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Chromium poisoning of the cathode remains a significant obstacle to the stable long-term performance of solid oxide fuel cells. This study reports, a quick, in-situ mitigation method, called electrochemical cleaning. By applying a mild anodic bias, the electrochemical deposition reactions of chromium-containing species are reversed. Chromium vapor species are formed, freeing active electrochemical sites in the air electrode. An LSM/YSZ-based cell was exposed to Cr vapors at 800ºC and then subjected to electrochemical cleaning. Cell performance recovery was evidenced by current-voltage and EIS measurements. Chromium removal was verified using SEM and EDS analyses. The cyclability of the electrochemical cleaning was tested by repeated poisoning and cleaning of another cell. Investigation into the effect of cell operating parameters (current density and cell temperature) on the rate of cleaning is discussed.

Chromium poisoning of the air electrode remains an obstacle to the long-term performance of solid oxide fuel cells (SOFCs). In Sr-doped LaMnO3 (LSM) air electrodes, the poisoning process results in two types of deposits, chromium oxide (Cr2O3), and Mn, Cr spinel (MnCr2O4). The former forms electrochemically and the latter forms via a chemical reaction. By applying a small anodic reverse bias, Cr2O3 deposits can be removed because their formation is electrochemical in nature. However, MnCr2O4 deposits remain because their formation is chemical, rather than electrochemical, in nature. In situ chemical decomposition of the Mn, Cr spinel was investigated as an alternate removal method as thermodynamics supports its decomposition into constituent oxides below ∼540 °C in pure oxygen. The spinel decomposition process was characterized using thermogravimetric and X-ray diffraction analyses. The experimentally determined rate of spinel decomposition was undetectable (very slow) with isolated MnCr2O4 powders. The addition of 10 mol% gadolinia doped ceria (GDC) and silver powders significantly increased the rate of decomposition. However, the rate is limited by the diffusion of oxygen through the decomposed oxide layer. Although one strategy may be the addition of GDC and silver to the LSM air electrode to enhance spinel decomposition, the more effective mitigation strategy would be to prevent the formation of MnCr2O4 spinel in the first place through the removal of the reactants: Cr2O3 via electrochemical cleaning and mobile Mn ions in the zirconia electrolyte by incorporating a diffusion barrier layer such as GDC between the air electrode and electrolyte.

The LBNL metal-supported solid oxide cell architecture contains zirconia electrolyte and porous backbones co-sintered between porous stainless steel supports. Advantages of this design include low-cost structural materials, mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These features enable a wide variety of applications including electrolysis for intermittent renewables, distributed power generation, and synthesis of valuable chemicals. Highlights from efforts in these areas are presented.

Stainless steel interconnects in solid oxide fuel cells can lead to chromium poisoning of the cathode, necessitating the use of protective coatings. Electrophoretic deposition is an efficient method to deposit coatings on substrates with complex microstructures. In this study, four spinel coatings; CuMn2O4, CuNi0.2Mn1.8O4, MnCo2O4, and MnFe0.34Co1.66O4, were deposited by direct-current electrophoretic deposition on flat SUS430 stainless steel substrates. The coatings were evaluated on multiple criteria, including microstructural stability, conductivity, Cr gettering ability, and the ability to act as a diffusion barrier at 700°C and 800°C. It was concluded that CuNi0.2Mn1.8O4is an excellent candidate at temperatures at and below 700oC, while MnFe0.34Co1.66O4coatings perform better at higher temperatures.

Electrochemical cleaning, a recently proposed mitigation strategy for chromium poisoning in solid oxide fuel cell (SOFC) cathodes, involves rapid in-situremoval of Cr2O3deposits from LSM-YSZ cathodes accompanied by a recovery of a large fraction of the cell performance originally lost due to Cr poisoning. By operating the cell briefly as a solid oxide electrolyzer cell (SOEC), the cleaning method effectively reverses the Cr deposition reactions, reforming Cr-containing vapor species, thereby freeing up electrochemically active sites and restoring cell performance. In practice, this method can be periodically applied to the system after a specified amount of degradation due to chromium poisoning has occurred. The current study investigates the efficacy of this method by cycling a single cell through a stage of accelerated poisoning followed by electrochemical cleaning for a total of three times. Current-voltage measurements demonstrate repeated loss in performance due to Cr poisoning and recovery in performance due to electrochemical cleaning, reinforcing the utility of this cleaning method over the lifetime of the cell operation.