The Formation of Polypyrrole at Iron from 1-Butyl-3-methylimidazolium Hexafluorophosphate

Abstract

The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, was used to deposit adherent and highly conducting polypyrrole coatings at pure iron using a simple potentiostatic technique. Adherent and highly conducting polypyrrole films were formed at the iron substrate using potentials in the range from 1.0 to 1.4 V and with pyrrole concentrations between 0.1 and 0.3 mol dmϪ3 . An increase in the applied potential, or the concentration of the monomer, gave rise to an increase in the rate of polymer growth. The polypyrrole-coated iron electrodes were electroactive and remained highly conducting and stable in the ionic liquid. Using electrochemical impedance spectroscopy, the charge-transfer resistance of the uncoated iron electrode was determined as 1.25 ϫ 10 4 ⍀ cm 2 compared to the much lower resistance of 1.90 ϫ 10 2 ⍀ cm 2 measured for the highly conducting polypyrrolecoated electrode in the ionic liquid. The room temperature ionic liquid systems based on the N,NЈ-dialkyl-substituted imidazolium cations have attracted increasing attention and interest in recent years.1-4 This is not surprising in light of their promising physical and chemical properties, which include high ionic conductivity, negligible volatility, nonflammability, excellent thermal and chemical stability, air and moisture stability, and, in terms of electrochemistry, a wide potential window.Research into the formation, or properties, of conducting polymers in ionic liquids dates back to the mid 1980s, with the work of Osteryoung and co-workers.5-7 However, the chloroaluminate ionic liquids used in these investigations were moisture sensitive. In more recent times, it has been shown that conducting polymers can be electrosynthesized in the ambient temperature imidazolium-based ionic liquids with anions such as hexafluorophosphate or tetrafluoroborate. [8][9][10][11][12][13][14] But of more significance is the fact that the conducting polymers cycled in, or electropolymerized from, these imidazolium-based ionic liquids exhibit greatly enhanced electrochemical stability, negligible polymer degradation and fast switching speeds. [8][9][10][11][12][13][14] For example, Lu et al. 10 found that polyaniline, polypyrrole, and polythiophene showed negligible loss in electroactivity when cycled in room-temperature ionic liquids composed of 1-butyl-3-methyl imidazolium cations with either tetrafluoroborate or hexafluorophosphate anions. Sekiguchi et al.13,14 used 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as an electrolyte for the electrochemical polymerization of pyrrole. The electrochemical capacity and conductivity of the polypyrrole were significantly increased when prepared from the ionic liquid. Other polymer systems that have been studied in these imidazolium-based ionic liquids include poly͑3,4-ethylenedioxythiophene͒ 15,16 and poly͑2-methoxy-5-͑2Ј-ethylhexyloxy͒-1,4-phenylene vinylene ͑MEH-PPV͒. 17These studies have all been conducted with inert electrodes. Although conducting polymers have been deposited at corrosion susceptib...

Electroconducting materials based on polypyrrole

“…Thus, at polymerization potentials some of the metals and their alloys, whether forms passive nonconductive layer (e.g., Zn) [56] or are dissolved in the solution used in the polymerization set up (iron, steel, etc.) [57][58][59]. Usually used substrates for polymer deposition are electrodes made of graphite, carbon fibers, glassy carbon, Indium-tin oxide (ITO), inert metals like Au and Pt [11,43,[60][61][62][63][64][65].…”

Conducting Polymers

“…There is also a range of different working electrodes available; existing studies of conducting polymer synthesis in ionic liquids almost entirely use platinum working electrodes, or indium titanium oxide (ITO) glass to allow spectroelectrochemical analysis of the polymer. The synthesis of poly(pyrrole) onto iron has also been studied [29], and a glassy carbon electrode has been used for the deposition of PEDOT [25]. As for all electrochemical techniques, the condition and cleanliness of the electrodes is of great importance; it has been reported that the morphology of poly(pyrrole) films can be greatly altered by inadequate polishing of the working electrode [30].…”

“…However, lower polymer redox currents were observed in the more viscous, less conductive pyrrolidinium ionic liquid compared to the imidazolium species ( 6 ] has also been studied in some detail [29,32,68]. Fenelon and Breslin used this ionic liquid to deposit poly(pyrrole) onto an iron electrode [29], an example of the electrochemical deposition of a conducting polymer from an ionic liquid onto a corrosionsusceptible electrode rather than the inert species used in the other studies.…”

“…However, lower polymer redox currents were observed in the more viscous, less conductive pyrrolidinium ionic liquid compared to the imidazolium species ( 6 ] has also been studied in some detail [29,32,68]. Fenelon and Breslin used this ionic liquid to deposit poly(pyrrole) onto an iron electrode [29], an example of the electrochemical deposition of a conducting polymer from an ionic liquid onto a corrosionsusceptible electrode rather than the inert species used in the other studies. The polymer was deposited onto iron using a relatively high potential (1.3 V vs. a Ag wire quasi-reference electrode) but was electroactive and conducting, indicating negligible polymer overoxidation problems compared to those associated with using aqueous systems or even those observed using a platinum working electrode at these potentials in this ionic liquid.…”

“…In both these studies, the polymers in the neat ionic liquids displayed slower ion transport compared to those in molecular solvents or diluted ionic liquids. Fenelon and Breslin [29] also used electrochemical impedance measurements to demonstrate the conductivity and stability of poly(pyrrole) deposited onto iron from [C 4 mim][PF 6 ].…”