Cross-linking polymer-modified electrodes

Carbon composite electrodes have also been made by cross-linking a polymer after mixture with powdered graphite or carbon black [30]. In some cases, these electrodes incorporate modifiers such as zeolites to affect reactivity. As... 

The adsorption of polymers, poly(vinyl pyridine) or poly(acrylonitrile) either to coordinate metal atoms or to adsorb biopolymers has been used to prepare chemically modified electrodes for immobihzation of enzymes either by physical or by chemical adsorption (carrier binding), cross-linking, and entrapping at lattice sites or in microcapsules [43]. A wide application of these types of electrodes has been made for electrochemical reactions of biological interest [44]. 

The interest in chemically modified electrodes that developed during the 1980s resulted in the synthesis of many redox-active polymers and surface-confined redox couples, including ferrocenes. These were subsequently adapted to electrochemical biosensors, and both surface-confined and polymeric ferrocenes have been widely used. Typically, polymeric ferrocenes that have been exploited in this way include poly(vinyl) ferrocenes, polysiloxanes, polyethylene oxide with covalently attached ferrocenes, poly(allylamine) ferrocene, and polacrylamide ferrocene cross-linked hydrogels." ... 

Electric Fuel Ltd. which was modified by the inclusion of an anionic polymeric membrane. The polymeric membrane was composed of interpenetrated network of two polymers. A polycationic cross-linked polyepichlorohydrin was used as the ionic network and poly(hydroxyl ethyl methacrylate) was used as the structural polymer to provide mechanical stability and reduced swelling. The cyclic performance of the cell using a saturated aqueous solution of LiOH and untreated ambient air is shown in Fig. 13b. Relatively high capacities were obtained however, on cycling the lithium metal formed a porous or columnar deposit that increased in volume and caused a loss of contact between the hthium metal and O-LATP [50]. The hfetime of this composite air electrode when used with untreated air in 5 M or saturated LiOH aqueous solution was increased firom 10 h without the anion exchange membrane to 1000 h. 

In 1955, it was demonstrated that redox polymers could be cross-linked into redox hydrogels [62]. Since the advent of the wired GOx anode described in the previous section, BFC electrodes using an osmium redox polymer hydrogel have appeared extensively in the literature [63-66]. Redox polymer mediators based on species other than osmium have also been demonstrated in recent BFC systems. Redox polymers based on ferrocene, for example, are a continuing area of research [56]. Sato et al. reported a glucose dehydrogenase BFC with a redox mediator based on vitamin K (see panel E of Table 9.1) in 2005 [57]. Six years later, Meredith et al. reported that a polyethylenimine polymer modified with 3-(dimethylferrocenyl)propyl redox centers is a durable and efficient mediator to GOx despite being a neutral molecule (see panel F of Table 9.1) [58]. 

This discussion shows that the gel electrolyte must match the use of the battery, requiring optimization of the composition of the gel polymer electrolyte, the supporting salt and its concentration, and the solvent. PAN gel electrolytes made using different solvents, lithium salts, and composition will display different behaviors with respect to the ionic conductivity, lithium-ion transference number, electrochemical window, cyclic voltam-metric behavior, and compatibility with electrodes. Table 11.1 lists the ionic conductivity at room temperature of some gel electrolytes based on PAN. Because the PAN chain contains highly polar -CN groups, which exhibit poor compatibility with lithium metal electrodes, the passivation of the interface between the gel electrolyte and lithium metal electrode is crucial. At the same time, PAN has a high crystallization tendency. At elevated temperatures, the liquid electrolyte and plasticizer will separate therefore, the polymer is modified, mainly by copolymerization and cross-linking. 

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