Deactivation of anode catalyst La0.75Sr0.25Cr0.5Mn0.5O3±δ in SOFC with fuel containing hydrogen sulfur: The role of lattice oxygen

The role of lattice oxygen in deactivation of La0.75Sr0.25Cr0.5Mn0.5O3±δ (LSCM55) as anode catalyst was studied in a solid oxide fuel cell (SOFC), where hydrogen sulfide (H2S) was utilized as fuel. After LSCM55 treated in H2S or H2-H2S, XRD patterns show that some impurities similar to La2O2S and MnOS are present. XPS spectra identify that S species in the impurities dominate on the anode catalysts in form of sulfate (SO42−), which depends on the treatments. S2p and O1s regions in XPS reveal that in the absence of oxygen, lattice oxygen not only on the surface but also in the bulk contributes to the formation of sulfate. Oxygen vacancies induced by H2 pre-reduction may provide the channel for lattice oxygen migrating from the bulk to the surface. Furthermore, it is found that LSCM55 with H2 pre-reduction achieves better lifespan of SOFC fueled by H2S than LSCM55 without H2 pre-reduction, which alleviates deactivation of anode catalyst, due to incomplete oxidation of H2S by residual lattice oxygen on the surface after H2 pre-reduction. However, improvement of H2 pre-reduction on anode catalysts LSCM55 is influenced to a certain degree after short-term operation under closed circuit.

Promotions between H2S and lattice oxygen on the surface of anode catalysts under closed circuit.Figure optionsDownload as PowerPoint slideHighlights
► Identification of sulfur distribution on the catalyst surface after treatments.
► Lattice oxygen in the bulk contributes to the sulfate formation.
► H2 pre-reduction improves sulfur tolerance of catalyst.
► Deactivation extent also depends on lattice oxygen migrating from the bulk.
► Deactivation is aggravated after short-term operation under closed circuit mode.