The Geometry Effect of Cathode/Anode Areas Ratio on Electrochemical Performance of Button Fuel Cell Using Mixed Conducting Materials

Intermediate temperature (IT) fuel cells using mixed conducting materials have been reported by many researchers by adopting different compositions, microstructures, manufacture processes and testing conditions. Most i(op)-V-op relationships of these button electrochemical devices are experimentally achieved based on anode or cathode surface area (i.e., A(an) not equal A(ca)). In this paper, a 3D multi-physics model for a typical IT solid oxide fuel cell (SOFC) that carefully considers detail electrochemical reaction, electric leakage, and e, ion and gas transporting coupling processes has been developed and verified to study the effect of A(ca)/A(an) on button cell i(op)-V-op performance. The result shows that the over zone of the larger electrode can enhance charges and gas transport capacities within a limited scale of only 0.03 cm. The over electrode zone exceed this width would be inactive. Thus, the active zone of button fuel cell is restricted within the smaller electrode area min(A(an), A(ca)) due to the relative large disc radius and thin component layer. For a specified V-op, evaluating the responded i(op) by dividing output current I-op with min(A(an), A(ca)) for a larger value is reasonable to present real performance in the current device scale of cm. However, while the geometry of button cells or other electrochemical devices approach the scale less than 100 mu m, the effect of over electrode zone on electrochemical performance should not be ignored.