Charge transfer kinetics, site

Nanostructured electrode morphologies can be used to address some of the intrinsic material s limitations and trade-offs mentioned above. The most obvious advantage of a nanostructured morphology is the increase in specific surface area. The concomitant increase in the number of surface sites greatly enhances the overall charge transfer kinetics at the semiconductor/electrolyte interface. 

V vs. SCE in CH2CI2/TBAH). The electroactive dendrimer film behaved almost ideally with rapid chaise transfer kinetics. These voltammetric features unequivocally indicate the surface-confined nature of the electroactive ferrocenyl moieties in the dendrimer. Surface coverage of electroactive ferrocenyl sites in the film r(mol cm ) was determined from the integrated charge of the cyclic voltanunetric wave. The obtained results correspond to about a close-packed monolayer of... 

The formation or dissolution of a new phase during an electrode reaction such as metal deposition, anodic oxide formation, precipitation of an insoluble salt, etc. involves surface processes other than charge transfer. For example, the incorporation of a deposited metal atom (adatom [146]) into a stable surface lattice site introduces extra hindrance to the flow of electric charge at the electrode—solution interface and therefore the kinetics of these electrocrystallization processes are important in the overall electrode kinetics. For a detailed discussion of this subject, refs. 147—150 are recommended. 

The chemisorption of ions plays another role in determining the properties of PEC devices. The adsorbed ions may create the chemical intermediates or specific reaction sites necessary for charge transfer and chemical product formation. The rapid kinetics in photoelectrolysis and wet photovoltaic cells are in no small part due to the fact that in most of these systems the redox species are strongly adsorbed. Knotek(10,ll) and others (12,13) have shown that the nature of the TiC>2 surface and the species adsorbed on it greatly affect its catalytic properties. 

Another interpretation would be to suppose that the adsorbed sulfide ion forms a surface state that can be directly oxidized by a hole in the valence band. In this case the shift in current onset to lower voltages would be due to an increase in the charge transfer rate rather than the decrease in the recombination rate discussed in the preceeding paragraph. The corrosion suppression associated with the sulfide could then be partially attributed to the rapid kinetics of hole capture by these surface sulfide ions and partially due to reduction of oxidized corrosion sites by sulfide ions in solution. 

By the method of introducing Pt into the DLC, the platinum metal is assumed to be distributed over the carbonaceous material bulk as discrete atoms or clusters [154], Essentially, Pt is not a dopant in the DLC, in the sense that the term is used in semiconductor physics. Nor is the percolation threshold surpassed, since the admixture of Pt (not exceeding 15 at. %) did not affect the a-C H resistivity, as was shown by impedance spectroscopy tests p 105 Q, cm, like that of the undoped DLC (see Table 3). It was thus proposed that the Pt effect is purely catalytic one Pt atoms on the DLC surface are the active sites on which adsorption and/or charge transfer is enhanced [75], (And the contact of the carbon matrix to the Pt clusters is entirely ohmic.) This conclusion was corroborated by the studies of Co tetramethylphenyl-porphyrin reaction kinetics at the DLC Pt electrodes [155] redox reactions involving the Co central ion proceed partly under the adsorption of the porphyrin ring on the electrode. 

Electron transfer reactions and spectroscopic charge-transfer transitions have been extensively studied, and it has been shown that both processes can be described with a similar theoretical formalism. The activation energy of the thermal process and the transition energy of the optical process are each determined by two factors one due to the difference in electron affinity of the donor and acceptor sites, and the other arising from the fact that the electronically excited state is a nonequilibrium state with respect to atomic motion (P ranck Condon principle). Theories of electron transfer have been concerned with predicting the magnitude of the Franck-Condon barrier but, in the field of thermal electron transfer kinetics, direct comparisons between theory and experimental data have been possible only to a limited extent. One difficulty is that in kinetic studies it is generally difficult to separate the electron transfer process from the complex formation... 

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