Optimal construction of Co3O4/Cu2O photo-assisted electrodes for aqueous Zn-ion hybrid capacitors: performance and mechanism

Abstract

Co₃O₄, with a high theoretical capacitance, is a promising electrode material for energy storage devices. However, the poor conductivity, low reaction activity and sluggish reaction kinetics of Co₃O₄ constrain its performance. Herein, light irradiation is employed to improve the electrochemical performance of Co₃O₄ as a cathode material in zinc ion hybrid capacitors (ZIHCs). To strengthen the favorable effect of light irradiation, Cu₂O is coupled with Co₃O₄ to construct a heterojunction, which enhances the separation and transfer of photo-induced charge carriers, thereby improving the conductivity, reactivity and reaction kinetics of materials. Two different heterojunction structures are constructed, and their photoelectric properties and photo-assisted charging performance are investigated. The optimal Co₃O₄/Cu₂O electrode (OC2) shows a specific capacitance of 793.0 F g⁻¹ at a current density of 4 A g⁻¹ under illumination, which is 77.2% higher than that in the dark and is 3.7 and 10.2 times the capacitance of pristine Co₃O₄ and Cu₂O, respectively. The mechanism analysis provides theoretical support for the photo-enhanced electrochemical performance of OC electrodes. The constructed OC2//Zn capacitor exhibits a high energy density of 255.3 Wh kg⁻¹ and an excellent power density of 15.9 kW kg⁻¹ under illumination. The device also demonstrates long-term stability with a capacity retention of 93.6% after 1000 cycles.