The Preparation Of Co₃O₄/NiCo₂O₄ Composites And Their Electrochemical Energy Storage Study

As some phenomena of climate change,energy crisis and environmental pollution caused by the use of fossil fuels have become increasingly prominent,the development and utilization of clean renewable energy has become an urgent task.Realizing the efficient use of these clean energy sources such as wind energy,solar energy,etc.is inseparable from an excellent energy storage system.Among them,electrochemical energy storage devices have attracted attention due to their high energy conversion efficiency.Supercapacitors have the advantages of high charge and discharge speeds,high power density,and long service life,thus they are considered as one of the most promising electrochemical energy storage devices and are widely used in modern consumer electronics and hybrid electric vehicles.However,the key to realize such high-performance supercapacitor is the preparation and modification of electrode materials.As a pseudocapacitors electrode material,Co₃O₄ has high theoretical specific capacitance(3560 F g^-1),low price and friendly environment,and has become a research hotspot for researchers.Unsatisfactorily,its low electrical conductivity limits the actual specific capacitance and long-term cycling stability.Based on the above deficiencies,it is of great significance to modify the material and prepare a material with excellent properties for enhancing the electrochemical energy storage performance of the supercapacitor.In this paper,we aim at using simple and flexible methods to modify the materials and prepare excellent electrode materials,which provide a useful exploration for the development of supercapacitor energy storage materials.The main content of this article are as follows:（1）Mesoporous Co₃O₄/NiCo₂O₄ nanorods were synthesized by one-step hydrothermal reaction and subsequent annealing treatment with the assist of nickel foam.During the hydrothermal process,the nickel foam was partially dissolved and resulted in the formation of NiCo₂O₄ in the thermal treatment.The characterization of this composition by X-ray diffraction,X-ray photoelectron spectroscopy,high-resolution transmission electron microscopy,energy dispersive spectra and Brunauer-Emmett-Teller analysis revealed that the nanorods consisted of Co₃O₄ and NiCo₂O₄ phase,exhibiting high porosity and rich crystal defects.The electrochemical data showed a specific capacitance of1173 mF cm^-2 and 606 mF cm^-2 at 2 mV s^-11 and 1 mA cm^-2,respectively.Its cycling performance was 83.9%at 3 mA cm^-22 after 4000 cycles.Furthermore,the asymmetric supercapacitor Co₃O₄/NiCo₂O₄//AC delivered an energy density of 11.7 Wh kg^-1 and power density of 760 W kg^-1.（2）The hierarchical NiCo₂O₄ nanosheets/Co₃O₄ nanonwires array structure grown directly on a nickel foam was successfully prepared by a flexible and simple method.The combination of Co₃O₄ and NiCo₂O₄ has a favourable synergistic effect on enhancing capacitor performance.The firstly-synthesized Co₃O₄ nanowire arrays provides a template or scaffold for the subsequent growth of NiCo₂O₄,avoiding material aggregation and ensuring sufficient diffusion space for ions.In addition,the introduction of NiCo₂O₄reduces the charge transfer resistance of Co₃O₄ so that electrons can rapidly transmission wthin the active material.Electrochemical test results show that the hierarchical composite array structure exhibits enhanced electrochemical performance compared to Co₃O₄ nanowire arrays and NiCo₂O₄ nanosheets:at 1mA cm^-2,the specific capacitance of Co₃O₄/NiCo₂O₄/NF array is 5 F cm^-2,which is greatly larger than 2 F cm^-2 of the Co₃O₄ nanowire arrays and 2.7 F cm^-2 of the NiCo₂O₄ nanosheets,even when the current density increases 20times after 20,000 cycles,the capacitance retention rate is still as high as 82%,showing an extremely long cycle life.Furthermore,the asymmetric full-capacity capacitor Co₃O₄/NiCo₂O₄/NF//AC was assembled,which exhibited an energy density of 30.75 W h kg^-1 and a power density of 2.3 kW kg^-1,demonstrating it can be regard as promising electrochemical capacitor material.