Functionalized Electrolytic Manganese Dioxide Nanostructure Prepared at Fixed pH for Electrochemical Supercapacitor

Abstract

MnO 2 samples are synthesized by an electrodeposition technique at a fixed pH and are tested as active electrode material for an electrochemical supercapacitor. The physicochemical properties of electrolytic manganese dioxide, including average Mn oxidation state, amount of incorporated water, porosity, crystal structure, morphology, and electrochemical performance, are characterized. The characterization is carried out by thermal gravimetry, composition analysis, the Barrett-Joyner-Halenda model, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry methods. The correlation between these properties and the deposition conditions ͑pH͒ is studied. The results show that the pH strongly influences the properties and, consequently, the activity of MnO 2 in an electrochemical supercapacitor.Manganese dioxide ͑MnO 2 ͒ is one of the most attractive materials due to its catalytic, ion-exchange, magnetic, and electrochemical properties. 1-5 It is used especially as an electrode material in batteries and supercapacitors because of its energetic compatibility in a reversible electrochemical system. 4-7 Electrolytic manganese dioxide ͑EMD͒ can be produced by an electrolysis of an aqueous solution of MnSO 4 . The electrodeposition of EMD is overlapped by the oxidation ͑Reaction 1͒ and reduction ͑Reaction 2͒ of species on the anode and the cathode, respectively 5,6 Mn 2+ + 2H 2 O → MnO 2 + 4H + + 2e − anodic reaction ͓1͔According to the anodic/cathodic reactions, the generation of excess H + ions is an inherent part of EMD electrodeposition. It leads to a large decrease in the pH value and to a change in the electrodeposition conditions and the properties of EMD deposits. 6,7 In a previous paper, we adjusted the pH at 2 and 5 and then characterized the samples. The results confirmed that the pH of the solution has remarkable effects on the nanostructure, crystal structure, porosity, and the electrochemical performance of the EMD as a cathode in rechargeable alkaline manganese dioxide batteries. The aim of this paper is to extend previous research and to characterize the manganese dioxide samples that were prepared at fixed pH ͑2, 3, 4, 5, and 6͒. The chemical composition, micro-and nanostructures, porosity ͑surface area, pore size, and pore-size distribution͒, and electrochemical performance of MnO 2 as an active material in supercapacitors are studied by attention to pH value. ExperimentalThe EMD samples were produced from a solution containing MnSO 4 ͑0.74 mol L −1 ͒ at a temperature of 80°C and an anodic current density of 0.8 A dm −2 . A titanium plate was used as the anode ͑area: 1 dm 2 ͒ between two Pb plates that were used as the cathodes ͑area: 2 dm 2 ͒. The pH of the solution was monitored in situ by a pH meter. Five samples were electrodeposited at fixed pH 2, 3, 4, 5, and 6 by adding NH 4 OH ͑10%͒. They are named M2-M6, as shown in Table I.The chemical composition of the samples was determined using the potentiometric titration approach of Vetter and Jaeger 8 based on the cation vacancy model propos...

Chemical bath deposition synthesis and electrochemical properties of MnO2 thin film: Effect of deposition time and bath temperature

“…Moreover, 3-D electrode materials facilitate the penetration of both electrolytes and reactants into the whole oxide matrix in order to maintain very smooth electron pathways in rapid charge-discharge reactions [8]. Preparation conditions for MnO 2 materials have a great influence on their physico-chemical properties, including nanostructures, morphology as well as chemical composition and porosity, which have an impact on important electrochemical activities [9][10][11][12][13]. The nature of the reactants, pH of the reaction medium, heating temperature and heating duration have all dramatic effects on the crystal structures of the phases formed [14].…”

Characterization of manganese dioxide electrodeposited by pulse and direct current for electrochemical capacitor

“…In electrochemical capacitor the specific capacitance delivered from either doublelayer or faradic process. It is clear that, at a high scan rate, the capacitance delivered from the double-layer charging/discharging, and at lower scan rates, the measured value of the specific capacity corresponded to the sum of the double-layer and faradic contributions [4,5,8,9,13].…”

“…The mass transfer property of the electrode depends on the morphology, and especially the porosity (specific surface area, pore volume, and pore-size distribution) of MnO 2 [4,8]. This mass transfer of cations is facilitated by a larger pore volume.…”

“…Many metal oxides, conducting polymers, and carbon composites are suitable as electrode materials in electrochemical capacitors [1][2][3][4][5][6]. Manganese dioxide (MnO 2 ) is a promising potential electrode material for use in electrochemical capacitors due to its low cost and environmental compatibility.…”

“…Manganese dioxide (MnO 2 ) is a promising potential electrode material for use in electrochemical capacitors due to its low cost and environmental compatibility. A major area of research is how to produce MnO 2 using different methods (such as sonochemical, sol-gel, electrodeposition and hydrothermal method) and how to improve its electrochemical performance [3][4][5][6][7][8][9][10][11].…”