Adsorption on Solid Metal Surfaces

Abstract

The importance of making measurements using clean and well- defined surfaces is stressed and the techniques by which this may be done will be outlined. The classical thermodynamic route for the study of adsorption is summarized. The significance of capacity/potential and current/potential curves (cyclic voltammograms) is discussed. The work function/pzc relation shows that the pzc will depend on crystal orientation and the experimental evidence that this is so will be presented. The immediate consequence is that analysis of results for polycrystalline surfaces becomes difficult if not impossible. This is illustrated for a series of systems of increasing complexity: (i) Interface of ‘ideal’ structure with no ‘specific adsorption’. The model consists of a ‘space charge’ of ions, a solvent monolayer and a more or less simple surface charge on the metal. Modern developments of this model will be discussed to assess how accurate the simple model may be; (ii) Interface with specific ionic adsorption. An explanation of the resultant modification of the capacity curves will be given with consideration of the possible occurrence of chemisorption with partial charge transfer; (iii) Interface as in (i) but with adsorption of non- ionic species. The consequent modification of the capacity will be discussed in terms of a simple molecular model; (iv) interface with ionic adsorption and non-ionic adsorption. The problems of analysing this complex but common situation is considered; (v) Adsorption with complete charge transfer will be discussed and the mobility of electrode surfaces exemplified.