Effect of Al Substitution on Structural Stability and Topotactic Oxygen Release Rate of LaNi_1–xAl_xO₃ with Perovskite Structure

Oxygen storage materials (OSMs) composed of transition metals are promising in the field of environment protection and energy conversion. In this study, we synthesized LaNi1–xAlxO3 (0 ≤ x ≤ 1.0) solid solutions with a rhombohedral perovskite structure and investigated the effect of Al substitution on their structural stability and oxygen release rate. X-ray diffraction measurements and thermogravimetric analysis revealed that Ni-containing LaNi1–xAlxO3 released/stored oxygen atoms topotactically and reversibly via the Ni3+ ↔ Ni2+ redox reaction. LaNiO3 decomposed into La2O3 and Ni0 at 470 °C in a reducing atmosphere (H2). However, Al-substituted LaNi1–xAlxO3 maintained their perovskite structure even at high temperatures (>800 °C for 0.6 ≤ x ≤ 1.0). The high structural stability of these compounds can be attributed to the suppression of oxygen vacancy ordering. Furthermore, LaNi0.2Al0.8O3 (x = 0.8) exhibited higher oxygen release rate (9.35 × 10–3 mol-O mol-Ni–1 s–1) than LaNiO3 (x = 0; 2.59 × 10–3 mol-O mol-Ni–1 s–1) at 400 °C because of its lower activation energy. This is consistent with the decrease of bond strength of the oxygen atoms as expected based on bond valence sum calculations. Such substitution effects of irreducible cations offer a wide opportunity to develop transition metal OSMs with desired structural stability and oxygen release rate.