Carbon/Transition-Metal-Oxide Composites As Electrode Materials For Supercapacitors

Supercapacitors as one of the most promising electrochemical energy storage technologies have already been applied in many fields,such as the aerospace,chemical industry,and electronic communication because of their long cycle life,fast charge/discharge capability,high power density and environment friendly between traditional electrostatic capacitors and rechargeable lithium batteries.Recently,the hybrid supercapacitors have attracted intensive attentions because they combine electrochemical double-layer materials as power sources with battery-type or paseudocapacitor materials as energy sources,which can simultaneously improve power and energy densities to meet the needs in practical applications.Benefiting from the synergistic advantage of the electrochemical properties of porous carbon and transition metal oxides,this paper synthesized porous carbon/transition metal oxide composites that serve as the electrode materials of supercapacitor,which delivers excellent electrochemical properties.1.A honeycomb-structured Co-W-B composite was prepared by a simple chemical reduction process in an alcohol solution.Electrochemical tests indicated that the Co-W-B composite exhibited a specific capacitance of 306.3 F g^-1 at a current density of 2 A g^-1.Furthermore,the Co-W-B composite retained 89.2%of its initial capacitance after 2500cycles.These results demonstrate that the honeycomb-structured Co-W-B composite is promising for use as an electrode material for supercapacitors.2.A highly dispersed CoO-NiO nanoparticle doped porous carbon（CoO-NiO@ZIF-C）was prepared by pyrolysis of Ni and Co ions impregnated ZIF-8.The resulted nanocomposite delivered a specific capacitance of 552.3 F g^-1 at current density of 1 A g^-1.Moreover,an asymmetric supercapacitor was successfully assembled using CoO-NiO@ZIF-C as positive electrode and reduced graphene oxide as the negative electrode,which delivered a maximum energy density of 43.5 Wh kg^-1 at a power density of 1892.1 W kg^-1,and long-term cycle stability,which holds great promise for use in practical application.3.A novel method for preparation of highly Co-Ni oxides dispersed 3D hierarchical graphene-like carbon nanosheets（CoO-NiO/3DG）was proposed.Co and Ni ions were firstly formed complexes with biopolymer.Followed by carbonization and oxidation,the carbon nanosheests-metal oxide composites were fabricated.Because of the unique structure of the obtained samples,it showed excellent electrochimical performance.It can deliver a high specific capacitance of 1586 F g^-1 at a current density of 1 A g^-1,as well as a capacitance retention of 94.5%after 10000 cycles.DFT calculations show that the prepared CoO-NiO/3DG exhibit excellent electrochemical properties due to the synergistic coupling between CoO and NiO.4.This section presents well-aligned molybdenum dioxide@nitrogen-doped carbon（MoO₂@NC）and copper cobalt sulfide（CuCo₂S₄）tubular nanostructures grown on flexible carbon fiber for use as electrode materials in supercapacitors.A flexible quasi-solid-state asymmetric supercapacitor composed of MoO₂@NC as the negative electrode and CuCo₂S₄as the positive electrode achieves an ultrahigh energy density of 65.1 W h kg^-1 at a power density of 800 W kg^-11 and retains a favorable energy density of 27.6 W h kg^-1 at an ultrahigh power density of 12.8 kW kg^-1.Moreover,it demonstrates good cycling performance with90.6%capacitance retention after 5,000 cycles and excellent mechanical flexibility by enabling 92.2%capacitance retention after 2,000 bending cycles.This study provides an effective strategy to develop electrode materials with superior electrochemical performance.