Indium(III)-hexacyanoferrate(III, II) as an inorganic material analogous to redox polymers for modification of electrode surfaces

Abstract

Polynuclear indium(III)-hexacyanoferrate(III, II) films were prepared electrochemically on a glassy carbon substrate. The deposition was performed by cycling the potential between 0.85 and 0.0 V vs sce in a fresh 0.5 mM InCl 3/0.5 mM K 3Fe(CN) 6/0.5 M KCl mixture at pH 2. During the negative scans, the cationic In 3+ species interact with the simultaneously generated anionic Fe(CN) 4− 6 to yield sparingly soluble mixed-valent coatings on the electrode surfaces. Different thicknesses, typically corresponding to 1–100 nmol cm −2, could be obtained by varying the cycling times. The modified electrode exhibits a single set of well-defined and highly reversible voltammetric peaks (related to the hexacyanoferrate redox transitions) in K +-containing electrolytes. Electrochemical charging is accompained by the cation motion, leading to the cation storage in the reduced state and its release upon oxidation. The results are consistent with high ionic conductivity of potassium in the film. Experiments in the other alkali metal electrolytes show that the cataion transport, necessary for the charge compensation during redox transitions, cannot be simply related to the size of a cation and the zeolitic structure of indium hexacyanoferrate.