APPLICATION OF “GREEN” MANGANESE DIOXIDE IN SOLID-STATE SUPERCAPACITORS

B. Mladenova¹, K. Pashova², I. Hinkov², M. Dimitrova¹, A. Stoyаnova¹

¹ Institute of Electrochemistry аnd Energy Systems, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., 10, 1113 Sofia, Bulgaria

² University of Chemical Technology and Metallurgy, bul. "Kliment Ohridski" 8, 1756 Sofia, Bulgaria

 

A green synthesis of MnO₂ is presented in this study. MnO₂ was obtained from KMnO₄ using plant extracts from Calendula officinalis or Tilia cordata as reducing agents. The obtained materials were structurally and morphologically characterized using by UV-Vis spectrophotometry, transmission electron microscope (TEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) methods.

"Green" MnO₂ samples were investigated as positive electrode materials in solid-state supercapacitor cells. The commercial product Aquivion®E87-05S membrane activated in 1M Na₂SO₄ solution was used as separator and electrolyte. Galvanostatic charge/discharge tests between 0.05 and 1.6 V and cyclic voltammetry in the same voltage window were carried out. Cells were subjected to continuous cycling at a current load of 240 mAg^-1 for up to 1000 cycles.

The synthesized MnO₂ from Calendula officinalis extract was found to exhibit very good capacitive behaviour, high energy density and stability, and is a suitable electrode material for the development of an eco-friendly solid-state supercapacitor.

 

 

COMPARATIVE STUDY OF ELECTROCHEMICAL PERFORMANCE OF SYMMETRIC SUPERCAPACITORS WITH AQUEOUS ELECTROLYTE AND WITH POLYMER EXCHANGE MEMBRANE

L. Soserov¹, B. Mladenova¹, A. Stoyanova¹, B. Karamanova¹, A.  Arenillas²

¹Institute of Electrochemistry and Energy Systems – BAS

10 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria

²Instituto de Ciencia y Tecnología del Carbono, INCAR-CSIC, Francisco Pintado Fe 26, 33011 Oviedo, Spain

The symmetric supercapacitors are electrochemical capacitors with higher energy density than conventional. Both their positive and negative electrodes contain the same type of electrode active material.

Carbon xerogels are a type carbon material which properties may be designed, structurally and chemically, in order to fit the requirements for their final application They possess tunable porosity, high purity and electrical conductivity and are very promising as active electrode materials for supercapacitors.

In this study, the electrochemical properties of symmetric supercapacitors based on an activated carbon xerogel (AX-1500) were compared in a polymer Aquivion^TM electrolyte membrane (used as electrolyte and separator) and in an aqueous solution of 1 M KOH. The membrane was previously exchanged to the K⁺ form by immersion in 1 M KOH. AX-1500 was prepared by polymerization of resorcinol and formaldehyde in a sol-gel process aided by microwave heating. Its physicochemical properties have been characterized by various methods.

Electrochemical tests were carried out by cyclic voltammetry, galvanostatic charge/discharge measurements, impedance analysis and long-term durability tests. The relationship between the structure and morphology of the carbon xerogel and the nature of the electrolyte was established, which may be relevant to the design of supercapacitors that provide high power and energy density.

Acknowledgement: This research was supported by contract No. DO1-286/ 07.10.2020, funded by the Ministry of Education and Science of Bulgaria, to whom the authors express their gratitude