In situ infrared spectroelectrochemical studies of the corrosion of a nickel electrode as a function of applied potential in cyanate, thiocyanate, and selenocyanate solutions.
This paper presents the first subtractively normalized interfacial Fourier transform infrared spectroscopic (SNIFTIRS) study of the corrosion system Ni/XCN(-) (X=O, S, Se), pH 11, [XCN(-)]=0.05 molL(-1), supporting electrolyte 0.1 molL(-1) KNO(3), for a nickel electrode as a function of applied potential. Cyclic voltammograms, in situ infrared spectra, and current-potential data (recorded while the infrared spectral acquisition was in progress) were recorded for a nickel electrode in a three-electrode thin-layer cell containing the pseudohalides OCN(-), SCN(-), or SeCN(-) ions at pH 11 in a supporting electrolyte of KNO(3). In general, the data showed that all of the pseudohalide ions studied caused corrosion of the nickel electrode by forming the respective nickel-pseudohalide complex ion species as the potential was stepped anodically. Two of the ions, SCN(-) and SeCN(-), caused surface modifications to the electrode which influenced the electrochemical reactions with respect to CO(2) formation. The Ni/SeCN(-) system, for instance, exhibited signs of instability during the spectroelectrochemical experiment, red-brown coatings observed on the electrode caused by the decomposition of the selenocyanate ion to colloidally dispersed elemental selenium. The selenium coated the electrode, hence modifying the surface and consequently the electrochemistry, by causing the "early" appearance of CO(2)-associated IR peaks in SNIFTIRS spectra recorded from the electrode system at potentials lower than those for the Ni/OCN(-) system. In contrast, CO(2) formation at the electrode surface was not observed in the Ni/SCN(-) system, which was likely to have been caused by nickel sulfide poisoning of the electrode surface. In the Ni/SCN(-) and Ni/SeCN(-) systems, IR spectra also indicated the buildup of Ni(SCN)(2) and Ni(SeCN)(2) salts in the thin layer by the appearance of a peak at ca. 2165 cm(-1) at anodic values of the applied potential.
Mucalo
Michael R
MR
Chemistry Department, University of Waikato, Private Bag 3105, Hamilton, New Zealand. m.mucalo@waikato.ac.nz
Li
Qiang
Q