Electrodes and electrolytes in micro-SOFCs: a discussion of geometrical constraints

Miniaturized solid oxide fuel cells (SOFCs), whose designs are compatible with conventional semiconductor fabrication technology, are considered from a theoretical point of view given their distinctive electrode and electrolyte geometries. Micro-SOFCs may be operated in either a single-chamber mode for which both electrodes are located on one side of a thin film electrolyte or in the more conventional two-chamber mode, in which electrodes are located on opposite sides of the electrolyte. The electrode geometries and film thicknesses necessary to achieve sufficiently low polarization resistances are evaluated for the single-chamber micro-SOFC. Interdigitated (comb-like) electrodes with characteristic feature sizes of a few micrometers are found to be essential to insure low polarization resistance. Requirements with respect to electrochemical properties of the electrodes are addressed as well. Numerical calculations are used to examine the correlation between decreasing electrolyte film thickness and ohmic polarization in two-chamber fuel cells. Current constriction at electrode particles or three phase boundaries render very low film thicknesses (below say 300 nm) not very sensible.