Oxygen sorption and desorption properties of Sr-Co-Fe oxide

SrCoFeO_x has been investigated as a new sorbent for air separation and oxygen removal at high temperatures. X-ray diffraction analysis of a SrCoFeO_x sample prepared by liquid citrate method reveals that the sample contains an intergrowth (Sr₄ Fe_{6 - x} Co_x O_{13 ± δ}), perovskite (SrFe_{1 - x} Co_x O_{3 - δ}), and spinel (Co_{3 - x} Fe_x O₄) phase. Both oxygen vacancies (V_{over(O, ̈)}) and interstitial oxygen ions (O_i^″) are involved in the oxygen adsorption and desorption process for SrCoFeO_x. Compared with the perovskite-type oxide La_0.1 Sr_0.9 Co_0.9 Fe_0.1 O_{3 - δ}, SrCoFeO_x has stronger structure stability in a reducing environment and it also exhibits a larger oxygen sorption capacity at temperatures higher than 800 ^{{ring operator}} C. Meanwhile, unlike La_0.1 Sr_0.9 Co_0.9 Fe_0.1 O_{3 - δ} which shows a fast adsorption rate and a slow desorption rate at 900 ^{{ring operator}} C, SrCoFeO_x shows a fast desorption rate and slow adsorption rate at the same temperature. X-ray diffraction data reveals that SrCoFeO_x samples sintered at 1140 ^{{ring operator}} C have a higher amount of the intergrowth phase than samples sintered at 950 ^{{ring operator}} C due to slow formation kinetics. X-ray diffraction and thermogravimetric analysis of SrCoFeO_x samples prepared by the citrate and solid state method show that the synthesis method strongly influences the amount of the three phases in a sample.