THE FORMATION OF BILAYERED NICKEL-IRON, CADMIUM-IRON AND CADMIUM-SILVER HEXACYANOFERRATES BY AN ELECTROCHEMICALLY DRIVEN INSERTION-SUBSTITUTION MECHANISM

Upon cyclic oxidation and reduction of a parent metal hexacyanoferrate , metal ions from the electrolyte solution can be driven into intersti tial positions of the zeolitic structure of the metal hexacyanoferrate . Whereas alkali metal ions are stable on these sites, some other meta l ions undergo a substitution reaction with the N-coordinated metal io ns, since the latter are only weakly bonded, This results in the forma tion of a layer of a daughter metal hexacyanoferrate covering the pare nt metal hexacyanoferrate. A bilayered structure is formed which can b e identified by its behaviour in cyclic voltammetry. There is no indic ation that the electron and ion transfer through the interface of the two layers is hindered. From this and the growth mechanism it is proba ble that the daughter hexacyanoferrate will form an epitaxial layer on top of the parent hexacyanoferrate, provided that the two hexacyanofe rrates do not differ too much in their lattice parameters. Experimenta l results, for which abrasive stripping voltammetry was used, are repo rted for a nickel hexacyanoferrate layer on Prussian blue, for a cadmi um hexacyanoferrate layer on Prussian blue, and for a cadmium hexacyan oferrate layer on silver hexacyanoferrate.