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

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 H-2 evolution, which leads to poor performance. In this work, we show that Co-doped Mo5N6 nanosheets (Co-Mo5N6 NSs) could improve the photocatalytic H-2 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 H-2 evolution rate reaches 3690.37 mu mol 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 mu mol h(-1) g(-1)), Mo5N6/g-C3N4 hybrids (577.54 mu mol h(-1) g(-1)) and Pt/g-C3N4 (907.07 mu mol h(-1) g(-1)), respectively. The apparent quantum efficiency value is 11.23% at lambda = 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 Delta G(H*) for the HER to promote the HER process.