Voltammetric response of the hexammino-ruthenium complex incorporated in zeolite-modified carbon paste electrode

Hexammino-ruthenium cation (Ru(NH3)(6)(3+)) was incorporated into a zeolite-Y-modified carbon paste electrode (ZMCPE). The electrochemical behaviour of Ru(NH3)(6)(3+) was examined in aqueous media by cyclic voltammetry. Two kinds of supporting electrolyte cation were used: non-size-excluded (sodium, Na+), sind conventionally size-excluded (tetrabutylammonium, TBA(+)) cations. Ion exchange reactions between hexammino-ruthenium ions and sodium ions were investigated. Quantitative in situ determinations of Ru(NH3)(6)(3+) and Ru(NH3)(6)(2+) species leaching from zeolite particles in the external solution were performed using linear scan voltammetry on a rotating disk electrode. The thickness of ZMCPE involved in the electrochemical reaction of these species has been found to increase with experiment time, as was also sh own for the methylviologen-incorporated ZMCPE. Ion exchange reactions of both Ru(NH3)(6)(3+) and Ru(NH3)(6)(2+) species with Na+ ions in zeolite Y have been found to exhibit a great selectivity for the large complexes. When using ZMCPE, cyclic voltammograms of Ru(NH3)(6)(3+) ions initially exchanged in bulk zeolite Y displayed two successive cathodic signals. The first wave, located at a potential value close to that observed for Ru(NH3)(6)(3+) in aqueous solution, was unambiguously attributed to the reduction of Ru(NH3)(6)(3+) species after being exchanged for the electrolyte cation. The origin of the second peak, appearing at more negative potentials, was not definitively stated and was interpreted in terms of possible activity effects and ion exchange under forcing conditions. This reduction step was not totally hindered by using a conventionally size-excluded electrolyte cation. Two hypotheses (non-ideality of the system and intrazeolite effects) were proposed to explain this unexpected behaviour.