Solar-driven Z-scheme water splitting using tantalum/nitrogen co-doped rutile titania nanorod as an oxygen evolution photocatalyst

Abstract

A visible-light-driven water-splitting system that involves two-step photoexcitation (Z-scheme) was constructed using rutile TiO₂ nanorod doped with Ta and N (TiO₂:Ta/N) as an O₂ evolution photocatalyst. The Ta-doped TiO₂ nanorods, prepared by a solvothermal synthesis, underwent nitridation to possess visible-light absorption under mild conditions, even at 623 K under an ammonia flow. The TiO₂:Ta/N powders modified with a RuO₂ cocatalyst were active under visible light up to 540 nm for water oxidation for producing O₂ in the presence of reversible electron acceptors (IO₃⁻ or Fe³⁺), while TiO₂:N exhibited negligible activity. The results of time-resolved infrared absorption spectroscopy indicated that co-doping Ta with N into TiO₂ prolonged the lifetime of photogenerated free electrons, leading to high photocatalytic activity. Simultaneous H₂ and O₂ evolution via water splitting was achieved using a combination of RuO₂-modified TiO₂:Ta/N, Ru-loaded SrTiO₃:Rh and an Fe³⁺/Fe²⁺ redox couple under visible-light irradiation (λ > 420 nm) and under AM 1.5G simulated sunlight.