Electrochemically initiated chain polymerization of pyrrole in aqueous media

Abstract

The electrochemical quartz crystal microbalance has been employed to investigate the electropolymerization of pyrrole in a variety of aqueous electrolytes. In contrast to the generally accepted cation–radical coupling process for the electropolymerization of pyrrole, an electrochemically initiated chain polymerization, featuring a high polymerization rate and involving little charge transport, was found under specific conditions in the presence of ClO−4, BF−4, and PF−6 electrolytes. The more typical cation‐radical coupling mechanism, characterized by a constant polymerization charge to mass deposited ratio, is observed in the presence of Cl−, NO−3, dodecyl sulfate, copper phthalocyanine tetrasulfonate, β‐cyclodextrin tetradecasulfate, and poly(styrene sulfonate). Electrochemical characterizations of polypyrrole films prepared in aqueous ClO−4 electrolytes reveal that the polymer formed via chain polymerization exhibits the ability to transport both cations and anions during electrochemical switching between redox states, while the polymer synthesized through cation‐radical coupling is only capable of transporting a single ionic species.

Vertically aligned ZnO nanorod core-polypyrrole conducting polymer sheath and nanotube arrays for electrochemical supercapacitor energy storage

“…By themselves, these are unstable but stabilize rapidly on interaction with the nearest cation radicals to form short chain oligomers by coupling and bond linkage with the involvement of deprotonation (-2H + ) n + m step [5,45,51,52]. A number of cation radicals ${\left[\mathrm{normalPy}\right]}_m^{+italic●}$ at the initiation step are also influenced by strongly interacting electrolyte ClO 4 - anions which result in conjugation of PPy short chain oligomers deposited over ZnO nanorods [53]. The current pulse off time replenishes the Py-monomers at the ZnO nanorods by diffusion in the aqueous medium.…”

Ion and solvent transfers accompanying redox switching of polypyrrole films immersed in divalent anion solutions

“…In the monovalent anion systems the film mass change increases (decreases) monotonically during positive-going (negative-going) potential scans. We use this well-known behavior [25,30,33,44], attributed to anion-dominated transfer during redox switching, as our "reference" behavior. However, in 0.1 M Na 2 SO 4 solution, the film mass change is qualitatively the inverse: it decreases (increases) during the polymer oxidation (reduction) process.…”

“…Fundamental studies have generally focused on PPy behavior when exposed to bathing solutions containing 1:1 electrolytes; these include small anions (typified by ClO 4 − , BF 4 − , PF 6 − , NO 3 − and Cl − ), moderate sized anions and large (polymeric) anions [25][26][27]. Weidlich et al proposed a general scheme to describe the behavior at polypyrrole of different counter ions in different electrolyte solutions [28].…”

Electrosynthesis of polypyrrole nano/micro structures using an electrogenerated oriented polypyrrole nanowire array as framework

“…The oxidation of pyrrole (Py) leads to the formation of polypyrrole under its oxidized form, doped with anions (A -), according to the following reaction [32,33]:…”