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

Abstract

A MnO 2 @BP nanocomposite was synthesized by simultaneously reduction of KMnO 4 with Mn(CH 3 COO) 2 .4H 2 O and highly porous Black Pearls 2000 at room temperature. The specific surface area, porosity, crystalline form and conductivity of MnO 2 @BP nanocomposite were characterized by nitrogen gas adsorption measurements, scanning electron microscopy, X-ray diffraction and 4-point probe measurements, respectively. The content of MnO 2 and BP in the composite was determined by thermogravimetric analysis. Chemical mapping using Raman spectroscopy was performed to investigate the distribution of MnO 2 and BP in a composite electrode film prepared with polytetrafluoroethylene (PTFE) as binder. This composite electrode exhibits more homogeneously distributed MnO 2 particles when compared to an electrode made by physical mixing of MnO 2 , BP and PTFE (MnO 2 /BP-PTFE). Also, Raman spectroscopy data of both composite electrodes indicates a loss of electrical conductivity of BP in the case of MnO 2 @BP-PTFE. The electrochemical properties were characterized by cyclic voltammetry in aqueous 0.65 M K 2 SO 4 . The specific capacitance of MnO 2 @BP-PTFE composite electrode was 122 ± 5 F/g, which is statistically equivalent to the capacitance of MnO 2 /BP-PTFE composite electrode (129 ± 6 F/g Owing to its large theoretical capacitance, low cost, environmental friendliness and high density, manganese dioxide (MnO 2 ) is an ideal candidate for positive electrode in asymmetric electrochemical capacitor.1-4 However the performance of MnO 2 -based electrodes is limited by the low electrical and ionic conductivities of MnO 2 . 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 10-14 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 7,15-24 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. Thus, the reported specific capacitance per mass of manganese dioxide is more dependent on the quantity of MnO 2 than the nature of the conductive carbon. 5,8,9,16,[21][22][23][25][26][27][28][29][30][31][32][33] Obtaining good electrochemical performance for MnO 2 -based composite electrodes requires that the electrical contact between MnO 2 and the carbon to be as intimate as possible. 21,34 An attractive approach to achieve it, involves the deposition of MnO 2 onto carbon. 15,22,31,[34][35][36][37][38] By this mean, the effective interfacial area between manganese oxide and the solution is greatly increased. Moreover the contact between MnO 2 and carbon will lead to a high electronic conductivity. MnO 2 has been deposited onto a carbon support by various methods such as sol-gel route, thermal decomposition, electrodeposition, sonochemical synthesis, and redox reaction. 18,31,[34][35]...

Healable, Flexible Supercapacitors Based on Shape Memory Polymers

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