How to Achieve Maximum Utilization of Hydrous Ruthenium Oxide for Supercapacitors

Abstract

The utilization of hydrous ruthenium oxide (denoted as RuO x·nH2O) 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 (CS,RuOx) of RuO x·nH2O, 1340 F/g (measured at 25 mV/s), very close to the theoretic value, was obtained from a composite consisting of AC and RuOx·nH2O coated on graphite (denoted as AC-RuOx/G) with 10 wt% of sol-gel-derived RuO x·nH2O nanodots annealed in air at 200°C for 2 h. The UV absorption spectral features showed a shift in λmax to the red as the mean particle size of RuOx·nH2O nanodots was increased, attributable to the surface plasmon resonance phenomenon. The average particle size of highly uniform RuO x·nH2O 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·nH2O nanodots, evidenced by cyclic voltammetry and electrical impedance spectroscopy results, revealed the important influences of interparticle electronic conductivities on the utilization of RuOx·nH2O. The RuOx·nH 2O 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.