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The Role of Effective Rate Constants in Interfacial Kinetics

Published online by Cambridge University Press:  10 February 2011

Joachim Maier
Joachim Maier*
Affiliation:
Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany, weiglein@chemix.mpistuttgart.mpg.de
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Abstract

A brief excerpt of a more comprehensive quantitative theoretical analysis on the role of effective rate constants in interfacial processes is given (in particular [1], see also [2,3]). Chemical incorporation, tracer incorporation and steady state electrical experiments are considered. It is shown that besides experimental differences there are mechanistic and conceptual differences between the three effective rate constants (kδ, k*, Qq). The treatment based on irreversible thermodynamics and chemical kinetics shows similarities and differences with respect to the analogous situation in the bulk. As special cases adsorption and transfer limited kinetics are considered. Having related the k-values to the exchange rates of the rate determining step and to the chemical capacitance outside the boundary zone, the characteristic dependencies on controlling parameters and also the correlation with diffusion coefficients can be derived. This is done for electron-rich materials such as SOFC cathodes. A further point which is briefly mentioned in this context is the fact that flux constriction effects may lead to apparent surface rate constants. The role of space charges is briefly discussed for the case of grain boundary kinetics [4]. In electron-poor materials such as SrTiO3(Fe2O3) or Zr02(Y203) additional mechanistic differences should occur, since in the tracer case mechanisms are possible at the surfaces which do not have to involve electrons directly. Here also discrepancies with respect to electrical experiments are predicted (leading to a surface analogue of a Haven ratio). Some experimental results obtained with SrTiO3 are discussed in this context.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 548: Symposia EE – Solid State Ionics V , 1998 , 415
Copyright
Copyright © Materials Research Society 1999

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References

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