Vertically grown p-n heterojunction FeCoNi LDH/CuO arrays with modulated interfacial charges to facilitate the electrocatalytic oxygen evolution reaction

Since four electrons need to be transferred in the oxygen evolution reaction (OER), the potential required to drive the OER is much higher than that required for the hydrogen evolution reaction (HER). Therefore, developing efficient OER catalysts is essential to enhance the rate of water electrolysis. Herein, p-n heterojunction arrays which consist of n-type FeCoNi layered double hydroxide (LDH) ultrathin nanosheets anchored vertically on p-type CuO nanowires are constructed on Cu foam. The difference in the Fermi levels of FeCoNi LDH and CuO leads to a built-in electric field at the heterogeneous interface, which induces charge transfer from FeCoNi LDH to CuO, making FeCoNi LDH more positively charged and therefore more favorable for the adsorption of the initial reactant OH⁻. FeCoNi LDH/CuO/Cu achieves a current density of 50 mA cm⁻² at an overpotential of 243.1 mV, and is more efficient than pristine CuO/Cu, FeCoNi LDH/Cu, and even RuO₂/Cu. Moreover, it can work continuously for 104 h at different applied potentials without significant degradation. Density functional theory (DFT) calculations confirm the strong trend of OH⁻ to adsorb more readily on FeCoNi LDH in the p-n heterojunction and that the adsorbates interact more strongly with the active sites, which leads to enhanced activity. FeCoNi LDH/CuO/Cu is a highly efficient catalyst with promising applications and would shed light on the method of optimizing the performance of catalysts by modulating the electronic structure of active sites.