Oxygen vacancies in oxygen evolution cocatalysts (OECs) can significantly improve the photoelectrochemical (PEC) water splitting performance of photoanodes. However, OECs with abundant oxygen vacancies have a poor stability when exposing to the highly-oxidizing photogenerated holes. Herein, we partly fill oxygen vacancies in a MnCo₂O_x OEC with N atoms by a combined electrodeposition and sol-gel method, which dramatically improves both photocurrent density and stability of a BiVO₄ photoanode. The optimized N filled oxygen vacancy-rich MnCo₂O_x/BiVO₄ photoanode (3 at.% of N) exhibits an outstanding photocurrent density of 6.5 mA·cm⁻² at 1.23 V_RHE under AM 1.5 G illumination (100 mW·cm⁻²), and an excellent stability of over 150 h. Systematic characterizations and theoretical calculations demonstrate that N atoms stabilize the defect structure and modulate the surface electron distribution, which significantly enhances the stability and further increases the photocurrent density. Meanwhile, other heteroatoms such as carbon, phosphorus, and sulfur are confirmed to have similar effects on improving PEC water splitting performance of photoanodes.

Owing to the relatively short hole diffusion length, severe charge recombination in the bulk of bismuth vanadate (BiVO₄) is the key issue for photoelectrochemical water splitting. Herein, we design a nanoporous MoO_3−x/BiVO₄ heterojunction photoanode to promote charge separation. The efficient electron transport properties of oxygen deficient MoO_3−x and the nanoporous structure are beneficial for charge separation, leading to a significantly enhanced PEC performance. The optimized MoO_3−x/BiVO₄ heterojunction photoanode exhibits a photocurrent density of 5.07 mA·cm⁻² for Na₂SO₃ oxidation. By depositing FeOOH/NiOOH dual oxygen evolution cocatalysts to promote surface kinetics, a high photocurrent density of 4.81 mA·cm⁻² can be achieved for PEC water splitting, exhibiting an excellent applied bias photon-to-current efficiency of 1.57%. Moreover, stable overall water splitting is achieved under consecutive light illumination for 10 h. We provide a proof of concept for the design of efficient BiVO₄-based heterojunction photoanodes for stable PEC water splitting.