A Novel Double Perovskite Oxide Semiconductor Sr₂CoWO₆ as Bifunctional Photocatalyst for Photocatalytic Oxygen and Hydrogen Evolution Reactions from Water under Visible Light Irradiation

Development of photocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) photocatalysts with a narrow bandgap is important for solar water splitting. Herein, narrow bandgap Sr₂CoWO₆ double perovskites with a light absorption edge of ≥700 nm are synthesized by a solid‐state reaction method varying the precursor ratios. The sample synthesized with a precursor Co/W ratio of 1:4 has a conduction band (CB) and valence band (VB) located at −0.82 and 0.95 V versus the normal hydrogen electrode (NHE) at pH = 7, respectively. As a result, both the photocatalytic OER and HER are observed even without loading any cocatalysts. After loading Pt and Rh cocatalysts, the average photocatalytic OER and HER rates are 188 μmol h⁻¹ g⁻¹ (apparent quantum efficiency of 3% at ≈420 nm) and 30 μmol h⁻¹ g⁻¹, respectively. Density functional theory calculations indicate that the OER active sites may shift from a high overpotential W‐site to a low overpotential Co‐site when the W content is increased, which renders high photocatalytic activity for W‐rich samples. Therefore, W‐rich Sr₂CoWO₆ double perovskite is identified as a novel narrow bandgap bifunctional semiconductor photocatalyst for photocatalytic OER and HER, which is rare for oxide semiconductor photocatalysts. This work opens up a new avenue for the development of oxide‐based double perovskite semiconductor photocatalysts for photocatalytic water splitting.