Organic Adsorption at Electrodes

Abstract

The types of information required for a discussion of adsorption of gases at metal surfaces have been enumerated by Bond [1]. With minor variations, similar information is desired from the measurements of adsorption of organic compounds on solid metal electrodes. This includes: 1. The conditions of adsorption; i.e., under what conditions of temperature, pressure, or concentration, etc. and on which metals does the compound in question chemisorb ? 2. The stoichiometry of the adsorption process; is chemisorption associative or dissociative, how many sites are involved for the adsorption of one molecule, is the adsorbed species mobile on the surface, what is the nature of bonding ? 3. The energetics of adsorption; the equilibrium constant and its temperature variation, free energy, heat and entropy of adsorption, their variation with coverage, the activation energy for adsorption and desorption, the strengths of the bonds involved in the adsorption process. 4. The adsorption isotherm; the variation of coverage with pressure or concentration, temperature, potential, solvent, and pH. 5. The kinetics of adsorption; the rates of adsorption and desorption. With the only recently developed interest in adsorption at solid metal electrodes, it should be obvious that very little of this information has been obtained for even one system. As a matter of fact, the desired information is far from complete for even a single system in gas phase adsorption [1, 2]. Therefore, any discussion of organic adsorption at solid electrodes must necessarily be incomplete with respect to experimental evidence and information. In this chapter we shall present much of the available data on the electrosorption of organic compounds, although no attempt is made at completeness. Information from adsorption on mercury, recently reviewed by Frumkin and Damaskin [3] and gas phase adsorption are presented where comparison seems justified.