Films of mixed nickel(II) and thallium(I) hexacyanoferrates(III,II): voltammetric preparation and characterization

Composite nickel/thallium. hexacyanoferrates were prepared as thin films on electrode surfaces. Electrodeposition of composite films was achieved by p otential cycling in the solution for modification containing, in addition t o potassium salt electrolyte, nickel(II), thallium(I), and hexacyanoferrate (III). Depending on the relative amounts of thallium to nickel, either a mi xed phase with respect to interstitial ions was formed in which Tl(I) catio ns substitute potassium countercations at interstitial positions of nickel hexacyanoferrate or mixed phases of hexacyanoferrates. of nickel and thalli um were produced. Due to large differences in ionic radii of Ni(II) and Tl( I), formation of heteronuclear nickel/thallium hexacyanoferrate, in which b oth nickel(II) and thallium(I) are nitrogen-coordinated within the cyanomet allate lattice, was rather unlikely. On basis of the stripping-like determi nations, we propose a stoichiometric formula, (K2 - zTlzNiII)-Ni-I[Fe-II(CN )](6) (z less than or equal to 1), for the system in which interstitial Kwas substituted with Tl(I); and a more general (KxTlzNyII)-N-I[Fe-II(CN)](6 ) formula that also reflects the possibility of codeposition. of separate n ickel hexacyanoferrate and thallium hexacyanoferrate microstructures during the film growth. Mixed nickel/thallium hexacyanoferrate films showed good stability during voltammetric potential cycling. In addition to potassium s alt electrolytes, well-defined and reversible cyclic voltammetric responses were also obtained in sodium and cesium electrolytes. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.