Subject interfacial charge transfer

There is therefore one essential conclusion from the comparison of electrodic e-i junctions and semiconductor n-p junctions The symmetry factor P originates in the atomic movements that are a necessary condition for the charge-transfer reactions at electrode/electrolyte interfaces. Interfacial charge-transfer processes that do not involve such movements do not involve this factor. By understanding this, ideas on P become a tad less underinformed. Chapter 9 contains more on this subject. 

Thus, it may be seen that, by reducing the particle radius, it is possible to obtain systems where transit from the particle interior to the surface occurs more rapidly than recombination, implying that quantum efficiencies for photoredox reaction of near unity are feasible. However, the achieving of such high quantum efficiencies depends very much upon the rapid removal of one or both types of charge carrier upon their arrival at the semiconductor surface, underlining the importance of the interfacial charge-transfer kinetics. This is the subject of the next section. 

The effective valence for dissolution increases from a value of about 2 at low current density to a value of 4 in the electropolishing domain [59-63, 67-69], as shown in Fig. 10a [63] and Fig. 10b [67]. While gravimetric determinations may be subject to a number of errors derived from oxide formation and hydrogen adsorption, these data show that the dissolution process associated with pore formation, in the absence of illumination, proceeds through interfacial charge transfer reaction involving two... 

It is now necessary to take a more unified view by considering situations in which the rate of the electrodic process at the interface is subject both to activation and to transport limitations. One refers to a combined activation-transport control of the electrodic reaction. Under such conditions, there will be, in addition to the overpotential T)c produced by the concentration change (from c° to c ) at the interface, an activation overpotential because the charge-transfer reaction is not at equilibrium. The total overpotential rj is the difference between the interfacial-potential difference... 

Interfacial electrochemistry is about electric charges at interfaces between phases, one of which is an electron conductor and the other an ion conductor. The kinetic part of the subject is about the rate at which these charges transfer across the interphase. However, this definition clearly embraces two limiting cases. 

The interfacial structure and charge-transfer mechanism of two immiscible electrolyte solutions, as revealed by the kinetics of the charge-transfer processes, is the subject of Chapter 5 by Z. Samec and T. Kakiuchi. Theoretical and experimental advances made over the last 10 to 15 years in the study of ion- and electron transfer are systematically and critically reviewed. 

This fact has a large implication for material science, because as material science deals predominantly with interfacial phenomena [i.e., the stability and material properties are controlled by interfaces (external or internal)], there is an electrical character about these happenings and thus they are subject to electrochemical science and electrochemical arguments. The main difference in an electrochemical (compared with a chemical) reaction, of course, is that an electronic charge transfer occurs in the electrochemical one. However, there are other differences which do not meet the eye. Electrochemical reactions always occur in two different locations. One cannot have an electrode operating in isolation in a solution. It always must be adjoined to another electrode, by an external circuit, in which electrons pass through a wire, and at this other electrode another electrochemical reaction takes place (Figure 2). 

In label-free or direct immunoassays, antibodies are immobilized on the sensor surface plate and subjected to the binding interaction with the antigen of interest. Upon specific molecular recognition of the ant n by the immobilized capture antibody, there will be changes in the interfacial charge, current, capacitance, impedance, mass, and thickness at the immunosensor surface, which in turn has a direct effect on the electron transfer... 

As it gives a nice and relatively simple illustration of the use of various characterization methods, we will discuss the subject of electron-hole recombination dynamics in the next sections, taking the n-GaAs photoanode as the main example. More complicated topics - related to interfacial transfer of photogenerated charge carriers - are discussed in Section 2.1.3.3. 

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