Manufacturing of Metal Foam Supported SOFCs with Graded Ceramic Layer Structure and Thinfilm Electrolyte Feng Han 1, Robert Semerad 2, and Rémi Costa 1 1 German Aerospace Center 2 Ceraco Ceramic Coating GmbH
www.dlr.de Chart 2 Motivation and Objectives (1) Demonstration of the feasibility of the metal foam supported cell concept and design. (2) Deposition of gas-tight thin-film electrolyte (~3 µm thick) layers to ensure low ASR (3) Development of metal foam supported SOFCs in combination with desired materials and catalysts to address issues of SOFC technologies: sulfur poisonning, redox stability
www.dlr.de Chart 3 DLR state-of-the-art Metal-supported SOFC (MSC) Full plasma sprayed cell Cathode Electrolyte Anode Conventional Porous metal Metal foam Replacement 2000 hours tests degradation rate <1.5%/kh P. Szabo, et. al., ECS Trans. 25 (2) (2009) 175 185.
www.dlr.de Chart 4 Electrolyte Manufacturing Routes on MSC Thick VPS electrolyte Prototype, low-risk and experienced approach Challenges: 1. Robust substrate 2. Gas-tight electrolyte 3. Efficient functional anode layer Thin PVD electrolyte High-risk and high impact approach Challenges: 1. Well-defined surface structure 2. Gas-tight thin electrolyte 3. Thermal stability of the multi-layers [1] [1] N. J. Escalona, Herstellung von Hochtemperatur-Brennstoffzellen über physikalische Gasphasenabscheidung, PhD thesis, 2008 Thinner electrolyte Lower ASR 200 µm 10 µm
www.dlr.de Chart 5 Performance on ASC cells with thin electrolyte 1.8 A/cm 2 @600 o C Cathode size 4 cm x 4 cm Up-scaling size 9 cm x 9 cm ASR < 0.05 Ω cm 2 @ 650 o C F. Han, et. al., J. of Power Sources, 218 (2012)157-162.
www.dlr.de Chart 6 Manufacturing of current collecting support Engineering of pore size 79 nm 164 nm 200 µm Coarsened particles Prolonged calcination 216 nm 355 nm 200 µm Pore size distribution of calcined NiCrAl alloy substrates with impregnated LST
www.dlr.de Chart 7 Example of graded layer structure Intermediate YSZ layer Mesoporous Abundance (%) 25 20 15 10 4 nm 7 nm 12 nm 26 nm 42 nm For intermediate layer coating b TEM of nano-particles 5 1 µm 0 1 10 100 1000 Particle size (nm) TEM of nano-particles 1 µm 4 µm Anode Macroporous F. Han, et. al., J. of Power Sources, 218 (2012)157-162.
www.dlr.de Chart 8 Surface Engineering Top view SEM: (a) NiCrAl foam, (b) NiCrAl foam with impregnated LST, (c) LST-GDC anode functional layer, (d) dip-coated YSZ layer
www.dlr.de Chart 9 Surface Engineering for supporting PVD GDC 200 nm 200 nm 200 nm 200 nm
www.dlr.de Chart 10 A Way to Thin Electrolyte GDC Electrolyte YSZ Anode Anode YSZ Sketch of cell design NiCrAl Metal foam NiCrAl Metal foam LST LST Anode: LST+GDC
www.dlr.de Chart 11 Dense and Gas-tight PVD GDC Electrolyte SEM of LST-GDC/YSZ/GDC interfaces: (a) cross section, (b) elemental mapping
Leakage rate of half cells with PVD electrolyte Leak rate of half cells 50mm 7x10-4 (hpa dm 3 )/(s cm 2 ) State-of-the-art half cells Gas-tightness is crucial for cell performance
www.dlr.de Chart 13 Thermal Stability of bi-layer Electrolyte Thermal Treatment @ 1000 o C on Half Cells with PVD GDC 500 nm 500 nm 2 µm 2 µm
Cell processing route with graded layer strcuture and PVD electrolyte anode YSZ GDC substrate Impregnation 1000 C 1000 C screen printing Dip-coating 600-1000 C PVD Challenges: -Defect-free anode layer -Adhesion of layers -Thermal stability solid oxide fuel cell cathode Dense electrolyte screen printing wet powder spraying
www.dlr.de Chart 15 Conclusion i. Half cells have been fabricated on substrates consisting of NiCrAl alloy foam as structural support and impregnated LST ceramic as anode material. ii. Thin-film YSZ-GDC bi-layer electrolytes were made of dip-coated 1 µm thick YSZ layer and 2 µm thick PVD GDC layer. iii. Despite the thin electrolyte, the leakage rate of the half cells with thinfilm YSZ-GDC bi-layers has been measured as low as 7x10-4 (hpa dm 3 )/(s cm 2 ), demonstrating an good gas-tightness. iv. Further optimization and electrochemical tests of the cells will follow in future work. v. Potentials for other application fields requiring low ASR at low temperature: SOECs, co-electrolysis, methanation, and etc.
www.dlr.de Chart 16 Acknowledgements The research leading to these results has received funding from the European Union s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement No. 303429 (Project EVOLVE).
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