Bifunctional NiCuOx photoelectrodes to promote pseudocapacitive charge storage by in situ photocharging

Abstract

Charging electrochemical devices by light irradiation may bring an essential change in energy-storage technologies. Herein, nickel copper mixed oxide (NiCuO_x)-based bifunctional photoelectrodes for integrated energy conversion and storage were developed to achieve significant capacitance enhancements by a photocharging process. NiCuO_x nanosheets have been directly grown on carbon cloth (CC) by a simple electrodeposition/annealing method. NiO/CuO_x heterojunctions have been formed in the CC@NiCuO_x nanosheet structures, which presented an intimate interfacial contact, endowing the materials with bifunctional properties for realizing photoenergy conversion and electrochemical charge storage simultaneously. When used as three-electrode supercapacitors, the as-prepared CC@NiCuO_x photoelectrodes demonstrated a maximum specific capacitance of 2937 mF cm⁻² under light irradiation, corresponding to 17.5% of enhancement compared to those delivered without light irradiation. Such a significant enhancement could be contributed by the in situ photocharging process, where the photo-generated holes from CuO_x (including CuO and Cu₂O) were transferred to neighboring NiO and then promoted the oxidation reactions of NiO. This work has provided a tentative study to show how photo-generated charge carriers can promote electrochemical charge storage.