Preparation And Capacitive Properties Of Cobalt Oxide Based Electrode Materials With Different Morphologies

Due to the gradual exhaustion of fossil energy and the increasingly serious environmental pollution,it is becoming one of the most pressing problems to use renewable energy instead of conventional energy sources.With the continuous adjustment of energy structure,one of the important ways to solve the problem is finding large-capacity energy storage devices.As a new energy storage device,the supercapacitor has gradually concerned by scientists due to its characteristics including higher power density and long cycle life.Based on charge storage mechanism,supercapacitor is classified into two categories,including electric double layer capacitor(EDLC)and pseudocapacitor.The pseudocapacitor material has a large potential development which has a higher energy density than double electrode layer supercapacitor.However,practical application is limited by the poor conductivity and low actual capacitance.The cobalt oxide based electrode materials are typical pseudocapacitance materials.The capacitive properties of cobalt oxide based electrode materials with different morphologies were studied on in this paper.The contents of this paper have been as follows:The precursor grown on the surface of nickel foam was synthetized with the assistance of surfactant via a simple hydrothermal method.Co3O4 with mesoporous structure was obtained by the annealing process subsequently.A controllable preparation of the morphology from nanowires of single phase(Co3O4NW)to nanowires and rectangular flakes(Co3O4NW-F)of both phases were achieved by changing the concentration of the reactants and surfactant.With a larger specific surface area of Co3O4 NW-F,the superior electrochemical properties were obtained.The specific capacitance of Co3O4NW-F reaches a value of 1230.65 F·g-1 at 1 A·g-1.An asymmetric supercapacitor exhibited a high energy density of 148.75 W·h·kg-1 by a power density of 3150 W·kg-1 with Co3O4NW-F as the positive electrode material and AC as the negative electrode material.In order to study the capacitance of pseudocapacitance materials composite with high conductivity materials,Sandwich-like,hetero-structured cobaltous oxide/carbon nanotubes and vanadium pentoxide/carbon nanotubes are prepared by incorporating modified carbon nanotubes(CNTs)into layered pseudocapacitance materials.Compared with single compound,the capacitance performance of complex effectively was improved by the CNTs insert.The specific capacitance of Co3O4/CNTs was higher than V2O5/CNTs.In addition,an asymmetric supercapacitor exhibited a high energy density(157.5 W·h·kg-1)at a power density of 2520 W·kg-1 based on Co3O4/CNTs as the positive electrode material and AC as the negative electrode material.Flower-like Co3O4/Polypyrrole(Co3O4/PPy)nanosheet networks are directly grown onto Ni foam involving the solution-based method and in-situ oxidative polymerization of pyrrole for supercapacitor electrode materials.The flower-like design provides a high contact area for electrolyte ion diffusion and electron transport further improve the conductivity of the composite and provide effective eletrical connection for both electrolyte ions and electrons.The specific capacitance of Co3O4/PPy reaches a value of 1299.62 at 1 A·g-1.An asymmetric supercapacitor exhibited a high energy density of 66.5 W·h·kg-1 by a power density of 2520 W·kg-1 with Co3O4/PPy as the positive electrode material and AC as the negative electrode material.Urchin-like MnCo2S4/MnCo2O4 and ZnCo2S4/ZnCo2O4 were synthesized using simple hydrothermal and ion-exchange method.EIS tests indicate the charge transfer resistance for complex electrode materials is obviously smaller than the pristine single compound,thus favouring a successful outcome for synergy effect As a result,the specific capacitance of MnCo2S4/MnCo2O4 reaches a value of 1933.33 F·g-1 at 1 A·g-1 by three-electrode system.An asymmetric supercapacitor exhibited an energy density of 50.75 W·h·kg-1 and power density of 1260 W·kg-1 as the positive electrode material in the two-electrode system.ZnCo2S4/ZnCo2O4 electrode material reaches a higher value of 1057.78 F·g-1 at current density of 1 A·g-1.An asymmetric supercapacitor is fabricated with ZnCo2S4/ZnCo2O4 as positive material and CNTs as negative material that it reach a high energy density of 127.4 W·h·kg-1 at a power density of 2413 W·kg-1.