All-Solution-Processed BiVO₄/TiO₂ Photoanode with NiCo₂O₄ Nanofiber Cocatalyst for Enhanced Solar Water Oxidation

BiVO4 has emerged as a promising photoanode for water oxidation. Technical barriers such as charge recombination and photocorrosion prevent its practical application. In the present work, a NiCo2O4 nanofiber cocatalyst with dual metal active sites was coupled with BiVO4 to overcome the limitations of surface recombination and sluggish water oxidation kinetics. This unique nanofiber morphology was synthesized by a facile hydrothermal technique. Photocorrosion of BiVO4 during water oxidation was addressed by conformal coating of TiO2 on BiVO4 using a simple spin-coating method. BiVO4/TiO2/NiCo2O4 exhibits a photocurrent density of 2.47 mA/cm2 at 1.23 V vs RHE without a hole scavenger, which is 12-fold higher than that of pristine BiVO4. NiCo2O4 nanofiber decoration significantly enhances the photocurrent density of BiVO4. While conformally deposited TiO2 serves as a protection layer, the NiCo2O4 nanofibers suppress the charge recombination by forming a p–n junction, which improves the water oxidation kinetics, leading to a cathodic shift in the onset potential. This strategy can assist in the development of an effective cocatalyst with a protection layer for sustainable photoelectrochemical applications.