Oxygen storage capacity of Sr3Fe2O7−δ having high structural stability

Abstract

The present study proves that Sr₃Fe₂O_6.75 has high performance for oxygen storage capacity as well as high structural stability under severe reduction conditions. The H₂ reduction of Sr₃Fe₂O_6.75 at 1223 K results in the formation of Sr₃Fe₂O₆, whereas SrFeO_2.84 easily decomposes to Sr₃Fe₂O₆ and Fe metal by the same treatment. The structural framework of Sr₃Fe₂O_6.75 is identical to that of Sr₃Fe₂O₆ bearing a space group of I4/mmm. In the crystal structure of Sr₃Fe₂O_6.75, three oxygen sites (8g, 4e and 2a) exist. Among these, only oxygen ions in the 2a site are eliminated by the H₂ reduction. The result unequivocally indicates that Sr₃Fe₂O_6.75 is topotactically reduced to Sr₃Fe₂O₆. The reversible redox cycles between Sr₃Fe₂O_6.75 and Sr₃Fe₂O₆ take place at a higher temperature above 773 K. The observation correlates with the topotactic oxygen intake/release ability between Sr₃Fe₂O_6.75 and Sr₃Fe₂O₆. The oxygen storage capacity of Sr₃Fe₂O_6.75 and its response rate are higher than those of the conventional Pt/Ce₂Zr₂O₈ even in the absence of Pt loading. Thus, Sr₃Fe₂O_7−δ must be of great promise as novel oxygen storage materials.