Organic compounds, electronically conducting

Another limiting factor is that it may not be possible to use some of these electronically conducting organic compounds in aqueous solutions. This is true of the polymer most used in new polymer batteries, polyacetylene, for which an appropriate solvent is propylene carbonate (see Fig. 4.115). 

Status of Polypyrrole. Polypyrrole (Diaz, 1981) has been examined and analyzed more than other electronically conducting organic polymers. It is the archetype of this class of compound. 

D. J. Fermin, J. Mostany, andB. R. Scharifker, Curr. Topics Electrochem. 2 132 (1993). Review of electronically conducting organic compounds. 

Were it possible to develop the promise of electronically conducting organic polymers, an ehnanced horizon would be revealed. Thus, even in the face of oil and natural gas shortages, CO2 could be used as a feedstock by reducing it electrochemically to useful compounds. The prospect for a long term supply of inexpensive, lightweight, non-corrodible electrode materials is hence improved. 

A second type of soHd ionic conductors based around polyether compounds such as poly(ethylene oxide) [25322-68-3] (PEO) has been discovered (24) and characterized. These materials foUow equations 23—31 as opposed to the electronically conducting polyacetylene [26571-64-2] and polyaniline type materials. The polyethers can complex and stabilize lithium ions in organic media. They also dissolve salts such as LiClO to produce conducting soHd solutions. The use of these materials in rechargeable lithium batteries has been proposed (25). 

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

Metals have a sea of delocalized electrons that are not bound to specific nuclei, and these are responsible for both their high electrical and heat conductivities. Organic compounds do not ordinarily have such delocalized electrons, and are poor electrical and heat conductors. In fact, they are used to coat electrical wires as insulators. If polymers can be made to conduct, then they could be of a great deal of utility, as they are light, can be processed at low temperatures and pressures, and the raw material does not depend on metal mining. However, the possibility of a conducting polymer did not arise till very recent times. 

To summarize, the chemistry occurring at the surface of a photo-excited semiconductor is based on the radicals formed from 02, H20, and electron-rich organic compounds. Also note that cations in aqueous solution can be directly reduced by conduction band electrons provided that the redox potentials of these cations are adequate (i.e., lying below the conduction band energy) (6). 

Nevertheless, the discovery that high electronic conductance could be induced in organic polymers is a most important event in electro-organic chemistry, and progress in research to develop the electrochemistry of such compounds (which began in the 1980s) is still far from reaching the exponential part of its S-shaped plot. 

There are some (Heinze, 1996) to whom the polaron explanation of the ionic introduction of electronic conductivity in organic compounds is specious The roughness factor of 400 would limit the degree of penetration of ions into the interstices of the polymer. However, Li+ or even CIOJ is of course much smaller than the test molecules (large dye molecules) which are generally used to probe the real area. Thus, one might conceive of a model of the polymer that is all fibers, the intercalation being all pervasive. It is obvious that an Li+ ion adsorbed on the surface of a fiber will promote an electron that may indeed be free to move under a field, i.e., to conduct. 

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. 

Also organic compound like metal phthalocya-nines [xxvi] and electronic conducting polymers [xxvii] are used as gas-sensitive layers in resistive sensors, POSFETs (polymer oxide silicon field-effect transistors), heterojunction diodes (e.g., polyrrole on... 

Although organic compounds by and large have very poor electronic conductivity with values of specific conductivity [Pg.554]

In class I mixed valence species, electron transitions between sites are energetically difficnlt to accomplish. In the sohd state, these materials are generally insnlators. However, with class II and class III compounds, electron transfer becomes much easier so that conducting and superconducting materials are obtained (see Sulfur Organic Polysulfanes). 

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