Abstract
Manganese oxide aerogels were successfully synthesized with an epoxide addition procedure by using MnCl2•4H2O as the precursor. The as-prepared aerogels possessed the crystalline phase of hausmannite of Mn3O4 and a BET specific surface area of 79m2/g. After heat treatment at 300 oC, the aerogels gave specific capacitances (SC) of up to 122F/g in 0.5M Na2SO4 solution, at a scan rate of 25mV/s, and within the window of 0.1~0.9V vs. Ag/AgCl. The resulting cyclic voltammetry (CV) loops appeared rectangular, implying high reversibility. After 2000 cycles of CV scans, the aerogels showed excellent cycle stability, retaining at least 96% of the maximum SC value. In order to improve on the issue of low electrical conductivity of manganese oxides, tin oxide aerogels (317m2/g) and carbon aerogels (577m2/g) of high specific surface areas and better electrical conductivities were used as the porous template to accommodate the functioning manganese oxides. Manganese oxides were electrodeposited into the aerogel templates with a simple 2-electrode potentiostatic procedure operated at different potentials. These composite electrodes, possessing high electrical conductivity backbone and rich redox reactions of transition metal oxides were found promising for supercapacitors. The SC of the manganese oxide (deposited at 2V)/tin oxide aerogel composite electrode was 253F/g, a significant enhancement over that of the plain manganese oxide aerogel, mainly because of the enlarged specific surface area provided by the tin oxide aerogel template. To seek further improvement, carbon aerogels of high conductivity (0.00148Ω/□) and high surface area were used as the template for manganese oxides. The SC value of this MnOx/CA, with MnOx deposited at 1.5 V, was as high as 503F/g, and retained 99% of the maximum SC value after 6000 cycles of CV scans, indicating the further boost in SC and excellent cycle stability. The SC value of this composite electrode remained high at 243F/g even at a very high scan rate of 500mV/s, retaining 62.8% of the SC values obtained at a scan rate of 25mV/s, and achieving a high specific energy density of 21.6Wh/kg and a high specific power density of 48.5kW/kg. This work demonstrates the advantages of using composite electrodes for the next-generation supercapacitors.