Electrode swelling

However, that is observed only within the range of the so-called safe voltage window of operation - for alkaline aqueous electrolytes it covers the range of l,12-l,24v, and depends on material purity and current density. Exceeding this voltage causes gassing, electrode swelling and loss of electric contact between particles in the electrode volume. 

Cell or stack aging is indicated by a loss in overall performance due to diminishing capacitance, slower charging and discharging rates, and increased series resistance. In addition, these signs can also be associated with macroscopic phenomena, for example, localized detachment of electrode materials from the metallic collector through electrode swelling, gas evolution, and loss of elements involved in faradic reactions. 

Eor the Gray-King coke-type assay test (91,92) coal is heated in a retort tube to 600°C and the product coke is compared to a series of standard cokes. Eor a strongly swelling coal, enough anthracite or electrode carbon is added to the coal to suppress the swelling. This method is primarily used in Europe. 

With respect to pH sensitivity and an adequate speed of response (time constant r = RC where R is the resistance of the measuring circuit and C the capacitance of the electrode), a certain degree of superficial swelling is needed however, the gel layer thus formed should remain thin in order to minimize the solubility of the glass and to guarantee sufficient durability of the electrode. In this respect lithium barium silicates offer an attractive compromise32. 

When the gel is placed so as to be separated from the electrodes, the pH of the solution affects the degree of deformation. In alkali and acid regions, both PAANa and PAA gels swell at the anode side on application of electric fields. 

In addition, these authors have discussed the deformation of a PAANa gel placed in contact with the cathode in a dc electric field. Because there is no interaction between the gel and the cathode, the gel swells at the anode side, as observed in the gel separated from the electrodes. It is concluded that the gel also swells at the anode side under an electric field. 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

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