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.

Thank you for your attention!

Krzysztof Kanawka

krzysztof.kanawka07@imperial.ac.uk