The mechanism of alkali promoting water splitting on g-C3N4

Abstract

Alkali solution can effectively promote hydrogen production in g-C₃N₄, which is not applied to all photocatalytic systems, but the mechanism is not clear. In this work, we investigate the effect of alkali on the electronic structure of H₂O/g-C₃N₄ and the dynamic process of water splitting from the atomic level. We find that both the alkali and the positive charge on g-C₃N₄ caused by it could quicken the decomposition of H₂O into H⁺. Subsequently, alkali further promotes the major migration path N–OH → C–OH → CO & N–H and hinders the minor one N–OH → NO & N–H, indicating that the interaction between alkali and OH is affected by the adsorption sites of OH. Then, alkali effectively reduces the free energy for H₂O splitting, in which the K changes the position of the rate-determining step. In addition, alkali reduces the energy difference between the VBM of H in the transition product and g-C₃N₄, making H capture the excited electrons from g-C₃N₄ and become H₂ more easily. Our work can help to further understand the mechanism of photocatalytic hydrogen production, and moreover provide theoretical support for better utilization of alkali.