Enhanced Performance of WO/SnO Nanocomposite Electrodes with Redox-Active Electrolytes for Supercapacitors.

For effective supercapacitors, we developed a process involving chemical bath deposition, followed by electrochemical deposition and calcination, to produce WO/SnO nanocomposite electrodes. In aqueous solutions, the hexagonal WO microspheres were first chemically deposited on a carbon cloth, and then tin oxides were uniformly electrodeposited. The synthesized WO/SnO nanocomposite was characterized by XRD, XPS, SEM, and EDX techniques. Electrochemical properties of the WO/SnO nanocomposite were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in an aqueous solution of NaSO with/without the redox-active electrolyte KFe(CN). KFe(CN) exhibited a synergetic effect on the electrochemical performance of the WO/SnO nanocomposite electrode, with a specific capacitance of 640 F/g at a scan rate of 5 mV/s, while that without KFe(CN) was 530 F/g. The WO/SnO nanocomposite catalyzed the redox reactions of [Fe(CN)]/[Fe(CN)] ions, and the [Fe(CN)]/[Fe(CN)] ions also promoted redox reactions of the WO/SnO nanocomposite. A symmetrical configuration of the nanocomposite electrodes provided good cycling stability (coulombic efficiency of 99.6% over 2000 cycles) and satisfied both energy density (60 Whkg) and power density (540 Wkg) requirements. Thus, the WO/SnO nanocomposite prepared by this simple process is a promising component for a hybrid pseudocapacitor system with a redox-flow battery mechanism.