IN-SITU FTIR SPECTROSCOPY CHARACTERIZATION OF THE NO ADLAYERS FORMED AT PLATINUM SINGLE-CRYSTAL ELECTRODES IN CONTACT WITH ACIDIC SOLUTIONSOF NITRITE

Adsorbed NO has been detected by in situ FTIR spectroscopy on Pt(100), Pt(111), and Pt(110) electrodes in contact with acidic solutions of n itrite. NO remains adsorbed on the platinum surface at potentials betw een 0.40 and 0.95 V, forming adlayers whose spectral properties are si milar to those previously observed under ultrahigh vacuum conditions f or NO dosed in the gas phase at high coverages. The N-O stretching mod e appears at around 1700 and 1760 cm(-1) for the Pt(111) and Pt(110) e lectrodes, respectively. In the case of Pt(100), two different bands h ave been observed at 1640 and 1700 cm(-1). This latter band can be rel ated with the existence of a denser adlayer which seems to be favored at the higher potentials in the range explored. As in the case of adso rbed CO, an increase in the electrode potential causes an upward shift of the N-O stretching frequency of the adsorbed molecule. This shift is less important in the ease of the Pt(110) surface. N2O has been det ected as an intermediate during nitrous acid reduction. Oxidation to n itrate takes place at potentials above 1.10 V.