Mg-doped SrTaO2N as a visible-light-driven H2-evolution photocatalyst for accelerated Z-scheme overall water splitting

Perovskite SrTaO₂N is one of the most promising narrow-bandgap photocatalysts for Z-scheme overall water splitting. However, the formation of defect states during thermal nitridation severely hinders the separation of charges, resulting in poor photocatalytic activity. In the present study, we successfully synthesize SrTaO₂N photocatalyst with low density of defect states, uniform morphology and particle size by flux-assisted one-pot nitridation combined with Mg doping. Some important parameters, such as the size of unit cell, the content of nitrogen, and microstructure, prove the successful doping of Mg. The defect-related carrier recombination has been significantly reduced by Mg doping, which effectively promotes the charge separation. Moreover, Mg doping induces a change of the band edge, which makes proton reduction have a stronger driving force. After modifying with the core/shell-structured Pt/Cr₂O₃ cocatalyst, the H₂ evolution activity of the optimized SrTaO₂N:Mg is 10 times that of the undoped SrTaO₂N, with an impressive apparent quantum yield of 1.51% at 420 nm. By coupling with Au-FeCoO_x modified BiVO₄ as an O₂-evolution photocatalyst and [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ as the redox couple, a redox-based Z-scheme overall water splitting system is successfully constructed with an apparent quantum yield of 1.36% at 420 nm. This work provides an alternative way to prepare oxynitride semiconductors with reduced defects to promote the conversion of solar energy.