Measurements and Analyses of Pressurized Solid Oxides Fuel Cells: Effects of Pressure, Temperature, and Mass Flow Rates

• Main Authors: Hao -Sheng, 鄭浩昇
• Other Authors: Shenqyang(Steven) Shy
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/97428774541685742726

碩士 === 國立中央大學 === 機械工程研究所 === 100 === This thesis uses the recently-established high-pressure double-chamber solid oxide fuel cell (SOFC) testing platform to quantitatively measure cell performance and electrochemical impedance spectra (EIS) of single unit cells with flow distributors, so that the effects of pressure (p), temperature (T), flow uniformity in interconnects, and the flow rates of anode and cathode in pressurized SOFCs can be studied. The testing platform from outside in includes an outer high-pressure chamber, a high-temperature controllable, and a single cell stack (single unit cell + two flow distributors). The single cell stack is consisted of an anode-supported unit cell, the crofer-22-APU supporting frames, and the two current collectors which are sandwiched by a pair of rib-channel flow distributors. The present experimental studies have three parts concerning various effects to the cell performance under elevated pressure conditions (p = 1 ~ 5 atm): (1) The effect of flow uniformity in flow distributors, (2) the effect of operating temperature (T), and(3) the effect of flow rates in both anode and cathode electrodes, as shown below respectively. (1) By comparing two different designs of rib-channel flow distributors using or not using small guide vanes in the same single-cell stack, the one with guide vanes having much higher flow uniformity than that without guide vanes has a better cell performance. Such enhancing performance due to the increasing degree of flow uniformity is found to be even more profound at higher pressure conditions, as can be electrochemical understood and explained by electrochemical impedance spectra (EIS) measurements. (2) While keeping p and the flow rates constant, the single-cell stack performance increases with T at least from 650℃ to 800℃ for all value of p = 1~5 atm studied. However, the open-circuit-voltage (OCV) is slightly reduced by increased T. At any fixed value of T, pressurization can increase OCV and the cell power density. From EIS measurements, it is found that both activation and concentration polarizations decrease with increasing p explaining why the cell performance is increasing with p. (3) At T = 850℃ and fixed anodic flow rate (0.5 slpm H2 + 0.5 slpm N2), the performance of the single-cell stack can be increased by increasing the air flow rates of cathode at least over the range from 0.5 slpm to 1 slpm. This increase is even more profound at higher p. On the other hand, the cell performance of the single-cell stack is rather insensitive to the increase of the anodic flow rates while keeping the cathodic flow rates constant (0.5 slpm air). These results should be useful to the development of pressurized SOFC integrating with gas turbines for future hybrid power generating system.