Electrochemical mechanisms of activated carbon, α-MnO2 and composited activated carbon-α-MnO2 films in supercapacitor applications

Pure alpha-MnO2 and activated carbon-MnO2 (AC-MnO2) films coated on Ni foam by electrophoretic deposition were applied as a supercapacitor electrode. The specific capacitance of AC-MnO2 films (155.03 F g 1) surpasses those of the pure AC (110.62 F g(-1)) and pure MnO2 film in the 1 M NaOH electrolyte. EDX and XPS detect an increase in the Na content and the reduction of Mn4+ to Mn3+ on the discharged MnO2 electrode (at 0.0 V), whereas a decrease in the Na content and the oxidation of Mn3+ to Mn4+ were obtained on the charged MnO2 electrode (at 0.45 V). Computational simulation of the Na inserted alpha-MnO2 structure displays the connection of Na to O atoms and the increasing electron density on Mn atoms. EDX of the charged AC-MnO2 (at 1.0 V) film detects a rise in the Na and a fall in the O contents, but the discharged AC-MnO2 film (at 0.0 V) shows a decrease in Na and increase in O contents. The AC-MnO2 film could retain 82.29% of the initial specific capacity after 10,000 cycles. Four series-supercapacitor coin cell assembled from the AC-MnO2 anode and MnO2 cathode delivers a power density of 2.79 kW kg (-1) and an energy density of 168.8 Wh kg (-1).

Automated summary

The study utilizes electrophoretic deposition to prepare AC-MnO2 films as supercapacitor electrodes, which exhibit high specific capacitance and cycling stability. Analysis by EDX and XPS reveals the changes in sodium content and manganese oxide valence states during discharge and charge processes. Computational simulation shows the atomic connections during sodium insertion into the α-MnO2 structure.