Experimental determination and interpretation of the electrosorption valency γ

Abstract

A short review concerning the definition of the electrosorption valency γF = (∂μh/∂Δϑ)Г = −(∂qm/∂Г)Δϑ is given. The electrosorption valency γ is a fraction describing the potential dependence of the electrosorption equilibrium and the charge flow caused by the electrosorption. The interpretation of γ is based on the relation γ = zg − λ(1 − g) + κad − νκw − F−1ʃ(∂CD/∂Г)Δϑ dΔπ with the geometric factor g, the partial charge transfer λ, the dipole factors κad, κw and a capacitive term. Methods for the experimental determination of γ are discussed. It is shown that all investigations of other authors which should give g, λ or κ factors actually yield only γ values. The methods and results are demonstrated for several electrosorption reactions. In the case of phenol and n-butanol at mercury the capacitive term dominates causing a negative (positive) value of γ at negative (positive) potentials. The influence of the dipole factor κ is demonstrated for thiourea as example. A charge transfer λ>0 seems to be improbable for Cl− at mercury, but λ>0.2 can be concluded for I− at mercury. The nearly complete discharge is discussed for hydrogen or copper ions at platinum and some other systems.