Interfadal electron transfer

Fig. 8-8. Energy levels for redox electron transfer reaction at a metal electrode (a) in equilibrium, (b) in anodic polarization with reao tion rate determined by interfadal electron transfer, (c) anodic polarization with reaction rate determined by both interfadal electron transfer and diffusion of hydrated partides. EF0)Eooxj.a= Fenni level of redox electrons at an interface.

Aust. J. Soil Res. 16 215-227 Joint Committee on Powder Diffraction Standards Mineral powder diffraction fde. Data book. Published by the JCPDS International Centre for Diffraction Data, Swarfhmore, Pennsylvania, U SA, pp. 942 Jolivet, J.P. Tronc, E. (1988) Interfadal electron transfer in colloidal spinel iron oxide. Conversion of Fe304 to y- Fe203 in aqueous medium. J. Colloid Interface Sci. 125 688—... 

M. R. Hofemann N. S. Lewis, Fluxmatching condition at Ti02 photoelectrodes Is interfadal electron transfer to O2 rate-limiting in the Ti02-catalyzed degradation of organics J. Phys. Chem. 1994, 98, 13385-13395. 

Interfadal Electron Transfer in Molecular and Protein Film Voltammetry... 

Chi, Q.)., Zhang, J.D., Jensen, P.S., Christensen, H.E.M., and Ulstrup, J. (2006) Long-range interfadal electron transfer of metalloproteins based on molecular wiring assemblies. Faraday Discussions, 131, 181-195. 

G. W., Andersen, J.E.T., and Ulstrup, J. (2000) Molecular monolayers and interfadal electron transfer of Pseudomonas aeruginosa azurin on Au(l 11). Journal of the American Chemical Society, 122, 4047-4055. 

The signal-triggered functions of these molecular assemblies have to be first characterized in bulk solution. Then, extensive efforts have been directed to integrate these photoswitchable chemical assemblies with transducers in order to tailor switchable molecular devices. The redox properties of photoisomerizable mono-layers assembled on an electrode surface are employed for controlling interfadal electron transfer [16]. Specifically, electrical transduction of photonic information recorded by photosensitive monolayers on electrode supports can be used in developing monolayer optoelectronic systems [16-19]. Electrodes with receptor sites exhibiting controlled binding of photoisomerizable redox-active substrates from the solution [20] also allow the construction of molecular optoelectronic devices. 

Fomeli, A., Palomares, E., Torres, T., and Durrant, J.R. (2009) Ru(II)-phthalocyanine sensitized solar cells the influence of co-adsorbents upon interfadal electron transfer kinetics. 

Khoudiakov, M. Parise, A. R. Brunschwig, B. S. Interfadal electron transfer in FeII(CN)6 -sensitized Ti02 nanoparticles a study of direct charge injection by electroabsorption spectroscopy. J. Am. Chem. Soc. 2003, 125, 4637—4642. 

A. Why Measure Fast Interfadal Electron Transfer Rate Constants And How ... 

Interfadal Electron Transfer. There have been several studies of electron transfer reactions[17, 38]and the connection with Marcus s theory[39]. It may be possible to use a Car-Parrinello like scheme on that part of the system directly affecting the electron transfer. There has also been very interesting studies of the ferro-ferri redox couple in solution[40, 41] that address many issues related to electron transfer from an electrode to a hydrated ion. Slow processes can be treated by transition state methods like the ones used in solid state ionic conducdvity[42]. 

Interfadal Electron Transfer in Photovoltaic Structures Probed by Time-Resolved Terahertz Spectroscopy... 

Next, we consider the interface M/S of a nonpolarizable electrode where electron or ion transfer is in equilibrium between a solid metal M and an aqueous solution S. Here, the interfadal potential is determined by the charge transfer equilibrium. As shown in Fig. 4-9, the electron transfer equilibrium equates the Fermi level, Enn) (= P (M)), of electrons in the metal with the Fermi level, erredox) (= P s)), of redox electrons in hydrated redox particles in the solution this gives rise to the inner and the outer potential differences, and respectively, as shown in Eqn. 4-10 ... 

For the hydrogen electrode, the interfadal potential between the electrode metal and the hydrogen gas film is determined by the electron transfer equilibrium and the interfacial potential between the hydrogen gas film and the aqueous... 

Figures 8-16 and 8-17 show the state density ZXe) and the exchange reaction current io( ) as functions of electron energy level in two different cases of the transfer reaction of redox electrons in equilibrium. In one case in which the Fermi level of redox electrons cnxEDax) is close to the conduction band edge (Fig. 8-16), the conduction band mechanism predominates over the valence band mechanism in reaction equilibrium because the Fermi level of electrode ensa (= nREDOK)) at the interface, which is also dose to the conduction band edge, generates a higher concentration of interfadal electrons in the conduction band than interfadal holes in the valence band. In the other case in which the Fermi level of redox electrons is dose to the valence band edge (Fig. 8-17), the valence band mechanism predominates over the conduction band mechanism because the valence band holes cue much more concentrated than the conduction band electrons at the electrode interface.

Next, we consider the anodic reaction current of redox electron transfer via the conduction band, of which the exchange reaction current has been shown in Fig. 8-16. Application of a slight anodic polarization to the electrode lowers the Fermi level of electrode fix>m the equilibrium level (Ep(sc)( n = 0) = eiiOTSDca)) to a polarized level (ep(8C)( n) = ep(REDox)- n)withoutchanging at the electrode interface the electron level relative to the redox electron level (the band edge level pinning) as shown in Fig. 8-20. As a result of anodic polarization, the concentration of interfacial electrons, n, in the conduction band decreases, and the concentration of interfadal holes, Pm, in the valence band increases. Thus, the cathodic transfer current of redox electrons, in, via the conduction band decreases (with the anodic electron im ection current, ii, being constant), and the anodic transfer current of redox holes, (p, via the valence band increases (with the cathodic hole injection... 

As discussed in Sec. 8.3.5, a redox reaction current due to electron or hole transfer depends not only on the concentration of interfadal electrons or holes at the electrode but also on the state density of the redox electrons or redox holes in the range of energy where the electron transfer takes place. Hence, it is important in the kinetics of electron or hole transfer to realize the level of the band edge Cc or Ev of the electrode relative to the most probable level cred or cox of redox electrons or redox holes in the hydrated redox particles. 

The cathodic current of electron transfer is proportional to the concentration of interfadal electrons, n and the anodic current of hole transfer is proportional to the concentration of interfacial holes, p., in semiconductor electrodes as described in Sec. 8.3. Since the concentration of interfacial electrons or holes depends on the quasi-Fermi level of interfacial electrons or holes in the electrode as shown in Eqn. 10-3 or 10—4 (n, = n + dra and p, =p + 4P ), the transfer current of cathodic electrons or anodic holes under the condition of photoexdtation depends on the quasi-Fermi level of interfadal electrons, nCp, or the quasi-Fermi level of interfadal holes, pEp It also follows from Sec. 8.3 that the anodic current of electron transfer (the ipjection of electrons into the conduction hand) or the cathodic current of hole transfer (the ipjection of holes into the valence band) does not depend on the... 

The next two chapters are devoted to ultrafast radiationless transitions. In Chapter 5, the generalized linear response theory is used to treat the non-equilibrium dynamics of molecular systems. This method, based on the density matrix method, can also be used to calculate the transient spectroscopic signals that are often monitored experimentally. As an application of the method, the authors present the study of the interfadal photo-induced electron transfer in dye-sensitized solar cell as observed by transient absorption spectroscopy. Chapter 6 uses the density matrix method to discuss important processes that occur in the bacterial photosynthetic reaction center, which has congested electronic structure within 200-1500cm 1 and weak interactions between these electronic states. Therefore, this biological system is an ideal system to examine theoretical models (memory effect, coherence effect, vibrational relaxation, etc.) and techniques (generalized linear response theory, Forster-Dexter theory, Marcus theory, internal conversion theory, etc.) for treating ultrafast radiationless transition phenomena. 

Theoretical Notions of Interfadal Chemical and Bioelectrochemical Electron Transfer... 

H. E.M., NazmudUnov, R.R., and Ulstrup, J. (2010) Approach to interfadal and intramolecular electron transfer of the diheme protein cytochrome c(4) assembled on Au(lll) surfaces. journal of Physical Chemistry B, 114, 5617-5624. 

Wackerbarth, H., Klar, U., Gunther, W., and Hildebrandt, P. (1999) Novel time-resolved surface-enhanced (resonance) Raman spectroscopic technique for smdying the dynamics of interfadal processes application to the electron transfer reaction of cytochrome c at a silver electrode. Applied Spectroscopy, 53, 283-291. 

Interfadal Electrochemical Organization and Electron Transfer of the Blue Copper Protein Azurin - a Nanoscale Bioelectrochemical Paradigm... 

As outlined in the Introduction, a couple of suggested pathways have been proposed for the first electron transfer step (a) dissociative chemisorption of O2 (rds) probably accompanied by e-transfer and followed by proton transfer (b) simultaneous proton and electron transfer to a weakly adsorbed O2 molecule. We have recently shown through CPMD [21,69] and DFT [75] results that both pathways may take place under different conditions of the interfadal structure i.e., proton transfer may be involved in the first reduction step depending on the relative location of the O2 molecule with respect to the surface and to the proton, on the degree of proton hydration, and on the surface charge which is dependent on the electrode potential. Moreover, it was shown that proton transfer may precede or follow the first electron transfer, but in most cases the final product of the first step is an adsorbed HOO. ... 

This first chapter to Volume 2 Interfadal Kinetics and Mass Transport introduces the following sections, with particular focus on the distinctive feature of electrode reactions, namely, the exponential current-potential relationship, which reflects the strong effect of the interfacial electric field on the kinetics of chemical reactions at electrode surfaces. We then analyze the consequence of this accelerating effect on the reaction kinetics upon the surface concentration of reactants and products and the role played by mass transport on the current-potential curves. The theory of electron-transfer reactions, migration, and diffusion processes and digital simulation of convective-diffusion are analyzed in the first four chapters. New experimental evidence of mechanistic aspects in electrode kinetics from different in-situ spectroscopies and structural studies are discussed in the second section. The last... 

If this condition is met there will be no visible response to electron transfer and therefore no measurable amplitude associated with electron transfer kinetics. Quite simply it means that the experimental conditions are such that the interfadal redox equilibrium is not disturbed by a ehange in the interfadal temperature the system was in equilibrium at T and will be in equilibrium at... 

PCET can also play an important role in interfadal charge transfer processes. Electrochemical PCET have recently been explored, both theoretically and experimentally. Hammes-Schiffer et al. have applied their theoretical framework to model systems where the proton transfer occurs within solvated hydrogen-bonded solute complexes while the electron is transferred between that solute complex and an immersed electrode Costentin et al. have investigated the mechanistic details of PCET in the oxidation of phenols, as model systems of central processes in oxygenic photosynthesis. The same groups have explored the experimental and theoretical aspects of PCET in model systems with proton relay networks. ... 

Many recent computational investigations that address lET processes demonstrate current limitations and capabilities of first principles modelling. In this section, some specific examples are used to illustrate results, particularly for computational studies of photoinduced surface electron transfer at molecule metal oxide interfaces. The examples that are discussed start from accurate quantum chemical descriptions of the initially photoexdted state of typical sensitizers, proceed to well-characterized interfadal systems used to investigate fundamental lET processes and end with a discussion of efforts to expand further the system complexity in the modelling. 

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