The Study Of Electrochemical Capacitance Based On Carbon Microspheres/metal Oxide Composite

Abstract:Supercapacitors, also called electrochemical capacitors, as a new kind of charge-storage device, has larger energy density compared to conventional capacitors and higher power density compared to secondary battery. Currently, supercapacitors are widely used in consumer electronics, transportation and military. The electrode material is the key component of capacitor to determine the electrochemical performance of supercapacitors. In this paper, carbon microspheres were synthesized by glucose as raw materials via a hydrothermal method. Besides, the carbon microspheres/ruthenium oxide composite (Cs/RuO2) and reduction of carbon microspheres/nickel oxide composite (rCs/NiO) were prepared, and their structures and electrochemical performances were investigated, respectively. In this context, three parts of work were discussed:(1) Preparation of carbon microspheres:carbon microspheres (Cs) were prepared by glucose as raw materials via a hydrothermal method at180℃. The carbon microspheres obtained are uniform with a diameter about100-200nm, exhibiting better monodispersity. Then the rCs were prepared by thermal reduction to remove surface oxygen functional groups. The electrochemical measurements indicate that the specific capacitance of Cs and rCs electrode is9and18F’g" at current densities of1A·g-1in1mol·L-1Na2SO4electrolyte, respectively.(2) Preparation of Cs/RuO2composite:the Cs/RuO2composite or Cs/RuO2composite was prepared by a sol-gel method, which improved the utilization rate of RuO2to some degrees, resulting in enhanced clectrochemical performances. At an ultrahigh current density of20A·g-1in1mol·L-1H2SO4solution, the specific capacitances of Cs/RuO2and rCs/RuO2composite could reach336F·g-1and491F·g-1, and the capacity retention rate of them is86.8%and80.0%, respectively. They also exhibit excellent capacity retention of97.7%and90.8%after5000charge/discharge cycles. Note that, the coulombic efficiency of Cs/RuO2and rCs/RuO2composite remains at almost100%during the cycling process. (3) Preparation of rCs/NiO composite:the rCs/NiO composites were obtained by hydrothermal and chemical precipitation method, respectively. Compared with hollow NiO, their rate and cycling properties were greatly enhanced. The capacity retention rate of the H-rCs/NiO and P-rCs/NiO composite is80%and77%at current densities of5A·g-1in2mol·L-1KOH electrolyte, respectively. They also exhibit excellent capacity retention of72.1%and67.1%after1000charge/discharge cycles.