Preparation And Electrochemical Properties Of Cobalt Tetroxide And Its Composite Materials For Supercapacitors

As a new type of green energy storage devices, supercapacitors have significant advantages, such as high power density, long cycling life, fast charging-discharging and environmental friendliness, which will become next-generation energy storage device. According to charge-storage mechanism, they are generally divided into two categories, i.e., electrical double-layer capacitors?EDLCs? and pseudocapacitors. Carbon materials, attributed to EDLCs, mainly store charges electrostatically through reversible ion adsorption at the electrode/electrolyte interface. Transition metal oxides?TMOs? and conducting polymers, attributed to pseudocapacitors, mainly exploit the fast and reversible Faradic redox process at the electrode surface. Currently, for pesudocapacitors, there has extensive interest in developing TMO electrode, as these TMOs are natural abundance, low cost. Typical Co₃O₄ has abundant Faradic redox reactions, and its theoretical capacitance is quite high. However, its cycling stability and rate capability still can not meet the demands of practical applications. Recently, owning to synergistic effects, multi-component composites made up of several electroactive materials exhibit excellent electrochemical performance. This paper introduces strategies based on design and synthesis of two Co₃O₄-based hybrid electrode materials aiming at improving the overall capacitive performance, and we fully study and discuss the electrochemical performance. The main contents of this paper are summarized as following:?1? We demonstrate the rational design and preparation of Co₃O₄@Ni Co₂O₄ hybrid electrode materials through a facile hydrothermal and chemical bath deposition process. The Co₃O₄@Ni Co₂O₄ hybrid electrode exhibits a large areal capacitance of 1.33 F/cm2 and specific capacitance of 1330 F/g at the current density of 3 m A/cm2, which is superior to pristine Co₃O₄ electrode?0.42 F/cm2 and 840 F/g?. Furthermore, this hybrid electrode also displays good rate capability, even at the current density of 30 m A/cm2, it still maintains 72% of the initial capacitance. Simultaneously, the overall capacitance retention for the Co₃O₄@Ni Co₂O₄ hybrid electrode is ultrahigh?100.7% after 5000 cycles?.?2? The Co₃O₄@PPy hybrid nanosheet arrays have been synthesized through a solvothermal and electrodeposition process. We investigated the impact of various pyrrole monomer concentration and deposition time on the morphology of hybrid materials, combining with the result of electrochemical test, and then delivered the optimized scheme?288 m M, 8 min?. A hybrid electrode made up of the Co₃O₄@PPy core/shell nanosheet arrays exhibits a high areal capacitance of 2.11 F/cm2 and specific capacitance of 1762 F/g at the current density of 2 m A/cm2, a ⁴-fold and ¹.6-fold enhancement compared with the pristine Co₃O₄ electrode?0.54 F/cm2 and 1082 F/g?. Furthermore, the equivalent series resistance?ESR? value of the Co₃O₄@PPy hybrid electrode?0.238 ?? is significantly lower than that of the pristine Co₃O₄ electrode?0.319 ??. In addition, the maximum energy density obtained for the hybrid electrode is 61.2 Wh/kg at a power density of 418 W/kg, and the energy density still reaches 39.7 Wh/kg even at a high power density of 4180 W/kg. Three-dimensional Co₃O₄@PPy hybrid electrode with mesoporous structure and high surface area can facilitate electronic and ion diffusion, accelerate charge transfer kinetics and improve the utilization of electrode materials.