A fundamental in situ IR spectroelectrochemical study of the electrical polarization of nickel, copper and gold electrodes in the presence of the unstable tellurocyanate ion in DMSO and DMF solutions

Abstract

Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) studies have been performed for the first time on the interaction of the tellurocyanate ion (TeCN⁻) with electrically polarised nickel (Ni), copper (Cu) and gold (Au) electrodes in dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) containing tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte. In general, it was conclusively shown that the TeCN⁻ ion decomposes at certain applied potentials on electrically polarized electrochemical cells to form elemental tellurium and cyanide (CN⁻) ion. The cause of the decomposition was reasoned to be due to the presence of electrodissolved metal ions from the electrode, which destabilise the TeCN⁻ ion through their polarising power as cations. The severity of the destabilisation was found to increase in the order Au⁺ > Cu⁺ > Ni²⁺, which is in general agreement with the relative polarising power of these metal ions. SNIFTIRS and IR transmission data from model solutions demonstrated that the metal complex ion speciation observed during the polarization experiments therefore arose directly from the interaction of the studied metal electrode with CN⁻ ions released by decomposition, rather than with the TeCN⁻ ion itself. The potential at which the electrochemical decomposition of the TeCN⁻ ion occurred and its rate of decomposition depended on the type of metal electrode used. In general, the instability of the TeCN⁻ ion in electrochemically polarized systems reflects its fundamental chemistry of decomposing in the presence of polarizing cations and that it may be of use as a sensor for these species in an electrochemical setting.