Composition-Graded ZnxCd1–xSe@ZnO Core–Shell Nanowire Array Electrodes for Photoelectrochemical Hydrogen Generation

One-dimensional oxide nanostructure arrays are widely investigated as photoelectrodes in solar cells or photoelectrochemical (PEC) solar hydrogen generation applications, for which it is highly desirable for the electrode to have a broad light absorption and an efficient charge separation. In this work, a composition-graded ZnxCd1–xSe@ZnO core–shell nanowire array is prepared through temperature-gradient chemical vapor deposition (CVD) of ZnxCd1–xSe layer onto the pregrown ZnO nanowires. The core–shell nanowire array photoelectrodes yield a continuous absorption edge from 2.7 (460 nm) to 1.77 eV (700 nm) across the sample surface. The core–shell heterostructure facilitates the photogenerated electron–hole pair separation and the electron transfer from ZnCdSe to ZnO. By using such core–shell nanowire arrays as photoanodes for solar hydrogen generation via a PEC cell, a photocurrent density of ∼5.6 mA/cm2 is achieved under 1 sun solar light illumination at zero bias versus Ag/AgCl. This method may be useful in the design of multijunction nanostructured semiconductor photoelectrodes toward more efficient solar fuel devices.