The Impact of Pressurization on Anode-Supported and Electrolyte-Supported Planar Solid Oxide Fuel Cells at 750oC ~ 850oC
In this work, we measure the pressurization influence on power generating characteristics and EIS for both anode-supported and electrolyte-supported cells (ASC and ESC) using a recently-established high-pressure SOFC facility. It is worth of noting that the present study has an important advantage due to the fact that both ASC and ESC use the same single-cell setup, a planar full cell having 40 × 40 mm2 effective reactive area sandwiched by a pair of rib-channel flow distributors (interconnectors) on both anode and cathode, under exactly the same experimental conditions. Specifically, both ASC and ESC apply exactly the same flow rates (Qanode = 0.5 slpm H2 + 0.4 slpm N2 and Qcathode = 0.9 slpm air) at three operating temperatures (T = 750 oC, 800 oC, 850oC), each T under five different pressures (p = 1, 2, 3, 4, 5 atm), having a total of 30 data sets for comparison. Hence, a direct comparison of experimental EIS data and power generating characteristics between ASC and ESC at elevated pressures can be clearly made. To the best knowledge of the authors, the present measured EIS comparison between ASC and ESC is new, and experimental EIS data of pressurized electrolyte-supported planar SOFC are still not available in literatures.
These ASC and ESC measurements under the same experimental conditions suggest the following points: (1) At T = 850oC and 0.7 V, power densities of ASC/ESC increase from 309/193 mW cm-2 to 476/250 mW cm-2, as p increases from 1 atm to 5 atm. As T increases from 750oC to 850oC at 0.7 V, power densities of ASC/ESC increase from 175/97 mW cm-2 to 309/193 mW cm-2 at p = 1 atm, while at p = 5 atm, the corresponding increases of power densities are 281/137 mW cm-2 to 476/250 mW cm-2. It is found that ASC is more sensitive to pressurization than ESC, while the latter is more temperature-sensitive than the former. (2) The ohmic resistance is not varied with the loaded current density and it is independent of pressure for both ASC and ESC cases. Furthermore, ESC has higher values of the ohmic impedance, about 16 % larger, than that of ASC. The thicker the electrolyte thickness is, the larger the ohmic impedance is. (3) The polarization impedance decreases noticeably with increasing p for both ASC and ESC cases at either unloaded or loaded conditions. This explains why power densities increase with increasing pfor both ASC and ESC. (4) These measurements reveal that the better cell performance of ASC than that of ESC is not simply due to the larger ohmic overvoltage of ESC as previously predicted by numerical simulations. The variation of the polarization overvoltage between ASC and ESC also plays an important role.
We hasten to note that it is not sure whether the present conclusions can be extended to all ASCs and ESCs due to different electrolytes and anodes used in the present ASC and ESC, but these results should be of help in the further development of PSOFC integrating with micro gas turbines for future stationary power generation.