Coadsorption of hydrogen and potassium on silver single crystal surfaces

Abstract

Adsorption and coadsorption of H 2 (D 2) and potassium on the single crystal silver surfaces (111) and (110) have been studied using TPD, angle-resolved TPD, work function measurements and LEED. Atomic hydrogen was used to cover the silver surfaces, since a very high activation barrier for molecular adsorption exists. From the Ag(111) surface hydrogen desorbs in a single peak with a close to second order reaction and a desorption energy of 7 kcal/mol. Hydrogen desorption from Ag(110) is characterized by two overlapping desorption peaks which are very sensitive to small amounts of water coadsorption. Angular distributions of the desorption probability following a cos 2.5Θ and a cos 3.5Θ function for Ag(111) and Ag(110) were observed, respectively. Upon hydrogen saturation (0.65 ML) on Ag(111) the work function increases by 240 meV. Coadsorbed potassium shifts the desorption temperature for H 2 dramatically by 250 K to higher temperature on both surfaces. Simultaneous desorption of hydrogen and potassium on both silver surfaces with a ratio of 1 K-atom to 4 H 2 molecules indicates a strong potassium-hydrogen interaction in the coadsorbate.