BiVO₄-Cu₂O/CuO Nanocubes with High Charge Injection and Charge Separation Rates for Enhanced Photoelectrochemical...

Bismuth vanadate (BiVO₄) shows promise as a photoanode for water oxidation, with a relatively low band gap of 2.4 eV. However, its performance is limited by poor carrier separation and surface recombination. To address these limitations, a BiVO₄-Cu₂O/CuO nanocube (NC) heterojunction was successfully developed, increasing the photogenerated oxygen evolution current density to 2.3 mA/cm² at 1.23 V vs RHE, compared to 1.4 mA/cm² for bare BiVO₄. Addition of drop-casted Cu₂O/CuO NCs on BiVO₄ increases both the charge injection efficiency and the charge separation efficiency to over 60% at 1.23 V vs RHE. In comparison, the addition of drop-casted CuO nanowires (NWs) to BiVO₄ increased the charge injection efficiency to over 65%, but it only moderately increased the charge separation efficiency to 49% at 1.23 V vs RHE. These results highlight the importance of the interface between BiVO₄ and the catalyst layer for an enhanced photocurrent. In the Cu₂O/CuO NCs, bulk Cu₂O likely serves as a hole-extracting heterojunction, while surface CuO likely functions as a catalyst. In contrast, the CuO NWs function primarily as a catalyst.