Effect of simultaneous electrochemical deposition of manganese hydroxide and polypyrrole on structure and capacitive behavior

Enhanced Performance of WO3/SnO2 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 WO₃/SnO₂ nanocomposite electrodes. In aqueous solutions, the hexagonal WO₃ microspheres were first chemically deposited on a carbon cloth, and then tin oxides were uniformly electrodeposited. The synthesized WO₃/SnO₂ nanocomposite was characterized by XRD, XPS, SEM, and EDX techniques. Electrochemical properties of the WO₃/SnO₂ nanocomposite were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in an aqueous solution of Na₂SO₄ with/without the redox-active electrolyte K₃Fe(CN)₆. K₃Fe(CN)₆ exhibited a synergetic effect on the electrochemical performance of the WO₃/SnO₂ nanocomposite electrode, with a specific capacitance of 640 F/g at a scan rate of 5 mV/s, while that without K₃Fe(CN)₆ was 530 F/g. The WO₃/SnO₂ 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 WO₃/SnO₂ 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 WO₃/SnO₂ nanocomposite prepared by this simple process is a promising component for a hybrid pseudocapacitor system with a redox-flow battery mechanism.

Simultaneous Electrodeposition of Ternary Metal Oxide Nanocomposites for High-Efficiency Supercapacitor Applications

Complex oxides and hydroxides of Ni, Co, and Mn from a precursor mixture were electrochemically deposited on both a cathode and an anode. On the Ni foam cathode, the complex metal hydroxides precipitated as nanolayers at -0.9 V. Simultaneously, the metal ions were oxidized and deposited as blocks on the Ni foam anode. While the concentrations of Ni(NO₃)₂ and Mn(NO₃)₂ were constant (80 mM for Ni²⁺ and 40 mM for Mn²⁺, respectively), the concentration of Co(NO₃)₂ was varied from 20 to 120 mM, which affected the morphology and electrochemical properties of the electrode: a Co:Ni:Mn molar ratio resulted in the highest specific capacitance (at a scan rate of 5 mV s^-1, 1800 F g^-1 for the cathode material and 720 F g^-1 for the anode material). This cathode material was assembled into symmetric supercapacitors, which demonstrated an excellent energy density of 39 Wh kg^-1 at a power density of 1300 W kg^-1 and a high capacitance retention of 90% after 3000 charge/discharge cycles. This high electrochemical performance was attributed to the optimized ratio of metal oxides, and this simple preparation strategy can be applied to other nanocomposites of complex metal oxides/hydroxides with desired characteristics for various applications.

Influence of Temperature on ZnO/Co3O4 Nanocomposites for High Energy Storage Supercapacitors

We developed a two-step chemical bath deposition method followed by calcination for the production of ZnO/Co₃O₄ nanocomposites. In aqueous reactions, ZnO nanotubes were first densely grown on Ni foam, and then flat nanosheets of Co₃O₄ developed and formed a porous film. The aspect ratio and conductivity of the Co₃O₄ nanosheets were improved by the existence of the ZnO nanotubes, while the bath deposition from a mixture of Zn/Co precursors (one-step method) resulted in a wrinkled plate of Zn/Co oxides. As a supercapacitor electrode, the ZnO/Co₃O₄ nanosheets formed by the two-step method exhibited a high capacitance, and after being calcined at 450 °C, these nanosheets attained the highest specific capacitance (940 F g^-1) at a scan rate of 5 mV s^-1 in the cyclic voltammetry analysis. This value was significantly higher than those of single-component electrodes, Co₃O₄ (785 F g^-1) and ZnO (200 F g^-1); therefore, the presence of a synergistic effect was suggested. From the charge/discharge curves, the specific capacitance of ZnO/Co₃O₄ calcined at 450 °C was calculated to be 740 F g^-1 at a current density of 0.75 A g^-1, and 85.7% of the initial capacitance was retained after 1000 cycles. A symmetrical configuration exhibited a good cycling stability (Coulombic efficiency of 99.6% over 1000 cycles) and satisfied both the energy density (36.6 Wh kg^-1) and the power density (356 W kg^-1). Thus, the ZnO/Co₃O₄ nanocomposite prepared by this simple two-step chemical bath deposition and subsequent calcination at 450 °C is a promising material for pseudocapacitors. Furthermore, this approach can be applied to other metal oxide nanocomposites with intricate structures to extend the design possibility of active materials for electrochemical devices.