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Wang et al. J Mater Inf 2023;3:3 https://dx.doi.org/10.20517/jmi.2022.45 Page 3 of 15

P(O ), and Sr content. The primary poisoning mechanism proposed was the formation of SrSO from the
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4
reaction of SO with SrO and O to form SrSO . Subsequent reactions would start to form other sulfur-
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4
2
containing phases like La O SO and La (SO ) through a reaction with the La components. However, much
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4 3
4
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2
remains unknown as to how these poisoning reactions are affected by the structure and composition of the
cathode material, which limits our ability to design cathodes with improved long-term stability in the
presence of natural SO impurities. Moreover, a comprehensive understanding of the relationship between
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the long-term degradation and single or eventually multiple gas impurities poisoning effects is still needed.
In this work, we have utilized a combined computational and experimental approach to understand the
sulfur poisoning mechanism(s) and improve the long-term durability of LSCF cathodes in order to develop
better-performing sulfur-tolerant cathode materials in the future. We first examined the agreement between
the simulation approach and the experimental observations at various conditions, confirming the reliability
of CALPHAD for poisoning simulations in these cathode systems. Using this approach, we then
investigated the accelerated testing protocol, which has become the standard method for conducting sulfur
poisoning experiments involving LSCF cathode materials. We found that our simulation approach is able to
predict in which systems (cathode material and treatment environment) the accelerated testing protocols
reflect actual operating conditions. Finally, in-depth simulations were done for LSCF and compared with
those for LSM to help understand the LSCF cell system and suggest directions toward alternative cathode
materials that have superior sulfur tolerance.

EXPERIMENTAL PROCEDURE
The as-received (La Sr ) Co Fe O (denoted as LSCF-6428) powders (FuelCellMaterials) were shaped
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0.8
0.4 0.95
0.2
0.6
into several pellets with thickness and diameter of around 1 and 13 mm, respectively. Afterward, the pellets
were pre-sintered in the ambient air at 1,200 °C for 2h to facilitate handling and remove the binders. Later,
the pre-sintered pellets were heat-treated at 800 °C, 900 °C, and 1,000 °C under SO -containing dry air
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(10ppm SO balanced with dry air, Airgas) or dry Argon (10ppm SO balanced with Argon, Airgas) in the
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2
tube furnace (OTF-1500X-III, MTI Corporation) for 2 days. The furnace was equipped with 3 independent
temperature zones, which allowed the above experiments with the same atmospheric but different
temperature conditions to be run in the same batch. Finally, the samples were collected after furnace
cooling for further characterization.
The crystal structures of all the samples, including the commercial powder, pre-sintered and heat-treated
pellets, were examined by X-ray Diffraction with a Cu tube (PANalytical EMPYREAN) in the range of 20-
60°. Later, the microstructure and elemental distributions of the heat-treated pellets were investigated by
Scanning Electron Microscopy (SEM) (JEOL JSM-7000F) coupled with Energy-dispersive X-ray
N
Spectroscopy (EDS) (Oxford Instrument X-MAX ) to characterize the secondary phases. Transmission
electron microscope (TEM) samples, ca. 100 nm thick cross-sections mounted on Cu support grids, were
prepared using a Thermo Fisher Helios 460F1 dual-beam focused ion beam (FIB-SEM) using a Ga ion beam
and standard FIB lift-out procedures to minimize ion damage/implantation. The electron beam was used to
deposit a carbon protective layer on the top surface of each lift-out lamella, and the voltage of the cutting
ion beam was progressively lowered as each lift-out lamella was thinned down to ca. 100 nm and cleaned.
Each FIB-prepared TEM sample was characterized by TEM imaging, diffraction, and spectroscopy
(elemental mapping).

Bright Field TEM images and diffraction patterns were obtained for each FIB-prepared TEM sample using a
Thermo Fisher Talos TEM equipped with a CETA-M camera, operating at 200 keV, gun lens = 4,
spot size = 8, CLA(2) = 70 µm, and beam current: ca. 0.3 nA. An objective lens aperture (OLA) of 70 µm was