Chemically Modified Electrode with a Film of Nano Ruthenium Oxides Stabilizing High Valent RuO4- Species and Its Redox-Selective Sequential Transformation to Polynuclear Ruthenium Oxide-Metallocyanates

High-valent (RuO4-)-O-VII (perruthenate) is a short-lived species in aqueous solutions (pH 1-14) and has scarcely been studied through electrochemistry. By a potential-controlled oxidative deposition method at I V vs Ag/AgCl using RuCl3 in a pH 2 KCl-HCl buffer solution, chemically modified glassy carbon (GCE) and indium tin oxide (ITO) electrodes were successfully prepared with a Film of hydrous nano ruthenium oxides RuO2 and RuO3, stabilizing the high-valent perruthenate anion (Ru(VII)-RuOx-CME, x = 2 and 3, CME = chemically modified electrode). The electrodes showed three distinct redox peaks corresponding to Ru2O3/RuO2, RuO2/RuO3, and RuO42-/RuO4- redox processes at pH 2, like the classical RuO2 electrodes in alkaline conditions. Solid state UV-visible spectra of the ITO/Ru(VII)-RuOx-CME showed characteristic absorption very close to chemically generated authentic RuO4 species in alkaline solution. Further, redox-controlled sequential procedures yielded polynuclear ruthenium oxide-hexacyanometallate films (RuOMCN-CME, M = Fe and Ru), in which Ru(VII)-RuOx-CME acted as a specific template. A controlled-potential activation (> 1 V) of Ru(VII)-RuOx-CME, stabilizing the key RuO4- species, in a solution of [Fe(CN)(6)](3-) or [Ru(CN)(6)](4-), should be a critical step for the formation of polynuclear RuO-MCN matrix.