Journal of Colloid and Interface Science 269 (2004) 370–380 www.elsevier.com/locate/jcis In situ infrared spectroelectrochemical studies of the corrosion of a nickel electrode as a function of applied potential in cyanate, thiocyanate, and selenocyanate solutions Michael R. Mucalo ∗ and Qiang Li Chemistry Department, University of Waikato, Private Bag 3105, Hamilton, New Zealand Received 30 April 2003; accepted 29 July 2003 Abstract This paper presents the first subtractively normalized interfacial Fourier transform infrared spectroscopic (SNIFTIRS) study of the corro- sion system Ni/XCN − (X = O, S, Se), pH 11, [XCN − ]= 0.05 mol L −1 , supporting electrolyte 0.1 mol L −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 spectroelectrochemi- cal 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.  2003 Elsevier Inc. All rights reserved. Keywords: Nickel electrode; Infrared; In situ spectroelectrochemistry; Cyanate; Thiocyanate; Selenocyanate; Corrosion 1. Introduction The application of in situ IR spectroelectrochemical tech- niques such as SNIFTIRS to probe the electrode/electrolyte interface has provided a wealth of information over the past two decades and continues to be used for obtaining informa- tion on a large variety of electrochemical processes such as surface adsorption/electrocatalysis [1], corrosion [2,3], and the formation of thin electrogenerated organic films [4]. The marriage of infrared spectroscopy with electrochemistry of aqueous solutions has necessitated the development of a spe- cial kind of cell which has the working electrode pushed against an IR-transmitting window such as CaF 2 , creating * Corresponding author. E-mail address: m.mucalo@waikato.ac.nz (M.R. Mucalo). a thin layer which minimizes the absorption by the aqueous or organic electrolyte of the IR radiation. This allows the relatively weak signals of the electrogenerated solution and surface-adsorbed species to be detected. The thin-layer spec- troelectrochemical cell approach is commonly used and has yielded many data in many systems despite induced com- positional changes occurring in the thin layer during elec- trochemical experiments [5]. The use of species exhibiting IR signals in the region 2400–1800 cm −1 (e.g., cyanide, cyanate, and carbonyl-containing species) where there ex- ists a spectral window in aqueous-based electrolytes renders the use of IR spectroelectrochemistry in tracking electro- chemical interactions of such compounds even more advan- tageous. The present study is concerned with following the cor- rosion of a nickel electrode surface immersed in a solution 0021-9797/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2003.07.004