Molten salt synthesis of Mn2O3 nanoparticle as a battery type positive electrode material for hybrid capacitor in KNO3-NaNO2-NaNO3 melts

Abstract An innovative kind of low-temperature inorganic molten salt hybrid capacitor was first put forward. Mn 2 O 3 nanoparticle was selected as battery type positive electrode of hybrid capacitor. The high crystallinity Mn 2 O 3 nanoparticles with large specific surface areas were successfully prepared by molten salt synthesis method using ternary alkali nitrates. Electrochemical performances of Mn 2 O 3 electrode were evaluated by cyclic voltammetry, square wave voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge in KNO 3 (53 wt%)-NaNO 2 (40 wt%)-NaNO 3 (7 wt%) melts at 423 K. The results illustrated that Mn 2 O 3 electrode transferred one electron during the reduction reaction and the Mn 2 O 3 nanoparticle exhibited a high specific capacity of 669.6 C g −1 (186.0 mAh g −1 , 2.51 F cm −2 ) at a current density of 5 mA cm −2 . Furthermore, Mn 2 O 3 electrode exhibited excellent cycle stability, and the capacity retention was up to 90.2% after 5000 cycles at a current density of 20 mA cm −2 . The hybrid capacitors with molten salt electrolyte could be considered as a potential application in some specific situation which requires the high-temperature demand.