3D hierarchically branched Cu2S/ZnO heterojunction nanowire arrays for enhanced solar water splitting

The construction of three-dimensional (3D) hierarchically heterostructured nanoarrays is proven to be an efficient approach to developing high-performance photoelectrochemical (PEC) cells for water splitting. Here, novel 3D hierarchically branched Cu2S/ZnO heterojunction nanowire arrays (NWAs) are fabricated as photocathodes for enhanced PEC water splitting. The pristine Cu2S NWAs are pre-grown on Cu substrates by a facile gas-solid reaction at room temperature, followed by ZnO nanospike branches decoration. The obtained 3D Cu2S/ZnO NWAs demonstrate an improved light trapping ability of 93.7-99.0% in the wide wavelength range of 250-850 nm. Furthermore, the photocurrent density of 3D photocathodes is more than four times higher than that of the pristine Cu2S NWAs, and it has an optimal incident photon to current efficiency (IPCE) of 10.5% at 450 nm. In addition, the mechanism of greatly enhanced PEC performance of the 3D heterostructures can be attributed to the increased light absorption and the stepwise band-edge structure for charge separation and transport. This strategy demonstrates an alternative route for the large-scale fabrication of high-performance PEC cells with lowcost nanostructured photocathodes.