Electroreduction of Ru(III) oxalate complexes on DME at variable supporting-electrolyte concentration

Abstract

The recharging of Ru(III) oxalate complexes is studied on DME in mixed sulfate–oxalate electrolytes of variable concentration. The discovered deceleration of the process with decreasing supporting-electrolyte concentration qualitatively agrees with the expected effect of the EDL structure on the recharging kinetics, but the obtained quantitative data are at severe variance with theory. At low supporting-electrolyte concentrations the process rate in freshly-prepared solutions depends on the concentration of oxalate ions. The dependence has nothing to do with trioxalate complexes of Ru(III) coexisting in the bulk solution with Ru(III) complexes, which have a reduced number of coordinated ligands, as such complexes emerge only after 2–3 days of storing the solutions. The most probable factor responsible for such a dependence seems to be a volume reaction of charge transfer from the formed Ru(II) complexes onto trioxalate complexes of Ru(III). The reaction has a catalytic effect on the hydration of the latter and seems to be responsible for the discrepancy between experiment and theory.