Descriptor-guided Fe/V co-doped hollow MoO₂ nanostructures for photo-assisted water splitting

Conductive oxides with chemically distinct local environments are attractive for bifunctional water splitting because hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) impose different requirements on adsorption and charge transfer. Here, a descriptor-informed Fe/V co-doping strategy is proposed to regulate MoO₂ for photo-assisted electrocatalysis. Density functional theory (DFT) screening based on incorporation thermodynamics, local M-O bond mismatch, and near-Fermi-level electronic states identifies V as the most favorable dopant for lattice incorporation and Fe as the dopant that minimizes local bond-length mismatch while strongly perturbing the electronic structure. Guided by this complementarity, Mo_0.9Fe_0.05V_0.05O₂ was synthesized and compared with pristine MoO₂ and single-doped controls. The co-doped catalyst preserves the MoO₂ framework and delivers the best overall performance, requiring 166 and 243 mV for HER and 253 and 281 mV for OER to reach 10 and 50 mA cm^-2 under illumination. Electrochemical measurements reveal improved charge-transfer behavior and enhanced light-induced current response. Optical characterization and finite-difference time-domain (FDTD) simulations indicate that the hollow architecture promotes optical-field localization, while DFT reaction energetics suggest site-dependent catalytic preferences, with V-associated sites favoring hydrogen adsorption and Fe-associated sites facilitating OER intermediate conversion. This study demonstrates that pairing dopants according to lattice compatibility and electronic perturbation is an effective route to activate MoO₂ for photo-assisted bifunctional water splitting.