Evaluation of the Redox Behavior of Hydrous Ruthenium Oxides: Effect of Temperature and Acid Concentration on the Electrochemical Behavior of Layered Ruthenium Oxide

Abstract

The effect of the H₂SO₄ concentration and cell temperature towards the pseudocapacitive behavior of layered ruthenic acid hydrate, H_0.2RuO_2.1·nH₂O, was examined. The increase in H₂SO₄ concentration resulted in a drastic decrease in the redox pair observed at 0.65 V vs. RHE, while the increase in cell temperature had little effect on this redox pair. The redox pair centered at ∼0.85 V vs. RHE was less dependent on the H₂SO₄ concentration and the charge associated with this peak increased with increasing cell temperature. It is suggested that the redox peak observed at ∼0.65 V vs. RHE is related to the adsorption of SO₄²⁻ ions on the outer surface of the microsized particles. The redox pair observed at ∼0.85 V vs. RHE is attributed to the penetration of protons or hydrated protons. The effect of cell temperature was negligible for nanoparticulate RuO₂·xH₂O, which indicates the difference in the charge storage mechanism of layered H_0.2RuO_2.1·nH₂O and nanoparticulate RuO₂·xH₂O.