Tuning Optoelectronic Properties and Photoelectrochemical Performance of β‐TaON via Vanadium Doping

ABSTRACT The application of β‐TaON for solar‐driven water splitting is hindered by limitations in phase purity, stoichiometry, crystallinity, visible‐light absorption, carrier mobility, and high recombination rates. This study investigates the impact of vanadium doping (0‐25 at.% V) on the structural, optoelectronic, and photoelectrochemical properties of β‐TaON using both experimental and density functional theory (DFT) approaches. Phase‐pure β‐TaON is retained up to 10 at.% V, beyond which secondary phases (Ta ₂ O ₅ and VN) form, indicating a threshold of ∼10 at.% under the applied synthesis conditions. All samples exhibit a porous microstructure. Increasing vanadium content induces a redshift in the absorption edge, reducing the bandgap from 2.72 eV (undoped) to 2.38 eV at 25 at.% V for the main β‐TaON phase, in agreement with DFT results. X‐ray photoelectron spectroscopy confirms substitutional incorporation of V ⁵⁺ for Ta ⁵⁺ in the β‐TaON lattice. DFT calculations reveal reduced electron effective mass, enhanced n ‐type conductivity, and favorable band edge shifts enabling spontaneous overall water splitting at ≤10 at.% V. Photoelectrochemical measurements show improved photocurrent and more negative onset potentials for 5–10 at.% V, while higher V doping degrades performance due to phase segregation, which likely increases recombination and hinders interfacial charge transport. Vanadium doping (≤10 at.% V) is an effective strategy for tuning the electronic structure and enhancing the optical properties and photoelectrochemical performance of β‐TaON.