Theoretical Insights into the Limitation of Photocatalytic Overall Water Splitting Performance of VIA Group Elements Doped Polymeric Carbon Nitride: A Density Functional Theory Calculation Predicting Solar-to-Hydrogen Efficiency

Polymeric carbon nitride (p-C₃N₄) is thermodynamically feasible for photocatalytic overall water splitting. Element doping is proved effective in enhancing the photocatalytic performance of p-C₃N₄. The effect of doping is usually interpreted from the angle of electronic structures by first-principles density functional theory (DFT) calculations. However, the information on electronic structures is insufficient for understanding and predicting the ultimate criterion of solar-to-hydrogen (STH) efficiency. Herein, a DFT calculation method is provided to investigate and predict the STH of VIA group elements doped p-C₃N₄ by calculating the efficiencies of both light absorption and carrier utilization. Particularly, significant efforts are made to calculate the energy barriers for the surface hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to determine the carrier utilization efficiency. Moreover, the chemisorption energies of the reactant intermediates are calculated to quantify the intermediates affinity for HER and OER on the surface. Among the VIA elements, oxygen is discovered as the most effective dopant in promoting the STH because oxygen-doped p-C₃N₄ has the lowest energy barriers for OER and the largest chemisorption energy for intermediates absorption. The calculation results highlight the importance of the surface reaction properties for efficient photocatalytic overall water splitting.