Electrochemically induced mass transfer and rheological changes of Nafion (R) coatings fully loaded with [Os(bpy)(3)](2+)

Nafion(R) coatings on electrodes are loaded with [Os(bpy)(3)](2+) and subje cted to electrochemistry. Mass transfer and rheological changes during thos e processes are studied by using a quartz crystal resonator and phase-measu rement interferometric microscope. In the loading process, the coating soak ed in a [Os(bpy)(3)]ClO4 aqueous solution is once swelled with water and th en gradually shrunk as protons in Nafioni(C) are exchanged with [Os(bpy)(3) ](2+). Upon the first oxidation of [Os(bpy)(3)](2+) coupled with two sulfon ate groups, acetate may be temporarily injected into the coating with water molecules to maintain electroneutrality, then [Os(bpy)(3)](3+) presumably reforms an ion pair with three sulfonate groups, ejecting surplus [Os(bpy)( 3)](3+) coupled with three acetate ions. In the steady-state redox reaction , the rheology of the coating changes. (C) 1999 Elsevier Science S.A. All r ights reserved.