Multi-element Transition Metal Oxygen(Sulfur) Heterostructure Construction And Their Supercapacitive Performance

In recent years,with worsening energy shortages and environmental pollution problems,it is of great significance to research and design efficient energy storage devices.Of which,supercapacitors are widely used in industry,electronics,medical,transportation,military industry et al due to their fast charging/discharging rate,high power density,long cycle life,and environmental protection.As an important part of supercapacitors,the electrode materials play a vital role in improving the electrochemical performance of supercapacitors.In this paper,we mainly take transition metal compounds as the research object,preparing Co₃O₄-Fe₃O₄,MgCo₂O₄-Fe₃O₄,and CoNi₂S₄-Ni₉S₈as the electrode materials of pseudocapacitors.The microscopic morphology,phase composition,chemical valence and electrochemical performances are deeply explored.The main research is as follows:The Co-MOF precursor was prepared on a carbon cloth substrate by hydrothermal method,and it was immersed in K₃[Fe(CN)₆]solution for ion exchange.Finally,Co₃O₄-Fe₃O₄with heterogeneous structure was successfully synthesized by annealing process.SEM and TEM characterization results show that the square-shaped Fe₃O₄is uniformly distributed on the surface of the Co₃O₄nanosheet.The influence of soaking time on the electrochemical performance of electrode materials was explored.Through comparison,it is found that the Co₃O₄-Fe₃O₄(CFO-2)sample prepared with a soaking time of 20 minutes has the best electrochemical performance.CFO-2 exhibits high specific capacitance of 1196.2 F g^-1at a current density of 1 A g^-1.When the current density is 5 A g^-1,after 10000 charging/discharging cycles,the specific capacitance retention rate is 74.8%;The assembled asymmetric supercapacitor shows CFO-2//AC a high operating voltage window of 1.6 V and the maximum energy density of 68.7 Wh kg^-1.After 14000charging/discharging cycles at a current density of 6 A g^-1,the specific capacitance retention rate is 80.5%.MgCo₂O₄and MgCo₂O₄-Fe₃O₄self-supporting electrodes were successfully prepared on the surface of nickel foam by simple hydrothermal and high-temperature calcination methods.The SEM and TEM characterization results show that the cubic mass of Fe₃O₄is uniformly distributed on the sea urchin-like MgCo₂O₄;The results of electrochemical performance test show that the specific capacitance of MgCo₂O₄-Fe₃O₄is 1648 F g^-1at a current density of 1 A g^-1.After 6000 charging/discharging cycles,the specific capacitance retention rate is 78.6%;The asymmetrical all-solid-state supercapacitor assembled by using MgCo₂O₄-Fe₃O₄electrode as the positive,activated carbon as the negative electrode,and PVA/KNO₃as solid electrolyte exhibits a high working voltage window of 1.6 V,and the maximum energy density of 78 Wh kg^-1.Ni-Co PBA(Prussian Blue Analogue)was prepared by a simple precipitation method.CoNi₂S₄-Ni₉S₈nanocube with a hollow structure was successfully synthesized by calcination and hydrothermal methods using Ni-Co PBA as a template,and different sulfide concentrations were explored.When the sulfur concentration is 0.2 mol L^-1,the specific capacitance of CoNi₂S₄-Ni₉S₈is the highest.The specific capacitance is as high as 1740 F g^-1at a current density of 1 A g^-1.After 10000 charging/discharging cycles,the specific capacitance retention rate of the CoNi₂S₄-Ni₉S₈electrode is 84.3%;The asymmetric supercapacitor assembled by CoNi₂S₄-Ni₉S₈as positive electrode,AC as negative electrode shows a specific capacitance of 104 F g^-1at a current density of 1 A g^-1.After 10000charging/discharging cycles,the specific capacitance retention rate of the device is 78.2%.