Electronic structure electronically conducting polymer

Activity in the battery area using electronically conducting polymers has been intense (see Fig. 11.19). The possibilities (MacDiarmid, 1997) point to the provision of cheap (because of the relative cheapness of organic compounds) batteries, e.g., for massive use as a power source for bicycles. The counter-point is the limited stability and hence lifetime of such structures, and the availability of, e.g., rechargeable MnOj-Li cells, in which the (bismuth doped) Mn02 is also a relatively cheap material. 

The major difficulty in the 1990s for the development of electronically conducting polymers lies in the limited understanding we have about the relation between the molecular structure of the organic material and the resulting electronic conductance. 

What are the structures of conductive polymers, and what is the mechanism for electronic transport in the solid-state ... 

In the 1970s, interest arose in the modification of electrode surfaces by covalent attachment of monolayers of different species to electrode surfaces. Electrodes modified with thicker polymeric films and inorganic layers were introduced later. Paralleling this work was activity in the field of electronically conductive polymers and organic metals, many of which can be produced electrochemically. More complex structures (bilayers, arrays, biconductive films) have also been prepared. 

The pristine conjugated polymers have been reported to contain electronic spins, presumably originating from inter-chain cross-linking in polyacetylene [25,26], formation of polynuclear structures in polypara-phenylene [27] and so on. The inter- and intra-chain reactions between these reactive sites can alter the chemical structure of conductive polymers even when they are pure, affecting their dopability and hence the electroactivity. 

Figure 28.3. Structural formulas of several electron-conducting polymers (a) frans-poly(acetylene), (b) cw-poly(acetylene), (c) poly(p-phenylene), (d) polyanUine (PAni), (e) poly(n-methylaniline) (PNMA), (f) polypyrrole (PPy), (g) polythiophene (PTh), (i) poly(3,4-ethylenedioxythiophene) (PEDOT), (j) poly(3-(4-fluorophenyl)thiophene) (PFPT), (k) poly(cyclopenta[2,l-b 3,4-dithiophen-4-one]) (PcDT), and (m) Mg polyporphine.

Hutchinson, G.R., Y.J. Zhao, B. Delley, A.J. Freeman, M. Ratner, and T. Marks. 2003. Electronic structure of conducting polymers Limitations of oligomer extrapolation approximations and effects of heteroatoms. Phys Rev B 68 035204. 

The foregoing is illustrative of the complexity of the electropolymerization process. There is obviously no universal mechanism determining what the surface structure of conducting polymers will be. However, from a practical standpoint these studies are very important to tailoring of the polymer surface to suit the application, be it electronic or electrochemical, since the needs for each application are unique. 

As part of an overall study of the electrode/electrolyte interphase of the electronically conducting polymer, polypyrrole, the surface structure and electronic properties have been investigated. 

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