Facile synthesis of hollow sphere amorphous MnO2: the formation mechanism, morphology and effect of a bivalent cation-containing electrolyte on its supercapacitive behavior

Abstract

Nearly X-ray amorphous hollow sphere manganese oxides (hollow sphere MnO 2 ) have been synthesized by a carboxylic acid-mediated system containing KMnO 4 and Na 2 S 2 O 4 under ambient conditions for supercapacitor applications. The product was characterized by powder XRD, Raman spectroscopy and thermal analysis. SEM and TEM were used to investigate the morphology of MnO 2 . The as-prepared MnO 2 was X-ray amorphous and had particles in the size range 0.1-1 mm. A mechanism has been proposed for the formation of hollow sphere structures in the micro-emulsion medium. Upon annealing the sample at temperatures greater than 500 C, the amorphous MnO 2 transforms into Mn 2 O 3 . Cyclic voltammetry and galvanostatic charge-discharge cycling were used to evaluate the electrochemical performance. The initial discharge capacities were found to be 283 and 188 F g À1 in 0.1 M Ca(NO 3 ) 2 and 0.1 M Na 2 SO 4 , respectively, at a current density of 0.5 mA cm À2 . The higher specific capacitance in the electrolyte with a bivalent cation is attributed to the reduction of two Mn 4+ to Mn 3+ by each of the bivalent cations present in the electrolyte.

Facile Synthesis of Flower-like (BiO)2CO3@MnO2 and Bi2O3@MnO2 Nanocomposites for Supercapacitors

“…In addition, at the temperature of about 200$530 C, TG curve presents a quite flat decrease which may be the loss of carbonate in (BiO) 2 CO 3 @MnO 2 (the weight loss is about 2.6%). There is also a 0.9% weight loss at around 560 C, which corresponds to the loss of oxygen from the MnO 2 lattice, resulting in the formation of Mn 2 O 3 [25,26]. According to Fig.…”

“…3f shows that thin MnO 2 nanosheets adhere on the surface of Bi 2 O 3 . Thermal analysis is a popular technique to estimate the water of crystallization, the content of each component, and to determine decomposition temperature [25], and the typical results of synchronous TGA and DTA analyses can be seen in Fig. 5.…”

Synthesis of Mn3O4 nanoparticles via chemical precipitation approach for supercapacitor application

“…Therefore, the transition metal oxides can greatly improve the energy density of supercapacitor. Various transition metal oxides were used as the electrode materials for supercapacitors, such as RuO 2 [14], NiO [15], Co 3 O 4 [16], SnO 2 [17] and manganese based oxides [18][19][20][21][22]. Among these materials, RuO 2 was the most widely studied metal oxide due to its high conductivity and high specific capacitance as well as its excellent chemical stability [23].…”

Chemical Mapping and Electrochemical Performance of Manganese Dioxide/Activated Carbon Based Composite Electrode for Asymmetric Electrochemical Capacitor

“…Approaches to increase the low specific capacitance of MnO 2 -based electrode include the addition of a conductive additive such as carbons [5][6][7][8][9] or conductive polymers [10][11][12][13][14] to MnO 2 for the fabrication of a composite electrode. On the other hand, the deposition of a thin MnO 2 layer on carbon with various (nano)architectures 7,[15][16][17][18][19][20][21][22][23][24] yielded high capacitance (∼700 F/g) when only the mass of MnO 2 was taking into account. 1,8,9,16 Such composite electrodes show typical specific capacitance in the range of 150-250 F/g.…”