Conducting solids

Fig. 5. Conductivity as a function of temperature for some highly conducting solid electrolytes, where X in CuX is Cl, Br, or I (11).

Complete qualitative and quantitative bulk elemental analysis of conducting solids to ultratrace levels... 

Increasing numbers of advanced batteries for all purposes depend on ionically conducting solid electrolytes, so it will be helpful to discuss these before continuing. It should be remembered that any battery can be described as an electron pump, and the role of the electrolyte is to block the passage of electrons, letting ions through instead. 

The adaptation of the Bischler-Napieralski reaction to solid-phase synthesis has been described independently by two different groups. Meutermans reported the transformation of Merrifield resin-bound phenylalanine derivatives 32 to dihydroisoquinolines 33 in the presence of POCI3. The products 34 were liberated from the support using mixtures of HF/p-cresol. In contrast, Kunzer conducted solid-phase Bischler-Napieralski reactions on a 2-hydroxyethyl polystyrene support using the aromatic ring of the substrate 35 as a point of attachment to the resin. The cyclized products 36 were cleaved from the support by reaction with i-butylamine or n-pentylamine to afford 37. 

M. Armand, M. Gauthier in High Conductivity Solid Ionic Conductors (Ed. T. Takahashi), World Scientific, Singapore, 1989, p. 114. 

Promotion We use the term promotion, or classical promotion, to denote the action of one or more substances, the promoter or promoters, which when added in relatively small quantities to a catalyst, improves the activity, selectivity or useful lifetime of the catalyst. In general a promoter may either augment a desired reaction or suppress an undesired one. For example, K or K2O is a promoter of Fe for the synthesis of ammonia. A promoter is not, in general, consumed during a catalytic reaction. If it does get consumed, however, as is often the case in electrochemical promotion utilizing O2 conducting solid electrolytes, then we will refer to this substance as a sacrificial promoter. 

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

E.C. Subbarao, and H.S. Maiti, Solid electrolytes with oxygen ion conduction, Solid State Ionics 11, 317-338 (1984). 

Figure 5.20. Left Schematic of an O2 conducting solid electrolyte cell with fixed P02 and PO2 values at the porous working (W) and reference (R ) electrodes without (top) and with (bottom) ion backspillover on the gas exposed electrodes surfaces, showing also the range of spatial constancy of the electrochemical potential, PQ2-, of O2. Right Corresponding spatial variation in the electrochemical potential of electrons, ]Ie(= Ef) UWR is fixed in both cases to the value (RT/4F)ln( P02 /pc>2 ) also shown in the relative position of the valence band, Ev, and of the bottom of the conduction band, Ec, in the solid electrolyte (SE) numerical values correspond to 8 mol% Y203-stabilized-Zr02, pc>2=10 6 bar, po2=l bar and T=673 K.32 Reproduced by permission of The Electrochemical Society.

X-ray photoelectron spectroscopic (XPS) studies of Ag63,64 and Pt6,56-62 films deposited on YSZ under positive current application conditions have confirmed the proposition2-4 that NEMCA with oxide ion conducting solid electrolytes is due to an electrochemically induced and controlled backspillover of oxide ions on the catalyst surface. 

As shown on Figure 9.1 when the circuit is opened (I = 0) the catalyst potential starts increasing but the reaction rate stays constant. This is different from the behaviour observed with O2 conducting solid electrolytes and is due to the fact that the spillover oxygen anions can react with the fuel (e.g. C2H4, CO), albeit at a slow rate, whereas Na(Pt) can be scavenged from the surface only by electrochemical means.1 Thus, as shown on Fig. 9.1, when the potentiostat is used to impose the initial catalyst potential, U r =-430 mV, then the catalytic rate is restored within 100-150 s to its initial value, since Na(Pt) is now pumped electrochemically as Na+ back into the P"-A1203 lattice. 

Figure A.l. Schematic presentation of a catalytic cylindrical Pt cluster interfaced with an O2 -conducting solid electrolyte (YSZ) showing the flux, N, of the promoting species.

Graphite, the most important component of the lead of pencils, is a black, lustrous, electrically conducting solid that vaporizes at 1700°C. It consists of flat sheets of sp2 hybridized carbon atoms bonded covalently into hexagons like chicken wire (Fig. 5.22). There are also weak bonds between the sheets. In the commercially available forms of graphite, there are many impurity atoms trapped between the sheets these atoms weaken the already weak intersheet bonds and let... 

The electrodes in the Daniell cell are made of the metals involved in the reaction. However, not all electrode reactions include a conducting solid directly. For example, to use the reduction 2 H+(aq) + 2e"- H2(g) at an electrode, a... 

The metallic hydrides are black, powdery, electrically conducting solids formed by heating certain of the d-block metals in hydrogen (Fig. 14.9) ... 

We can understand the differences in properties between the carbon allotropes by comparing their structures. Graphite consists of planar sheets of sp2 hybridized carbon atoms in a hexagonal network (Fig. 14.29). Electrons are free to move from one carbon atom to another through a delocalized Tr-network formed by the overlap of unhybridized p-orbitals on each carbon atom. This network spreads across the entire plane. Because of the electron delocalization, graphite is a black, lustrous, electrically conducting solid indeed, graphite is used as an electrical conductor in industry and as electrodes in electrochemical cells and batteries. Its... 

Electro- chemical Conducting solids Dissolution is based on redox process Iron in acid Fe + 2 H+ — Fe2+ + H2... 

Very efficient method for multi-element analysis of conducting solid samples... 

Huggins, R. A., Ionically conducting solid state membranes, AE, 10, 323 (1977). 

An important developing area that lies in the region between polymer chemistry, ceramic science, and metals, involves the search for new electrically-conducting solids. Linear polymers may conduct electricity by electronic or ionic mechanisms. As will be discussed, polyphosphazenes have been synthesized that, depending on the side group structure, conduct by either of these two processes. 

Extended solid state n systems facilitate CT, particularly when doped [4-6]. The analogy between DNA and conductive solid state -stacks therefore establishes that a requisite condition for CT may exist in DNA. DNA contains an array of heterocyclic aromatic base pairs, stacked at a distance of 3.4 A, wrapped within a negatively charged sugar phosphate backbone [7] (Fig. 1). The interactions between the n electrons of the DNA base pairs provide the electronic coupling necessary for CT to occur. 

Most of the available data have been recorded under conditions such that only the terms for eddy transport and conduction through the solid are significant. Equation 12.7.19 requires that /c increase with particle diameter, mass velocity, and the conductivity of the solid. It is consistent with data for low conductivity solids, but some discrepancies arise for very high conductivity solids (108). At Reynolds numbers greater than 40, the contribution of the molecular conduction term is negligible. 

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