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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 PNNL In-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 cm 2 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 H 2 • 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 Similarity Index (%) 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 Fe 3 O 4 and Co 3 O 4 exhibited peak shifts • Lattice parameters were diverging from one another 11 29.9 30.1 30.3 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 30.6 30.8 31 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 35.1 35.3 35.5 35.7 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 35.9 36.4 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 37.2 37.3 37.4 37.5 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 42.8 43 43.2 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 56.7 56.8 56.9 57 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 h 62.3 62.4 62.5 62.6 Intensity (Counts) 2θ () 200 h 400 h 600 h 800 h 1000 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 Similarity Index (%) Power Density (W/cm2) Time (h) Cell Performance 200 h XRD 50 h XRD 1 hr XRD Linear (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 Operating LSCF 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 Fe 3 O 4 Lattice Parameter (Å) Time (h) OCV 0.8 V • Fe 3 O 4 lattice parameter was larger and constant in the operating cathode. • It expanded over time in the resting cathode.
