Tailoring the Electronic Band Gap and Band Edge Positions in the C2N Monolayer by P and As Substitution for Photocatalytic Water Splitting

Exploiting earth-abundant and low-cost photocatalysts for high efficiency photocatalytic water splitting is of profound significance. Herein, we report an improved photocatalytic water splitting activity by P and As substitution at the N-site in the C2N monolayer using state-of-the-art hybrid density functional calculations. Our results show that the band gap can be reduced in C2N by increasing the concentrations of P and As substitution, and at the same time the obtained band gap value is higher than the free energy of water splitting except for As with concentrations of x = 0.333. This indicates that these new compositions of P/As substituted C2N monolayers are thermodynamically suitable to drive hydrogen evolution reaction. The calculated effective mass of charge carriers illustrates that charge transfer to the reactive sites would be easier in the substituted system than the pure C2N, and also our results suggest that the recombination rate would be lower in the substituted system, indicating the enhancement in the efficiencies of photocatalytic water splitting. The band edge position with respect to the redox potentials of water shows that P/As substituted C2N monolayers are the potential photocatalysts for water splitting than the pristine C2N monolayer. From the optical absorption spectra, we found that P/As substituted C2N monolayer shows optical absorption extended more into the visible region, indicating enhanced energy harvesting. Our results reflect that the P/As substituted C2N monolayer could be the potential visible-light photocatalyst for overall water splitting.