Electrodeposited manganese oxides on three-dimensional carbon nanotube substrate: Supercapacitive behaviour in aqueous and organic electrolytes

Thin amorphous manganese oxide layers with a thickness of 3-5 nm are electrodeposited on a carbon nanotube (CNT) film substrate that has a three-dimensional nanoporous structure(denoted as MnO2/CNT electrode). For the purpose of comparison, manganese oxide films are also electrodeposited on a flat Pt-coated Si wafer substrate (denoted as MnO2 film electrode). The pseudocapacitive properties of the MnO2 film and MnO2/CNT electrodes are examined in both aqueous electrolyte (1.0 M KCl) and nonaqueous organic electrolyte (1.0 M LiClO4 in propylene carbonate). While both types of electrode show Pseudocapacitive behaviour in the aqueous electrolyte, only the MnO2/CNT electrode does so in the organic electrolyte, due to its high oxide/electrolyte interfacial area and improved electron conduction through the CNT substrate. Compared with the MnO2 film electrode, the MnO2/CNT electrode shows a much higher specific capacitance and better high-rate capability, regardless of the electrolyte used. Use of the organic electrolyte results in a similar to 6 times higher specific energy compared with that obtained with the aqueous electrolyte, while maintaining a similar specific power. The construction of a three-dimensional nanoporous network structure consisting of a thin oxide layer on a CNT film substrate at the nm scale and the use of an organic electrolyte are promising approaches to improving the specific energy of supercapacitors. (C) 2008 Elsevier B.V. All rights reserved.