ADSORPTION OF UREA ON THE PT(100) ELECTRODE - EXPERIMENTS AND LATTICE-GAS MODELING

We report a complete experimental and theoretical description of urea adsorption on the Pt(100) electrode. We have used voltammetry, radioch emistry, LEED and quantitative Auger electron spectroscopy, as well as Monte Carlo simulations of a lattice-gas model developed for this stu dy. We demonstrate that the simulation results agree well with those o f our experiments. These include an ordered c(2 x 4) adsorbed urea pha se and sharply peaked voltammograms. We interpret our observations as associated with a phase transition between the urea phase for potentia ls on the positive side of the voltammetric peak and a (1 x 1) monolay er of hydrogen phase on the negative side. The main products of this r esearch are the lattice-gas model that describes the microscopic adsor ption geometry and the effective lateral interaction energies of the u rea surface species involved in the phase transition behavior.