Electrode Properties of Mn₂O₃ Nanospheres Synthesized by Combined Sonochemical/Solvothermal Method for Use in Electrochemical Capacitors

Abstract

We report here an efficient single step combined sonochemical and solvothermal synthesis process to obtain bulk quantities of nanospherical particles of cubic Mn 2 O 3 and characterized its pseudocapacitive characteristics in relevance to electrochemical capacitors for the first time. It has been found that quantitative determination of specific capacitance yielded a value of capacitance of ∼100 Fg −1 within 0-0.4 V (versus SCE) potential range in a 6 M KOH alkaline electrolyte. The as-prepared nanopowders after being subjected to heat treatment at 400 • C were characterized by using XRD which shows a typical cubic single-phase structure (space group Ia-3), the broad crystalline peaks indicating the presence of explicit nanostructure. Electron microscopic studies (FE-SEM and TEM) revealed that the synthesized powders exhibit nanospherical morphology with uniform sphere-like grains of ∼10-15 nm range. Two heat-treated samples were studied in the context of crystallinity versus electrochemical capacitance using rate-dependent cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode system. The excellent well-refined redox behavior corroborates with EIS measurements. The presence of near symmetric redox couple observed in CV has been attributed to pronounced one-electron-transfer process owing to the presence of facile Mn redox centere facilitating the reversible one-electron transfer that accounts for its pseudocapacitance.

Mixed valence nanostructured Mn3O4 for supercapacitor applications

“…35 But Mn 2 O 3 nanospheres exhibit a specific capacitance of 40-50 F g −1 with 6 M KOH electrolyte at the scan rate of 5 mV s −1 . 36 In the present case, high values of specific capacitance was obtained for smaller scan rate 0.01 mV s −1 while at higher scan rates the specific capacitance is rather low. These values are much smaller than that reported for hydrous RuO 2 , viz., ∼720 F g −1 .…”

One-step synthesis of crystalline Mn2O3 thin film by ultrasonic spray pyrolysis

“…[18] So far, several deposition techniques of Mn 2 O 3 were reported in literature such as hydrothermal, facile solvothermal, calcination and reduction of MnO 2 . [18][19][20] The limitation of these methods is the complexity of preparation. These routes require the use of polymers and include several steps, which in some cases can be time consuming and suffer from contamination of organic…”

Facile fabrication of coaxial-cable like Mn 2 O 3 nanofiber by electrospinning: Application as electrode material for supercapacitor

“…It is obvious that all of the CV curves exhibit two significant redox peaks, suggesting that the specific capacitance primarily originate from the pseudocapacitive capacitance based on a redox mechanism, which is very different from that of electrical double layer capacitors that usually produce a CV curve close to an ideal rectangular shape. Moreover, for most MnO x electrodes in neutral electrolyte, the CV curves usually exhibit rectangular shapes and no clear redox peaks can be found [38,39] to the OH − chemisorption/intercalation into Mn 2 O 3 structure according to the following equation [40] :…”