Gerischer’s model

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. 

Figure 18. Density of states as a function of electron energy (Gerischer s model).24...

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 s distribution curves can be interpreted as representing the energy dependence of the electron transfer rate constants involving the reduced and oxidized species. Only a few electrochemical studies have attempted to evaluate the model and quantify the distributions and reorganizational parameters [17, 18]. Nevertheless, it has become common practice to draw a pictorial representation of the distributions when discussing interfacial electron transfer kinetics relevant to dye sensitization. 

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