In situ synthesis of 3D Co@Co₃O₄ nanosheet arrays for hybrid supercapacitors with ultra-high rate performance

Co₃O₄ has been extensively studied for its ultra-high theoretical specific capacitance (3560 F g⁻¹) and cost-effectiveness. However, its poor conductivity originating from the relatively wide band gap, results in a low specific capacitance, a low energy density and a poor rate performance. In order to improve the rate performance of Co₃O₄, an in situ formed Co@Co₃O₄ structure was assembled with a post-heat treatment. Therein, Co nanosheet arrays (NSAs) were deposited on the activated carbon cloth (ACC) with a simple electrodeposition method. The Co@Co₃O₄ core-shell structure was characterized with XRD, HRTEM and XPS after argon ion etching. In addition, the kinetic analysis of redox reaction was introduced to quantify the contribution of redox pseudocapacitance and intercalated pseudocapacitance (“battery-type” materials). The Co@Co₃O₄ nanosheets show a high specific capacitance of 1520 F g⁻¹ at 1 A g⁻¹ and the specific capacitance retention at 10 A g⁻¹ takes 80.3% of the value at 1 A g⁻¹. The assembled hybrid supercapacitors (HSCs) show a superb energy density (60 Wh kg⁻¹) as well as a long lifespan (82.6% of the initial value after 10000 cycles). The eminent performance stems from the synergistic effect of Co@Co₃O₄ core-shell nanostructure, ensuring the structural stability and the rapid transmission of electrons.