One-Dimensional p-ZnCo₂O₄/n-ZnO Nanoheterojunction Photoanode Enabling Photoelectrochemical Water Splitting

This work demonstrates the photoelectrochemical (PEC) water splitting activity of a one-dimensional n-ZnO/p-ZnCo2O4 nanoheterojunction photoanode synthesized by using the chemical bath deposition and electrodeposition methods. The nanoheterojunction photoanode exhibits an improved solar light-harvesting performance. The type-II analogous band alignment occurs because of p–n junction formation between p-ZnCo2O4 and n-ZnO nanorods (NRs), which accelerates the charge separation and transfer, significantly reducing the photogenerated electron–hole pair recombination. The ZnCo2O4 surface overlayer also passivates the surface states in ZnO, resulting in a remarkable reduction in photocarrier recombination. Additionally, the p-ZnCo2O4 shell layer acts as the oxygen evolution reaction (OER) catalyst to influence the PEC reactions at the electrode/electrolyte interface, boosting the charge transfer process and water oxidation reaction kinetics. Overall, an innovative nanoheterojunction photoanode is constructed to improve the PEC water oxidation of ZnO NRs by incorporating p-ZnCo2O4, which acts both as an OER catalyst and a p-type light-harvesting semiconductor.