V-doped KNbO₃ perovskite for enhanced photocatalytic hydrogen production from first-principles calculations

Photocatalytic water splitting represents a promising route for sustainable hydrogen production using solar energy. In this study, Density Functional Theory (DFT) is applied to investigate the influence of vanadium (V) doping on the electronic and optical properties of cubic KNbO₃ (KNO). Simulations on KNb_1-x V _x O₃(KNVO), with x = 0.11, were performed using the CASTEP module under both GGA-PBE and mGGA-RSCAN functionals to reach better computational reliability. The mGGA-RSCAN functional exhibits better accuracy in reproducing the experimental bandgap values. 11.11% V substitution at the Nb site significantly reduces the bandgap from 1.82 eV to 1.53 eV (PBE) and from 2.30 eV to 1.86 eV (RSCAN), enhancing visible-light absorption. Optical and conductivity analyses reveal improved absorption and charge transport properties in V-doped systems. XRD analysis confirms the cubic structural stability. The valence and conduction band edge potentials obtained from Mulliken electronegativity satisfy the redox potential criteria for water splitting. These findings suggest V-doped KNbO₃ as a viable photocatalyst for visible-light-driven hydrogen production.