Semiconductor/electrolyte interface, Gerischer

In contrast to metal electrodes, for a semiconductor-electrolyte interface most of the potential drop is located in the semiconductor making it difficult to study interfacial processes using potential perturbation techniques [11,20,55,58,60-65,75-78]. H. Gerischer [76] proposed a model in which electrons and holes are considered as individual interfacial reactants. Distinct and preferential electron transfer reactions involve either the conduction band or valence band as dependent on the nature of the redox reactants of the electrolyte, with specific properties dependent upon the energy state location. 

Salvador [100] introduced a non-equilibrium thermodynamic approach taking entropy into account, which is not present in the conventional Gerischer model, formulating a dependence between the charge transfer mechanism at a semiconductor-electrolyte interface under illumination and the physical properties thermodynamically defining the irreversible photoelectrochemical system properties. The force of the resulting photoelectrochemical reactions are described in terms of photocurrent intensity, photoelectochemical activity, and interfacial charge transfer... 

Solar energy conversion in photoelectrochemical cells with semiconductor electrodes is considered in detail in the reviews by Gerischer (1975, 1979), Nozik (1978), Heller and Miller (1980), Wrighton (1979), Bard (1980), and Pleskov (1981) and will not be discussed. The present chapter deals with the main principles of the theory of photoelectrochemical processes at semiconductor electrodes and discusses the most important experimental results concerning various aspects of photoelectrochemistry of a semiconductor-electrolyte interface a more comprehensive consideration of these problems can be found in the book by the authors (Pleskov and Gurevich,... 

In this section, we first consider a general model of the faradaic processes occurring at the semiconductor-electrolyte interface due to Gerischer [11]. From Gerischer s model, using the potential distribution at the interface, we may derive a Tafel-type description of the variation of electron transfer with potential and we will then consider the transport limitations discussed above. We then turn to the case of intermediate interactions, in which the electron transfer process is mediated by surface states on the semiconductor and, finally, we consider situations in which the simple Gerischer model breaks down. 

The exponential dependence of the current on applied potential for p-type silicon and highly doped n-type silicon in the pore formation regime can be analyzed using the Gerischer model of the semiconductor/electrolyte interface [77]. In the absence of surface states, the hole current for a p-type semiconductor is given by ... 

Charge transfer processes at semiconductor-electrolyte interfaces in connection with problems of catalysis. H. Gerischer, Surface Science 18, 97 (1969). 

Gerischer H. (1984), Effects of the Helmholtz layer capacitance on the potential distribution at semiconductor electrolyte interface and the linearity of the Mott-Schottky plot , J. Electrochem. Soc. 131, 2452-2453. 

Sparnaay M. J., Gerischer H., Butler J. N., Memming R. and Los J. (1969), Discussion of charge bansfer processes at semiconductor-electrolyte interfaces in connection with problems of catalysis . Surf. Sci. 18, 121. 

The pressing need for a detailed description of the semiconductor-electrolyte interface is becoming increasingly apparent Gerischer has given an excellent and timely general account of photoassisted interfacial electron transfer, in which particular attention is paid to the role of surface states at the semiconductor-electrolyte interface. Kowalski et al have used the SCF-A -scattered wave method to calculate the position and character of surface states at various characteristic interfaces, and then used these results to develop a model of photoelectrolysis at Ti02 surfaces. 

Other Semiconductors. Gerischer,41 in a very helpful paper on electrochemical photo and solar cells, has explained the mode of action of the semiconductor-electrolyte interface (when the semiconductor is in its depletion mode) as a Schottky barrier, and how this can lead to separation of hole-electron pairs... 

In 1839, Becquerel [1] first discovered the PV phenomena in electrochemical systems. Brattain and Garret [2, 3] were pioneers explaining aspects of the properties of semiconductor-electrolyte interfaces. Fujishima and Honda [4] reported the first indication of a practical application of a photoelectrochemical (PEC) system in 1972. This paper sparked off a wave of investigations all over the world. It would be appropriate, however, to suggest that the interest in photoelectrochemistry of semiconductor blossomed only after the pioneering work of Gerischer [5] and Myamlin and Pleskov [6]. These studies... 

Figure 9.26 Schematic diagrams for energy vs. density of states for semiconductor-electrolyte interface (SEI). (a) An ideal interface described by Gerischer s model, where direct transfer of charge between bulk energy states of semiconductor and redox takes place, and (b) transfer of charge mediated through surface states. The hashed curves represent filled states. 2 represents solvent reorganization energy from Marcus theory. Adapted from reference (40).

Gerischer and Nozik have stated that the formation of an inversion layer can also cause a shift of band edges. For small bandgap semiconductors, this effect may be more important. The formation of an inversion layer has been shown experimentally at several semiconductor/electrolyte interfaces. " ... 

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