Cobalt doped Mo5N6 as a noble-metal-free novel cocatalyst for promoting photocatalytic hydrogen production of g-C3N4 nanosheets

Abstract

As one of the 2D transition metal nitrides, Mo₅N₆ nanosheets (NSs) have been studied because of their excellent conductivity and tunable electronic structure. However, their higher valence state metal ions tend to capture excessive intermediates (H*) in photocatalytic H₂ evolution, which leads to poor performance. In this work, we show that Co-doped Mo₅N₆ nanosheets (Co–Mo₅N₆ NSs) could improve the photocatalytic H₂ evolution of g-C₃N₄ nanosheets (NSs). The Co dopant activates the basal plane of Mo₅N₆ by modulating its local electronic structure and exposing more active sites. As a result, the photocatalytic H₂ evolution rate reaches 3690.37 μmol h⁻¹ g⁻¹ for Co–Mo₅N₆/g-C₃N₄ under simulated sunlight, 119.7, 6.39 and 4.07 times that of g-C₃N₄ NSs (30.82 μmol h⁻¹ g⁻¹), Mo₅N₆/g-C₃N₄ hybrids (577.54 μmol h⁻¹ g⁻¹) and Pt/g-C₃N₄ (907.07 μmol h⁻¹ g⁻¹), respectively. The apparent quantum efficiency value is 11.23% at λ = 370 nm for Co–Mo₅N₆/g-C₃N₄. DFT calculations show that the loading of Co–Mo₅N₆ provides more catalytic sites on g-C₃N₄ and reduces the ΔG_H* for the HER to promote the HER process.