Release Time:2019-03-09  Hits:

Indexed by: Journal Article

Date of Publication: 2011-04-07

Journal: JOURNAL OF PHYSICAL CHEMISTRY C

Included Journals: EI、SCIE、Scopus

Volume: 115

Issue: 13

Page Number: 5413-5421

ISSN: 1932-7447

Abstract: Nanostructured mesoporous manganese oxides were easily prepared by mixing KMnO(4) with ascorbic acid in an aqueous solution under ambient conditions. The obtained manganese oxides were identified as having an alpha-MnO(2) tunnel structure composed of an edge-shared network of [MnO(6)] octahedra. TEM observations revealed that the obtained MnO(2) materials had three-dimensional frameworks which consisted of homogeneous nanoparticles with sizes of ca. 5 nm. Nitrogen sorption analyses showed that these MnO(2) nanoparticles exhibited a type IV isotherm, indicating a mesoporous character. Large surface areas up to 284 m(2) g(-1) were recorded. The electrochemical performances of the synthesized alpha-MnO(2) nanoparticles as supercapacitor electrode materials were studied using cyclic voltammetry and galvanostatic charge-discharge cycling in a three-electrode system at a potential range from 0 to 1.0 V vs a saturated calomel electrode in 0.5 M sodium sulfate solution. The result showed that mesoporous MnO(2) with three-dimensional frameworks exhibit a high capacitance up to similar to 200 F g(-1). Furthermore, a hybrid supercapacitor was assembled by using MnO(2) mixed with a small amount of activated carbon as the positive electrode and activated carbon as the negative electrode in a 0.5 M Na(2)SO(4) electrolyte. By balancing the mass of MnO(2) and activated carbon, a practical cell voltage of 1.8 V could be obtained in aqueous medium with a capacitance of 23.1 F g(-1). After 1200 cycles, the maximum energy density is 104 Wh kg(-1) and power density is 14.7 kW kg(-1). Thus, the obtained alpha-MnO(2) nanoparticles are suitable for use as supercapacitor electrode materials.