Electrochemical and electrocatalytic reactions of a ruthenium oxo complex in solution and in cation exchange beads in carbon paste electrodes

Abstract

A strategy for electrode immobilization of an ionic reagent as a counterion of an ion exchange matrix is described along with an electrocatalytic application of the reagent. Carbon paste electrodes, CPE, were prepared which contain microparticle beads of a strong cation exchanger, Dowex 50W×8, that had been loaded with the electrocatalytic oxidant reagent, [Ru II(trpy)(phen)(OH)] + ( I) (trpy = 2,2′, 2″-terpyridine, phen = 1,10-phenanthroline). At pH 13 I is reversibly electro-oxidized by one two-electron, one-proton step to produce the Ru(IV) oxidant, [Ru IV(trpy)(phen)O] 2+ ( oxI). At lower loadings of I in the Dowex resin, semi-infinite molecular diffusion of the reagent within the microparticle beads is the major means of charge transport. Benzyl alcohol oxidation by oxI, with electrochemical regeneration of I, served in basic solution as a system to probe electrocatalysis. On very slow experimental time scales, the electrochemical process is controlled solely by the rate of reaction of oxI with benzyl alcohol inside the ion exchanger. An electrocatalytic rate constant, k 1 = 10.8 ± 4 M −1 s −1 was measured in 0.1 M NaOH. The electrocatalytic rate constant measured at naked glassy carbon electrodes and at CPE containing no ion exchanger, and with I and benzyl alcohol dissolved in the solution, was within a factor of three of the above k 1.