Ion flux during electrochemical charging of Prussian Blue films

Abstract

Thin (approximately 100 nm) films of Prussian Blue were electrochemically deposited onto mass-sensitive oscillating quartz-crystal electrodes. Changes in electrode mass during the electrodeposition process indicated that the as deposited films were highly hydrated. Mass changes upon electrochemical reduction and oxidation of the Prussian Blue films in the nitrate salts of K+, Rb+, and Cs+ at pH 4, were measured. Some weight gain occurred upon the original reduction and reoxidation, indicating that an irreversible structural reorganization occurred. Subsequent electrochemical cycling produced a reversible mass gain upon reduction, and a reversible mass loss upon oxidation, indicating that alkali metal cations enter and exit the film upon reduction and oxidation, respectively. The mass/charge behavior of the films was studied in 0.5 M RbNO3, over the pH range 2.7-6.4. The pH dependence indicated that considerable proton expulsion can occur upon oxidation of the Prussian Blue, and some proton inclusion can accompany reduction. The film mass losses upon oxidation in 0.5 M RbNO3 and 0.5 M RbOOCCH3, pH 4, were virtually indistinguishable, implying that the supporting electrolyte anions played little role in the electrochemistry in these media. © 1987.