“fabrication of intermediate sofcs via plasma...

US Nanocorp®, Inc., 74 Batterson Park Road, Farmington, CT 06032

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SECA Core Technology Workshop

“Fabrication of Intermediate SOFCsVia Plasma Spray”

Sponsors1. DOE SBIR Phase I: Contract No: DEFG0201ER833402. Siemens Westinghouse Power Corporation (“SWPC”)

Danny Xiao, Ph.D.

US Nanocorp, Inc.

June 18, 2002


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Program ObjectivesThe program objectives are to demonstrate the feasibility of:• Synthesizing a novel mixed ionic and electronic

conductor (“MIEC”) yttrium-doped strontium titanate anode material Sr1-1.5xYxTiO3 (“SYT”)

• Plasma spray fab. SOFC testing cells using LSM cathode, LSGM electrolyte, and Sr1-1.5xYxTiO3 anodefor intermediate temperature (500 - 800oC) appls.

• Plasma spray fab. SOFC cells using SWPC’s cathodetubes, LSGM electrolyte, and LDC40 + Ni anode forintermediate temperature (500 - 800oC) appls.

DO

E SB

IR P

hase

ISW

PC


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Fuel Cell SystemsSystem one: DOE Program:

Anode- Nano Sr1-1.5xYxTiO3Electrolyte – La0.8Sr0.2Ga0.8Mg0.2O3Cathode – La0.8Sr0.2MnO3

System two: SWPC Program:Anode- LDC40 + NiInterlayer LDC40Electrolyte – La0.8Sr0.2Ga0.8Mg0.2O3Cathode – SWPC proprietary

tubular substrate

SYT

LSM

LSGM

LDC40 + Ni

SWPC tubeLSGM

LDC40


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StableNot stableLong term phase stability

500 – 800oC800 –1000oC

Operation temperatures

ExtendedLimitedAvailable reaction sites

NoYesSulfur Poisoning

NoYesCarbon deposition

US NanocorpNanostructured

SYT

Nickel –ceramic anode

Properties

Nanostructured MIEC SYT Anode

Particle size stability Yes Yes@ 500 – 800oC


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(1). Prepare precursor solutions of Sr-, Y-, and Ti-containing salt solutions, and a reducing solution

(2). Reaction of the precursors at 60-100o C to form apreceramic gel-like powder

(3). Initial calcinations of the Sr-Y-Ti-O complex at 350oC to form to form intermediate powder

(4). Calcination of the intermediate powder at 650oC to form nanostructured Sr1-1.5xYxTiO3 anode material

Synthesis of Sr1–1.5xYxTiO3 nanoparticles


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TEM micrographs showing the microstructures of SYTnanoparticles synthesized by wet chemical synthesis

100 nm

Lin

(Cou

nts)

206

0

2-Theta - Scale

20 30 40 50 60 70

XRD spectra of the synthetic SYT powders with average SYT grain size ~ 50 nm.


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13 14 15 16 17 18 19 200

10

20

30

40

50

60

70(a)

(b) :(g)

σ (S

/cm

)

-log PO2

(atm)

0 .00 0 .05 0 .10 0 .150

10

20

30

40

50

60

70

800 oC & PO

2

=10 -19 atm

σ (S

/cm

)x in Sr1-1 .5xY xTiO 3-δ

Conductivity as a function of Y-doping level at 800oC and oxygen partial pressure of 10-19 atm.

Electrical conductivity vs partial O2 pressures at 800oC for donor doped SYT (a) Sr0.88Y0.08TiO3-δ, (b) Sr0.25La0.50TiO3-δ, (c) Sr0.88Yb0.08TiO3-δ, (d) Sr0.88Gd0.08TiO3-δ, (e) Sr0.88Sm0.08TiO3-δ, (f) Sr0.85La0.10TiO3-δ, (g) Ca0.88Y0.08TiO3-δ.


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20 30 40 50 60 70

(a)

*

x

**

*

xx

*

x

* SYTx YSZ

Inte

nsity

(b)

2θ

XRD for the sintered mixtures (a) SYT + YSZ, (b) SYT + LSGM. No new phase has been detected

0 200 400 600 800 1000

0

2000

4000

6000

8000

10000

12000 LSG M

Y SZ

SY T

Exp

ansi

on (p

pm)

T em perature (oC )

Thermal expansion plots for SYT, LSGM, and YSZ

Compatibility of SYT Nanoparticles


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Problems of Nanopowders in Thermal Spray

• Cannot be fed into the existing industrial thermal spray systems

• Too low mass

• Inability to be carried in a moving gas stream

• Inability to be deposited onto a substrate to form a dense coating


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Thermal Spray Feedstock Specifications

· Solid spherical particles, 15 to 100 mm

· Fully sintered solid agglomerates

· Flow freely in the existing thermal spray powder feeding

· Right porosity for anode application


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20 µm

5 - 20 nmparticles

reconstituted sprayable form

5 - 20 nmparticles

non-agglomerated

5 - 20 nm particles

loosely agglomerated

hollow shell agglomerates

30 µm

Thermal Spray Feedstock Reconstitution


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Thermal Spray Feedstock Reconstitution

• Dispersion of SYT nanoparticles into a solvent

• Addition of surfactants and binders

• Reconstitution of the nanoparticle slurry into agglomerated micrometer sized particles

• Heat treatment to remove binder and nanoparticle sintering

• Agglomerated particle size classification


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SEM micrograph showing the reconstituted nanostructured SYT thermal spray feedstock

100 µm 10 µm


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Thermal spray GunNanocoated Component

Nanomaterial feedstock Substrate

Thermal Spray Fab. Thermal Batteries

Anode electrode

Cathode electrode

Electrolyte


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Advantages of T/S Fab. Vs. Other Fab of SOFC

• Rapid fabrication and sequential fabrication of cells• Thickness of each material can be accurately controlled• Robotic control / continuous operation• Potential low cost production (automation)• Graded & multilayer structures (porosity & composition)• Excellent interfacial contact• Nanostructured materials• Large area and free geometry• Unlimited substrates (room temperature)


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Photos of plasma sprayed free standing SOFC single cells porous consisting anode and cathode, and dense electrolyte


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50 µm

SYT

LSGM

LSM

50 µm

YSZ/Ni

LSGM

LSM

SEM image for the thermal spray SYT– LSGM – LSM/LSGM layer

SEM image the thermal spray YSZ/Ni-LSGM-LSM/LSGM layer


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YSZ/Ni

LSGM

SYT/Ni

LSGM

LSM

LSGM

SYT

LSGM

SEM micrographs showing excellent interfacial bonding between anode/electrolyte, electrolyte/cathode using the

plasma spray technique.


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XRD for Thermal Sprayed Materials

25 35 45 55 65 75

Two Theta (degrees)

Inte

nstiy

(arb

. uni

ts)

LSGM feedstock

LSGM spray layer

spray layer, 500 c

spray layer, 700c

spray kayer, 800c

spray layer, 900c

25 35 45 55 65 75Two Theta (degrees)

Inte

nsity

(arb

uni

ts)

LSM feedstock

LSM spray layer

LSGM feedstock

LSGM spray layer

XRD patterns for the feedstock and thermal spray layers of LSM and LSGM

XRD Patterns showing thermal sprayed LSGM annealing at different temperatures

Non – Annealed Annealed


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Photo of the fuel cell evaluation system

R

CA

ES

O2Fuelgas

A

V

Schematic setup

Fuel Cell Performance Evaluation


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Stability of Open-Circuit Voltage

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60

Time hour

Volta

ge V 700oC

0

0.2

0.4

0.6

0.8

1

1.2

250 350 450 550 650 750

Temperature /oC

Vol

tage

/V

3oC/min

Open circuit voltage vs timeOpen-circuit voltage vs. temperature


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Voltage-power vs. current density

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 3500

10

20

30

40

50

60

70

80

90

current density mA/cm2

volta

ge V

650oC

power m

W/cm

2

800oC

750oC

700oC

600oC

800oC

750oC

Preliminary Data on Lab Testing Rig*

*Low values due to poor crystallinity of the electrolyte


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Technical Issues Concern T/S LSGM SOFCMechanical strength:

– Normally LSGM is weak. When it is deposited ona substrate, such as SWPC’s tubular cathode design, this coating becomes more durable

Pinhole issue: – Studies indicated ~ 50 µm thickness of LSGM,

pinholes are unavailable. Also SWPC’s thermalsprayed YSZ has to be > 80 mm thick to avoid pinholes. From our preliminary results using lab scale cell, we have eliminated all pinholes usingour plasma parameters for ~50 µm thickness.


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Plasma Spraying LSGM SOFC using SWPC’s Cathode Tubes

Thermal spray Gun LSM tube

LSGM feedstock

LSGM electrolyteLDC40+Ni anode

SWPC’s tubular substrateLDC40 interlayer

(a)

(b)


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Thermal Spray Process Description

Cathode: SWPC’s proprietary substrate

Electrolyte: LSGM powder or liquid

Interlayer: LDC powder or liquid spray

Anode: Nickel + LDC both via: (1) plasma spray powder (2) plasma spray liquid feedstock


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Pump

Tungsten Anode

Tungsten Cathode

Atomizing Nozzle

Work pieceYSZ Liquid Feed Stock

+

+-

Gas

Gas

Plasma

Liquid Feedstock Plasma Spray


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Advantages of Liquid Spray Anode

• Forming 3-D porosity structure, leading to high fuel gas permeability toward LSGM electrolyte

• Forming nanostructured anode, increase surface area of fuel – solid interaction

• Enable thin layer coating formation

• Higher thermal shock resistance


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50 µm

30 µm

30 µm

LSGM

SWPC cathode

SWPC cathode

SWPC cathode

LDC40

LDC40 + Ni

LSGM


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Conclusions1. Demonstrated the feasibility of synthesizing

nanostructured SYT anode material using a wet chemical synthesis route and reconstitute into thermal spray feedstock

2. Demonstrated the feasibility of fabricating single SOFC units via sequential plasma spray technique, for porous SYT anode, dense LSGM electrolyte, and porous LSM


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Conclusions – continued

3. Demonstrated acceptable performance of the single SOFC using plasma spray technique

4. Demonstrated the feasibility of fabricating single SOFC units via sequential plasma spray technique, where the anode electrode is formed by a novel liquid feedstock technique


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Future Studies1. Cell polarization vs. components

2. Crystallinity of thermal sprayed LSGM electrolyte – Post annealing temperature vs. crystallinity– Cell performance vs. crystallinity

3. Pinholes– Thickness of LSGM electrolytes – Plasma spray parameters

4. Anode conductivity– Ionic conductivity – Electronic conductivity

“fabrication of intermediate sofcs via plasma...

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