Surface Recombination Suppression in BiVO ₄ Photoanodes Through Sequential Deposition of FeCoO x and NiO x Thin Films

Bismuth vanadate (BiVO 4 ) is a well‐known n‐type semiconductor that has been investigated as an efficient photoanode for water oxidation. However, pristine BiVO 4 suffers from sluggish water oxidation kinetics, largely attributed to its short hole diffusion length and high surface charge recombination. To overcome these challenges, we prepare a BiVO 4 (BVO) photoanode modified with FeCoO x and NiO x thin layers via magnetron sputtering. The resulting BVO/FeCoO x /NiO x heterojunction demonstrates a 1.85‐fold improvement in photocurrent density (1.85 mA/cm 2 ) at 1.23 versus RHE related to the pristine BiVO 4. The improved photocurrent density was attributed to reduced surface recombination of photogenerated electrons and holes and accelerated sluggish water oxidation at the BiVO 4 surface by FeCoO x and NiO x thin layers. Femtosecond transient absorption (fs‐TA) spectroscopy shows that the heterojunction of FeCoO x and NiO x thin layers at the BiVO 4 surface significantly delays the electron‐hole recombination process, thus improving charge separation and PEC performance. Furthermore, a SiO 2 thin layer deposited on BVO/FeCoO x /NiO x improved the stability of the heterojunction by 72% after 1 h of reaction.