Sr₂NiWO₆ Double Perovskite Oxide as a Novel Visible-Light-Responsive Water Oxidation Photocatalyst

Screening of stable visible-light-responsive water oxidation semiconductor photocatalysts is highly desired for the development of photocatalytic water splitting systems. Herein, a visible-light-absorbing Sr₂NiWO₆ double perovskite oxide photocatalyst was successfully prepared via a conventional solid-state reaction method. The intrinsic Sr₂NiWO₆ shows photocatalytic oxygen evaluation reaction (OER) activity of 60 μmol h^-1 g^-1, even without loading any cocatalysts. The DFT calculation indicates that the Ni species on the surface is the active site for the OER. The photocatalytic OER activity was further improved by loading Pt and RuO₂ dual redox cocatalysts on the surface of Sr₂NiWO₆ to achieve a photocatalytic OER activity of 420 μmol h^-1 g^-1, which corresponds to a remarkable apparent quantum efficiency (AQE) of 8.6% (λ ≈ 420 nm). The result indicates that Sr₂NiWO₆ is one of the best double perovskite oxide-based photocatalysts for the photocatalytic OER, and the activity is even comparable to the benchmark BiVO₄-based photocatalyst. The improvement of the photocatalytic OER activity is due to the provision of more active redox sites as well as the synergetic effect of the dual redox cocatalysts in facilitating charge separation and transfer. This work demonstrates that double perovskite oxides may serve as a novel class of efficient and stable oxide-based semiconductor photocatalysts for water splitting.