POLYNUCLEAR NICKEL HEXACYANOFERRATES - MONITORING OF FILM GROWTH AND HYDRATED COUNTER-CATION FLUX STORAGE DURING REDOX REACTIONS

An electrochemical quartz crystal microbalance (EQCM) was employed to monitor directly the growth of nickel(II) hexacyanoferrate(III) (NiHCN Fe) films on gold substrates during electrodeposition as well as a res ult of sol-gel aggregation in colloidal nickel ferricyanide solutions used for modification. Frequency changes due to mass changes of the go ld/crystal working electrode were correlated with cyclic voltammetric (CV) data. Evidence is also provided for the sorption of counter-catio ns (Li+, Na+ and K+), and associated water molecules, during redox rea ctions of the film. There is a strict relationship between the amount of alkali metal ions incorporated into the film during reduction, or e xcluded from the film during oxidation, and the frequency changes duri ng EQCM measurements. The amount of solvent (H2O) transferred and sorb ed in the NiHCNFe film reflects the degree of hydration of the investi gated counter-ions. Anions also seem to participate in NiHCNFe electro chemistry, but their role is much less pronounced.