Enhanced Performance of WO 3 /SnO 2 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 3 /SnO 2 nanocomposite electrodes. In aqueous solutions, the hexagonal WO 3 microspheres were first chemically deposited on a carbon cloth, and then tin oxides were uniformly electrodeposited. The synthesized WO 3 /SnO 2 nanocomposite was characterized by XRD, XPS, SEM, and EDX techniques. Electrochemical properties of the WO 3 /SnO 2 nanocomposite were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in an aqueous solution of Na 2 SO 4 with/without the redox-active electrolyte K 3 Fe(CN) 6 . K 3 Fe(CN) 6 exhibited a synergetic effect on the electrochemical performance of the WO 3 /SnO 2 nanocomposite electrode, with a specific capacitance of 640 F/g at a scan rate of 5 mV/s, while that without K 3 Fe(CN) 6 was 530 F/g. The WO 3 /SnO 2 nanocomposite catalyzed the redox reactions of [Fe(CN) 6 ] 3 /[Fe(CN) 6 ] 4- ions, and the [Fe(CN) 6 ] 3- /[Fe(CN) 6 ] 4- ions also promoted redox reactions of the WO 3 /SnO 2 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 -1 ) and power density (540 Wkg -1 ) requirements. Thus, the WO 3 /SnO 2 nanocomposite prepared by this simple process is a promising component for a hybrid pseudocapacitor system with a redox-flow battery mechanism.