Double-layer capacitance mechanism

However, the storage capability from the fiber electrode based on bare carbon nanomaterial is poor owing to the double-layer capacitance mechanism. Therefore, pseudocapac-itive materials, such as metallic oxide and conducting polymer can also be incorporated into the CNT fiber to enhance the capacitance. For example, CNT/PANI composite fibers... 

Understanding the oxidation mechanism is important. Impedance spectroscopy was recently used to study methanol electrooxidation, and kinetic parameters can be deduced from impedance spectra. Figure 6.58 shows an equivalent circuit that was developed for methanol oxidation on a Pt electrode, but which is common for all electrochemical reactions. In this circuit, a constant phase element was used rather than a double-layer capacitance, since a CPE is more realistic than a simple capacitor in representing the capacitive behaviour. 

I o expressed as mA/lOO gF of double-layer capacitance, hence, real area. Mechanisms I and II were defined earlier in this chapter. From Arikado et al. (357). 

Various other kinds of departure from (5.8.7) and (5.8.8) can be observed. See Chapter 12 for a discussion concerning the diagnosis of prominent homogeneous reaction mechanisms. The large body of chronoamperometric theory for systems with coupled chemistry can be used directly to describe chronocoulometric experiments, because there are no differences in fundamental assumptions. The only differences are that the response is integrated in chronocoulometry and that the chronocoulometric experiment manifests more visibly the contributions from double-layer capacitance and electrode processes of adsorbates. 

The popularity of the cychc voltammetry (CV) technique has led to its extensive study and numerous simple criteria are available for immediate anal-j sis of electrochemical systems from the shape, position and time-behaviour of the experimental voltammograms [1, 2], For example, a quick inspection of the cyclic voltammograms offers information about the diffusive or adsorptive nature of the electrode process, its kinetic and thermodynamic parameters, as well as the existence and characteristics of coupled homogeneous chemical reactions [2]. This electrochemical method is also very useful for the evaluation of the magnitude of imdesirable effects such as those derived from ohmic drop or double-layer capacitance. Accordingly, cyclic voltammetry is frequently used for the analysis of electroactive species and surfaces, and for the determination of reaction mechanisms and rate constants. 

The frequency-response behavior is interpreted in an analytical, mathematical manner, based on electrochemical kinetic reaction mechanisms, together with a double layer capacitance. It must be emphasized that a given reaction mechanism dictates the equivalent circuit expected of it However, fitting the experimental data to the theoretical impedance behavior is generally difficult and hence, great... 

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