Activation blocked electrodes

Rogozhnikov [95] has analyzed the impedance response of an Ag electrode in cyanide solutions. The impedance spectra have shown time evolution of the surface blocking. Time evolution of the active Ag electrode area after immersion in CN containing solutions has been analyzed by Baltrunas et al. [96]. A time of20-60 s was required for settling down the blocking (dependent also on CN concentration). 

Caprani et al. [104], defining the cut-off frequency as the intersection of the low and high-frequency asymptotes, as indicated on Fig. 10.18, have given an approximate method to deduce the size of active sites on a partially blocked electrode from the ratio of the two cut-off frequencies ... 

Figure 15.5 Concentration field over a partially blocked electrode. The active parts of the electrode are displayed in gray and the concentration is dimensionless d = c/c(oo). (Taken from Caprani et al. )...

For a partially blocked electrode, the diagrams show two characteristic frequencies and, whatever the mean rotation speed Ci, fall onto a single curve when plotted versus a dimensionless frequency p = cofCi, where co/ln is the frequency modulation. The high-frequency domain is characteristic of the response of the sum of the active sites, as if they were not coupled by their diffusion layers. 

This result is phenomenologically based on the theoretical analysis given by Deslouis et al. for the frequency response of a small electrode to a flow modulation. The response of a partially blocked electrode surface was obtained from numerical calculations. The main result of this approach is that, at vairiance with the case of a uniform active disk electrode, such a surface shared between active and passive sites displays two characteristic frequencies, one in the low-... 

Activation of Blocked Electrodes by Competitive Adsorption of a Catalyst... 

In the SPS-PEG-C1 system the central role of the SPS-based catalyst is to open channels in the PEG-C1 blocking layer, thereby allowing the Cu2+/Cu+ reaction to proceed unhindered. This effectively accelerates the metal deposition reaction without requiring any change in the Cu2+/Cu reduction mechanism, that is, activation of a blocked electrode. Accelerated copper deposition occurs in the proximity of SPS adsorption sites. Chloride adsorbed in neighboring sites may also... 

An electrochemically heterogeneous electrode is one where the electrochemical activity varies over the surface of the electrode. This broad classification encompasses a variety of electrode types [1, 2] including microelectrode arrays, partially blocked electrodes, electrodes made of composite materials, porous electrodes and electrodes modified with distributions of micro- and nanoscale electroactive particles. In this chapter, we extend the mathematical models developed in the previous chapter, in order to accurately simulate microelectrode arrays. Fbrther, we explore the applications of a number of niche experimental systems, including partially blocked electrodes, highly ordered pyrolytic graphite, etc., and develop simulation models for them. 

Since the subject of SCP is an extremely broad one, it is necessary to limit its scope for the present discussion. First, no further consideration will be given to ordinary dielectric response, although electrical behavior arising from the presence of electric dipoles may often be confused with SCP behavior and vice versa, especially in blocking electrode situations and especially when a distribution of relaxation times is invoked to explain putative dielectric response behavior. Incidentally, it is worth mentioning that the expressions frequently used to describe a distribution of thermally activated relaxation times are inappropriate when applied over a range of temperatures and when the enthalpy involved in the thermally activated dipole behavior is itself distributed. ... 

Raleigh [25] also studied the potentiostatic transient response of cells of type V. Under these conditions, Eq. (7) applies. Silver bromide equilibrated with gaseous bromine conducts electronically via electron holes [26]. Under these conditions, the activity of silver at the blocking electrode is. 

The so-called partially blocked electrodes containing active and passive sites can be also treated as microelectrode arrays, when the charge transfer is utterly impossible at the passive area. Simulations of their electrochemical behavior under linear potential sweep conditions showed [15] that a good agreement... 

In this case, the gaps between electroactive sites will not be filled by expanding diffusion layers as quickly as in areas where all electrodes are active, and so the current is proportionally reduced from that predicted by Case 4 theory. See also the discussion on partially blocked electrodes (Problem 6.8). 

W Wagner s DC polarisation cell. The negative electrode is a reversible electrode and the activity of M is unity at the MIP MX interface. A DC potential E is applied so that the activity of M at the P MXIion-blocking electrode interface is exp(-EFIRT) at steady state. Boltzmann statistics for an ideal solid solution are assumed for the electrons and electron holes in P MX. The concentration of electrons and electron holes are denoted by C and C respectively. The superscript zero denotes that the concentration in P /MX is at equilibrium with M. 

Like selectively blocking electrodes grain boundaries can also exhibit a filter-effect. This is due to changes of the transference number at grain boundaries. Hence the grain boundary is not only electrically active due to its own resistance and capacitance, also a bulk polarization (as discussed above) can be induced as was measured by impedance spectroscopy and d.c. experiments for SrTiOa [613,307, 614]. 

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