This article was published in the Journal of Solid State Electrochemistry [© Springer-Verlag] and the definitive version is available at: http://dx.doi.org/10.1007/s10008-012-1811-7Prussian-blue (PB) film for electro-chromism can be electro-deposited on to an electrode (usually tin-doped indium oxide/glass) either directly from a PB colloid or from ferric ferricyanide in a two-electrode electro-chemical cell by applying a reductive potential. Alternatively, a “sacrificial” electron-producing silver flag electrode in the solution, when connected to the PB-receiving electrode, can effect the required reductive deposition. A silver spot, here innovatively applied as silver paint directly onto the deposition electrode, produces PB film on immersion in the iron(III)(III) solution, obviating the separate counter-electrode method

AM Soutar

D Ellis

D-Y Shin

David R. Rosseinsky

DR Rosseinsky

Frank Marken

H Kellawi

Hassan Kellawi

KC Ho

PMS Monk

R Cisternas

Ray T. Barton

Roger J. Mortimer

VD Neff

Prussian-blue (PB) film for electro-chromism can be electro-deposited on to an electrode (usually tin-doped indium oxide/glass) either directly from a PB colloid or from ferric ferricyanide in a two-electrode electro-chemical cell by applying a reductive potential. Alternatively, a “sacrificial” electron-producing silver flag electrode in the solution, when connected to the PB-receiving electrode, can effect the required reductive deposition. A silver spot, here innovatively applied as silver paint directly onto the deposition electrode, produces PB film on immersion in the iron(III)(III) solution, obviating the separate counter-electrode method

Ray Barton (1248126)

Hassan Kellawi (7162973)

Frank Marken (1741489)

Roger J. Mortimer (1942423)

David R. Rosseinsky (2703775)

Loughborough University Institutional Repository

   This item was submitted to Loughborough’s Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.      For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/  1  Simplest Prussian-blue deposition from ferric ferricyanide solution by a reducing Ag spot put onto an ITO substrate   Ray T Barton • Hassan Kellawi • Frank Marken • Roger J Mortimer • David R Rosseinsky  Abstract Prussian blue (PB) film for electrochromism can be electro-deposited on to an electrode [usually tin-doped indium oxide /glass ] either directly from a PB colloid, or from ferric ferricyanide  in a two-electrode  electrochemical cell by applying a reductive potential. Alternatively, a “sacrificial” electron-producing silver flag electrode in the solution, when connected to the PB-receiving electrode, can effect the required reductive deposition.  A silver spot, here innovatively applied as silver paint directly onto the deposition electrode,  produces PB film on immersion in the iron(III)(III) solution,  obviating the  separate counter-electrode method. Key words:  Prussian blue, thin films, silver, electrochromic   R. T. Barton •  R. J. Mortimer  Department of Chemistry,  Loughborough University,  Loughborough, Leicestershire LE11 3TU, UK  H. Kellawi Department of Chemistry,  The University of Damascus,  Damascus   Syria  F. Marken Department of Chemistry,  The University of Bath, Claverton Down Bath BA2 7AY, UK  D. R. Rosseinsky (*) School of  Physics The University of Exeter Exeter EX4 4QL, UK email:  d.r.rosseinsky@ex.ac.uk  2  Introduction     Prussian Blue (PB), “ferric ferrocyanide”, comprises a widely-used group of materials [1] M+Fe3+FeII(CN)6  where M can be any alkali cation  (or ⅓Fe3+  in the “insoluble PB” form).  In historical and current use as a pigment [2], the colouration arises from the optical charge-transfer between the FeII  and the Fe3+.   In recent decades Neff [3, 4] showed PB to be  an electrochrome [1] of extensive applicability, as recently exemplified [5].  The PB electrochromic reaction, via externally-applied electrochemistry, is basically Fe3+FeII(CN)6  [PB, blue] + e- → Fe2+FeII(CN)6  [clear] where the reduced, clear, form is “Prussian White” (PW) [1] . The substrate is commonly transparent tin-doped indium oxide (ITO)/glass.            For PB  electrochromism  there are two main methods of preparation. Commonly, electro-deposition  (electrochemical reduction) from ferric ferricyanide solution, on to transparent conductive ITO/glass, is effected by an applied external potential [1] (note that Neff  [3, 4] just immersed a pre-cathodised Pt or Au surface  for the required reduction). Alternatively, colloidal PB has been directly electrodeposited straight onto the receiving electrode [6]. Ho [7, 8] introduced a variation of the former by using a separate silver metal electrode connected directly to the ITO also immersed in the iron(III)(III) deposition solution: sacrificial Ag dissolution causes  reductive deposition of  PB via the Ag-liberated electrons. Here, we describe the use of a silver metal spot directly applied to the ITO/glass, which, on total immersion of the assembly into the iron(III)(III) solution, undergoes just that sacrificial-silver reaction to produce a uniform PB film. This dispenses with the need of an electrochemical cell and a separate stand-alone Ag metal electrode. The Ag spot comprises silver paint as is commonly used to make external electrical connections to electrodes.   3  Experimental       Two sizes of  ITO-coated glass ( Image Optics Components Ltd., Basildon, Essex,  typically 20 Ω per square), were used, either 0.9 x 5.5 cm2  (the lower 0.9 x 4.0 cm2 area is immersed in solution in electrochromic operation), or for larger electrodes, 20 x 25 cm2 (1.5 cm protruding atop in electrochromic use).  The ITO/glass pre-cleaned in ethanol was sonicated in aqueous detergent for ca  1 h,  well washed with tap water then  de-ionised water (nominal 18.2 MΩ cm).  When dry  a small spot of  E1660-136 silver ink (a suspension of finely divided silver in a  resin, from  Ercon Inc., Wareham, MA, USA)  was applied  with a Pasteur pipette to give a thin spot of area ~ 0.04 cm2 onto a corner of the ITO/glass electrode. This Ag-spot ITO/glass was oven-dried for 1 h then cooled over silica gel.        The PB deposition bath comprised 0.002 mol dm-3  K3Fe(CN)6  (BDH AnalaR) with  HCl to pH ~ 3-4, followed by slow addition with vigorous stirring of either solid FeCl3.6H2O  or Fe(NO3)3.6H2O (both Fisher Scientific for analysis) to 0.002 mol dm-3; the pH avoided hydrolysis of the Fe3+(aq).  The resultant Fe3+FeIII(CN)6  complex is light brown in solution..      On immersion of the ITO/glass in the iron(III)(III) solution, the PB-forming reaction takes several minutes to deposit a uniform film on the smaller electrode. On the large electrode the deposition took several hours. Lighter PB deposits result by removing the Ag/ITO-glass/PB assembly from the deposition solution sooner.  The PB films were well washed with DI water, drip-dried  then kept in a desiccator over blue silica gel for reproducible H2O content.      For electrochromism, the PB/ITO-glass electrode is immersed in an appropriate electrolyte-containing cell with a second, counter, electrode [1]. The preparative Ag spot is isolated here with say silicone cement if not employed as part of the external connection that is isolated from the echrome-cell electrolyte. This can be KCl solution [1] or an ionically conductive polymer [5]. 4      Well- rehearsed in the literature e.g. [6], the widened CVs of thick PB ( between  ca _0.3 V and + 0.3 V vs the calomel electrode) are as previously recorded [1],  while thin-film PB traces conform with the corresponding published CVs [9].  Ag-deposited PB is more uniform than ordinarily electrodeposited PB especially for large areas [7, 8], undergoing the on/off echrome reactions PB + e-  ⇄  PW  with satisfactory uniformity. Discussion      A novel shortcut to PB electrodeposition, that employs just a single ITO substrate in the place of a preparative electrochemical cell, has been established here in a modified “sacrificial Ag anode” method, by using a silver spot deposited directly onto the PB-receiving electrode. The solution concentrations were not especially critical, as for example the ferric ferricyanide concentration when halved had no deleterious effect, only slowing the deposition.  Faster deposition ensues with extra deposited Ag spots (alongside the original, to avoid subsequently insulated blots in the electrochromic area).  Liberated Ag+  will complex with deposition- solution species. The quality of deposited PB is entirely satisfactory (our trial Ag-flag deposited PB being initially less adherent,  perhaps from  poor deposition-cell geometry). In later experiments (McPhaden L, personal communication), ageing the original Fe(III)(III) solution in daylight for  > 48 h  partly reduced the original solution to green, a well-known state [1], by photo-reaction with H2O. The Ag-driven PB deposition was hereby markedly accelerated, a subject of ongoing research. The Ag spot method was foreseen in an early study [1, 10].      A just-published preparation [11] of a fine Ag network on glass, that is almost completely transparent and conductive (1 Ω per square), promises highly uniform PB deposition by our method. Enough residual Ag might provide a conduction system free of  ITO. Acknowledgements H K acknowledges leave from Damascus University.  5    References 1. Monk PMS, Mortimer RJ,  Rosseinsky DR (2007) Electrochromism and Electrochromic Devices. Cambridge University Press, Cambridge.  Chapter 8 2. Kirby J, Saunders D (2004) National Gallery Technical Report, London  25:73-99  3. Neff V D (1978) J Electrochem Soc 125:886-887 4. Ellis D,  Eckhoff M, Neff VD (1981)  J Phys Chem 85:1225-1231 5.  Soutar AM,  Rosseinsky DR, Freeman W,  Zhang X, How X, Jiang HJ,  Zeng XT, Miao X (2012) Sol Energy Mater Sol Cells 100:268-270   6. Cisternas R, Muñoz E, Henríquez R, Córdova R,  Kahlert H,  Hasse U, Scholz F (2011) J Solid State Electrochem 15:2461–2468 7.  Ho KC (1994 Proc Electrochem Soc, 94:170-171 8. Ho KC(1999). Electrochim. Acta 44: 3227-3235          9.  Rosseinsky DR,  Glidle A (2003)  J Electrochem Soc 150: C641-C645                    10.  Kellawi H,  Rosseinsky D (1982) J Electroanal Chem 131:373-376 11. Shin D-Y,  Jung M, Chun S (2012) J Mater Chem 22:11755-11764        

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Simplest Prussian-blue deposition from ferric ferricyanide solution by a reducing Ag spot put onto an ITO substrate

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Journal of Solid State Electrochemistry

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Simplest Prussian-blue deposition from ferric ferricyanide solution by a reducing Ag spot put onto an ITO substrate

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