Composition-graded Zn _xCd _1-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 Zn _xCd _1-xSe@ZnO core-shell nanowire array is prepared through temperature-gradient chemical vapor deposition (CVD) of Zn _xCd _1-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/cm ² 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.