Synchronously introducing and encasing non-stoichiometric defects in TiO2 nanowires by NEG coating and interface reconstruction for sustainable photoelectrochemical water oxidation

Abstract

Manipulation of photoanodes by introducing reduced TiO₂ nanowire arrays with non-stoichiometric defects such as oxygen vacancies (V_o) has been verified to boost photoelectrochemical (PEC) water oxidation. The metastability of non-stoichiometric defects on the surface, however, severely limits their practical application in PEC water splitting for hydrogen production under harsh operational conditions. Here, we propose a scalable defect engineering strategy by Ti non-evaporable getter (NEG) coating on TiO₂ nanowires, followed by interface reconstruction in an inert atmosphere. The Ti NEG coating under air exposure instantly forms a passivation layer on the surface, which effectively prevents deep oxidation of the underlying Ti metal film and produces Ti³⁺ interstitials. After thermal annealing in an anaerobic environment, the residual Ti reductive species extracts partial lattice oxygen from the TiO₂ nanowire to generate an embedded transition layer filled with V_o–Ti³⁺ defects. This TiO₂ photoanode not only retains 73–93% of its superior initial activity after 8-hour operation across a wide pH range, but also demonstrates improved oxidation resistance against applied potentials extended to 4.5 V vs. RHE and exceptional air stability after 4-month exposure. This work provides a universal paradigm for designing durable TiO₂ nanowire array photoelectrodes by integrating defect engineering with surface passivation.