Coulombic efficiency polypyrrole

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

Recently Osaka et al [260] studied a lithium/ polypyrrole secondary battery system using PEO-LiC104 as a solid polymer electrolyte. The battery showed fairly high coulombic efficiency of about 95% with an output voltage of 3.0 V and performed very well for 1400 charge-discharge cycles after initial 100 scans required to reach optimum value. However, efficiency... 

The doping limit of polypyrrole in Li/polypyrrole batteries was investigated by many researchers and charge-discharge coulombic efficiency of almost 100% was obtained up to 20-30% doping (per monomer unit) [36]. 

Figure 5,8 Relationship between coulombic efficiency, charge end voltage and charge capacity of Li-Al/polypyrrole cells. Reprinted from [29] by permission of Elsevier Sequoia S.A.

Figure 20.21 demonstrates how cyclic voltammetry can be effectively combined with EQCM for the study of a complex electrochemical process such as the reduction of Te(IV) [82]. Voltammetry alone would have provided only a limited glimpse into the subtleties of the reduction process. Combination of EQCM with cou-lometry [i.e., combination of Eqs. (6) and (12)] affords a sensitive probe of the electron stoichiometry and Far-adaic (Coulombic) efficiency for polymer deposition processes. For example. Fig. 20.22 and Table 20.5 contain assays of the platinum content thus obtained for polypyrrole-Pt composites [83] considered later in this chapter. 

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