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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
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
Group introduction
Topic: hollow fibre membranes fabricated via phase inversion
Hollow fibres
Polymeric
Ceramic
Hydrogen generation
Oxygen production
SOFC
Filtration
Topic of this presentation
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 ºC) and (sometimes) reduction in hydrogen.
- Ceramic materials: Al2O3, YSZ, NiO, CGO, LSM, LSCF…
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)
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 ºC)
Materials: YSZ (yttria stabilized zirconia) and NiO (nickel oxide) Fuel: 5% H2 (95% Ar), Oxidiser: air
Anode support
(Attempt to overcome electrolyte support limitations)
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
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.
Dual Layer Ni/Ni-YSZ
Ni – YSZ anode
Ni current collector
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)
Spinning
Triple-orifice spinneret
Inner layer dope (Ni)
Internal coagulant (water)
Outer layer dope (Ni,YSZ) Air gap
Precursor dual-layer fibersWater
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 ºC)
Reduction (700 ºC)
…after all these steps dual layer Ni/Ni-YSZ anode hollow fibre was achieved.
Results
SEM Photomicrographs Thin, inner nickel layer
Thick, outer anode Ni-YSZ layer
Results
Porous, “mesh-like” nickel layer
Adhesion between layers
Results
Electrical conductivity test – dual layer
(Separate inner layer – 47 x 10^5 S/m)Distance between terminals (cm)
1 2 3 4 5
Ele
ctri
cal c
on
duc
tivity
x1
0^5
(S
/m)
0
2
4
6
8
10
44
46
48
50
Results
Mec
hani
cal s
tren
gth
[MP
a]
0
50
100
150
200
250
300
Sintered dual layer Ni/Ni-YSZReduced dual layer Ni/Ni-YSZHighly asymmetric YSZ electrolytes
Mechanical properties
Highly asymmetric YSZ electrolytes: from Kanawka et al 2010 (manuscript submitted and accepted)
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 μm in size).
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.