Effects of Heat Treatment on the Hierarchical Porous Structure and Electro-Capacitive Properties of RuO2/Activated Carbon Nanofiber Composites

Electrochemical capacitors based on hierarchical porous activated carbon nanofiber (RuO2 /ACNF) composites are fabricated by one-step electrospinning, and then stabilized at different activation temperatures. The effect of the activation temperature on the structural properties and electrochemical behavior of the RuO2 /ACNF composites is intensively investigated in 6 M KOH electrolyte. The RuO2 /ACNF-800 composites activated at high temperature possess abundant mesopores and larger pores, which improve the electrochemical performance, especially at high charge–discharge rates. The energy storage capabilities of the RuO2 /ACNF-800 electrode prepared at high temperature are as follows: a maximum specific capacitance of 150 F/g and an energy density of 14–20 Wh/kg in the respective power density range of 400 to 10 000 W/kg in an aqueous solution. Furthermore, this electrode exhibits high-rate electrochemical performance with a specific capacitance reduction of less than 28% of the initial value at a discharge current of 20 mA/cm2. Therefore, the hierarchical porous RuO2 /ACNF composites with well-developed mesoporous structure provide low resistance for charge diffusion and a short pathway for ion transportation, yielding good capacitive behavior.