Gradient‐Tuned VO4 Vacancies in BiVO4 Photoanode for Boosting Bulk Hole Transport and Oxygen Evolution Reaction Performance

Abstract Although bismuth vanadate (BiVO 4 ) photoanode has been widely used, the solar‐driven oxygen evolution reaction (OER) performance is constrained due to the substantial bulk recombination and poor mobility of charge carriers. Herein, a facile solvothermal post‐treatment approach that employs N,N‐dimethylformamide (DMF) is developed to induce a VO 4 vacancy gradient from bulk to surface of BiVO 4 film, which not only improves the charge diffusion but also establishes an advantageous upward band gradient to promote the bulk hole transport. Under Air Mass 1.5 Global (AM1.5G) simulated solar illumination, the optimized BiVO 4 photoanode with a VO 4 vacancy gradient (denoted as B(VO) 1‐δ ) exhibits excellent OER performance with a charge separation efficiency of 74.4% at 1.23 V versus reversible hydrogen electrode (RHE) and incident‐photon‐to‐current conversion efficiency of 30.7% at 445 nm, 1.2 and 1.4 times higher than that of the pristine BiVO 4 , respectively. After loading nickel‐iron hydroxyl oxide (NiFeOOH) as a cocatalyst, the photocurrent density of B(VO) 1‐δ escalates to 5.92 mA cm −2 in a hole scavenger (Na 2 SO 3 ) solution and 5.07 mA cm −2 in a potassium borate buffer solution at 1.23 V versus RHE, far superior to the pristine BiVO 4 . This work highlights that the gradient‐tuned VO 4 vacancies can effectively modulate the bulk band structure and charge transfer in BiVO 4 photoanode, providing a new strategy for boosting solar water splitting performance.