EQCM Study of Ru and RuO2 Surface Electrochemistry

The present study represents comparative analysis of voltammetric and microgravimetric behavior of active ruthenium (Ru), electrochemically passivated ruthenium (Ru/RuO₂) and thermally formed RuO₂ electrodes in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. It has been found that cycling the potential of active Ru electrode within E ranges 0 V–0.8 V and 0 V–1.2 V in 0.5 M H₂SO₄ and 0.1 M KOH solutions, respectively, leads to continuous electrode mass increase, while mass changes observed in alkaline medium are considerably smaller than those in acidic one. Microgravimetric response of active Ru electrode in 0.5 M H₂SO₄ within 0.2 V–0.8 V has revealed reversible character of anodic and cathodic processes. The experimentally found anodic mass gain and cathodic mass loss within 0.2–0.8 V make 2.2–2.7 g F^?1, instead of 17 g F^?1, which is the theoretically predicted value for Ru(OH)₃ formation according to equation: Ru+3H₂O?Ru(OH)₃+3H⁺+3e^?. In the case of Ru/RuO₂ electrode relatively small changes in mass have been found to accompany the anodic and cathodic processes within E range between 0.4 V and 1.2 V in the solution of 0.5 M H₂SO₄. Meanwhile cycling the potential of thermally formed RuO₂ electrode under the same conditions has lead to continuous decrease in electrode mass, which has been attributed to irreversible dehydration of RuO₂ layer. On the basis of microgravimetric and voltammetric study as well as the coulometric analysis of the results conclusions are presented regarding the nature of surface processes taking place on Ru and RuO₂ electrodes.