Infrared Spectroelectrochemistry of Nitrite in Absolute Methanol

Abstract

A highly polished planar Pt electrode was used in an in situ reflection−absorption infrared cell to examine the chemical products of electrochemical reactions of NaNO2 in a methanolic solution in the 2500−1100 cm−1 range. Analysis of the resulting infrared bands showed that methanol reacts directly with the electro-oxidation products of nitrite. The predominant oxidation product was methyl nitrite, with apparent smaller quantities of NO2, NO3 −, and NO. The reduction product of in situ-generated methyl nitrite was N2O, presumed to occur via adsorbed N- and O-type species. No other species arising from N x O y H z were observed; however, bands associated with the stretching modes of O−H and N−H that would clearly identify any such products were outside the accessible spectral range examined here due to interfering absorptions from methanol.

Oxidative IR Spectroelectrochemistry of Copper in Methanol Containing Carbon Monoxide

“…The potential induced migration of ions into, or out of, the optical path along with their methanol sheath is the likely cause for the loss of the methanol peaks in the SNIFTIRS as the potential was stepped to potentials more positive than 0.6 V. The assignment of methanol vibrational modes in the SNIFTIR spectra at platinum has been given previously. 32,40 At copper, a very small peak at 2341 cm −1 (CO 2 ) and a broad band at 1371 cm −1 are the only new features to appear for SNIFTIR spectra collected up to 1.0 V with a background potential of −0.2 V. The assignment of the 1371 cm −1 peak is not clear at this time, but may be an artifact from a sloping background. The observation of so few infrared bands can only be consistent with the voltammetry if the products from the methanol oxidation reaction were infrared inactive species dispersed into the bulk of solution or adsorbed and having vibrational modes with dynamic dipoles coplanar with the electrode surface, and thus spectroscopically undetectable (surface selection rule).…”

“…SNIFTIR spectra in methanol at Cu (Figure ) and at Pt , display nonlinear sloping backgrounds when E s becomes sufficiently positive. The curvature of the slope (concave or convex) is pH dependent and can obscure the accurate determination of an absorption feature.…”

“…The CO 2 peak tracks with the "CO" peak during the forward potential scan, and the loss of CO 2 can arise from solution pH changes associated with copper oxide formation. 40 Although the direct electro-oxidation of CO (or CO ads ) to CO 2 is also unexplored, if this were occurring then we would expect the CO 2 band intensity to increase significantly.…”