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.