Enhanced Photoelectrocatalytic Activity of CuO/CuNb2O6 Heterojunction Photocathodes for Efficient Solar Water Splitting

CuNb2O6 (CNO), a novel ternary metal oxide, has garnered much attention since it has a modest bandgap and potentially high current density. However, the reported photocurrent density so far is still much lower than the theoretical value. In this study, a CuO/CNO photoelectrode heterojunction was synthesized for the first time by using a solution-based spray pyrolysis method. The properties of the heterojunction were investigated through various characterization techniques, including Mott-Schottky analysis, time-resolved photoluminescence, surface photovoltage analysis, chopper linear sweep voltammetry, and electrochemical impedance spectroscopy. The optimized maximum photocurrent density of the CuO/CNO heterojunction was similar to 0.75 mA/cm(2) at 0.4 V vs. reversible hydrogen electrode (RHE), which is 2.8 times higher compared to the bare CNO photocathode. The improvement is attributed to the enhanced transport properties of charge carriers and promoted better separation of photo-generated electrons and holes in the photoelectrode by the heterostructure. By the generation of heterojunctions, this work provides a new foundation for the design and construction of photocathodes with high charge separation efficiencies. This is also useful for future studies on water decomposition using heterojunctions as photoelectrode materials.