Manganese oxide/graphene aerogel composites as an outstanding supercapacitor electrode material

Graphene aerogels (GA), prepared with an organic sol-gel process, possessing a high specific surface area of 793 m(2)  g(-1) , a high pore volume of 3 cm(3)  g(-1) , and a large average pore size of 17 nm, were applied as a support for manganese oxide for supercapacitor applications. The manganese oxide was electrochemically deposited into the highly porous GA to form MnO2 /GA composites. The composites, at a high manganese oxide loading of 61 wt. %, exhibited a high specific capacitance of 410 F g(-1) at 2 mV s(-1) . More importantly, the high rate specific capacitances measured at 1000 mV s(-1) for these composites were two-fold higher than those obtained with samples prepared in the absence of the GA support. The specific capacitance retention ratio, based on the specific capacitance obtained at 25 mV s(-1) , was maintained high, at 85 %, even at the high scan rate of 1000 mV s(-1) , in contrast with the significantly lower value of 67 % for the plain manganese oxide sample. For the cycling stability, the specific capacitance of the composite electrode decayed by only 5 % after 50,000 cycles at 1000 mV s(-1) . The success of this MnO2 /GA composite may be attributed to the structural advantages of high specific surface areas, high pore volumes, large pore sizes, and three-dimensionally well-connected network of the GA support. These structural advantages made possible the high mass loading of the active material, manganese oxide, large amounts of electroactive surfaces for the superficial redox events, fast mass-transfer within the porous structure, and well-connected conductive paths for the involved charge transport.