Enhanced low-temperature capacitance of MnO2 nanorods in a redox-active electrolyte

The negative effect of low temperature on the capacitive behavior of MnO2 nanorods in 4 M KOH is studied by cyclic voltammetry, constant current charge/discharge and electrochemical impedance techniques. The results show the discharge specific capacitance reduces from 270 to 80 F g(-1) at 0.2 A g(-1) as the temperature decreases from 20 to -20 degrees C due to the faded mass transportation and charge transfer processes at low temperature. After introducing p-phenylenediamine (PPD) in the electrolyte, the specific capacitance reaches to 156 F g(-1) at 2 A g(-1). The improvement on low-temperature capacitance is thought to come from the synergic effect of PPD and MnO2 by combining two pseudocapacitance chargestorage mechanisms taking place in the electrode and electrolyte together. (C) 2013 Elsevier B.V. All rights reserved.