Redox energy levels, oxide

The chemical species shown on the left are oxidants (oxidizing agents) which can be regarded as possessing vacant electron-free energy levels. A redox reaction will be spontaneous only if the reductant ( electron source in the table) is located above that of the desired electron sink . 

Based on correlations between energy level positions and electrochemical redox potentials, it has been estabHshed that polymethine dyes with reduction potentials less than —1.0 V (vs SCE) can provide good spectral sensitization (95). On the other hand, dyes with oxidation potentials lower than +0.2 V ate strong desensitizets. 

Figure 4 Operating principles and energy level diagram of a dye-sensitized solar cell. S/S+/S = Sensitizer in the ground, oxidized and excited state, respectively. R/R = redox mediator (I3 / I-).

Fig. 2-36. Electron energy levels in hydrated oxidant Fe and reduc-tantFe AG = energy to organize hydrate structures dGj t = energy required for dehydrated redox ions to donate or accept gaseous electrons ep.2> o = most probable electron donor level of Fe Spe +.A = most probable electron acceptor level of Fe Hj05,2.,p,j = hydrated structures cgn) = standard gaseous electron level (s 0).

In the fluctuation band of electron energy of hydrated redox particles, the donor band of the reductant is an occupied band, and the acceptor band of the oxidant is a vacant band. The level erotsDcno at which the donor state density equals the acceptor state density (Aai/e) = Dox(e)) is called the Fermi level of the redox electron by analogy with the Fermi level e, of metal electrons [Gerischer, 1961]. From Eqns. 2—48 and 2—49 with f BED(e) =-DoxCe), we obtain the Fermi level Tiixxox.) (the redox electron level) as shown in Eqn. 2-51 ... 

Figure 3.6 shows the various relationships between the energy levels of solids and liquids. In electrolytes three energy levels exist, Ep, redox, Eox and Ered- The energy levels of a redox couple in an electrolyte is controlled by the ionization energy of the reduced species Ered, and the electron affinity of the oxidized species Eox in solution in their most probable state of solvation due to varying interaction with the surrounding electrolyte, a considerable... 

The energy levels in the solution are kept constant, and the applied voltage shifts the bands in the oxide and the silicon. The Gaussian curves in Figure 4b represent the ferrocyanide/ferricyanide redox couple with an excess of ferrocyanide. E° is the standard redox potential of iron cyanide. With this, one can construct (a) to represent conditions with an accumulation layers, (b) with flatbands, where for illustration, we assume no charge in interface states, and (c) with an inversion or deep depletion layer (high anodic... 

The oxide redox energy levels for all elements except gold are cathodic to the redox level of the H2O/O2 couple. Gold, however, is an impractical component for compound semiconductors. All other compound semiconductors employed as electrolysis photoanodes will undergo surface oxidation in aqueous electrolytes to produce a surface oxide film which normally constitutes the stable surface of the photoelectrode. Our proposed mechanism indicates that the proton induced oxide dissolution reaction arises from product ir ion interactions with the oxide anion (0=). 

The lowest energy level of the conduction band defines the reduction potential of the photoelectrons, while the highest one of the valence band determines the oxidizing power of the photoholes, respectively. When the reagents spread on the catalyst surface they are adsorbed on the active site and they can participate in redox reactions. 

However, there are really two distributions of electronic energy levels associated with redox, due to the fact that O and R, having different charges, have different solvations the energy of R is slightly lower than that of O. The density of states is shown schematically in Fig. 4.6. Overlap between EF and the distribution for E0 shows that oxidized species can be reduced. 

In this type of doping the number of electrons does not change the energy levels are rearranged, however. The most common example for redox doping is polyanaline that has different appearances or oxidation states, as shown in Scheme 11.3. The average oxidation state of polyanaline (y) can be varied continuously 1> y > 0 leuco-emeraldine (y = 1, fully reduced, insulator), emeraldine (y = 0.5, half-oxidised, semi-conductor) and pernigraniline (y = 0, fully oxidised, insulator). 

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