ON THE VOLTAMMETRIC AND SPECTROSCOPIC CHARACTERIZATION OF NITRIC-OXIDE ADLAYERS FORMED FROM NITROUS-ACID ON PT(H,K,1) AND RH(H,K,1) ELECTRODES

Cyclic voltammetry and in situ FTIR spectroscopy have been employed to characterize NO adlayers at platinum and rhodium single-crystal elect rodes. These adlayers, which are generated upon surface decomposition of nitrous acid, give infrared spectra similar to those observed for t he same surface at high NO coverages under UHV conditions. The N-O str etching frequency turned out to be potential dependent with a signific ant upward shift as the electrode potential increased. The analysis of the absolute spectra obtained for NO-covered Pt(lll) and Rh(lll) elec trodes shows a linear variation of the band center frequency of linear ly bonded NO with slopes of 65 and 20 cm(-1) V-1, respectively. In add ition to this potential dependence of the N-O stretching frequency, th e spectra obtained with the Rh(lll) electrode suggests the existence o f a change from bridge to linearly bonded NO as the electrode potentia l increases. Parallel voltammetric experiments allowed the determinati on of the surface coverage.