Abstract
This work reports the design, synthesis, and characterization of a novel redox-active conjugated polyaniline containing quinone moiety as a solid state reference electrode. The union of electro-active quinone with π-conjugated polyaniline was created by the first chemical synthesis of para-dimethoxybenzene-functionalized aniline as a monomer using a palladium-mediated coupling. The successful polymerization of the as-prepared monomer was accomplished without acid additives. Its post-polymerization modification with strong Lewis acid boron tribromide furnished unique poly (aniline quinone/hydroquinone) with desired properties for all-solid-state reference electrode (RE) applications. The electrochemical responses from the conjugated polyaniline backbone in this unique polymer have been “suppressed” by the quinone pendant. The resulting poly (aniline quinone) showed a quasi-reversible redox process from the redox behavior of the pendant quinone. The stable electrode potential of this poly (aniline quinone/hydroquinone) suggested that it was a single phase in which the amounts of totally reduced and totally oxidized species could be maintained at a constant in various solvents and electrolytes. Its electrochemical stability was excellent with 95% peak current retention after continuous cyclic voltammetric testing. The aniline and quinone moieties in poly (aniline quinone/hydroquinone) render it to have both hydrophilic and hydrophobic compatibility. It showed excellent behavior as a reference electrode in aqueous and non-aqueous media and can be used in both non-zero current and zero-current conditions, providing a stable potential with a maximum potential drift of ~4.7 mV over ten consecutive days.
Highlights
Electrochemistry is a discipline that studies chemical reactions that involve the exchange of electric charges between two substances
The stable electrode potential of this poly suggested that it was a single phase in which the amounts of totally reduced and totally oxidized species could be maintained at a constant in various solvents and electrolytes
The stable electrode potential of the novel poly suggested that it was a single phase in which the amounts of totally reduced and totally oxidized species could be maintained at a constant in various solvents and electrolytes
Summary
Electrochemistry is a discipline that studies chemical reactions that involve the exchange of electric charges between two substances. Quasi-reference electrodes (QRE), typically just a metal wire (e.g., Ag or Pt) are often used in non-aqueous solvents or electrolytes. One of the major research areas in electrochemistry is to develop miniaturized reference electrodes that can provide highly stable electrode potential with ease of fabrication at low cost for electrochemical micro-sensor development. Mandler modified the glassy carbon electrode with polyethylenimine (PEI), a highly charged polymer that bound strongly with Fe(CN)6 3−/4− anions This modified glassy carbon was used as a relatively stable RE in organic solvents, but it requires incubation for several hours in acetonitrile before reaching a stable potential. The stable electrode potential of the novel poly (aniline quinone/hydroquinone) suggested that it was a single phase in which the amounts of totally reduced and totally oxidized species could be maintained at a constant in various solvents and electrolytes. The aniline and quinone moiety in poly (aniline quinone/hydroquinone) render it to have both hydrophilic and hydrophobic compatibility with both aqueous and non-aqueous solvents so that its solvation and configuration can quickly reach a global equilibrium in both media
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