Fabrication And Electrochemical Performance Of Metal Oxide And Composite Material For Supercapacitor

Supercapacitors attract considerable attention due to its excellent properties.They can deliver higher power density than batteries and larger energy density than conventional capacitors.The electrode materials play an important role on the evaluation for the supercapacitors.This paper is focused on pseudocapacitor electrode which contains metal oxide and composite materials including metal oxide as well as carbon nanotubes.The metal oxide electrode takes advantage of preferential growth and the optimized surface structure which is able to improve the electrochemical activity.The composite material electrode utilizes the schottky barrier and synergistic effect to store more electric charge which can enhance the electrochemical properties.The schottky barrier height regulation function as a“switch”during the charge-discharge process.The main works are as follows:1.Mn₃O₄ cubes interlocked with each other have been fabricated and the electrochemical properties have been studied.The formation of the Mn₃O₄ cubes is according to a“surface wrapping”growth mechanism.High specific capacitance was exhibited through electrochemical measurements in 6 M KOH electrolyte under three-electrode system.The specific capacitance is 667 F g^-1 at low scan rate of 1mV s^-1.When the current density reached 40 A g^-1,the specific capacitance is 153 F g^-1.The retention of specific capacitance is 71.8%after 1200 cycles.The structure provides abundant space for electrolyte infiltrating into active materials which ensure sufficient faradic reactions can take place.The Mn₃O₄ cubes could be a promising candidate as electrode material for supercapacitors.2.Co₃O₄ porous nanosheets have been fabricated and the electrochemical properties have been studied.The uniformly distributed pores on nanosheets were formed through annealing treatment.The galvanostatic charge-discharge test shows a high specific capacitance of 833 F g^-1 at a current density of 1 A g^-1.The Co₃O₄//AC asymmetric supercapacitor provides a high voltage window of 0-1.7 V.The capacitance retention of the as-made material is 83.5%after 10000 cycles.The energy density varies from 33 to 21 Wh kg^-1 at a power density ranging from 798 to18900 W kg^-1.There are two pairs of redox peaks in the cyclic voltammetry curves which reveal that both Co²⁺and Co³⁺participate in the faradic reaction,indicating good redox behavior of Co₃O₄ porous nanosheets.The pores on nanosheets facilitate ions transportation between the electrode and electrolyte.More ion exchange happened which can bring excellent electrochemical properties.3.NiO octahedrons with?111?exposed face have been successfully fabricated and applied in supercapacitor applications.NiO octahedrons preferred orientation growth along?111?face.The electrochemical tests were carried out in 6M KOH electrolyte.The specific capacitance is 1330 F g^-1 at a scan rate of 1 mV s^-1.The asymmetric supercapacitor with NiO octahedrons as positive electrode and commercial active carbon as negative electrode was tested under two-electrode system.The specific capacitance of asymmetric supercapacitor retains 92.3%after10000 cycles.The energy density has reached 41.54 Wh kg^-1 at a power density of1670 W kg^-1 and maintained 28.9 Wh kg^-1 at high power density of 17055 W kg^-1.The exposed face?111?belongs to high energy surface.The oxygen of the surface is in the highly unsaturated statement which possess high activity.NiO octahedrons with?111?exposed face exhibit improved electrochemical activity which can provide more faradic reaction between the electrode and electrolyte.4.CeO₂/CNTs nanocomposite has been synthesized and its electrochemical performance has been researched.The CeO₂ grows on CNTs substrates.The composite has achieved 818 F g^-1 at a scan rate of 1 mV s^-1.The hybrid displays excellent capacitance retention of 95.3%after 2000 cycles.The specific energy changes from 143 to 74 Wh kg^-1 at a power density with the range from 3237 to80727 W kg^-1.The regulation of schottky barrier height at the interface between CeO₂ and CNTs plays an important role as a“switch”during the charge-discharge process.In the charging process,the barrier height decreases with the increment of carrier concentration and vice versa.The variation of the barrier height regulates the electron storage and release.More electrons can be released in the process of discharge.The electrochemical properties have been improved due to the synergistic effect of the two materials.5.The?-Ni?OH?₂/CNTs composite has been prepared and applied as supercapacitor electrode.Hierarchical?-Ni?OH?₂ grows along the direction of CNTs backbones.The specific capacitance reached 2325 F g^-1 at a sweep rate of 1 mV s^-1.Long cycle life can be achieved which retains 83.6%of the initial specific capacitance after 10000 cycles.According to?-Ni?OH?₂/CNTs based asymmetric supercapacitor device,the energy density is 47.15 Wh kg^-1 at the power density of428 W kg^-1.When the power density is 7958 W kg^-1,the energy density keeps 28.74Wh kg^-1.The schottky barrier formed at the interface between?-Ni?OH?₂ and CNTs is beneficial for better electron storage capacity.It functions as a“switch”which can control the electron storage and release.During charging process,carrier concentration increases while potential barrier height reduces.On the contrary,potential barrier height increases with the decreasing carrier concentration in discharging process.The barrier height regulation results in rectifying behavior which promotes electron storage.The enhanced conductivity of the composite can also improve the electrochemical properties.