Enhancement of electrochemical capacitive properties based on complementation of morphologies

Manganese dioxides octahedral molecular sieve nanowires with 2 × 2 tunnels (designated OMS-2) and amorphous manganese dioxides were synthesized via a hydrothermal treatment and a sol–gel method, respectively. Amorphous MnO2 nanoparticles were incorporated into the matrix of OMS-2 nanowires to form homogenous nanocomposites. The structures and morphologies of as-synthesized OMS-2 nanowires and amorphous MnO2 nanoparticles were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Electrochemical behaviors of the as-prepared nanocomposites with varying ratios were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge and potentiostatic electrochemical impedance spectroscopy (EIS) using a three-electrode system in a 0.5 M Na2SO4 aqueous solution. Pure OMS nanowires exhibit a specific capacitance of about 37 F g−1, and amorphous MnO2 nanoparticles demonstrate relatively higher specific capacitance of about 106 F g−1 at a scan rate of 2 mV s−1. The enhancement of specific capacitance can be carried out by mixing OMS-2 nanowires and amorphous MnO2 nanoparticles to form nanocomposites and the optimized mole ratio of OMS-2 nanowires to amorphous MnO2 as 1:5 can be achieved. The improved specific capacitance can be attributed to the increase of electrode conductivity and the effective interfaces between MnO2 active materials and electrolyte.