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. The introduction of oxygen vacancies into barium stannate plays a crucial role in reducing the bandgap energy and suppressing electron–hole recombination. A simple chemical reduction method for synthesizing high‐performance photoanodes with tunable band structures is proposed.