FTIRS AND ELECTROCHEMICAL CHARACTERIZATION OF NO ADLAYERS ON PT(HKL) GENERATED UPON IMMERSION IN AN ACIDIC SOLUTION OF NITRITE

Nitric oxide adlayers on platinum single crystal electrodes have been studied by means of IR spectroscopy and cyclic voltammetry. These adlayers were generated upon immersion of the sample in an acidic solution of nitrite. The in-situ FTIR spectra obtained for each electrode agree with those previously reported under UHV conditions suggesting that similar NO adlayers could be formed in all cases. At saturation, only one bipolar band was observed for Pt(111) and Pt(100) centered at 1680 and 1630 cm(-1), respectively. In the case of non-saturated adlayers, a different behavior was observed for each basal orientation. The NO/Pt(111) system showed spectra with two bands at 1680 and 1430 cm(-1). The spectrum corresponding to Pt(100) presented a single band directly related to that observed under UHV conditions in the whole range oi coverages. The nonsaturated NO adlayer on Pt(110) was characterized by a spectrum having a single bipolar feature located at around 1590 cm(-1). It has also been shown that the adsorbed NO molecules undergo a surface redox process in the case of Pt(100) and Pt(111). There is some spectroscopic and voltammetric evidence indicating that the oxidized form of the adlayer consists of adsorbed nitrite anions.