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

Abstract

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 = 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 µm, the effect of over electrode zone on electrochemical performance should not be ignored. Energies 2018, 11, 1875 2 of 16 within mixed conducting CeO 2−x electrode [12]. S. Wang et al. compared the performances of various LSCF-based cathodes and found that LSCF-SDC exhibited a larger activation overpotential than did the single-phase LSCF cathode [13]. More interestingly, the LSM-coated LSCF composite electrode was reported to exhibit a lower activation overpotential compared with that in a pure LSCF cathode [13]. Furthermore, proton conducting oxides [14], such as BaZr 0.7 Pr 0.1 Y 0.2 O 3_d [15] and BaZr 0.1 Ce 0.7 Y 0.2 O 3_d [16] were also greatly invented to be used in IT-SOFCs because of their low activation energy and high ionic conductivity around IT-range.Generally, the electrochemical reaction processed within an IT-SOFC using mixed conducting materials or proton conducting oxides are very different from those using conventional composite electrodes [17]. Taking the cathode of LSCF-SDC/SDC/NI-SDC IT-SOFC using mixed conducting materials as an example [13], the electrochemically active sites not only can be taken placed around the percolated three phase boundary sites (i.e., LSCF-SDC-pores and LSCF-dense electrolyte interfaces), but also can happen around the percolated double phase boundary sites (e.g., LSCF-pore) [18]. Up to now, many IT-SOFC button cells using the mixed conducting materials have been reported by many researchers by adopting different compositions (or materials), volume fractions, microstructure parameters, manufacture processes, operating conditions and different cell geometry sizes. It is interesting to note that differe...

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