CHARACTERIZATION OF SOL-GEL-DERIVED COBALT OXIDE XEROGELS AS ELECTROCHEMICAL CAPACITORS

Very fine cobalt oxide xerogel powders were prepared using a unique so lution chemistry associated with the sol-gel process. The effect of th ermal treatment on the surface area, pore volume, crystallinity, parti cle structure, and corresponding electrochemical properties of the res ulting xerogels was investigated and found to have significant effects on all of these properties. The xerogel remained amorphous as Co(OH)( 2) up to 160 degrees C, and exhibited maxima in both the surface area and pore volume at this temperature. With an increase in the temperatu re above 200 degrees C, both the surface area and pore volume decrease d sharply, because the amorphous Co(OH)(2) decomposed to form CoO that was subsequently oxidized to form crystalline Co3O4. In addition, the changes in the surface area, pore volume, crystallinity, and particle structure all had significant but coupled effects on the electrochemi cal properties of the xerogels. A maximum capacitance of 291 F/g was o btained for an electrode prepared with the CoOx xerogel calcined at 15 0 degrees C, which was consistent with the maxima exhibited in both th e surface area and pore volume; this capacitance was attributed solely to a surface redox mechanism. The cycle life of this electrode was al so very stable for many thousands of cycles.