Half-cell potentials of semiconductive simple binary sulphides in aqueous solution

Theoretical consideration of the charge-transfer mechanism operative in cells with an electrode of a semiconductive binary compound leads to the conclusion that the half-cell potential of such a compound is not only a function of ionic activities in the electrolytic solution, but also a function of the activities of the component elements in the compound phase. The most general form of the electrode equation derived for such a compound with a formula M_iX_j which dissociates into M^j+ and Xⁱ⁻ ions in aqueous solution is

E_MiXj = E_MiXj⁰ + RT">RT2ij">2_ij ln [(suaMj+)aqi· (suaX)jMiXj">(suaM^j+)_aqⁱ· (suaX)^jM_iX_j/(suaXi−)aqj· (suaM)iMiXj">(suaXi−)aq^j· (suaM)ⁱM_iX_j],

where

E_MiXj⁰ = 12">12(E_M,M^j+0 + E_Xⁱ⁻,_X).

The equation can be modified to other forms. When applied to semiconductive simple binary sulphides, these equations appear to give better descriptions of the observed electrode potentials of such sulphides than any other proposed equations.