Display devices Prussian Blue

Figure 8.1 Beer s law-type plot of change in optical absorbance against charge density q for the cell WO3 polymer electrolyte Prussian Blue. Reprinted from Inaba, H Iwaka, M., Nakase, K., Yasukawa, H., Seo, I. and Oyama, N., Electrochromic display device of tungsten trioxide and Prussian Blue films using polymer gel electrolyte of methacrylate , Electrochim. Acta, 40, 227-232 (1995), Copyright 1995, with permission from Elsevier Science.

The redox chemistry of the Prussian blue family (Table 7) has attracted considerable attention. The generation of thin films of Prussian blue has led to studies of its mediation in electron transfer reactions and of the electrochemical processes involved in its deposition and redox reactions. This work has been spurred by its electrochromic properties which have been used in prototype electronic display devices based, for example, on Prussian blue modified Sn02 electrodes. A recent review deals with the electrochemistry of electrodes modified by depositing thin films of PB and related compounds on them. Interestingly, true Prussian blue is somewhat difficult to process and modern iron blue pigments such as Milori blue are derived from the oxidation of rlin white Fe(NH4)2[Fe(CN)e] to give iron(III) ammonium ferrocyanides. 

The addition of ferric ions to an aqueous solution of Fe(II) hexacyanide results in the formation of a highly colored colloidal precipitate known as Prussian blue (PB), a material regarded as the oldest coordination compound reported in the scientific literature.t It has been found recently that films of PB deposited on electronically conducting substrates are capable of undergoing a reversible blue-to-transparent color transition when the electrode potential is changed between two appropriate values. This is an illustration of what has been referred to as electrochromism, a phenomenon that may find wide application in connection with electronically controlled color display devices. 

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