Reaction of Nickel Electrode Surfaces with Anionic Metal-Cyanide Complexes: Formation of Precipitated Surfaces

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Anionic metallocyanide complexes (Fe(CN)63-, Ru(CN)63-, Mn(CN)63-, [Fe(CN)6-xLx]n-) (L = H2O, NO, histidine, 1, 2-cyclohexyldiamine) capable of precipitating aqueous Ni2+ are immobilized on Ni electrodes by potentiostating the electrode in aqueous solutions of the anions. The surface coverage obtained is shown to be a function of composition of derivatizing solution, nickel surface pretreatment, electrode potential, and the reaction time. Diffuse-reflectance FT IR spectra of derivatized Ni surfaces show a cyano-bridged bimetallic structure. The cyclic voltammograms of surface-immobilized Fe(CN)63- and Ru(CN)63- show zero peak to peak separation and 110-mV peak width at half-height, close to the ideal case for surface-attached species. These surfaces are very stable with ~10% loss on >18000 potential cycles between the FeII and FeIII states. The E1/2value and the shape of the surface cyclic voltammetric wave are shown to depend strongly on the supporting electrolyte cation. These surfaces also show a cation selectivity, indicating an ordered structure. Such surfaces are shown to stabilize the Ni electrode surface against oxide formation while allowing various solution redox couples to react at the electrode. Thus, reaction specificity can be induced by this type of derivatization.



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