Enhancing photoelectrochemical activity with three-dimensional p-CuO/n-ZnO junction photocathodes

Designing photoelectrodes with particular nanostructure and composition has been regarded as a promising approach to improve the photoelectrochemical (PEC) water splitting efficiency. We report the design and synthesis of a three-dimensional (3D) nanostructure with CuO nanocones as backbones and ZnO nanorods as branches, using a facile water bath reaction process together with the atomic layer deposition (ALD) technology. As utilized in photocathodes, the optimized CuO/ZnO nanostructure, 37 cycles of ALD ZnO seedlayer and 55 min of water bath reaction of ZnO nanorods, demonstrate highly improved PEC performance. The ratio of photo to dark current density for the 3D CuO/ZnO is 6.4, much higher than the value of 2.7 for the CuO electrode. The enhanced activity is attributed to the synergistic effects of effective carrier separation and collection, reduced charge recombination, and increased carrier lifetime in the CuO/ZnO heterojunction. This work demonstrates the feasibility of designing novel 3D nanostructures by ALD technology as efficient photoelectrodes.