Proton and Electron Conductivity in Hydrous Ruthenium Oxides Evaluated by Electrochemical Impedance Spectroscopy:  The Origin of Large Capacitance

Abstract

Electrochemical impedance spectroscopy was conducted on a series of hydrous ruthenium oxides, RuO(2).xH(2)O, (x = 0.5, 0.3, 0) and a layered ruthenic acid hydrate (H(0.2)RuO(2.1).nH(2)O) in order to evaluate their protonic and electronic conduction. The capacitor response frequency was observed at lower frequency for RuO(2).xH(2)O with higher water content, which was suggested to be due to electrolyte exhaustion within the film and/or utilization of hydrated interparticle micropores that have high ionic resistance. Analysis of the impedance data indicated that the charge-transfer resistance through the film is not significantly affected by the water content in RuO(2).xH(2)O, and the capacitor frequency response is dominated by the protonic conduction. The capacitor response frequency of layered H(0.2)RuO(2.1).nH(2)O was comparable to RuO(2).0.5H(2)O. The high specific capacitance at low frequency for layered H(0.2)RuO(2.1).nH(2)O is attributed to the utilization of the expandable hydrous interlayer, which accounts for the ionic conduction. The present results demonstrate the importance of hydrous regions (either interparticle or interlayer) to allow appreciable protonic conduction for high energy and high power electrochemical capacitors.

Flexible ruthenium oxide-activated carbon cloth composites prepared by simple electrodeposition methods

“…6 for the electrode prepared by the potentiostatic method is similar to that reported for a thin film of ruthenium oxide [35,[43][44][45]. On the positive 11 scan direction it can be observed the hydrogen region in which the ionization of adsorbed hydrogen atoms overlaps with the adsorption of water on ruthenium atoms [43,44] Besides, proton diffusion into defect sites, interstitial sites, and/or grain boundaries is also taking place in this potential region [47]. Table 3 shows the values of specific capacitance obtained for all the composites prepared by chronoamperometry (electrodes 1 to 4), cyclic voltammetry (electrode 5 and 6) and chronopotentiometry (electrode 7 to 9) techniques.…”

“…Besides, proton diffusion into defect sites, interstitial sites, and/or grain boundaries is also taking place in this potential region [47]. Table 3 shows the values of specific capacitance obtained for all the composites prepared by chronoamperometry (electrodes 1 to 4), cyclic voltammetry (electrode 5 and 6) and chronopotentiometry (electrode 7 to 9) techniques.…”

Effect of Pore Packing Defects in 2-D Ordered Mesoporous Carbons on Ionic Transport

“…Hence, it is quite important to further investigate the influence of ordered mesoporous structure on ion diffusion based on EIS, which has been considered as a powerful method to obtain dynamic ion diffusion information. [13][14][15][16] The formation of EDL capacitance under an alternative electric field for a mesoporous/microporous electrode should involve three processes: (a) a high-frequency region where mass transfer is inhibited, so charge aggregation at the surface of carbon powder electrode in contact with the bulk electrolyte would be dominant; (b) a medium-frequency region where the dominant process would be ion diffusion in mesoporous channels which contributes the most to the development of capacitive behavior; and (c) a low-frequency region where inhomogeneous diffusion in the less-accessible sites (like micropores) may govern the impedance. 13 Thus, the inferior dynamic capacitive performance of CS-1 at high voltage scan rates ought to be related to the ion diffusion ability in mesoporous channels which is identified as the mediumfrequency region in both Nyquist and Bode plots.…”

Synthesis of ordered mesoporous ruthenium by lyotropic liquid crystals and its electrochemical conversion to mesoporous ruthenium oxide with high surface area

“…In addition to metallic Ru, high surface area ruthenium oxide is also an important material for various applications, including electrocatalysts for chlorine evolution [24], electrochemical capacitor electrodes [25][26][27][28][29], as well as fuel cell electrocatalysts [30][31][32][33][34][35][36][37][38][39]. The small particle size (1-2 nm) and the existence of appreciable pores are important requirements for the high capacitance [40][41][42]. The synthesis of high capacitance RuO 2 (~700 F g -1 ) have been conducted mainly by sol-gel synthesis, leading to materials with random micropores [25,26].…”