Data_Sheet_1_Sulfur Poisoning and Performance Recovery of SOFC Air Electrodes.PDF

The sulfur poisoning and performance recovery of the state-of-the-art SOFC cathodes (La0.80Sr0.20)0.95MnO3±δ (LSM) and (La0.60Sr0.40)0.95Co0.20Fe0.80O3–δ (LSCF), have been studied. Electrochemical impedance spectroscopy measurements of LSCF|GDC and LSM|YSZ half-cells are carried out in alternating atmospheres of air and SO2–air at 700°C for hundreds of hours. In the presence of SO2, the electrochemical performance of both the cells decays with ohmic and non-ohmic losses, owing to the absorption and chemical interaction of SO2 with the electrodes. In LSCF, the SrO segregated on the surface tends to absorb and react with SO2, forming SrSO4 followed by the exsolution of Co-Fe. As for LSM, SO2 is absorbed onto the Sr-rich areas of LSM, including the active reaction sites near the TPBs, leading to Sr exsolution and SrSO4 formation, leaving a Sr-deficient LSM. During the subsequent exposure to air, the performance of the sulfur-contaminated LSM is almost restored. The LSM particles, exposed to alternating atmospheres of air and SO2-air during the electrochemical tests, show a relatively clean surface with sparsely distributed SrSO4 particles, indicating a high stability against sulfur poisoning. It is suggested that the loosely adsorbed SO2 at the TPBs is readily swept away by the SO2-free air flow, recovering its ORR activity, whereas the Sr-deficient LSM due to Sr-exsolution stays modified, contributing to the incomplete performance restoration. Unlike the case of LSM, the performance of the sulfur-poisoned LSCF partially recovers during the subsequent exposure to air. Correspondingly, the LSCF particles have a modified morphology covered with numerous nanoparticles, mostly SrSO4, showing the irreversible aspect of the sulfur poisoning. The morphology modification is not concentrated near the electrode/electrolyte interface but over the entire cathode, indicating that the degree of recovery from sulfur poisoning is closely related to the presence of SrO and chemical activity of Sr in the electrodes at the solid-gas interface. These results also show the potential application of LSM for a sulfur sensor available in high-temperature harsh conditions.

本研究针对当前主流的固体氧化物燃料电池（Solid Oxide Fuel Cell，SOFC）阴极材料——(La0.80Sr0.20)0.95MnO3±δ（LSM）与(La0.60Sr0.40)0.95Co0.20Fe0.80O3–δ（LSCF）的硫中毒行为与性能恢复特性展开了系统研究。研究人员在700℃条件下，于空气与SO₂-空气交替气氛中，对LSCF|钆掺杂氧化铈（Gadolinium Doped Ceria，GDC）半电池及LSM|钇稳定氧化锆（Yttria-Stabilized Zirconia，YSZ）半电池开展了长达数百小时的电化学阻抗谱测试。当体系中存在SO₂时，两种半电池的电化学性能均因SO₂与电极的吸附作用及化学相互作用，出现欧姆损耗与非欧姆损耗并发生衰减。对于LSCF而言，其表面偏析的SrO易与SO₂发生吸附与反应，生成SrSO₄，随后伴随Co-Fe相的析出。而对于LSM，SO₂会吸附在其富锶区域——包括三相边界（Triple Phase Boundary，TPBs）附近的活性反应位点——进而引发Sr析出与SrSO₄生成，最终形成锶缺陷型LSM。在后续置于空气气氛中时，受硫污染的LSM的电化学性能几乎完全恢复。电化学测试过程中，交替暴露于空气与SO₂-空气气氛的LSM颗粒表面相对洁净，仅稀疏分布少量SrSO₄颗粒，表明其具备优异的抗硫中毒稳定性。分析表明，三相界面处松散吸附的SO₂可被无SO₂的空气流快速吹扫脱除，从而恢复氧还原反应（Oxygen Reduction Reaction，ORR）活性；而因Sr析出形成的锶缺陷型LSM结构发生了改性，导致性能恢复不完全。与LSM的情况不同，受硫中毒的LSCF在后续置于空气气氛中时仅能实现部分性能恢复。相应地，LSCF颗粒的形貌发生了显著改性，表面覆盖有大量以SrSO₄为主的纳米颗粒，体现出硫中毒的不可逆性。这种形貌改性并非集中于电极/电解质界面，而是遍布整个阴极，这表明硫中毒后的恢复程度与固-气界面处电极中的SrO存在形式及Sr的化学活性密切相关。本研究结果同时证明，LSM在高温严苛环境下具备用作硫传感器的潜在应用价值。