Charge solid electrolytes

M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

It is important to realize that the migration in an electric field depends on the magnitude of the concentration of the charged species, whereas the diffusion process depends only on the concentration gradient, but not on the concentration itself. Accordingly, the mobility rather than the concentration of electrons and holes has to be small in practically useful solid electrolytes. This has been confirmed for several compounds which have been investigated in this regard so far [13]. 

Though solid electrolytes for multivalent ions offer the advantage of a larger charge transfer, their conductivities are much lower than those of monovalent ions at ambient temperature because of a higher activation enthalpy for the ionic motion... 

Direct-current sputtering is not generally applicable for the preparation of thin-film solid electrolytes since these compounds are electronic insulators. The target surface would be charged with the same polarity as that of the ions in the plasma, and the sputtering plasma would rapidly break down. 

Figure 13. Voltage relaxation method for the determination of the diffusion coefficients (mobilities) of electrons and holes in solid electrolytes. The various possibilities for calculating the diffusion coefficients and from the behavior over short (t L2 /De ) and long (/ L2 /Dc ll ) times are indicated cc h is the concentration of the electrons and holes respectively, q is the elementary charge, k is the Boltzmann constant and T is the absolute temperature.

Figure 14. Charge-transfer technique for measurement of the concentration of electrons or holes in solid electrolytes. Two samples of different length are polarized by the same voltage.

CTI charge-tranfer resistance between electrode and solid electrolyte phase III.6... 

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 ... 

Thus, as will be shown in this book, the effect of electrochemical promotion (EP), or NEMCA, or in situ controlled promotion (ICP), is due to an electrochemically induced and controlled migration (backspillover) of ions from the solid electrolyte onto the gas-exposed, that is, catalytically active, surface of metal electrodes. It is these ions which, accompanied by their compensating (screening) charge in the metal, form an effective electrochemical double layer on the gas-exposed catalyst surface (Fig. 1.5), change its work function and affect the catalytic phenomena taking place there in a very pronounced, reversible, and controlled manner. 

Electrocatalysis Again by definition, an electrocatalyst is a solid, in fact an electrode, which can accelerate a process involving a net charge transfer, such as e.g. the anodic oxidation of H2 or the cathodic reduction of 02 in solid electrolyte cells utilizing YSZ ... 

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. 

Furthermore, to the extent that the entire solid electrolyte cell under consideration is overall neutral, i.e. carries no net charge, one can show using Gauss s law of electrostatics, that the constant C in Eq. (5.27) is zero, i.e. that ... 

Figure 5.19. The physical origin of NEMCA When a metal counter electrode (C) is used in conjunction with a galvanostat (G) to supply or remove ions [O2 for the doped Zr02 (a), Na+ for P"-A1203 (b)] to or from the polarizable solid electrolyte/catalyst (or working electrode, W) interface, backspillover ions [O6 in (a), Na5+ in (b)] together with their compensating charge in the metal are produced or consumed at the tpb between the three phases solid electrolyte/catalyst/gas. This causes an increase (right) or decrease (left) in the work function of the gas-exposed catalyst surface. In all cases AO = eAUWR where AUWr is the overpotential measured between the catalyst and the reference electrode (R).

The non-zero value of e Fw-e FR in Eq. (5.35) implies that there are net surface charges on the gas exposed electrode surfaces. These charges (q+,q.) have to be opposite and equal as the cell is overall electrically neutral and all other charges are located at the metal-solid electrolyte interfaces to maintain their electroneutrality. The charges q+ = -q. are quite small in relation to the charges, Q, stored at the metal-electrolyte interface but nevertheless the... 

This does not imply that this double layer is at its point of zero charge (pzc). On the contrary, as with every other double layer in electrochemistry, there exists for every metal/solid electrolyte combination one and only one UWr value for which this metal/gas double layer is at its point of zero charge. These critical Uwr values can be determined by measuring the dependency onUWR of the double layer capacitance, Cd, of the effective double layer at the metal/gas interface via AC Impedance Spectroscopy as discussed in Chapter 5.7. 

The sample temperature should be sufficiently high to ensure sufficient conductivity of the solid electrolyte and thus avoid charging of the solid electrolyte. This means temperatures above 300°C for YSZ and above 100°Cfor p"-Al203. 

Calcium fluoride, solid electrolyte, 92, 420 Capacitance charging current, 2... 

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