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Two mixed ionic-electronic conducting, Fe-containing perovskites were investigated regarding their reducibility in dry H 2 , namely lanthanum strontium ferrite (LSF4, La 0.6 Sr 0.4 FeO 3-δ ) and strontium titanium ferrite (STF3, SrTi 0.7 Fe 0.3 O 3-δ ). Upon treatment under comparable reduction conditions, LSF4 is by far more affected by reduction and is reduced more deeply than STF3. Thermal treatments of fully oxidized or slightly reduced LSF4/STF3 at decreased O 2 partial pressure lead to spontaneous desorption of O 2 . Temperature-programmed desorption (TPD) spectra of H 2 reveal distinct differences in H 2 and H 2 O desorption. A simple mass balance of H 2 reveals that oxygen vacancies formed on STF3 are more resilient towards O 2 re-oxidation compared to those on LSF4. The results also imply that substantial amounts of hydrogen are dissolved in the bulk of LSF4 or STF3. 4.9 × 10 -2 mol H 2 per mol LSF4 and 1.6 × 10 -2 mol H 2 per mol STF3 are incorporated if the specimens are heated in flowing/dry H 2 up to 550 °C and 612 °C, respectively. For LSF4 this equals about 13 hypothetical ML of H 2 and for STF3 about 20 hypothetical ML of H 2 . This conclusion is also supported by Fourier-transform infrared spectroscopy (FT-IR). FT-IR reveals water formation during static H 2 reatment of LSF4/STF3, which indicates perovskite reduction. Furthermore, both samples behave extraordinarily hydrophobic and no chemistry involving surface hydroxy groups was observed.

physical chemistry chemical physics

Evidence for dissolved hydrogen in the mixed ionic–electronic conducting perovskites La0.6Sr0.4FeO3−δ and SrTi0.7Fe0.3O3−δ