Enhanced photoelectrochemical properties of ZnO/ZnSe/CdSe/Cu_2-xSe core–shell nanowire arrays fabricated by ion-replacement method

The core-shell structures are designed to take advantages of each material to improve the photoelectrochemical (PEC) performance. Here we report a facile ion-replacement strategy for fabricating ZnO/ZnSe/CdSe/Cu_2-xSe core–shell nanowire arrays grown on Fluorine-doped tin oxide (FTO) glass under hydrothermal conditions. Under illumination with AM 1.5G, the designed ZnO/ZnSe/CdSe/Cu_2-xSe core–shell nanowire arrays exhibit superior PEC performance with the highest photocurrent density of 20.57 mA/cm², which is 29.4 times higher than that of the ZnO nanowire arrays at 0 V versus Ag/AgCl, and achieve the incident photon conversion efficiency (IPCE) of 87.6% at 410 nm without applying bias potential. The superior PEC performance of the ZnO/ZnSe/CdSe/Cu_2-xSe core–shell nanowire arrays results from the synergistic effects of each material. Vertical aligned ZnO hexagonal prisms provided large specific surface area and electron access along the axial direction. ZnSe layer further extended specific surface area and the range of light absorption. CdSe layer enhanced the visible light absorption vastly and fully utilized the incident light. P-type Cu_2-xSe layer produced p-n junctions, which could not only prevent the recombination, but also promote the separation and transmission of photo-generated electron-hole pairs. The synergistic action of each component in ZnO/ZnSe/CdSe/Cu_2-xSe core–shell nanowire arrays led an outstanding PEC performance. The synthetic strategy achieved in this work can have promising applications for designing highly efficient electrodes of other materials for water splitting.