Theory of electron-transfer rates across liquid-liquid interfaces. 2. Relationships and application

Abstract

In part 1 an expression was obtained for the exchange current rate constant k^(ii)_(12) for an electron transfer between a reactant in one liquid and a second reactant in a second immiscible liquid, across an (assumed) sharp interfacial boundary. This expression is used to obtain a relation between k^(ii)_(12) and the self-exchange rate constants k_(11) and k_(22) for electron transfer in homogeneous solutions, each redox species being in its respective liquid phase. The relation provides an extension of the "cross-relation" for one-phase electron transfer to this two-phase case. An expression is also given relating k^(ii)_(12) to the usual metal-liquid electrochemical exchange current rate constants k^(el)_1 and k^(el)_2 these k^(el)’s referring to each reactant in its respective solvent phase. An alternative limiting model for the interfacial region is also considered, in which that region is now broad, instead of sharp. The results of both models are compared with the limited available kinetic data, and the desirability of further experimental studies is noted.