Reinforcement of Visible-Light Harvesting and Charge-Transfer Dynamics of BiVO₄ Photoanode via Formation of p–n Heterojunction with CuO for Efficient Photoelectrocatalytic Water Splitting

High photoinduced charge recombination process and indolent water oxidation kinetics are major drawbacks of the bismuth vanadate (BiVO4) photoanode in photoelectrocatalytic (PEC) water splitting. To address these issues, a bismuth vanadate/copper oxide (BiVO4/CuO) p–n junction electrode was fabricated via the electrodeposition method, and its PEC performance was studied using 0.1 M potassium phosphate (KPi) as an electrolyte under AM 1.5G (100 mW cm–2) irradiation. At an optimized condition, the BiVO4/CuO p–n junction electrode showed improvement in the current density of 2.05 mA cm–2 at +1.23 VRHE, which was ∼2-fold higher than the BiVO4 electrode (0.99 mA cm–2). The applied bias photon-to-current efficiency (ABPE) of the BiVO4/CuO electrode was also ∼2.5-fold higher than the BiVO4 electrode. Loading of CuO over the BiVO4 surface improved the light absorption ability of the electrode in the entire UV–vis region, leading to generation of a greater number of photoinduced charge carriers, and it also enhanced the reactive sites for water oxidation as per the calculation of double-layer capacitance (Cdl). The formation of inner electric field (IEF) at the interface between BiVO4 and CuO offered well-separated electron–hole pairs in association with improvement in the lifetime of charge carriers, and as a consequence, the BiVO4/CuO electrode showed a transient decay time of 4.45 s, which was ∼1.6-fold higher than the BiVO4 electrode (2.81 s). The formation of p–n junction between BiVO4 and CuO significantly reduced the charge transfer resistance (Rct) at the electrode/electrolyte interface (EEI), and as a result, the BiVO4 and BiVO4/CuO electrodes show Rct values of 454.4 and 201.9 Ω, respectively, under light illumination. Moreover, the Bode phase analysis confirmed quick hole consumption in the presence of the BiVO4/CuO electrode over the pristine BiVO4 electrode during water oxidation process. Overall, the formation of a p–n junction facilitated well-separated electron–hole pairs and improved the hole transfer at the EEI for an efficient PEC water oxidation process.