Implications of the Experimental Results

We start by considering a schematic representation of a porous metal film deposited on a solid electrolyte, e.g., on Y203-stabilized-Zr02 (Fig. 5.17). The catalyst surface is divided in two distinct parts One part, with a surface area AE is in contact with the electrolyte. The other with a surface area Aq is not in contact with the electrolyte. It constitutes the gas-exposed, i.e., catalytically active film surface area. Catalytic reactions take place on this surface only. In the subsequent discussion we will use the subscripts E (for electrolyte) and G (for gas), respectively, to denote these two distinct parts of the catalyst film surface. Regions E and G are separated by the three-phase-boundaries (tpb) where electrocatalytic reactions take place. Since, as previously discussed, electrocatalytic reactions can also take place to, usually,a minor extent on region E, one may consider the tpb to be part of region E as well. It will become apparent below that the essence of NEMCA is the following One uses electrochemistry (i.e. a slow electrocatalytic reaction) to alter the electronic properties of the metal-solid electrolyte interface E. 

This perturbation is then propagated via the spatial constancy of the Fermi level Ef throughout the metal film to the metal-gas interface G, altering its electronic properties thus causing ion migration and thus influencing catalysis, i.e. catalytic reactions taking place on the metal-gas interface G. 

We then concentrate on the meaning of UWr, that is, of the (ohmic-drop-free) potential difference between the catalyst film (W, for working electrode) and the reference film (R). The measured (by a voltmeter), 

As already noted the electrochemical potential of electrons in a metal, jl, is related to the Galvani potential q via  

Equation (5.21) is based on the electrochemical way of counting the energy difference between zero (defined throughout this book as the potential energy of an electron at its ground state at infinite distance from the metal) and the Fermi level Ep (Eq. 5.15). The latter quantity must not be confused with the Fermi energy go which is the energy difference between 

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A promising beginning has been made in applying physical techniques to the problem of membrane structure. The use of these methods is growing rapidly and will become increasingly important. The number of systems that have been studied is limited, and generalizations must be made cautiously, but some important points have already been established. Since the data are sparse, a membrane model will not be suggested. Instead some of the implications of the experimental results will be discussed. 

Chapters 5 and 6 deal with systems where interaction between temperature gradient, concentration gradient and potential gradients without any barrier are involved. In these chapters, theoretical and experimental studies relating to thermal diffusion, Dufour effect, Soret effect, thermal diffusion potential, thermo-cells, precipitation and dissolution potential have been described. Physical implications of the experimental results have also been described. 

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