Cyclic voltammetry high resistive conditions

ABSTRACT. Several aspects of electrochemistry at ultramicroelectrodes are presented and discussed in relevance to their application to the analysis of chemical reactivity. The limits of fast scan cyclic voltammetry are examined, and the method shown to allow kinetic investigations in the nanosecond time scale. On the other hand, the dual nature of steady state at ultramicroelectrodes is explained, and it is shown how steady state currents may be used, in combination with transient chronoamperometry, for the determination of absolute electron stoichiometries in voltammetric methods. Finally the interest of electrochemistry in highly resistive conditions for discussion and investigation of chemical reactivity is presented. 

Figure 13 shows a typical electrochemical response of graphite and disordered carbon electrodes (a, b, respectively), related to the diffusion and accumulation of hthium in the bulk carbon particles. The differential capacitance of these electrodes is nicely reflected by slow scan cyclic voltammetry. As already discussed in detail [105-107], the peaks in the CV of Figure 13a (4 sets of redox peaks) reflect phase transition tetween Li-graphite intercalation stages (indicated in the figure), and they correspond to the plateaus in Figure 11a Their shape depends on the resolution of these experiments. The resolution of the voltammetric response of these electrodes depends on the thickness of the electrode, the resistance of the surface films, and the potential scan rate [108]. The best resolution in electrochemical studies of these systems is obtained in experiments with single particles [109-110]. Such experiments, however, are difficult and require special apparatus. Using composite electrodes, a condition for meaningful results, is a situation in which the electrodes are thin and the solution reaches the entire active mass, and, in fact, aU the particles interact in parallel with both the current collector and solution species. In such a situation, the composite electrodes can be considered as an array of microelectrodes, and then toe resolution of the measurements and their reliability are high.

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