Interface conductivity effect

FIGURE 2.12 Effect of Ni content on the electrode/electrolyte interface conductivity (aE) and the ohmic resistance (Wohm) for Ni-YSZ cermet anodes prepared using NiO-YSZ powder mixtures precalcinated at 1400°C and sintered at 1500°C. (From Kawada, T. et al.,./. Electrochem. Soc., 137 3042-3047, 1990. Reproduced by permission of ECS-The Electrochemical Society.)... 

Possible space charge situations and the respective conductance effects parallel ( ) or perpendicular (J.) to the interface.105 (Reprinted from S. Kim, J. Fleig and J. Maier, Space charge conduction Simple analytical solutions for ionic and mixed conductors and application to nanocrystalline ceria. , Phys. Chem. Chem. Phys. 2268-2273, 5, Copyright 2003 with permission... 

Shablakh et al. (1984) investigated the dielectric properties of bovine serum albumin and lysozyme at different hydration levels, at low frequency. Besides a relaxation attributed to the electrode—sample interface, they detected a further bulk relaxation that can be confused with a d.c. conduction effect. The latter relaxation was explained by a model of nonconductive long-range charge displacement within a partially connected water structure adsorbed on the protein surface. This model has nonconventional features that differ from the assumptions of other more widely accepted models based on Debye relaxations. 

Rawlett, A.M. et al., Electrical measurements of a dithiolated electronic molecule via conducting atomic force microscopy, Appl. Phys. Lett. 81, 3043-3045, 2002. Yaliraki, S.N. and Ratner, M.A., Molecule-interface coupling effects on electronic transport in molecular wires, J. Chem. Phys. 109, 5036-5043, 1998. 

The effect of impurities on fuel cells, often referred to as fuel cell contamination, has been identified as one of the most important issues in fuel cell operation and applications. Studies have shown that the component most affected by contamination is the MEA [3]. Three major effects of contamination on the MEA have been identified [3,4] (1) the kinetic effect, which involves poisoning of the catalysts or a decrease in catalytic activity (2) the conductivity effect, reflected in an increase in the solid electrolyte resistance and (3) the mass transfer effect, caused by changes in catalyst layer structure, interface properties, and hydrophobicity, hindering the mass transfer of hydrogen and/or oxygen. 

Oxygen reduction can be catalyzed by enzymes, and air-breathing cathodes with laccase and bUimbin oxidase as enzymatic catalysts, for example, have been demonstrated [10-15]. Enzymatically catalyzed cathodes avoid many of the problems discussed for platinum and other precious metal catalysts, but they often provide lower power density and Umited stability. Specifically with air-breathing cathodes, enzymes that catalyze oxygen reduction must be immobilized at the tripoint between hydrophilic (H" conductivity), hydrophobic (O2 supply), and conductive (e conductivity) interfaces for effective catalysis (Figure 16.1) (see Chapter 3). 

A gas phase can also be used as the defect-inducing second phase [267,284]. Figure 5.101 illustrates the conductivity effect of the adsorption of NH3 on AgCl interfaces. 

Fig. 5.109 Left TH-stacking fault phase formed at the /J-Agl/AbOs contact [262, 289]. The enormous conductivity effects at the interface can be understood if we think of the boundary layer phase as a cation-disordered heterostructure in the sub-nm range. Right Ion redistribution occuring at each interface of the heterostructure leads, for small enough spacing, to almost predominant disorder. The charge carrier concentrations (v, i) are much higher than in the bulk [263]. According to Ref. [262].

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