A layered compound composed of crystalline ruthenic acid sheets interleaved with layers of water can be exfoliated (delaminated) to yield colloidal nanosheets. This material is a mixed conductor where the crystalline nanosheets contribute to the electron conductivity and the hydrous interlayer supplies proton transport (see diagram). A large active surface area and a high specific capacitance is promising for electrochemical supercapacitor applications.

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.

Abstract

No abstract

The charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides was evaluated by various electrochemical techniques (cyclic voltammety, hydrodynamic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy). The effects of various factors, such as particle size, hydrous state, and structure, on the pseudocapacitive property were characterized. The electric double layer capacitance (C dl), adsorption related charge (C ad), and the irreversible redox related charge (C irr) per unit mass and surface area of electrode material has been estimated and the role of structural water within the material either in micropores or interlayer are discussed.