Abstract
Chromium (Cr) vapor species from chromia-forming alloy interconnects are known to cause cathode performance degradation in solid oxide fuel cells (SOFCs). To understand the impact of Cr-poisoning on cathode performance, it is important to determine its effects on different cathode polarization losses. In this study, anode-supported SOFCs, with a (La,Sr)MnO3 (LSM) + yttria-stabilized zirconia (YSZ) cathode active layer and a LSM cathode current collector layer were fabricated. At 800°C, cells were electrochemically tested in direct contact with Crofer22H meshes, under different cathode atmospheres (dry air or humidified air) and current conditions (open-circuit or galvanostatic). Significant performance degradation was observed when cell was tested under galvanostatic condition (0.5 A/cm2), which was not the case under open-circuit condition. Humidity was found to accelerate the performance degradation. By curve-fitting the experimentally measured current-voltage traces to a polarization model, the effects of Cr-poisoning on different cathodic polarization losses were estimated. It is found that, under normal operating conditions, increase of activation polarization dominates the cathode performance degradation. Microstructures of the cathodes were characterized and Cr-containing deposits were identified. Higher concentrations of Cr-containing deposits were found at the cathode/electrolyte interface and the amounts directly correlated with the cell performance degradations.
Highlights
This work was made openly accessible by BU Faculty
Taniguchi et al reported that Cr moves to cathode/electrolyte interface by cathodic current, and cathode polarization increases in correlation with the intensity of chromium at the interface.[8]
Et al used the distribution of relaxation times (DRT) method to separate the impedance spectra into single loss contributions, and they discovered that the process which couples oxygen surface exchange at the triple phase boundaries (TPB’s) and oxygen ion diffusion in the bulk cathode was impacted by Crpoisoning.[15]
Summary
Citation (published version): Ruofan Wang, Uday Pal, Srikanth Gopalan, Soumendra Basu. 2017. Citation (published version): Ruofan Wang, Uday Pal, Srikanth Gopalan, Soumendra Basu. "Chromium poisoning effects on performance of (La, Sr) MnO3-based cathode in anode-supported solid oxide fuel cells." Journal of The Electrochemical Society, Volume 164, Issue 7, pp. Chromium Poisoning Effects on Performance of (La,Sr)MnO3-Based Cathode in Anode-Supported Solid Oxide Fuel Cells. Cathode active layer slurry was prepared by mixing (La0.8Sr0.2)0.95MnO3-δ (Fuel Cell Materials, USA) and 8YSZ (Tosoh Corp., Japan) powders in 50:50 wt% and ball milling for 10 hours in alpha-terpineol (Alfa Aesar, USA) with the desired amount of pore former (Carbon lampblack, Fisher Scientific, USA) and binder (V6, Heraeus, USA). A gold gasket (Scientific Instrument Services, Inc., USA) on the cathode side and a mica gasket (Fuel Cell Materials, USA) on the anode side were compressed by spring loading of approximately 5 kg to obtain gas tightness. Dry air was obtained by passing compressed air through desiccant, and 10% humidified air was obtained by passing the dry air through a water bubbler maintained at 46◦C
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