Doping/undoping

FIGURE 4-22 Typical response of polypyrrole detector to carbonate (S , 1 x 10-4M S2,2.5x lO M S3, 5 x 10 m) based on the doping-undoping process. (Reproduced with permission from reference 74.)... 

Mogi, I., Watanabe, K and Motooka, M. (1999) Effects of magnetoelectropolymerization on doping-undoping behavior of polypyrrole. Electrochemistry,67,1051—1053. 

This contribution reviews recent results on [Si(Pc)0]n (Pc = phthalocyaninato) solid state electrochemistry and the structural interconversions that accompany electrochemical doping/undoping processes. In aceto-nitrile/(a-Bu)4N+BF4, it is found that a significant overpotential accompanies initial oxidation of as-polymerized [Si(Pc)0]n. This can be associated with an ortho rhomb ic- te tr agonal structural transformation. 

Doped silicon, conductivity in, 23 35 Doped/undoped electrochromic organic films, 6 580-582 Dope-dyeing, 9 197 Dope-making process, in acrylic fiber solution spinning, 11 204 Dope solids, in air gap spinning, 11 209 Doping, 23 838—839 calcium, 23 842-844 conducting polymers, 7 528-529... 

Apparent permselectivity and compensatoiy motion. Although normalised mass change data for the "doping/undoping" of PBT films were very similar to those predicted by permselectivity in the absence of solvent transfer (cf. electroneutrality), the differences were real. Furthermore, systematic variation of the anion or cation or deuteration of the solvent produced consistent trends in the departure from "simple" behaviour. Insight into the overall processes involved (the thermodynamics) is gained by considering the kinetics of mobile species transfer. 

Experimental mass changes during PBT doping/undoping do not conform to the >j = 0 requirement. Figure 2 contains representative data for tetraethylammonium hexafluorophosphate (TEAPF) as the electrolyte. In accord with the general activity constraint (see above), solvent and salt do transfer. For PBT, these net neutral species transfers are in opposite directions. 

Conducting polymers are promising electrode materials because the kinetics of the charge-discharge process, i.e., the doping-undoping, is generally fast because... 

PPP [5] (cf. below). The highly conducting PA found by Naannann in 1987 [285, 286] could not make up for this disadvantage. Such a high conductivity is not at all necessary for battery applications. The rate of electrochemical doping/undoping (anions) is rather low due to the extremely small diffusion coefficient in the fabrils [287]. Today, the earlier interest in this material for batteries has totally disappeared. 

The necessary porosity for thicker layers was introduced by appropriate current densities [321-323], by co-deposition of composites with carbon black [28, 324] (cf. Fig. 27), by electrodeposition into carbon felt [28], and by fabrication of pellets from chemically synthesized PPy powders with added carbon black [325]. Practical capacities of 90-100 Ah/kg could be achieved in this way even for thicker layers. Self-discharge of PPy was low, as mentioned. However, in lithium cells with solid polymer electrolytes (PEO), high values were reported also [326]. This was attributed to reduction products at the negative electrode to yield a shuttle transport to the positive electrode. The kinetics of the doping/undoping process based on Eq. (59) is normally fast, but complications due to the combined insertion/release of both ions [327-330] or the presence of a large and a small anion [331] may arise. Techniques such as QMB/CV(Quartz Micro Balance/Cyclic Voltammetry) [331] or resistometry [332] have been employed to elucidate the various mechanisms. 

The comparatively weak reversible peaks at low potentials and strong irreversible peaks at high potentials are observed when conductive polymers are used as electrode materials in electrochemical systems. They are attributed to doping-undoping reactions and over-oxidation respectively. 

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