Breathing Kagome Lattice-Based Nb ₃ I ₈ Monolayer: Theoretical Insights into Enhanced Hydrogen Evolution Catalysis

Photocatalytic water splitting is a promising strategy for clean energy production, but its efficiency is restricted by poor light absorption, charge recombination, and slow reaction kinetics in photocatalytic materials. To address these challenges, a breathing Kagome lattice-based Nb3I8 monolayer is considered in the present study. Its photocatalytic performance is assessed via descriptors including the effective d-band center, spin-dependent carrier mobility, Gibbs free energy, and exchange-current density. The results based on density functional theory predict that the Nb3I8 monolayer is a type II magnetic semiconductor, with spin-up and spin-down bandgap energies of 1.06 and 1.77 eV, respectively. The application of biaxial strain can effectively further tune its electronic structure. An optimized ±2% biaxial strain straddles the reduction potential of water with Gibbs free energy differences (ΔG) of −0.25 and −0.52 eV, respectively, facilitating the hydrogen evolution reaction (HER). Meanwhile, the oxygen evolution reaction (OER) remains constrained by the endothermic formation of the OOH* intermediate, even under the applied strain. These results show that the breathing Kagome lattice-based Nb3I8 monolayer is a promising nanoscale material for spin-engineered photocatalysts, particularly for enhancing the HER in water-splitting applications.