Controlled Synthesis Of Cu-based Nanostructures And Their Electrochemical Performance For Supercapacitors

The extensive dependence on fossil fuels has caused significant environmentalpollution as well as energy resource crisis. Sustainable exploration and use of energysource depend on discovery of new energy source and development of novel energydevices. Among various emerging energy storage technologies, supercapacitors haveattracted tremendous attention because of their high power density, excellent pulsecharge-discharge characteristics, super-high cycling life and safe operation. It is wellknown that electrode materials play a crucial role in the electrochemical performance ofsupercapacitors, so research for the novel electrode materials is the key problem forsupercapacitors. In particular, transition metal oxides have been extensively investigatedas supercapacitor electrode material due to their high energy density, high theoreticalcapacity and excellent reversibility. In this work, various CuO nanostructures andCuO-based composites electrode materials for supercapacitors have been prepared bydifferent methods. The crystal structure, morphologies, and specific surface area wereinvestigated by X-ray diffraction (XRD), scanning electron microscopy (SEM),transition electron microscopy (TEM), and N2adsorption-desorption measurements.Electrochemical properties were characterized by cyclic voltammetry (CV),galvanostatic charge/discharge and electrochemical impendance spectroscopy (EIS).The research content and the main conclusion are listed as below:Firstly, CuO with diverse morphologies have been synthesized by wet-chemicalmethod at room temperature, in which the Cu(NO3)2·3H2O was used as Cu source,tetraoctylammonium bromide (TOAB) as surfactant, ammonia (NH3·H2O) and sodiumhydroxide (NaOH) were used as precipitant, respectively. In addition, the effects ofmorphology on the electrochemical properties were investigated. The electrochemicaltests demonstrated that the electrochemical performance of CuO nanoribbon was thebest among the nanostructures. Remarkably, the CuO nanoribbon electrode exhibited aspecific capacitance of137F g-1with capacitance retention of88.1%after500cycles.In order to improve the electrochemical performance of CuO, flower-likeCuO/NiO and CuO/MnO2composites were synthesized by a one-step hydrothermalmethod, respectively. The results indicated that the surface of CuO was homogeneouslycovered with a layer of dense NiO nanosheets and MnO2nanosheets, respectively,leading to a higher specific surface area which could improve the capacitive performance of the electrode material. The electrochemical tests demonstrated that thecapacitances of CuO/NiO and CuO/MnO2composite were280and167.2F g-1whichwere much higher than the pristine flower-like CuO (65F g-1). Moreover, the uniquecomposites exhibited good rate capability and excellent cycling stability.The CuO@MnO2core-shell nanostructures were prepared by hydrothermalreaction with KMnO4, in which Cu nanowires were utilized as the template. Theelectrochemical tests in the three-electrode configuration demonstrated that theCuO@MnO2core-shell nanostructures acquired a specific capacitance as high as276Fg-1at a current density of0.6A g-1, and a long-term cycling stability (remains92.1%ofits original state after1000cycles), thereby indicating the excellent cycling stability. Anasymmetric supercapacitor with CuO@MnO2core-shell nanostructure as the positiveelectrode and activated microwave exfoliated graphite oxide (MEGO) as the negativeelectrode yielded an energy density of22.1Wh kg-1and a maximum power density of85.6kW kg-1, rendering the CuO@MnO2core-shell heterostructures promising as theelectrode materials for the high-performance supercapacitors.In principle, the facile synthetic strategy in our work could be useful to designother novel Cu-based oxides nanostructures. Simultaneously, the obtainedself-assembled Cu-based nanostructures in this work exhibited excellentelectrochemical performance and they could be the optimized nanomaterials forsupercapacitors.