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.
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