Solid charge-transfer reaction

Keller, H. J., and Soos,-Z. G. Solid Charge-Transfer Complexes of Phenazines. 127, 169-216 (1985). Kellogg, R. M. Bioorganic Modelling — Stereoselective Reactions with Chiral Neutral Ligand Complexes as Model Systems for Enzyme Catalysis. 101, 111-145 (1982). 

The experimental setup is depicted schematically in Figure 1.2. Upon varying the potential of the catalyst/working electrode the cell current, I, is also varied. The latter is related to the electrocatalytic (net-charge transfer) reaction rate re via re=I/nF, as well known from Faraday s law. The electrocatalytic reactions taking place at the catalyst/solid electrolyte/gas three-phase-boundaries (tpb), are ... 

The reference electrode-solid electrolyte interface must also be non-polarizable, so that rapid equilibration is established for the electrocatalytic charge-transfer reaction. Thus it is generally advisable to sinter the counter and reference electrodes at a temperature which is lower than that used for the catalyst film. Porous Pt and Ag films exposed to ambient air have been employed in most previous NEMCA studies.1,19... 

In the latter case one would like to know the length Apb of the metal-solid electrolyte-gas three-phase-boundaries (tpb) (in m or in metal mols, for which we use the symbol Ntpb throughout this book) and the value of the exchange current I0, where (W2F) expresses the value of the (equal and opposite under open-circuit conditions) forward and reverse rates of the charge-transfer reaction 4.1. 

If the electrolyte components can react chemically, it often occurs that, in the absence of current flow, they are in chemical equilibrium, while their formation or consumption during the electrode process results in a chemical reaction leading to renewal of equilibrium. Electroactive substances mostly enter the charge transfer reaction when they approach the electrode to a distance roughly equal to that of the outer Helmholtz plane (Section 5.3.1). It is, however, sometimes necessary that they first be adsorbed. Similarly, adsorption of the products of the electrode reaction affects the electrode reaction and often retards it. Sometimes, the electroinactive components of the solution are also adsorbed, leading to a change in the structure of the electrical double layer which makes the approach of the electroactive substances to the electrode easier or more difficult. Electroactive substances can also be formed through surface reactions of the adsorbed substances. Crystallization processes can also play a role in processes connected with the formation of the solid phase, e.g. in the cathodic deposition of metals. 

Suitable solid electrolytes can be employed as the electrolyte in an electrochemical cell. The electrolyte is used in the form of a membrane which is impermeable to gas phase transport. Electroactive materials, or electrodes, are deposited on both sides of the electrolyte to increase the rates of charge transfer across the electrolyte interface and it is important that the active molecules in the gas phase have easy access to the electrode/electrolyte interface where they can participate in the charge-transfer reactions. For this reason it is necessary, in most cases, to ensure that the electrode has a high porosity while, at the same time, remaining electrically continuous. 

Figure 32. The kinetic data for the intramolecular charge transfer reaction of DMAPS in alcohol solutions, ktra is plotted as a function of the solvent relaxation fceT,. These data span the temperature range from — 50°C to +30°C. The solid line corresponds to the case where t, = t, the expected result for a solvent controlled chemical reaction. The solvents plotted are ethanol ( + ), propanol ( ), butanol(x), pentanol (Ok and hexanol ( ). From Ref. 87 with permission from Chem. Phys. Lett., in press.

Figure 11. Photoion photoelectron coincidence studies of charge-transfer reactions of state-selected ions. Cross sections for nitric oxide symmetric charge-transfer reaction are plotted as function of reactant-ion kinetic energy and reactant-ion vibrational state (o = 0,1,2,3,4,5). Solid lines are linear least-squares fits to experimental data (not shown).86c...

Figure 16. Cross section as function of ion kinetic energy for charge-transfer reaction B+(N20,B)N20+ A, cross section for reaction of B+(IS) produced from BI3 O, cross section for reaction of B+ produced from BF3 (35.3% 3P and 64.5% S ) solid line, cross section for reaction of B+(3/1) obtained by taking difference between two lower curves and correcting for appropriate abundance.7 ...

Fig. 3.9 Current-potential curves for a slow charge transfer reactions at spherical electrodes calculated from Eqs. (3.66) (solid lines), (3.73) (dotted lines), and (3.74) (dashed lines). The values of k° (in cm s-1) and of the electrode electrode radius (in microns) are shown in the curves, a = 0.5,...

Aluminosilicate zeolites because of their structure, composition, and properties offer a superior ionic strength environment [172,173], Even though these materials are electronic insulators, when hydrated, they are solid solutions of high ionic mobility, and when dehydrated exhibit fair ionic conductivity (see Section 8.2.7) [38,112,119,172], The properties of aluminosilicate zeolites that are responsible for affecting the charge-transfer reactions in electrochemical systems are [172,174] ... 

The main purpose of this contribution, however, is to review recent advances in solid state ionics achieved by means of microelectrodes, i.e. electrodes whose size is in the micrometer range (typically 1-250 pm). In liquid electrolytes (ultra)-microelectrodes are rather common and applied for several reasons they exhibit a very fast response in voltametric studies, facilitate the investigation of fast charge transfer reactions and strongly reduce the importance of ohmic drops in the electrolyte, thus allowing e.g. measurements in low-conductive electrolytes [33, 34], Microelectrodes are also employed to localize reactions on electrodes and to scan electrochemical properties of electrode surfaces (scanning electrochemical microscope [35, 36]) further developments refer to arrays of microelectrodes, e.g. for (partly spatially resolved) electroanalysis [37-39], applications in bioelectrochemistry and medicine [40, 41] or spatially resolved pH measurements [42], Reviews on these and other applications of microelectrodes are, for example, given in Ref. [33, 34, 43-47],... 

In solutions and also in solids electron or proton transport may be coupled to the ionic charge transport via electron exchange reactions (- electron hopping or electron transfer reaction) or proton jumping (see - charge transfer reaction). 

C. Conducting Composites Formed by Direct Charge-Transfer Reaction Between Two Solid Components... 

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