Electrolyte redox potential

Fig. 7 Flatband situation for RuS2 in different electrolytes as measured by Ktxhne and Tributsch (1985), interpreted by us as due to a RuS2/Ru02-Schottky junction pinned to the electrolyte redox potential...

Trinidad P, Ponce de Leon C, Walsh EC. The use of electrolyte redox potential to monitor the Ce(IV)/Ce(III) couple. J Environ Manage 2008 88 1417-25. 

For a simple electron transfer reaction containing low concentrations of a redox couple in an excess of electrolyte, the potential established at an inert electrode under equilibrium conditions will be governed by the Nemst equation and the electrode will take up the equilibrium potential for the couple 0/R. In temis of... 

H. Gerischer, and W. Ekardt, Fermi levels in electrolytes and the absolute scale of redox potentials, Appl. Phys. Lett. 43(4), 393-395 (1983). 

The photoelectrolysis of H2O can be performed in cells being very similar to those applied for the production of electricity. They differ only insofar as no additional redox couple is used in a photoelectrolysis cell. The energy scheme of corresponding systems, semiconductor/liquid/Pt, is illustrated in Fig. 9, the upper scheme for an n-type, the lower for a p-type electrode. In the case of an n-type electrode the hole created by light excitation must react with H2O resulting in 02-formation whereas at the counter electrode H2 is produced. The electrolyte can be described by two redox potentials, E°(H20/H2) and E (H20/02) which differ by 1.23 eV. At equilibrium (left side of Fig. 9) the electrochemical potential (Fermi level) is constant in the whole system and it occurs in the electrolyte somewhere between the two standard energies E°(H20/H2) and E°(H20/02). The exact position depends on the relative concentrations of H2 and O2. Illuminating the n-type electrode the electrons are driven toward the bulk of the semiconductor and reach the counter electrode via the external circuit at which they are consumed for Hj-evolution whereas the holes are dir tly... 

As is well documented, formation of chemisorbed oxygen species on a Pt surface at V > 0.75 V occurs in an inert atmosphere on Pt in contact with an aqueous, or hydrous polymer electrolyte, by anodic discharge of water molecules to form OHads on metal sites, according to the Reaction (1.3). It is this chemisorbed oxygen species, derived from water discharge, that will be considered in the following discussion. Significantly, the Reaction (1.3) is associated with a redox potential K(H20)/Pt-OHads which is quite different from the redox potential for the faradaic ORR process,... 

Heterogeneous ET reactions at polarizable liquid-liquid interfaces have been mainly approached from current potential relationships. In this respect, a rather important issue is to minimize the contribution of ion-transfer reactions to the current responses associated with the ET step. This requirement has been recognized by several authors [43,62,67-72]. Firstly, reactants and products should remain in their respective phases within the potential range where the ET process takes place. In addition to redox stability, the supporting electrolytes should also provide an appropriate potential window for the redox reaction. According to Eqs. (2) and (3), the redox potentials of the species involved in the ET should match in a way that the formal electron-transfer potential occurs within the potential window established by the transfer of the ionic species present at the liquid-liquid junction. The results shown in Figs. 1 and 2 provide an example of voltammetric ET responses when the above conditions are fulfilled. A difference of approximately 150 mV is observed between Ao et A" (.+. ... 

Table 4.6 yield a redox potential range of at least (0.78 4- 0.83) + (1.23 + 0.52) = 3.36 V. Another important effect, already published by Tafel (Ch. 3, ref. 7), is that an increase in the electrolytic current density often results in a further rise of the overpotentials (and therefore of the redox potential range) (cf., eqn. 3.38 and Fig. 3.16 for non-amalgamating metals in polarography). 

Before mentioning some more literature data on non-aqueous voltammetry, we suggest on the basis of our previous discussions that the choice of the experimental conditions used in the techniques must be a compromise between a sufficient solubility of the analyte in the solution, an ample redox potential range of the solvent, a suitable type of indicator electrode and adequate conductance of the solution with supporting electrolyte added. In this connection Fig. 4.20 may be a useful guide. 

Let us choose, as an arbitrary reference level, the energy of an electron at rest in vacuum, e ) (cf. Section 3.1.2). This reference energy is obvious in studies of the solid phase, but for the liquid phase, the Trasatti s conception of absolute electrode potentials (Section 3.1.5) has to be adopted. The formal energy levels of the electrolyte redox systems, REDox, referred to o, are given by the relationship ... 

Based on extensive screening of hundreds of ruthenium complexes, it was discovered that the sensitizer s excited state oxidation potential should be negative of at least —0.9 V vs. SCE, in order to inject electrons efficiently into the Ti02 conduction band. The ground state oxidation potential should be about 0.5 V vs. SCE, in order to be regenerated rapidly via electron donation from the electrolyte (iodide/triiodide redox system) or a hole conductor. A significant decrease in electron injection efficiencies will occur if the excited and ground state redox potentials are lower than these values. 

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