A highly enhanced photoelectrochemical performance of BiVO4 photoanodes modified with CoPi groups by increasing energy band bending, accelerating hole separation and improving water oxidation kinetics

Abstract

BiVO₄ is one of the most attractive photoanode materials for photoelectrochemical water splitting. Herein, a cobalt phosphate (CoPi) modified BiVO₄ (BiVO₄/CoPi) photoanode is prepared by electrodeposition. The physical and chemical characterization shows that the BiVO₄/CoPi photoanode has a three-dimensional porous structure formed by the aggregation of nanoparticles. Amorphous CoPi is successfully deposited on the surface of BiVO₄. The photocurrent density of BiVO₄/CoPi increases to 5.87 mA cm⁻² at 1.23 V_RHE (3.24 times that of BiVO₄). Based on the law of conservation of energy, it can be inferred that CoPi acts as an effective co-catalyst to reduce the activation energy (E_a) of the oxygen evolution reaction. The chopping current density–time curve indicates that CoPi, as a hole extractor, can reduce the charge accumulation on the BiVO₄ surface. The Mott–Schottky curve shows that CoPi increases the band bending of BiVO₄. It can be found that the applied bias photon-to-current efficiency (ABPE), charge separation efficiency (η_sep) and charge injection efficiency (η_inj) of BiVO₄/Co-Pi are enhanced. This is attributed to the synergistic effect of CoPi: increasing energy band bending, accelerating the hole separation and acting as an oxygen evolution co-catalyst with faster water oxidation kinetics. This work may provide new insights into the comprehensive effects of CoPi on the photoelectrochemical water oxidation of the BiVO₄ photoanode.