Total Area Specific Resistance Research Articles

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells: I. Cross Validation of Polarization Measurements by Impedance Spectroscopy and Current-Potential Sweep

The aim of this paper is to address three issues in solid oxide fuel cells (SOFC): (i) cross-validation of the polarization of a single cell measured using both dc and ac approaches, (ii) the precise determination of the total area specific resistance (ASR), and (iii) understanding cathode polarization with cathodes. The ASR of an SOFC is a dynamic property, meaning it changes with current density. The ASR measured using impedance spectroscopy (low frequency interception with the real -axis of the ac impedance spectrum) matches that measured from a dc current–voltage sweep (the tangent of a dc curve). Due to the dynamic nature of ASR, we found that an impedance spectrum measured under open-circuit voltage or on a half-cell may not represent the cathode performance under real operating conditions, particularly at a high current density. In this work, the electrode polarization was governed by the cathode activation polarization; the anode contribution was negligible.

A-Site Deficient ( Pr0.6Sr0.4 ) 1 − sFe0.8Co0.2O3 − δ Perovskites as Solid Oxide Fuel Cell Cathodes

Five A-site deficient perovskites (, 0.05, 0.10, 0.15, and 0.20) were synthesized using the glycine-nitrate process. The perovskites were characterized with powder X-ray diffraction (XRD), dilatometry, four-point dc conductivity measurements, and electrochemical impedance spectroscopy using cone-shaped electrodes on a electrolyte. XRD revealed that only the compounds with 0.01 and 0.05 were of single phase. The other compounds contained an additional phase in the form of a Co–Fe spinel. The thermal expansion coefficient decreased systematically with an increase in . The total conductivity followed the small polaron hopping process below a certain characteristic temperature. The total conductivity decreased with increasing . It was likewise shown that the polarization resistance found a minimum for the compound with 0.05, with a total area specific resistance more than 3 times lower than the weakly A-site deficient perovskite.

High-performance bilayered electrolyte intermediate temperature solid oxide fuel cells

The ESB/GDC bilayer electrolyte concept has been proved to improve open circuit voltage and reduce the effective area specific resistance of SOFCs utilizing a conventional single-layer GDC electrolyte. However, high performance from such bilayer cells had not yet been demonstrated. The main obstacles toward this end have been fabrication of anode-supported thin-film electrolytes and the reactivity of ESB with conventional cathodes. Recently, an ESB-compatible low area specific resistance cathode was developed: microstructurally optimized Bi 2Ru 2O 7-ESB composites. In addition, we recently developed a novel anode functional layer which can significantly enhance the performance of SOFC utilizing GDC electrolytes. This study combines these recent achievements in SOFC studies and shows that exceptionally high performance of SOFC is possible using ESB/GDC bilayer electrolytes and Bi 2Ru 2O 7-ESB composite cathodes. The result confirms that the bilayer electrolyte and the Bi 2Ru 2O 7-ESB cathode can increase the open circuit potential and reduce the total area specific resistance. The maximum power density of the bilayered SOFC was improved to 1.95 W cm −2 with 0.079 Ω cm 2 total cell area specific resistance at 650 °C. This is the highest power yet achieved in the IT range and we believe redefines the expectation level for maximum power under IT-SOFC operating conditions.