Urea adsorption on platinum single crystal stepped surfaces

Urea adsorption has been studied at Pt(110) and stepped platinum electrodes with orientations vicinal to Pt(111) in the [1 (1) over bar0] and [01 (1) over bar] zones. In situ infrared spectra and cyclic voltammograms obtained in the urea-containing solutions have been analyzed as a function of the (110) or (100) step densities. At the same time, voltammetric data have been combined with charge displacement experiments in order to determine the potential of zero total charge (pztc) in the presence of urea. The variation of the pztc with the step density is similar to that previously observed for the same surfaces in sulfuric acid solutions thus confirming the anion-like behavior of urea molecules at platinum electrodes. Potential-dependent changes in the bonding of urea at the Pt(110) electrode have been found to be similar to those previously reported for Pt(111), with N-bonded and O-bonding urea predominating at low and high coverages, respectively. The same behavior is observed for stepped surfaces containing (111) terraces and (110) steps. On the other hand, urea molecules bonded through the two nitrogen atoms are detected in the whole coverage range at surfaces with a high density of (100) steps.