Abstract: A process for synthesizing iron(III) hexacyanoferrate(II) as a blue insoluble product on the surface of a working electrode is disclosed which comprises immersing a pair of electrodes in a solution mixture of an iron(III) ion-containing solution and a hexacyanoferrate(III) ion-containing solution and effecting electrolysis with one of the electrodes as an anode and the other as a cathode, whereby iron(III) hexacyanoferrate(II) is deposited on the surface of the cathode.

Abstract: An electrochromic display device comprises an electrolyte contained between a pair of spaced-apart substrates. A set of electrodes are disposed on at least one of the substrates in contact with the electrolyte and a layer of electrochromic material is disposed on at least one of the electrodes to define a display electrode. The electrochromic material comprises a color-reversible salt of iron(III) hexacyanoferrate(II) which, depending on its oxidation-reduction state, exhibits different colors. A source of electric charge is connected through circuitry to effect reversible electrochemical oxidation and reduction of the salt of iron(III) hexacyanoferrate(II) to effect a corresponding reversible color change exhibited by the display electrode.

Abstract: A functional electrode is disclosed which is usable as an electrochromic display electrode, as a catalytic electrode effective to catalyze the evolution of oxygen and chlorine gases and the like. The electrode is composed of a conductor and a film deposited on the surface of the conductor, the film being comprised of a compound of the formula M.sup.I M(III)[M'(II)(CN).sub.6 ] or M(III).sub.4 [M'(II)(CN).sub.6 ].sub.3 wherein M(III) is Fe(III), Ru(III) or Os(III), M'(II) is FE(II), Ru(II) or Os(II) and M.sup.I is an alkali metal cation, with the proviso that said compound does not contain both Fe(III) and Fe(II). The functional electrode is produced by electrodepositing a compound of the formula M.sup.I M(III)[M'(II)(CN.sub.6)] or M(III).sub.4 [M'(II)(CN).sub.6 ].sub.3 on a conductor, from an aqueous solution containing M(III) ions and [M'(III)(CN).sub.6 ].sup.3- ions, wherein M(III), M'(II) and M.sup.