Cost-Effective Highly Robust SOFC Interconnect Coating Process

Solid oxide fuel cells (SOFCs) offer exceptional promise for electrical power generation with reduced carbon footprint, but SOFC reliability must be improved. SOFCs utilize ferritic stainless steel sheets as interconnect plates between the fuel and air chambers. They are sealed using alkali earth - silicate glass that remains vitreous at operating temperatures, typically 650-850C. Reactivity of the alkali earth elements in the seal glass with chromium oxide in the steel interconnect leads to diffusion formed voids in the glass, which in turn cause seal failures. Yttrium stabilized zirconia (YSZ) has been identified as a potential barrier to prevent alkali earths in the seal glass from reacting with the interconnect. To be successful, YSZ with a high degree of density, structural perfection and uniformity must be formed in cost effective way over rough interconnect surfaces. The project will leverage atomic layer deposition (ALD) to form the YSZ barrier. The objective is to demonstrate YSZ barriers with high density and conformality, using a simple masking technique, to permit large production lots of 1000-2000 interconnects, with the barrier limited to the interconnect perimeter. Phase I demonstrated exceptionally dense, adhesive and uniform YSZ barrier layers on ferritic stainless steel interconnects, and a novel masking technique was developed. Reliability testing, performed by a major fuel cell manufacturer, showed this barrier significantly reduced diffusion at the interconnect/glass interface, demonstrating feasibility of the technology. A detailed cost analysis projects barrier cost in line with DOE targets for a mature process. All Phase I Tasks were successfully completed. Phase II will systematically optimize YSZ barrier film performance on ferritic stainless steel, extend the Phase I masking approach to full sized interconnects, and evaluate long-term performance of the barrier. Experiments will employ a prototype coating tool that can process 50-100 full size interconnects. Phase II will result in a completely defined barrier manufacturing process, including design of a full-scale coating system. Commercial Applications and Other Benefits High performance YSZ barrier films will dramatically increase SOFC reliability, which will multiply the demand and applications of the technology, and leverage the expanding supply of natural gas in the U.S. Other thermal barrier applications may benefit from this technology, particularly for use in engines and turbines, leading to increased efficiency.