Dual modification of BiVO₄ photoanode by enriching bulk and surface oxygen vacancies for enhanced...

The introduction of oxygen vacancies (Ov) into photoanodes has been considered an effective method to enhance the photoelectrochemical (PEC) water splitting performance. The efficiency of water splitting is related to light absorption, charge separation to the electrode surface, and charge injection into the electrolyte. However, introducing Ov from a single level cannot meet the above objectives. In this work, we present the fabrication of BiVO₄ (BVO) photoanodes with bulk and surface Ov, and their respective roles in the PEC performance have been studied. The bulk O_V of the photoanode could increase the carrier density and improve the separation efficiency of photogenerated electrons and holes. The surface Ov provide abundant surface active sites, and enhance the charge injection efficiency. Charge separation efficiency of the nitrogen-treated BVO (N:BVO) (69.1 % at 0.75 V vs RHE and 85.1 % at 1.23 V vs RHE) has a noticeable increase compared with that of BVO (51.2 % at 0.75 V vs RHE and 64.6 % at 1.23 V vs RHE), nevertheless, only a minor enhancement of charge injection efficiency (from 49.1 % to 56.5 % at 1.23 V vs RHE). After the deposition of NiFeOOH, the photoanodes present superior charges injection efficiency in the whole range of applied potential. The as-synthesized N:BVO/U-NiFeOOH photoanode exhibits a photocurrent density of 5.52 mA·cm^-2 at 1.23 V vs RHE with a 97 % Faradaic efficiency for O₂/H₂ evolution. Thus, there is a synergistic effect between the bulk O_V and surface O_V on the BVO photoanode, exhibiting highly promoted PEC water splitting activity relative to the individual O_V decorated BVO for oxygen evolution reaction, which provides a promising strategy for fabricating efficient solar water splitting systems.