Material Characterization and Electrochemical Performance of Hydrous Manganese Oxide Electrodes for Use in Electrochemical Pseudocapacitors

Abstract

Hydrous manganese oxide with promising pseudocapacitive behavior was deposited on a carbon substrate at anodic potentials of 0.5-0.95 V vs. saturated calomel electrode ͑SCE͒ in 0.25 M Mn(CH 3 COO) 2 solution at 25°C. The effects of the deposition potential on the material characteristics and electrochemical performances of the hydrous manganese oxide prepared were investigated. Porous manganese oxide with higher crystallinity was formed at a lower deposition potential. When the deposition potential was 0.8 V SCE or higher, the deposited oxide consisted of an inner layer with a laminated structure and a rough outer layer with nodules on the surface. X-ray photoelectron spectroscopy was also carried out to examine the chemical state of the deposited oxide. Analytical results indicated that the oxide was composed of both trivalent and tetravalent manganese oxides at a deposition potential of 0.5 V SCE. However, the tetravalent manganese oxide became the dominant species in the film deposited at above 0.65 V SCE. The manganese oxide formed at 0.5 V SCE exhibited a specific capacitance as high as 240 F/g, as evaluated by cyclic voltammetry ͑CV͒ with a potential scan rate of 5 mV/s in 2 M KCl at 25°C. Increasing the CV scan rate reduced the specific capacitance. Only about 70% of the capacitance at 5 mV/s could be maintained when the CV scan rate was increased to 100 mV/s, for all the manganese oxide electrodes prepared. Moreover, a high deposition potential gave rise to a low specific capacitance of the manganese oxide formed.

Materials and fabrication of electrode scaffolds for deposition of MnO2 and their true performance in supercapacitors

“…It is clear that the passed charge directly links to the thickness and mass of the MnO 2 deposits [35,225], and the passed charge depends on the current density and deposition time, while the former has a close relationship with deposition potential. The deposition potential decides whether the deposition is carried out via electron or mass transfer controlled condition, and further influences the structure and oxidation states of the deposits [203]. On the other hand, the current density is correlated to the nucleation and growth rate of the MnO 2 deposits, thus have significant influences on the morphologies of the MnO 2 deposits [216,223].…”

A review of electrode materials for electrochemical supercapacitors

“…Several typical techniques reported in the literature are thermal decomposition, co-precipitation, sol-gel processes, electrodeposition, mechanical milling processes, and hydrothermal synthesis. 50,54,269,273,278,280,288,302,311,[335][336][337][338] Among these, the hydrothermal route has been proven to be an effective and controllable method to produce Mn oxides with various nanostructures such as nanowhiskers, nanoplates, and nanorods. 302,311,339 Note that the mechanical milling process can lead to a sequential phase transition from g-MnO 2 to the thermodynamically stable a-Mn 2 O 3 and subsequently to Mn 3 O 4 , depending on the duration of mechanical grinding.…”

Synthesis and Electrochemical Characterization of Silica-Manganese Oxide with a Core-shell Structure and Various Oxidation States

“…[8][9][10][11][12][13][14][15][16] Changes in the synthesis parameters such as current density, temperature, reactant concentration, and pH result in different physical, chemical, and electrochemical properties of manganese oxide. The synthesis conditions determine the intrinsic properties of the manganese oxide produced.…”