NiFe Prussian blue analog cocatalyzed TiO2/In2S3 type-II heterojunction for solar water splitting

Due to the excellent stability of titanium dioxide (TiO2), 2 ), there is still value in improving its solar-to-hydrogen conversion efficiency through tremendous attempts. Metal sulfides with a narrow bandgap are good candidates to broaden the ultraviolet light absorption of TiO2 2 into the visible light region. However, sulfides suffer from the photocorrosion issue, leading to poor stability. Herein, a type-II heterojunction of TiO2/In2S3 2 /In 2 S 3 is fabricated by a hydrothermal method, and a NiFe Prussian blue analog (NFP) overlayer is deposited on the surface of TiO2/In2S3 2 /In 2 S 3 through a chemical bath deposition technique. Under AM1.5G illumination, a photocurrent density of 1.81 mA cm-2 can be obtained with NFP coated TiO2/In2S3 2 /In 2 S 3 at 1.23 V vs. reversible hydrogen electrode, which is six folds of the photocurrent of TiO2. 2 . This photocurrent value can reach up to about 90% of its theoretical photocurrent. During a 12 h stability test, the TiO2/In2S3/NFP 2 /In 2 S 3 /NFP photoanode exhibits a high photocurrent retention of 95.17% after an initial transient decrease. The type-II heterojunction of TiO2/In2S3 2 /In 2 S 3 can efficiently boost the charge separation because of the built-in electric field and enhance the visible-light absorption because of the narrow bandgap of In2S3. 2 S 3 . A NFP overlayer serves as the cocatalyst for water oxidation reaction due to its valence changes of nickel and iron elements. NFP cocatalyst can rapidly extract the photogenerated holes from In2S3 2 S 3 and then improve the charge separation/injection efficiencies. Thanks to chemical stability of NFP, its coating can also make In2S3 2 S 3 resistant to photocorrosion by physically separating the photoanode from the electrolyte. Therefore, there is a good synergistic effect between the TiO2/In2S3 2 /In 2 S 3 heterojunction and NFP cocatalyst. This work provides some crucial insights for the interface engineering and material design in photoelectrochemical systems.