EDX, Spectroscopy, and Composition Studies of Electrochromic Iron(III) Hexacyanoferrate(II) Deposition

Persistent questions regarding the electrochromic ferric-ferrocyanide chromophore, Prussian blue (PB), are addressed and definitively resolved by detailed chemical and energy-dispersive X-ray analyses and spectroscopy: (i) What is the nature of the initially deposited film? (ii) Restructuring of freshly deposited PB that occurs in the first voltammetric cycle in KCl(aq): why is only one-third of the maximum possible K + taken up? (iii) Is the presence of KCI in the electrodeposition solution beneficial or destructive? and (iv) What underlies the appreciable spectroscopic shifts of the charge-transfer peak at ∼700 nm, that depend on which alkali-metal ion M + is incorporated in PB? The KCl-cycled PB after electrodeposition is shown to be K + 0.33Fe 2+ 0.33Fe 3+ [Fe(CN) 4- 6] in a mechanism explaining the limited (0.33) uptake of K + . Similar compositions are found with other M + except Cs + , which interacts exceptionally.