ELECTROCHEMISTRY AND ELECTROCHROMISM OF VANADIUM HEXACYANOFERRATE

Vanadium hexacyanoferrate (VHCF) is an electrochromic material closely related structurally to Prussian blue. The deposition, characterization, and spectroelectrochemistry of films of VHCF are reported here. The electrodeposition of VHCF films is shown to involve the reduction of vanadium(V) ion in the presence of ferricyanide ion. X-ray diffraction data confirm a cubic crystal structure for VHCF, similar to that of Prussian blue. However, chemical analyses give a higher than expected ratio of V to Fe, which suggests the presence of interstitial vanadium. While VHCF films are visually electrochromic, switching from green in the oxidized state to yellow in the reduced state, UV-vis-near-IR spectra show that most of the electrochromic modulation occurs in the ultraviolet region. From X-ray photoelectron spectroscopy and coulometric results, coupled with other electrochemical data, we conclude that the electrochromic reaction involves only the oxidation and reduction of the iron centers in the compound. The vanadium ions, found to be present predominantly in the +4 state, are unaffected by the reaction. Multiple ferrous sites are suggested to be responsible for the complex electrochemistry of VHCF. © 1990, American Chemical Society. All rights reserved.