Anodically Polarized Nickel Electrodes in DMSO or DMF Solutions of Pseudohalide Ions: IR Spectroelectrochemical Studies

Abstract

A novel subtractively normalized interfacial Fourier transform infrared spectroscopic (SNIFTIRS) investigation of anodically polarized nickel electrodes in pseudohalide-containing DMF or DMSO solutions (i.e. OCN−, SCN−, SeCN−), in supporting electrolyte, tetrabutylammonium perchlorate (TBAP), is presented. In general, the data showed that nickel demonstrated irreversible anodic dissolution in all solutions studied at very high values of the applied potential, > +500 mV (AgCl/Ag). The predominant speciation of nickel in these systems was as complex ions consisting of Ni2+ ion complexed to pseudohalide ions and solvent molecules. Insoluble films and dissolved CO2 were also detected, though mostly in the Ni/OCN− systems studied. Ni(II)/pseudohalide complex ion species detected were modeled using solutions containing Ni2+ ion mixed with pseudohalide ion in different mole ratios. In general, the Ni/OCN− electrochemical system behaved differently relative to those of Ni/SCN− and Ni/SeCN− due to the difference in colors observed in cell solutions after SNIFTIRS experiments which was mirrored in the model solutions. Ni(II)-cyanate species had a different, coordination geometry and gave a characteristic bright blue color due possibly to Ni(NCO)42− ion while Ni(II) thiocyanate and selenocyanate complex ion species had octahedral coordination geometries containing solvent and one coordinated pseudohalide ion and formed greeny yellow solutions.