The Preparation Of MnO/C Nanofibers And The Effect Of Oxygen Vacancy Concentration On Their Capacitance Properties

Facing the dual test of energy crisis and environmental challenges,human society has extensively developed various types of energy storage devices.Electrochemical supercapacitors（ES）have become a research hotspot in recent years due to their unique advantages such as wide operating temperature range,long cycle life,and short charge and discharge time.Among the various types of ES electrode materials,transition metal oxides have a higher specific capacitance than carbon materials due to their pseudocapacitance storage effect.Therefore,transition metal oxides have been widely studied as ES electrode materials in recent years.In previous studies,MnO₂ has been widely used as a capacitor material because of its low cost and high theoretical capacitance(1110 F g^-1).Comparing with MnO₂,MnO has a higher theoretical specific capacitance(1350 F g^-1),but MnO is rarely used as ES electrode material.Like other transition metal oxides,poor conductivity and poor cycle stability are the bottleneck problems hindering the wide application of MnO.The combination of MnO and conductive matrix is expected to solve the above problems.In this work,MnO/C nanofibers were successfully prepared by electrospinning and vacuum annealing using MnO₂ as manganese source and polyacrylonitrile（PAN）as carbon source.The effect of different amounts of MnO₂ added on the capacitance performance of the prepared MnO/C materials was studied by changing the addition ratio of MnO₂ in spinning solution,and the effect of different concentrations of oxygen vacancy defects on the capacitance performance of MnO/C materials was studied by changing the vacuum annealing temperature.The practical application of MnO materials in the field of ES electrode materials can be effectively improved through the adjustment of these two directions.The XRD and XPS characterization techniques were used to prove the synthesis of the target product,and the relative size of oxygen vacancy concentration in each sample was characterized by XPS test technology.Through a series of electrochemical tests,it is proved that both the mass fraction of MnO₂ and the concentration of oxygen vacancy have a great influence on the capacitance performance of MnO/C material,but neither of them has a monotonically changing rule on the capacitive performance of MnO/C material.The appropriate amount of MnO₂ and the appropriate concentration of oxygen vacancy will make the actual capacitance performance of MnO/C material reach the optimal value.When the mass ratio of MnO₂to PAN was 55%and 650°C vacuum annealing treatment was carried out,the MnO/C material has the highest graphitization degree and the highest electrical conductivity,so its capacitance performance is the best.The sample is prepared as an electrode sheet for electrochemical test in 6 M KOH electrolyte,the specific capacitance of the sample reaches 163.6 F g^-1 at current density of 1 A g^-1.After 5000 cycles of constant current charge and discharge at a current density of 2 A g^-1,it has excellent cycle stability with a capacitance retention rate of 89.3%.Therefore,the method described in this paper can provide a new solution for improving the application of MnO and other transition metal oxides in the field of ES electrode materials.