Some Consequences of the Significantly Different Mobilities of Hydrophilic and Hydrophobic Metal Complexes in Perfluorosulfonated Ionomer Coatings on Electrodes

Abstract

Thin coatings of Nafion on glassy carbon rotating disk electrodes were saturated with hydrophilic [Ru(NH3)63+, Co(NH3)63+] or hydrophobic [Ru(bpy)32+] counterions. With both types of counterions, the plateau currents obtained when the electrodes were rotated in solutions of the cations matched the currents obtained with the uncoated electrodes in the same solutions at all accessible rotation rates. The high rates of cross-coating charge propagation demonstrated by these results involved physical diffusion of the hydrophilic complexes and electron hopping between adjacent, immobile pairs of the hydrophobic complexes. The approximate concentration profiles that develop within, and just outside of, Nafion coatings on disk electrodes that are rotated in solutions of electroactive counterions are depicted.