Extended Duration (1000 h) In-situ XRD of Operating LSCF

Extended Duration (1000 h) In-situ XRD of Operating LSCF Cathodes John S. Hardy, Jared W. Templeton, and Jeffry W. Stevenson

New SOFC Research Capability was Developed at PNNLIn-situ XRD of Anode-supported SOFCs during Operation

Bruker D8 Advance XRD…

…with Anton Parr HTK 1200 Heating Chamber

XRD-compatible SOFC Test Fixture

Small-scale (13 mm dia) button cell• 0.5 cm2 LSCF-6428 Cathode on SDC Interlayer• Ni-YSZ Anode-supported ~10µm YSZ

Electrolyte

Experimental Parameters for ~1000 hour tests Cell Tests • Operating Cell: Constant Current simulating 800 mV • Resting Cell: OCV • Feed Gas: Flowing air and moist H2 • Temperature: 750°C XRD • Repeated 1 hour scans • 2θ Range: 25 - 85° • Step Size: 0.02° • Time/Step: 1.1 seconds

Resting Cell (at OCV) Operating Cell (~0.8 V)

60

65

70

75

80

85

90

95

100

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

0 200 400 600 800 1000 1200

Similarity Index (%

)

OCV

(V)

Time (h)

OCV

1 h XRD

50 h XRD

88.5

89

89.5

90

90.5

91

91.5

92

92.5

93

0 5000 10000 15000 20000 25000 30000

Sim

ilari

ty In

dex

(%)

Intensity of Au Peak at 43.8° 2θ (Counts)

Changes in SI were due to changes in peak intensity of the Au current collector

• No significant changes detected in LSCF peaks over time • Secondary phases of Fe3O4 and Co3O4 exhibited peak shifts

• Lattice parameters were diverging from one another

11

29.9 30.1 30.3

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

30.6 30.8 31

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

35.1 35.3 35.5 35.7

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

35.9 36.4

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

37.2 37.3 37.4 37.5

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

42.8 43 43.2

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

56.7 56.8 56.9 57

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

62.3 62.4 62.5 62.6

Inte

nsit

y (C

ount

s)

2θ ( )

200 h400 h600 h800 h1000 h

75

78

81

84

87

90

93

96

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 200 400 600 800 1000 1200

XRD Sim

ilarity Index (%)Po

wer

Den

sity

(W/c

m2)

Time (h)

Cell Performance200 h XRD50 h XRD1 hr XRDLinear (60 h Test)

• SI of 1 hour patterns followed exponentially decaying trend • Power density also follows exponentially decaying trend

• Inspection of XRD patterns did not identify the specific changes responsible for the decrease in SI.

Comparison of Resting vs Operating Cells

OCV OperatingLSCF 97 wt% 91 wt%LaCoO3 <2 wt% <2 wt%Fe3O4 <2 wt% 7 wt%Co3O4 <2 wt% ---

Cathode Composition

Summing 1000 hours of XRD scans made it possible to resolve trace phases

• LSCF lattice of operating cathode was larger than that of the resting cathode • A shoulder peak was present on the low angle side of LSCF peaks of operating cathode, suggesting the presence of a second perovskite composition

8.42

8.422

8.424

8.426

8.428

8.43

8.432

8.434

0 200 400 600 800 1000 1200

Fe3O

4La

ttic

e Pa

ram

eter

(Å)

Time (h)

OCV

0.8 V

• Fe3O4 lattice parameter was larger and constant in the operating cathode. • It expanded over time in the resting cathode.