Electrolyte solutions in liquid ammoniax. A cyclic voltammetric examination of electron transfer between solvated ruthenium(III) and ruthenium(II) cations, and anodic passivation of platinum electrodes
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Single electron transfer between the hexammine cations of Ru(III) and Ru(II) at a Pt metal electrode in liquid ammonia closely follows Nernstian behaviour during the first voltammetric cycle if the voltage sweep rate is low. The redox electrode based on the Ru(III)/Ru(II) couple at a Pt metal surface deviates from voltammetric reversibility as: (i) the voltage ramp rate, (ii) the concentration of Ru(NH3)3+6 cation, and (iii) the number of applied voltammetric cycles, are increased. X-ray photoelectron spectra of the surface layer of Pt metal after exposure to anodic potentials in excess of 0.3 V reveal the Pt metal surface is oxidized in liquid ammonia (electrolytically and in voltammetric cycles) to a gold-coloured compound containing equimolar amounts of Pt(II) and Pt(IV). These results are discussed in the light of previous contentious reports about the use of H2 gas on Pt as a primary standard electrode for work with liquid ammonia solutions. 1988.
