Stability of [RuII(tpy)(bpy)(OH2)]^2+-Modified Graphite Electrodes during Indirect Electrolyses

The stability of a graphite felt electrode modified by covalent attachment of [RuII(tpy)(bpy)(OH2)]^2+ is investigated during the indirect electrolyses of alcohols in a flow cell. The continuous increase of the local potential of the electrode during the electrolyses attests to its degradation. Cyclic voltammetry analyses of the modified electrode after electrolyses show a total decrease of 80-90% of the wave corresponding to the RuIII/II couple. The concentration of remaining alcohol measured at the outlet of the cell is almost constant during all the electrolyses but increase when the potential exceeds 0.95 VSCE. At low potentials, the electrode can be regenerated by reaction with RuIICl2(DMSO)(tpy) and then CF3SO3H, followed by hydrolysis, showing that the bipyridine ligand remains covalently attached to the electrode. At high potentials, the graphite is oxidized and the catalyst is partly lost in the reaction medium. XPS analyses of Ru core levels reveal that the ruthenium disappeared after electrolysis, showing that the degradation of the modified electrode is due to the demetalation of the oxidized complex.