Urea-assisted hydrothermal synthesis of manganese dioxides with various morphologies for hybrid supercapacitors

Two MnO2 samples (MO-1 with thorn spheres and MO-2 with long nanowires) were synthesized by adding urea into KMnO4-H2SO4 reaction system at various hydrothermal temperatures. Urea could decrease the reaction temperature, and its hydrolysis could influence the morphology of MnO2. The as-prepared samples were analyzed by XRD and SEM. Their capacitive properties were investigated by electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge/discharge test. The initial specific capacitance values of AC//MO-1 and AC//MO-2 hybrid capacitors were 24.99 and 27.58 F g(-1) in 1 M Li2SO4 electrolyte, respectively. After 1000 cycles, the capacitance retention was 91.40% for AC//MO-1 and 96.93% for AC//MO-2. Therefore, AC//MO-2 exhibited better capacitive properties than AC//MO-1. (C) 2015 Elsevier B.V. All rights reserved.