Three-Dimensional Cu-Based Nanostructures for Photoelectrochemical Water Splitting and Electrochemical Carbon Dioxide Reduction

Photoelectrochemical (PEC) water splitting and electrochemical carbon dioxide (CO2) reduction have emerged as viable methods for future solar-to-chemical conversion. Among various candidates, copper oxide (CuO) stands out as a promising photocathode material due to its suitable optical band gap, favorable band alignment, and low cost. Here, we report a low-temperature solution process to fabricate CuO branched nanowires (b-NWs) to explore the effect of surface morphology on the activity of PEC water splitting. CuO b-NWs provide a larger surface area, homogeneous surface crystallinity, and higher light absorption in near-surface regions than the conventional CuO NWs. As a result, CuO b-NWs serve as an efficient photocathode for PEC water splitting, exhibiting an approximately 2.6 times improved photocurrent density. Moreover, CuO b-NWs could be electrochemically reduced to Cu b-NWs, and then Sn nanoparticles are coated to form Cu-Sn b-NWs for electrochemical CO2 reduction. As the geometric structure became more complex in the order of Cu-Sn film, NWs, and b-NWs, carbon monoxide (CO) selectivity and production rate increase. The optimized Cu-Sn b-NWs result in the highest CO faradaic efficiency of 99.8% at -0.8 V-RHE. This study demonstrates that the rational design of three-dimensional nanostructures can enhance the optical properties of a photoelectrode and improve the electrochemical performance.