Electroactive impurity, influence

If we measure a residual current-potential curve by adding an appropriate supporting electrolyte to the purified solvent, we can detect and determine the electroactive impurities contained in the solution. In Fig. 10.2, the peroxide fonned after the purification of HMPA was detected by polarography. Polarography and voltammetry are also used to determine the applicable potential ranges and how they are influenced by impurities (see Fig. 10.1). These methods are the most straightforward for testing solvents to be used in electrochemical measurements. 

Figure 8. Influence of an electroactive impurity on the interfacial potential-dye concentration relationship. The x axis is the logarithm of the dye concentration, the y axis is the logarithm of the ratio of water volume to nitrobenzene volume, and the z axis is the difference between interfacial potential with and without the impurity. Standard potentials of transport for the impurity cation A (p — — 100 mV and for the anion A (p — +100 mV c = 1 X 10 5 mol/L.

The existence of a small degree of non-stoichiometry (and thus mixed valence states for iron) may explain why this system is electroactive, given that both end members have such poor electronic conductivity. It should be noted, however, that kinetic effects, surface impurities, and the presence of defects [179,182-184] also influence the shape of the Li/LiFeP04 discharge profile. This makes it hard to... 

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