The mechanism of specific capacitance improvement of supercapacitors based on MnO2 at an elevated operating temperature

Abstract

Amorphous nanostructured MnO2 film was anodically deposited onto economical duplex stainless steel substrate. The obtained MnO2 film was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy for microstructural, morphological, and compositional studies. The capacitive behavior was systematically investigated by cyclic voltammetry, charge–discharge cycling and electrochemical impedance spectroscopy (EIS) in 1M Na2SO4 electrolyte at different operating temperatures ranging from 20 to 60°C. The specific capacitance (SC) was improved with an increase of operating temperature, and the highest SC of 398F/g was achieved at a scan rate of 10mV/s and operating temperature of 60°C. The mechanism of SC improvement at elevated operating temperature was investigated using EIS. With an increase of operating temperature, the conductivity of electrolyte was improved, and the charge-transfer resistance (Rct) was decreased. The temperature dependence of 1/Rct follows an Arrhenius equation. The MnO2 film was electrochemically activated at 60°C due to the formation of NayMnO2 after discharging.