Electrode materials voltage limits

By applying a specific voltage on the reference electrode it is possible to compensate non-linearities during exposure to higher gas concentrations and/or to increase the sensitivity and selectivity to different gas species. The fifetime of this kind of electrochemical cell is limited by the consumption of electrode material. 

However, there are still some drawbacks in the use of CNT that need to be solved for practical applications. Not only large reversible capacities but also large irreversible capacities have been reported on CNTs [179, 183]. Such irreversible capacity together with the lack of voltage plateau during lithium extraction (hysteresis) limits the use of nanotubes as electrode material in LI Bs. However, an active study (based on CNT treatments, surface modification, use of CNT nanocomposite matrices, etc.) is being carried out in order to overcome such difficulties [184]. 

Figure 5.19 Voltage limits for various electrode materials in several solvents (TEAP = tetroethylammonium perchlorate).

Figure 5.19 summarizes the positive and negative voltage limits for some commonly used electrode materials in several solvents. Wherever possible, the data for a particular solvent has been referred to a single reference electrode. Absolute values of the electrode potential for different solvent systems cannot be directly compared, however, because they are often referred to different reference electrodes and because of the uncertainty in our knowledge of junction potentials between different solvent systems. 

Potentiometry is a method of electroanalytical measurement in which the equilibrium voltage of the cell consisting of an indicator electrode and a proper reference electrode is measured using a high-impedance voltmeter, i.e., effective at zero current. The potential of the indicator electrode is a function of particular species present in solutions and their concentration. By judicious choice of electrode material, the selectivity of the response to one of the species can be increased, and thus, interferences from other ions can be minimized. The method allows the determination of concentrations with detection limits of the order of 0.1 pmol per liter, although in some cases, as little as lOpmol differences in concentration can be measured. 

Mercury is a liquid under normal experimental conditions and thus presents a smooth homogeneous surface to the solution. It is a good electrical conductor and provides a surface for the required electrode reaction. A good electrode material provides a high voltage limit in anodic and cathodic directions and thus a wide voltage window for analysis. 

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