The transfer of oxygen molecules at the ambient/solid oxide interface follows a complex reaction path, including adsorption and dissociation, charge transfer at different stages and incorporation into the oxide lattice. Knowledge of this process is of significant importance for cathode materials in solid oxide fuel cells (SOFC), semipermeable membranes for oxygen separation and oxygen related sensors. Porous mixed electron-ion conducting materials (MIEC’s) are often used as cathodes in these applications, with the idea that surface exchange of oxygen and subsequent oxygen ion transport through the bulk of the MIEC are responsible for the electrode performance. But there are also indications that surface diffusion of oxygen is a viable alternative route.
In order to get a starting knowledge of the possible routes of this process modelling with the powerful Comsol Multiphysics package should be undertaken. The simulation is based on finite element analysis, in which a two- or three-dimensional network of connected triangles is defined. The current along the vertices and potentials at the shared corners follow regular (differential) equations. Internal numerical procedures result in a pattern of equipotential lines, mapped current densities and global parameters.
The idea is to start with the modelling of a simple noble metal electrode on an oxygen ion conducting electrolyte. For the system Pt/Bi2Cu0.1V0.9O5.35 a series of measurements and a simple global model are available (see figure).
- B.A. Boukamp, “Small signal response of the BiCuVOx/ noble metal /oxygen electrode system”, Solid State Ionics 135-137 (2000) 75-82.
- B.A. Boukamp, “Elucidation by EIS of the electrode reaction of the BiCuVOx/noble metal/oxygen electrode system”, ACH-Models in Chemistry 137 [2/3] (2000) 225-242.
- I.C. Vinke, B.A. Boukamp, K.J. de Vries and A.J. Burggraaf, “Three-electrode current-voltage measurements on erbia-stabilized bismuth oxide with sputtered noble metal electrodes”, Solid State Ionics 51 (1992) 249-259.
- N. Hildenbrand, P. Nammensma, D.H.A. Blank, H.J.M. Bouwmeester, B.A. Boukamp, “Influence of configuration and microstructure on performance of La2NiO4+δ intermediate-temperature solid oxide fuel cells cathodes”, J. Power Sources 238 (2013) 442-453.
Bernard A. Boukamp