Electrode charge transfer

Figure 6.19. Simplified equivalent circuit for single-electrode reaction [e.g., Eq. (6.6)] Qi, double-layer capacitance of test electrode charge-transfer resistance of electrode reaction.

We have thus far talked about the chemisorption of ions at the semiconductor/electrolyte interface and charge transfer in the semiconductor surface layer. The main charge transfer process of interest is the transfer of electrons and holes across the semiconductor/electrolyte interface to the desired electrolyte species resulting in their oxidation or reduction. For any semiconductor, electrode charge transfer can occur with or without illumination and with the junction biased in the forward or reverse direction. 

Under closed-circuit conditions, the electrochemical reactions involve a number of sequential steps, including adsorption/desorption, surface diffusion of reactants or products, and the charge transfer to or from the electrode. Charge transfer is restricted to a narrow (almost one-dimensional) three-phase boundary (tpb) among the gaseous reactants, the electrolyte, and the electrode-catalyst. 

The surface layer formation is a crucial phenomenon as it affects the electrode charge transfer rate. Low-conductivity films determine high electrode overvoltages and lower battery performance. The charge transfer resistance can be monitored by impedance spectroscopy measurements, which represent a useful tool for the in-situ characterization of resistive and capacitive processes occurring in different time scales (1 mHz-100 kHz) [80]. 

Thus far, only much simpler idealizations of the general problem have been solved, and in Section 2.2.3.3 we shall discuss some of their results. When the simpler solutions are thought to be adequate, they may be used to analyze experimental data and obtain estimates of such interesting quantities as electrode charge-transfer reaction rate. Many of the simpler solutions can be represented exactly or... 

As shown in Fig. 3.10, for the reaction to occur A has to be transported to the electrode, charge transfer possibly via intermediates occurs resulting in product B, which is then transported back into the bulk of the electrolyte. The rate of difiFusional transport of A to the electrode (see Section 2.3) is ... 

In the low current density range, the contribution of mass transfer polarization is negligible and the electrode charge transfer and membrane resistance polarization are significant. In this case, Equations 1.130 and 1.131 can be simplified into Equations 1.132 and 1.133, respectively. 

An electrochemical reaction involves at least the following steps transport of the reactants to the surface of the electrode, adsorption of the reactants onto the surface of the electrode, charge transfer through either oxidation or reduction on the surface of the electrode, and transport of the product(s) from the surface of the electrode. The purpose of the electrochemical characterizations is to determine the details of these steps. 

Note I A primary radical may be formed by the action of heat, irradiation or electrode charge transfer. 

On the other hand, if the charge transfer is totally irreversible, the starting species cannot be regenerated via an opposite electrode charge transfer, so that no faradic current flows once reversing the potential scan direction. 

Hj/Oj feed, where cathodic charge transfer is present and the catalyst layer can be represented by a transmission-line model combining electrode charge-transfer reaction, electrolyse resistance, and double layer... 

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