MnCO3 as an electrode material for supercapacitor is slowly gaining momentum. So far, wet chemical methods have been used to synthesize MnCO3 for supercapacitor applications. The electrode fabrication of thus prepared MnCO3 requires a certain percentage of conductive additive and binder; both of them do not contribute significantly to the measured capacitance. Herein, we report electrodeposition of MnCO3 and its capacitance properties. MnCO3 has been electrodeposited from an aqueous mixture of MnSO4 and Na3C6H5O7 by chronopotentiometry. X‐ray diffraction and Raman spectroscopic studies confirm the formation of MnCO3. Microscopic studies reveal the formation of micron‐sized spherical particles by the agglomeration of sub‐micron sized cubes. Electrodeposited MnCO3 delivers a specific capacitance of 194 F g−1 at a specific current of 0.5 A g−1 and demonstrates good rate capability. Further, it also exhibits high cycling stability over 10,000 cycles with retention of 92% of its initial specific capacitance value and 100% coulombic efficiency.
We report here the potential competency of MnCO 3 versus MnO 2 for supercapacitor applications. MnCO 3 was synthesized by a hydrothermal method using KMnO 4 as a manganese source and either sugar or pyrrole as carbon source. MnCO 3 synthesized using sugar and pyrrole as carbon source is referred hereafter as MnCO 3 (s) and MnCO 3 (p), respectively. The synthesized products were characterized by powder X-ray diffraction, scanning electron microscopic and transmission electron microscopic studies. Microscopic studies revealed that MnO 2 possesses micro-flower-like morphology constructed by self-assembled nano-petals. While the morphology of MnCO 3 (s) is sub-micron size particles of different shape, the morphology of MnCO 3 (p) is crystalline particles of 10-20 nm dia. The capacitive characteristics of MnO 2 , MnCO 3 (s) and MnCO 3 (p) were evaluated in aqueous 0.1 M Mg(ClO 4 ) 2 electrolyte between 0 and 1 V using cyclic voltammetry and galvanostatic charge/discharge cycling. Specific capacitance (SC) values of 216 and 296 F g −1 obtained for MnCO 3 (s) and MnCO 3 (p) are 35 and 85 % higher than SC value of 160 F g −1 obtained for MnO 2 , respectively. Besides better capacitive storage characteristics, MnCO 3 (s) and MnCO 3 (p) have also exhibited better rate capability and cycle life than MnO 2 .
Nanocrystalline MnCO 3 is synthesized by hydrothermal reduction of KMnO 4 using different amounts of pyrrole. The effect of molar ratio of KMnO 4 :pyrrole on the phase purity, size of the particle, textural and capacitance properties of MnCO 3 is studied systematically using various physico-chemical and electrochemical techniques. While X-ray diffraction studies confirm decline in the phase purity of MnCO 3 , FTIR, Raman spectroscopic and thermogravimetric studies reveal an increase in the amount of adsorbed water and residual carbon content on increasing the pyrrole concentration during the synthesis. An increase in the size of the particles and reduction in the number of mesopores are observed from the morphological and sorption studies on increasing the pyrrole concentration during the synthesis. A highest specific capacitance value of 296 F g −1 is obtained at a current density of 0.16 A g −1 for the nanocrystalline MnCO 3 , and this capacitance value found to decrease on increasing the concentration of pyrrole during the synthesis of nanocrystalline MnCO 3 (166 and 140 F g −1 for the KMnO 4 :pyrrole ratio of 1:1 and 1:2, respectively).
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