Interfacial electronic coupling

Dowdy CE, Leopold MC. Enhanced electrochemistry of nanoparticle-embedded polyelectrolyte films interfacial electronic coupling and distance dependence. Thin Solid Films 2010 519 790-796. 

Another area that is subject to significant interest concerns substrate variations, for example comparisons of lET processes for Ti02 and ZnO substrates, which have been carried out both experimentally and theoretically. Calculations suggest that the interfacial electronic coupling can also be sufficiently strong to mediate ultrafast lET for ZnO, but there may be other differences that are important experimentally for the ZnO performance, such as surface stability and screening of injected charges. ... 

Variations in interfacial electronic coupling of different electronic levels of a pyrene chromophore interacting with a Ti02 nanoparticle via an ethynylene-IPA spacer + anchor unit. The ground state HOMO level shows weak interaction with the Ti02 substrate bands, while there is strong interfacial electronic interaction of the unoccupied adsorbate levels involved in photoinduced electron injection. ... 

As discussed above, interfacial electron transfer at molecule-semiconductor interfaces may in many cases be limited mainly by the interfacial electronic coupling, rather than requiring structural activation processes. From a multiscale perspective that attempts to split complex materials processes into separable problems, this can be taken advantage of by performing electron dynamics simulations on structures that have been previously determined from either quantum chemical calculations or MD simulations. 

Tafel s law is the primary law of electrode kinetics, in the sense that Arrhenius law is the basic law of thermal reaction. It applies universally to all processes that are controlled in rate by the interfacial transfer of electrons or by a rate-determining surface reaction that may be coupled to the interfacial electron [Fig. 9.25(a)]. Redox reactions without surface intermediates demonstrate Tafel s law well [Fig. 9.25(b)]. 

A number of electrode reactions have been carried out on carbon surfaces containing preadsorbed redox polymers of varying thicknesses (thus designing a new electrode surface). In respect to the oxidation of Fe2+, a protonated vinyl film has been used containing (IrCI6)3 /4- as the redox couple. The reaction rate at a given overpotential per geometric unit area is increased. There is dual control of the reaction rate between interfacial electron transfer and diffusion of the Fe2+ reactant into the film. 

The interfacial kinetics processes at semiconductor/liquid contacts for reactions with one-electron, outer-sphere, redox species can be understood in a conventional theoretical framework. The rate constant can be broken down into a term representing the attempt frequency, Vn, a term representing the electronic coupling between the electrons in the conduction band of the semiconductor and the redox acceptor state, k x, and a term representing the nuclear reorganization energy in the transition state from reactants to products, For outer-sphere electron transfer processes, the nuclear term is well-known to be ... 

Zaban and co-workers reported the use of chemical redox titrations to measure the potential of sensitizers bound to Ti02 [136], An unexpected result from these studies is that redox couples that are not pH sensitive in fluid solution become pH dependent when bound to the semiconductor surface. The magnitude of the pH-induced shift varied from 21 to 53 mV per pH unit depending on the physical location of the sensitizer. Sensitizers inside the semiconductor double layer track the 59 mV pH shift of the semiconductor. When sensitzers were outside the double layer, their potential was almost independent of the semiconductor. This finding has important implications for the determination of interfacial energetics for dye sensitization and interfacial electron transfer studies [136]. 

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