Page 35 - Read Online

Wang et al. J Mater Inf 2023;3:3 https://dx.doi.org/10.20517/jmi.2022.45 Page 13 of 15

predict that ambient SO will be insufficient to drive SrSO stability, the use of accelerated testing can
2
4
potentially generate erroneous experimental results regarding SrSO poisoning related to standard testing
4
[17]
conditions . Using this simulation approach, the reliability of accelerated testing can be scrutinized for
different cathode materials under different environmental conditions.
The threshold diagrams of the LSCF cathode suggest that LSCF has poor sulfur tolerance under operating
conditions, and finding an alternative sulfur-resistant cathode material thus remains of great importance.
To better understand the sulfur poisoning of LSCF cathode in the context of other potential cathode
materials, CALPHAD threshold diagrams were created for LSM20 and compared to LSCF-6428 in terms
[17]
of P(SO ) and temperature under air and argon atmospheric conditions, as shown in Figure 9. Simulations
2
predict that LSM20 has superior sulfur resistance to LSCF-6428 both in the air and argon conditions.
Specifically, the threshold of SrSO stability for LSM20 is around 10 atm at 800 °C in air, while it is 10 atm
-7
-10
4
for LSCF-6428. Unlike LSCF-6428, LSM20 could be free from sulfur poisoning at ambient SO . This sulfur
2
[6]
resistance behavior was also experimentally observed by Liu et al. , where LSM20 was found to be free from
sulfur poisoning even following exposure to 1ppm of SO for 1,000 h, and the degradation rate at 20 ppm
2
SO for LSCF-6428 was 8 times higher than that of LSM20. These computational and experimental results
2
confirmed that the LSCF cathode is a poor sulfur-tolerant material in comparison with LSM. One potential
solution for the poor sulfur resistance of LSCF is to place an additional sulfur filter before contacting the
LSCF cathode to purge the sulfur concentration to below the threshold concentration. Another solution
[32]
would be to utilize a core-shell structure , having LSM as the sulfur-protecting shell and LSCF cathode as
the core.
CONCLUSIONS
In this work, we have evaluated the sulfur poisoning behavior of LSCF cathode materials in the presence of
SO with a combined computational and experimental approach and tested the reliability of the simulation
2
method for predicting sulfur poisoning behavior under different environmental conditions. The results
from CALPHAD simulations regarding the stability of the secondary phases were validated using the
experimental characterization, XRD, SEM, and TEM, of the same cathode materials following operations at
the simulation conditions. Further simulation predictions were made to better understand the effects that
other determining factors, such as temperature, P(O ), P(SO ), and cathode Sr-composition, have on the
2
2
formation of SrSO and the overall sulfur poisoning behavior. We find that the formation of SrSO on LSCF
4
4
cathodes (sulfur poisoning) is more thermodynamically favorable at lower temperatures, higher P(SO ),
2
higher P(O ), and higher Sr composition. Finally, comparisons were made between LSCF-6428 and LSM20
2
cathode materials, which confirmed that LSCF-6428 has a much lower sulfur tolerance than LSM20, in
agreement with recent literature. The CALPHAD simulation approach used here can be extended to other
potential cathode systems to theoretically test their tolerance to poisoning at different environmental
conditions, which has the potential to accelerate the experimental development of novel poisoning-resistant
cathode materials.

DECLARATIONS
Authors’ Contributions
Made substantial contributions to conception and design of this research, data analysis, writing the draft
and editing: Wang R
Performed data analysis, figures preparation, writing-review and editing: Parent LR
Made substantial contributions to conception and design of this research, data analysis, funding acquisition,
writing and editing: Zhong Y