Formation of a Nano-Scale Catalyst Phase in SOFC Anodes via Controlled Precipitation

INVENTION: A new method for introducing Ni or another electrocatalyst phase (e.g. Ru) only in the anode active layer, after high temperature firing. The process provides well dispersed nano-scale catalyst microstructure without additional processing relative to conventional anode-supported SOFC methods.

ADVANTAGES: The metal enriched anode materials generated sustain a fine catalyst phase during operation with catalytic enhancement and improved SOFC performance over time.

SUMMARY: Alternative materials to the currently utilized Ni-YSZ cermet SOFC anode is driven by 1) the degradation of cell performance due to carbon deposition on anodes during hydrocarbon fuel utilization, 2) the mechanical failure of Ni-YSZ cermets under reduction-oxidation cycling, and 3) Ni poisoning by sulfur fuel impurities.

The LSCV-GDC-Ni alternative anode system has demonstrated significant increases in cell performance with the inclusion of small amounts of Ni in these ceramic SOFC anodes. Despite the presence of Ni, redox stability and short-term direct hydrocarbon utilization have been demonstrated with these anodes, likely due to their low Ni content. Fabrication of such anode systems is adversely effected by the high temperature co-firing usually employed with Ni-YSZ cermets. Coarsening of Ni particles, and to a lesser extent the entire anode microstructure results in significant cell performance decrease observed with increasing anode sintering temperature.

To address this limitation a new method of introducing the electrocatalyst metal in the anode active layer was developed. It is now demonstrated that a Ni or other catalyst phase, e.g. Ru, could be precipitated out of the anode after high temperature firing and other SOFC processing steps were completed. The catalyst is dissolved on the B-site of LaCrO3 affording single phase La0.8Sr0.2Cr1-xNixO3 and La0.8Sr0.2Cr1-xRuxO3 materials which were mixed with GDC to form the SOFC anodes as usual. Upon initial cell operation and anode reduction, the catalyst phase precipitates out of the oxide phase forming a new anode catalytic microstructure. The precipitate particles form after high-temperature firing and thus avoiding coarsening. This process affords enhanced SOFC activity for both Ru and Ni doped anode systems. As the metals precipitate over time SOFC power density improves (Figure 1), open circuit voltage increased (Figure 2) and individual resistances decreased, consistent with overall enhanced cell performance. These advances are realized in SOFCs without additional process steps versus conventional anode-supported fabrication methods.

STATUS: A patent application has been filed.

Inventor(s): Scott Barnett, Brian Madsen, Worawarit Kobsiriphat

Type of Offer: Licensing

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