Development of MnO2/porous carbon microspheres with a partially graphitic structure for high performance supercapacitor electrodes

We report the development of MnO2/porous carbon microspheres with a partially graphitic structure for high performance supercapacitor electrode materials. Micro- and mesoporous carbon microspheres were fabricated based on a hydrothermal emulsion polymerization and common activation process. Manganese nitrate was introduced into the pores of the carbon microspheres, followed by thermal treatment to transform it into amorphous MnO2. As-prepared MnO2/porous carbon microspheres with high specific surface area (up to 1135 m(2) g(-1)) and regular geometry (0.5-1.0 mu m in diameter) benefit fast ion-transport and rapid charge-discharge, and contribute double layer capacitance to the hybrid electrode. Besides, manganese dioxide shows high pseudocapacitive behaviour due to faradaic redox reaction. Furthermore, the introduction of MnO2 greatly promotes the graphitization degree of the carbon matrix. A typical MnO2/carbon sample shows a partially graphitic structure with a very low intensity ratio of Raman D to G band (I-D/I-G = 0.27), which substantially increases the electronic conductivity and reduces the internal resistance (decreased from 0.42 to 0.20 Omega). As a result, the MnO2/porous carbon microspheres as supercapacitor electrodes exhibit excellent electrochemical performance (459 F g(-1) at 1.0 A g(-1) and 354 F g(-1) at 20.0 A g(-1) in 6 M KOH electrolyte). The well-developed MnO2/carbon hybrid materials with a high charge-discharge rate capability coupled with a high electrochemical capacitance highlight the great potential for widespread supercapacitor applications.