Mass measurements using isotopically labeled solvents reveal the extent of solvent transport during redox in thin films on electrodes.

Thin films of nickel ferrocyanide are grown at nickel electrode surfaces by electrochemical oxidative treatment. This report describes some new microgravimetric, quartz crystal microbalance (QCM) experiments using isotopically substituted solvents which detail the transport of solvent during the redox process of the Fe sites. The results show that solvent incorporation accompanies cesium ion expulsion during oxidation, and vice versa during reduction. The relationship between the numbers of moles of expelled cesium ions and incorporated water molecules indicates that considerable void space exists within the lattice of the reduced form of the metallocyanide film as a result of a 'discreteness of size' effect. To our knowledge, these experiments represent the first accurate, unambiguous measurements of solvent transport in thin films on electrodes.