Faradaic and capacitive currents

Electrochemical interfaces modified with inorganic NPs behave as nanoelectrode ensembles. In principle, the electroanalytical detection limit at a nanoelectrode ensemble can be much lower than that at an analogous macrosized electrode because the ratio between the faradaic and capacitive currents is higher.19-23... 

Ever since Feldberg s original model separating faradaic and capacitance current associated with a conducting polymer that behaves like a porous metal, " there have been various attempts to rationalize experimentally the nature of the current at a conducting polymer. Apart from impedance models, there has not been so much effort placed on modeling the system. Experimental efforts to examine processes at conducting-polymer-modified electrodes consisted of voltam-metry, " impedance, " and quartz crystal microbalance. However the... 

Pulse and square wave voltammetry are much better candidates than linear sweep or cyclic voltammetry for incorporation into a chemical sensor. The primary reason for this is the ability of the former techniques to discriminate between faradaic and capacitative currents. When a potential pulse is applied to an electrode, the capacitative current that flows is proportional to the... 

Fignre 18. Decrease in faradaic and capacitive current with elapsed time from the imposition of a potential pulse ( =Faiadaic current / = Capacilive current... 

Smirnov, W., Yang, N., Hoffman, R. et al (2011) Integrated all-diamond ultramicroelectrode arrays optimization of Faradaic and capacitive currents. Anal Chem., 83, 7438. 

The Faradaic and capacitive components of the current both increase with the scan rate. The latter increases faster (proportionally to v) than the former (proportionally to y/v), making the extraction of the Faradaic component from the total current less and less precise as the scan rate increases, particularly if the concentration of the molecules under investigation is small. The variations of the capacitive and Faradaic responses are illustrated in Figure 1.7 with typical values of the various parameters. The analysis above assumed implicitly that the double-layer capacitance is independent of the electrode potential. In fact, this is not strictly true. It may, however, be regarded as a good approximation in most cases, especially when care is taken to limit the overall potential variation to values on the order of half-a-volt.10 13... 

Section 4.2.4, the faradaic currents fall off more slowly with time in that they decrease as a function of the square root of time (i oc l/V ). Consequently, the time dependence is a diagnostic test to discriminate between faradaic and capacitive (i.e. non-faradaic) currents. 

Residual currents, also referred to as background currents, are the sum of faradaic and nonfaradaic currents that arise from the solvent/electrolyte blank. Faradaic processes from impurities may be practically eliminated by the careful experimentalist, but the nonfaradaic currents associated with charging of the electrode double layer (Chap. 2) are inherent to the nature of a potential sweep experiment. Equation 23.5 describes the relationship between this charging current icc, the double-layer capacitance Cdl, the electrode area A, and the scan rate v ... 

What is meant by the terms Faradaic current and capacitive current ... 

Pulse techniques improve detection limits since they benefit from the different variation of diffusion and capacitive current intensities with time when carrying out measurements at the pulse end, the capacitive current is practicably negligible, the value of the Faradaic current still being significant (see eqn [3] and Figure 3). 

Porosity effects during the charging process have long been considered in discussions of the faradaic and capacitive contributions to the current, especially in the case of electronically conducting polymers. For instance, the peaks of cyclic voltam-mograms were attributed to the faradaic process while the plateaus of the cmrent were considered to be an indication of the capacitive term [99,105,106,211-215]. However, this straightforward analogy to the metal/solution interface does not work in reality the obviously faradaic process of the redox transformation of the redox species in the surface layer does not lead to a direct current, unlike similar reactions for solute species. 

The analysis of the faradaic and charging current components requires the simulation of differential equations when the two time constants become similar and when the interfacial capacitance exhibits CPE character [104]. 

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