IN-SITU FTIR SPECTROSCOPY CHARACTERIZATION OF THE NO ADLAYERS FORMED AT PLATINUM SINGLE-CRYSTAL ELECTRODES IN CONTACT WITH ACIDIC SOLUTIONS OF 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 nitrite. NO remains adsorbed on the platinum surface at potentials between 0.40 and 0.95 V, forming adlayers whose spectral properties are similar to those previously observed under ultrahigh vacuum conditions for NO dosed in the gas phase at high coverages. The N-O stretching mode appears at around 1700 and 1760 cm(-1) for the Pt(111) and Pt(110) electrodes, respectively. In the case of Pt(100), two different bands have been observed at 1640 and 1700 cm(-1). This latter band can be related 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 adsorbed 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 detected as an intermediate during nitrous acid reduction. Oxidation to nitrate takes place at potentials above 1.10 V.