Polarising Ability of the Metal Surface Atoms of a Catalyst and the Work Function

摘要

An attempt was made to determine the polarising ability of metal surface atoms. On the basis of an analysis of the metal cohesive energy and the electron binding energy in ionic cores, a new parameter was proposed called the polarising ability of surface atoms as defined by the equation: P_(surf) = ((αΔG_(subM)~0 E_(EBE))~(1/2)/R)/(r/a_0) where E_(EBE) denotes the electron binding energy at the outermost shell of the ionic core, the product (αΔG_(sub)~0) determines the surface Gibbs energy that is proportional (the quantity a denoting the proportionality factor) to the standard Gibbs energy of sublimation of the metal (ΔG_(subM)~0), r is the metallic radius (half the length of the metallic bond), a_0 is the radius of the first Bohr orbit and R is the Rydberg constant. It was shown that the above parameter is proportional to the work function and that, in a similar fashion to the ionisation energy of ions, this can indicate the polarising ability of the surface atoms. The correlation between the polarising ability parameter and the initial heat of adsorption of H_2, O_2, CO and N_2, and between the limiting exchange current (log i_0) of the hydrogen evolution on metals, was demonstrated.