In Situ IR Studies on the Electro-Oxidation of Cyanide on Ni, Cu and Au Electrodes Electrically Polarized in Dimethyl Sulfoxide (DMSO) Electrolyte Media

Abstract

Subtractively normalised Fourier transform infrared spectroscopy (SNIFTIRS) studies are reported on the electrical polarisation of nickel (Ni), copper (Cu) and gold (Au) electrodes in KCN dissolved in the polar aprotic solvent, dimethyl sulfoxide (DMSO) with tetrabutyl ammonium perchlorate (TBAP) (0.1 mol L−1) as supporting electrolyte. These studies have shown clearly that each of the metal electrodes investigated oxidised (as the applied potential was adjusted in an anodic direction) to form Ni(II), Cu(I) and Au(I)-cyano complex ions of [Ni(CN)4]2−, [Cu(CN)3]2−, [Cu(CN)2]− and [Au(CN)2]−. The distribution of other electro-oxidation products of cyanide observed, namely KOCN(s) and CO2 depended on the electrode under consideration. For Ni electrodes, DMSO-solvated CO2 and solid KOCN were observed together as the oxidation products while on Cu and Au electrodes CN− was oxidised to DMSO-solvated CO2 exclusively without any solid cyanate salt film deposition being simultaneously observed. Cu was found to be particularly electrocatalytic towards the electro-oxidation of CN− ion to CO2 with high current density values being observed. It is proposed that the metal-cyano complex ion species observed in SNIFTIRS experiments are implicated in the oxidation mechanism of CN− to KOCN and/or CO2 on these electrodes, particularly on the Cu and Au electrodes. This resembled the electrochemistry observed in similar systems involving the electrochemical oxidation of cyanide on Cu electrodes in aqueous media.