Introduction of MnO₂ nanoneedles to activated carbon to fabricate high-performance electrodes as electrochemical supercapacitors

Synthesis of activated carbon/MnO₂ composites for use as high-performance materials in supercapacitors is reported by the following synthetic procedure: first, activated carbon was thermally treated to create oxygen-containing functional groups in order to provide anchor sites between the activated carbon and MnO₂ nanoneedles. Formation of MnO₂ nanoneedles was subsequently achieved on the activated carbon surface. Characterizations indicated that the MnO₂ nanoneedles in the composite were homogeneously dispersed on the thermally treated activated carbon surface. Before fabricating activated carbon/MnO₂ composites, the extent of the oxidation of the activated carbon was determined. The electrode made from the activated carbon subjected to 6 h of thermal treatment (AC6) showed the highest specific capacitance (90.5 F g^-1), which was attributed to the fast redox process caused by the oxygen functional groups. The specific capacitance of the AC6/MnO₂ composite formed with a MnO₂/AC6 feeding ratio of 3:1 (AC6/MnO₂(3)) showed the highest value among the AC6/MnO₂ composite electrodes fabricated, which was attributed to the synergistic effect of both the activated carbon porous structure and redox reaction of the MnO₂ nanoneedles. This procedure is a promising fabrication method for supercapacitor electrodes.