Doping electrochemical, polymers

Pseudocapacitance is used to describe electrical storage devices that have capacitor-like characteristics but that are based on redox (reduction and oxidation) reactions. Examples of pseudocapacitance are the overlapping redox reactions observed with metal oxides (e.g., RuO,) and the p- and n-dopings of polymer electrodes that occur at different voltages (e.g. polythiophene). Devices based on these charge storage mechanisms are included in electrochemical capacitors because of their energy and power profiles. 

It has been shown that the chemical and electrochemical doping of polymers may be described as a redox reaction which involves the... 

The occurrence of bipolaronic states in the polymer chains promotes optical absorption prior to the n-n gap transitions. In fact, referring to the example (9.30) of the band structure of doped heterocyclic polymers, transitions may occur from the valence band to the bipolaronic levels. These intergap transitions are revealed by changes in the optical absorptions, as shown by Fig. 9.8 which illustrates the typical case of the spectral evolution of polydithienothiophene upon electrochemical doping (Danieli et al., 1985). 

Here I would like to mention attempts of synthesizing carbynoid structures by Kijima et al. [6,9] using electrochemical approach. Cathodic electrolysis of a solution of poly(vinylidene fluoride) (PVDF) in DMF containing tetrabutylammonium perchlorate, and tert-butyl alcohol as a mediator was found to produce -doped conjugated polymers consisting of 76% of poly(fluoro-acetylene) and 24% of carbynoid moieties [6] (Scheme 12.7) ... 

Redox conductivity of conducting polymers involves anion insertion associated to oxidation processes (p-type doping) and cation insertion coupled with reduction ones (n-type doping). Efficient polymer-based electronic devices require lowering of the redox potential of the involved electron transfer processes, and electrochemical reversibility is necessary to allow repetitive charge/discharge processes. In the... 

Figure 17.3.16 Results for oxidation of formic acid (dotted curves) and methanol (solid curves) at a fuel-cell anode (Pt/Ru) with phosphoric-acid-doped polybenzimidazole polymer electrolyte, 170°C. (a) current density and (b) mass signal for CO2 at a scan rate of 1 mV/s. [From M. Weber, J.-T. Wang, S. Wasmus, and R. F. Savinell, J. Electrochem. Soc., 143, L158 (1996), reprinted by permission of the publisher. The Electrochemical Society, Inc.]...

Various matrices are used to immobilize CyDs on electrodes. Polypyrrole-sulfated j5-CyD films can be prepared electrochemically using a mixture of pyrrole monomer and sulfated CyD. The presence of the CyD in the film is proved voltammetri-cally and by dispersive X-ray analysis. CyD preferentially dopes the polymer even in the presence of large concentrations of perchlorate [73]. 

Hanack and coworkers [158] reported a study on 103a and a new polymer 110 (Chart 12.17), which was produced from a larger analogous polymer precursor [158]. The properties of 103a agreed well with the other studies, while polymer 110 exhibited almost identical electrochemical behavior. From the difference of the redox processes, an Eg value of 0.65 eV was determined for 110, also very similar to the 0.60 eV value of 103a. The primary difference between the two polymers was a reduced stabflity to n-doping for polymer 110. 

Imae, L, K. Moriwaki, K. Nawa, N. Noma, and Y. Shirota. 1995. Synthesis and electrical properties of novel electrochemically-doped vinyl polymers containing end-capped quaterthiophene and quinquethiophene as pendant groups. Synth Met 69 285-286. 

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