Amorphous ruthenium-chromium oxides for electrochemical capacitors

Amorphous Ru1-yCryO2. xH(2)O has been synthesized by a reduction of aqueous K2Cr2O7 with RuCl3. xH(2)O at greater than or equal to pH 6.5 followed by drying in air at T less than or equal to 200 degrees C. The samples have been characterized by X-ray powder diffraction, elemental analysis using wavelength dispersive spectroscopy, thermogravimetric analysis, and surface area measurements. The Cr content, y, in the samples depends on the reaction pH. The amorphous samples transform into crystalline rutile-type Ru1-yCryO2 on heating to T > 250 degrees C. The Cr-substituted Ru1-yCryO2. xH(2)O samples exhibit higher capacitance values (up to about 840 F/g) than the unsubstituted RuO2. xH(2)O (720 F/g). Although the capacity tends to fade for samples with higher Cr content, good cyclability with an initial capacitance of around 740 F/g could be achieved for samples with lower Cr content y approximate to 0.15. (C) 2000 The Electrochemical Society. S1099-0062(99)11-066-6. All rights reserved.