Fabrication and electrochemical characterization of cobalt-based layered double hydroxide nanosheet thin-film electrodes

A continuous cobalt-based layered double hydroxide (LDH) nanosheet thin-film electrode has been fabricated by drying a nearly transparent colloidal solution of cobalt-based LDH nanosheets on an indium tin oxide (ITO)-coated glass plate substrate. The effects of varying the Al content, the film thickness, and the heating temperature on the electrochemical properties of the as-deposited thin-film electrode have been investigated. A thin-film electrode with a Co/Al molar ratio of 3:1, which has a large specific capacitance of 2500 F cm(-3) (833 F g(-1)) and a good high-rate capability, shows the best performance when used as an electrode in thin-film supercapacitors (TFSCs). As the thickness of the thin film was increased from 100 to 500 nm, the specific capacitance of the thin-film electrode remained essentially unchanged, which is due to the porous microstructure generated in the original electrochemical process and the low internal resistance of the thin-film electrode. The specific capacitance of the thin-film electrode showed no observable change after heating at 160 degrees C, but decreased on further heating to 200 degrees C, indicating that the electrochemically active Co sites inside the thin-film nanosheet electrode are already essentially fully exposed in the as-prepared material and hence cannot be further exposed through heating. Such a thin-film electrode made up of nanosheets may be a potential economical alternative electrode for use in TFSCs. (C) 2008 Elsevier B.V. All rights reserved.