Oxygen‐Vacancy‐Introduced BaSnO3−δ Photoanodes with Tunable Band Structures for Efficient Solar‐Driven Water Splitting

To achieve excellent photoelectrochemical water-splitting activity, photoanode materials with high light absorption and good charge-separation efficiency are essential. One effective strategy for the production of materials satisfying these requirements is to adjust their band structure and corresponding bandgap energy by introducing oxygen vacancies. A simple chemical reduction method that can systematically generate oxygen vacancies in barium stannate (BaSnO₃ (BSO)) crystal is introduced, which thus allows for precise control of the bandgap energy. A BSO photoanode with optimum oxygen-vacancy concentration (8.7%) exhibits high light-absorption and good charge-separation capabilities. After deposition of FeOOH/NiOOH oxygen evolution cocatalysts on its surface, this photoanode shows a remarkable photocurrent density of 7.32 mA cm^-2 at a potential of 1.23 V versus a reversible hydrogen electrode under AM1.5G simulated sunlight. Moreover, a tandem device constructed with a perovskite solar cell exhibits an operating photocurrent density of 6.84 mA cm^-2 and stable gas production with an average solar-to-hydrogen conversion efficiency of 7.92% for 100 h, thus functioning as an outstanding unbiased water-splitting system.