Electrochemical preparation and characterisation of bilayer films composed by Prussian Blue and conducting polymer

doi:10.1016/S1388-2481(02)00440-X

Electrochemistry Communications

Volume 4, Issue 10, October 2002, Pages 753-758

https://doi.org/10.1016/S1388-2481(02)00440-X Get rights and content

Abstract

Preparation and electrochemical behaviour of bilayer films consisting of iron(III) hexacyanoferrate, well known as Prussian Blue, and of poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene], on a platinum electrode, are reported. The electrochemical features of the Prussian Blue/conducting polymer bilayer system are examined in aqueous and acetonitrile solutions. Cyclic voltammetric studies show that, in acetonitrile solvent, the inner layer Prussian Blue is electroactive to some extent, though the electrochemical response of the system is mainly accounted for by poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene] outer layer. On the other hand, in aqueous solution Prussian Blue exhibits good electroactivity. Under specific experimental conditions, the individual redox behaviour of each constituent of the bilayer is evidenced in the two solvents separately, i.e., that of PB and that of poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene] in aqueous and in organic solvent, respectively. However, interesting reciprocal influences are evident in the current/potential curves recorded under conditions which are discussed.

Introduction

During the last decade, there has been a great deal of interest in electrically conducting polymers (CPs), due to their applications in electrochemical displays, in sensors, in secondary batteries, and in catalysis [1], [2], [3]. CPs can be deposited under the form of dense modifying layers on usual electrode substrates to work as electrochemical, mainly amperomeric, sensors [4], [5], [6].

On the other hand, during the last 15 years the use of metal hexacyanoferrates for the modification of electrode surfaces has attracted much interest as well [7]. Among metal hexacyanoferrates, Prussian Blue (PB), i.e., iron(III) hexacyanoferrate, is one of the most extensively studied, due to the electrochromic properties and the electrocatalytic activity and stability in aqueous solutions [8], [9]. PB has been used in the electrocatalytic reduction of CO₂ [10], H₂O₂ [11], hydrazine [12], and in the oxidation of ascorbic acid and dopamine [13], [14]. The presence of two well distinct redox couples ascribes it selectivity with respect to the redox processes that can or cannot be electrocatalysed by an electrode modified by PB. However, the stability of PB is only satisfactory in acidic aqueous solutions, while at alkaline or neutral pH decomposition occurs [15], [16]. The thermodynamics of redox systems in which PB is involved is of great interest when considering bilayer electrode coatings, for which it has been proposed both as the inner and as the outer phase.

The bilayer electrode coatings have been proposed since the early 1980s by Murray et al. [17] who developed a 'double redox couple system' that exhibited the interesting property of rectifying the current flow, acting similarly to a diode electronic device. Since that time, a lot of bilayer systems have been proposed, based on many different inorganic and organic materials [18], aimed at pursuing the original scopes, as well as at realising a variety of novel devices with various properties. In particular, bilayer systems consisting of PB films and different organic polymers have been realised. The organic polymer layer was a CP [19], [20], [21], [22], such as polyaniline or polypyrrole, or an ion-exchange polymer, such as Nafion^® [18]. It is evident that in the case that one layer is a CP and the other is PB, the system as a whole will be affected by the conductive or insulating state of both components. This means that the response of the system will not only depend on the nature of the two layers, but also on the potential of the underlying electrode. In principle, by properly combining a suitable hexacyanoferrate, i.e., not necessarily iron hexacyanoferrate, with a suitable CP, a wide choice of possible selectivity in the correspondence to different potentials can be realised. It is, however, very important to test carefully the experimental conditions, since formation of mixed-valence states could vanish any project based on strict thermodynamic arguments [23], [24].

In the recent past, we worked extensively on S-alkyl substituted polythiophenes, in particular on the poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene] (PBSBT) [25], [26], [27], [28], [29], [30], [31], i.e., a CP that proved to posses unique stability properties, from both a mechanical and a chemical point of view. This allowed us to perform time-consuming measurements [28], [29] devoted to the electrochemical characterisation of the CP coating. In two recent papers, we reported the capabilities of PBSBT modified conventional-size and microelectrodes in analyses performed in aqueous media at neutral pH, by linear sweep (LSV) and differential pulse voltammetry (DPV) [30], [31].

Aiming at obtaining stable bilayer PB-CP films, in view of the advantages offered by PBSBT, we have studied preparation and electrochemical features of a PB/PBSBT bilayer coating deposited on a platinum electrode. The PB/PBSBT coverage is prepared electrochemically by a two-step method. We first electrodeposited a PB layer onto a platinum electrode in aqueous solution. In the second step, the electrochemical deposition of PBSBT film over the Pt/PB modified electrode was carried out in an organic medium. Hereafter, the electrochemical behaviour and the stability of the bilayer coating are studied in both organic and aqueous solutions. The very good adherence of PBSBT to PB, in addition to the well known stability of the PB film on metal electrodes, allowed quite a stable bilayer coating system to be realised.

Section snippets

Chemicals

All chemicals: FeCl₃ (Merck), K₃[Fe(CN)₆] (Feinbiochemica), HCl (Aristar), and KCl (Carlo Erba, RPE) were used as received. 4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene (BSBT) was synthesised as described previously [32]. Tetrabutylammonium hexafluorophosphate supporting electrolyte (TBAPF₆) from Fluka, puriss., acetonitrile (AN) solvent from Aldrich, 99.8%+ pure, anhydrous, packaged under nitrogen were used as received. Doubly distilled water was always used to prepare aqueous solutions for

Pt/PB modified electrode

PB was deposited onto the electrode by potentiostatic method at a potential value of +0.40 V, from an aqueous solution containing $2×10^{−3} M$ K₃[Fe(CN)₆] and $2×10^{−3} M FeCl_{3}$ in 0.1 M KCl + 0.01 M HCl. The electrolysis was prolonged for 60 s. After deposition, the modified electrodes were rinsed with doubly distilled water and immersed into a solution containing 0.1 M KCl and 0.01 M HCl, where the electrode potential was cycled between 0.00 and +1.00 V at a scan rate of $0.05 V s^{−1}$ , until a stable

Conclusions

The work described in this paper has been planned in order to check the possibility of preparing and working with a novel bilayer system consisting of an inner inorganic phase that attracted so many interest as a redox mediator and that includes two distinct redox couples, and of an outer phase consisting of a CP that proved us to posses lot of interesting properties. The system is studied under the potentiodynamic conditions that are usually proper of electroanalytical tests. Studies devoted

Acknowledgements

S.L. appreciates a fellowship from the Romanian Ministry of National Education (MEN) supporting a six months stay at the Department of Chemistry, University of Modena.

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Electrochemical preparation and characterisation of bilayer films composed by Prussian Blue and conducting polymer

Abstract

Introduction

Section snippets

Chemicals

Pt/PB modified electrode

Conclusions

Acknowledgements

Talanta

Electrochim. Acta

J. Electroanal. Chem.

J. Electroanal. Chem.

J. Electroanal. Chem.

Electrochim. Acta

Electrochim. Acta

J. Mater. Chem.

Electroanalysis

Acc. Chem. Res.

Electroanalysis