Oxygen storage capacity of Sr3Fe2O7-δ having high structural stability

The present study proves that Sr3Fe2O6.75 has high performance for oxygen storage capacity as well as high structural stability under severe reduction conditions. The H-2 reduction of Sr3Fe2O6.75 at 1223 K results in the formation of Sr3Fe2O6, whereas SrFeO2.84 easily decomposes to Sr3Fe2O6 and Fe metal by the same treatment. The structural framework of Sr3Fe2O6.75 is identical to that of Sr3Fe2O6 bearing a space group of I4/mmm. In the crystal structure of Sr3Fe2O6.75, three oxygen sites (8g, 4e and 2a) exist. Among these, only oxygen ions in the 2a site are eliminated by the H-2 reduction. The result unequivocally indicates that Sr3Fe2O6.75 is topotactically reduced to Sr3Fe2O6. The reversible redox cycles between Sr3Fe2O6.75 and Sr3Fe2O6 take place at a higher temperature above 773 K. The observation correlates with the topotactic oxygen intake/release ability between Sr3Fe2O6.75 and Sr3Fe2O6. The oxygen storage capacity of Sr3Fe2O6.75 and its response rate are higher than those of the conventional Pt/Ce2Zr2O8 even in the absence of Pt loading. Thus, Sr3Fe2O7-delta must be of great promise as novel oxygen storage materials.