Electroconductive membrane film

Before discussing these aspects we have to clarify the state of BP on the surface of the positive electrode material. We measured the depth profile of thecobalt positive electrode after 200 cycles by Auger electron spectroscopy (AES), as shown in Fig. 19.18. Thickness of the electroconductive membrane (ECM) film is estimated by the AES depth profiles atomic concentration of cobalt and oxygen. It reaches 90% with and without BP addition as shown in Fig. 19.18. The observed ECM film thicknesses are as follow in the basic electrolyte, the ECM film thickness was 45 A in the functional electrolyte containing 1% of BP, the ECM film thickness was 68 A in the functional electrolyte having 2% of BP, the ECM film thickness was 214 A. These results clearly show that the ECM film thickness on the positive electrode increased with the amount of BP. Based on these results, the cycle life of the basic electrolyte cell should be better, but the cells with the functional electrolyte containing the small amount of BP (the film thickness of 68 A) afford the best results. 

The electrochemical properties and cyclabiLity of the additives have been investigated. The additives are foimd to decompose on the cathode to form a very thin film. This resulting novel-t) e thin surface film has been addressed as an electroconductive membrane... 

CHEMFET devices or chemically sensitive field-effect transistors are potentiometric devices in which the metal layer of a solid-state insulated gate field-effect transistor (IGFET) f29] is replaced with a chemically sensitive electroconductive polymer membrane film. Changes in polymer membrane potential modulate the drain impedance of the space-charge region beneath the insulator. The result is a change in drain current /o under a fixed drain voltage Vd- The potential of the membrane may be modulated in the standard way (as in po-tentiometry, above) or may be modulated by an inert electrode placed beneath the film (but isolated from both the source and drain electrodes) and connected to an efficient electrode for the candidate analyte [30]. 

Another approach is to occlude into the electroconductive polymer film a second polymer that contains functionalities to which indicator molecules may be conveniently covalently attached. Guiseppi-Elie and Wilson [180] coelectropolymerized pyrrole and 3-(l-pyrrolyl)-propionic acid in the presence of poly(styrenesuIfonic acid) and polyvinylamine (PVAm). Incorporation of the PV Am into the polymer film confers free primary amines on the surface of the film. Using aqueous cross-linking chemistry Guiseppi-Elie and Wilson conjugated the suc-cinamide ester of NHS-LC-biotin to the primary amine sites of the polymer surface. A simple variation on this theme can produce a wide variety of chemical and biological sensors. The occlusion of human serum albumin (HSA) [154] or bovine serum albumin (BSA) by electropolymerization in electroconductive polymer can also provide —COOH, —NH2, and —SH sites for the convenient attachment of indicator molecules. Likewise, macromolecular counteranions may be functionalized prior to or following occlusion into the CEP membrane. 

Other methods to confer specificity include ion exchange and the deposition of metallic islands and semiconductor particles. Ion exchange occurs spontaneously between counteranions or countercations (in the case of macromolecular anions) and ions that bathe the CEP membrane. Repeated redox cycling encourages the exchange of mobile ions within the film with ions drawn from the solution in which the film is bathed. This becomes a convenient means to introduce catalytic ions into CEPs to confer a measure of specificity [29,126,183]. Another approach used has been to deposit islands of catalytic metal onto the surface or within the electroconductive polymer membrane [187-190], Wrighton et al. [11] deposited platinum particles. Semiconductor particles have also been used [174]. 

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