3N4 toward photocatalytic hydrogen generation. In this work, this problem is partially overcome by a dual-gas-phase treatment protocol, first ammonia and followed by phosphine annealing. Owing to facilitated contact between gas precursor and layered g-C3N4, the ammonia annealing created N vacancies provide cross-plane diffusion channels for efficient bulk charge separation and more active sites due to decreased aggregation. Despite the band gap broadening being accompanied by ammonia annealing, the introduction of a secondary impurity (P atom) in corner carbon sites narrows down the band gap to 2.56 eV. The combination of N defects (amine groups) and P dopants (carbon defects) allows capturing as many atomic Pt as possible as cocatalyst, with weakened binding energy between Pt and H atom by 0.42 V when compared to Pt–H binding in pristine g-C3N4. This leads to a low overpotential for materials to efficiently break energy barriers in the process of interfacial charge transfer. As a result, the target material beyond the one obtained by traditional solid or liquid doping delivers a hydrogen evolution rate up to 1959 μmol·h–1·g–1 under visible light (λ > 420 nm), nearly 8 times higher than that of pristine g-C3N4/Pt (250 μmol·h–1·g–1). The results demonstrate the success of our dual-gas-phase activation strategy and the importance of rational dual-defect engineering for improving the photocatalytic activity of layered materials, not limited to g-C3N4.