Abstract
The utilization of hydrous ruthenium oxide (denoted as RuO x ·nH 2 O) was promoted by annealing the oxide in air as well as by mixing it with conductive activated carbon (AC) due to the significant improvement in intra- and interparticle electronic conductivity, respectively, The maximum specific capacitance (C S,RuOx ) of RuO x ·nH 2 O, 1340 F/g (measured at 25 mV/s), very close to the theoretic value, was obtained from a composite consisting of AC and RuO x ·nH 2 O coated on graphite (denoted as AC-RuO x /G) with 10 wt% of sol-gel-derived RuO x ·nH 2 O nanodots annealed in air at 200°C for 2 h. The UV absorption spectral features showed a shift in λ max to the red as the mean particle size of RuO x ·nH 2 O nanodots was increased, attributable to the surface plasmon resonance phenomenon. The average particle size of highly uniform RuO x ·nH 2 O nanodots, ranged from 2.05 to 3.01 nm, was estimated from the high-resolution transmission electron microscopy. The dependence of capacitive performance on the size and content of RuO x ·nH 2 O nanodots, evidenced by cyclic voltammetry and electrical impedance spectroscopy results, revealed the important influences of interparticle electronic conductivities on the utilization of RuO x ·nH 2 O. The RuO x ·nH 2 O nanodots with and without annealing in air at 200°C for 2 h showed the amorphous structure from both the X-ray diffraction and electron diffraction analysis. © 2004 The Electrochemical Society. All rights reserved.