1. Fabrication of Dual Layer Ni/Ni-YSZ Hollow Fibers for Anode Support via Phase Inversion and Sintering Method Krzysztof Kanawka, Nicolas Droushiotis, Zhentao Wu, Geoff H. Kelsall and Kang Li Department of Chemical Engineering and Technology, Imperial College London, South Kensington, London SW7 2AZ, United Kingdom

2. Plan of presentation 1.Group introduction – phase inversion 2.Solid Oxide Fuel Cells in our group 3.Anode support geometry 4.Co-extrusion fabrication method 5.Dual Layer Ni/Ni-YSZ hollow fibres 6.Fabrication, characterisations and results 7.Conclusions

3. Group introduction Topic: hollow fibre membranes fabricated via phase inversion Hollow fibres Polymeric Ceramic Hydrogen generation Oxygen production SOFC Filtration Topic of this presentation

4. Phase Inversion (and sintering) - Key point – exchange of solvent (DMSO) with non-solvent (water) with corresponding precipitation of a polymer. - Fabrication of hollow fibres (HF) – spinneret as one of key components. - Proper control of fabrication parameters – enhanced control of a microstructure. - Ceramic HF – ceramic particles mixed with polymer in solvent. - Ceramic HF: additional sintering step at elevated temperatures (1200-1600 º C) and (sometimes) reduction in hydrogen. - Ceramic materials: Al2O3, YSZ, NiO, CGO, LSM, LSCF…

5. Few examples of ceramic hollow fibres Kingsbury and Li 2009 (filtration) Othman et al 2010 (SOFC) Kanawka et al 2010 (SOFC) (manuscript submitted and accepted) Zydorczak, Tan and Li 2010 (oxygen production)

6. Hollow Fibre Solid Oxide Fuel Cells Micro-tubular (hollow fibre) geometry: several advantages over other designs (increased surface area, sealing and cracking issues, packing etc) SOFC Electrolyte support (Highly asymmetric YSZ electrolyte hollow fibres: 18 mW/cm2 at 800 º C) Materials: YSZ (yttria stabilized zirconia) and NiO (nickel oxide) Fuel: 5% H 2 (95% Ar), Oxidiser: air Anode support (Attempt to overcome electrolyte support limitations)

7. Anode Support Geometry Way to overcome electrolyte support limitations. Better anode conductivity, microstructure and performance. Deposition of thin electrolyte layer by a different method. First attempt undertaken in 2008: single layer Ni-YSZ hollow fibres. Result: electrical conductivity - 1 – 2,25 x 10^5 S/m How to improve it? Possible answer – co-extrusion. Droushiotis et al 2009

8. Co-extrusion – dual layer fabrication Advantages of co-extrusion: - Two layers of different properties can be fabricated at the one step with improved adhesion. - Lower fabrication cost and time. - Lower number of required steps (e.g. sintering). These advantages are critical for micro-tubular anode SOFC: effective current collection. - Existing methods of current collection from HF are ineffective and often require manual skills.

9. Dual Layer Ni/Ni-YSZ Ni – YSZ anode Ni current collector

10. Dual Layer Ni/Ni-YSZ Fabrication Solvent + Additives (DMSO, dispersant) Polymer (PESf) Ceramic Particles (NiO, YSZ) Mixing / milling Hollow fibre fabrication (phase inversion) DMSO: Dimethyl Sulfoxide (solvent) PESf: Polyethersulfone (polymer)

11. Spinning Triple-orifice spinneret Inner layer dope (Ni) Internal coagulant (water) Outer layer dope (Ni,YSZ) Air gap Precursor dual-layer fibers Water

12. Dual Layer Ni/Ni-YSZ Fabrication Solvent + Additives (DMSO, dispersant) Polymer (PESf) Ceramic Particles (NiO, YSZ) Mixing / milling Hollow fibre fabrication (phase inversion) Sintering (1400 º C) Reduction (700 º C) …after all these steps dual layer Ni/Ni-YSZ anode hollow fibre was achieved.

13. Results SEM Photomicrographs Thin, inner nickel layer Thick, outer anode Ni-YSZ layer

14. Results Porous, “mesh-like” nickel layer Adhesion between layers

15. Results Electrical conductivity test – dual layer (Separate inner layer – 47 x 10^5 S/m)

16. Results Mechanical properties Highly asymmetric YSZ electrolytes: from Kanawka et al 2010 (manuscript submitted and accepted)

17. Conclusions - Conductivity: several times higher than previous results (Ni-YSZ single layer). - Conductivity: rising with distance (due to presence of current collector layer). - Conductivity: current collector (47x10^5 S/m). - Microstructure: inner layer (current collector) is ‘mesh-like’ (most pores are circa 1-2 μ m in size).

18. Conclusions - Mechanical properties: approximately 190 MPa (suitable for anode support design). - Microstructure: adhesion between layers. - Reproducibility of results: limited ‘manual’ influence. One step closer to effective micro-tubular SOFC system with stable and higher performance.

19. Thank you for your attention! Krzysztof Kanawka krzysztof.kanawka07@imperial.ac.uk