Investigation of the Redox Behaviour of Double Perovskite PrBaMn2O5+δ

Abstract

Double perovskite PrBaMn2O5+δ (l-PBM) has recently shown interesting properties as electrode for solid oxide fuel cell (SOFC) technology, such as high stability, good ionic and electronic conductivity in both oxidising and reducing atmosphere [1]. It is obtainable by the reduction at high temperature of the starting mixed cubic-hexagonal perovskite Pr0.5Ba0.5MnO3-δ (m-PBM), where the Pr3+ and Ba2+ cations are stochastically disposed in the A-site of the lattice. Conversely, the double perovskite shows ordinated and alternated layers of PrO and BaO, intercalated by MnO2 planes [2].Here, we use a multi analytical approach and temperature programmed techniques of analysis (temperature programmed X-ray diffractometry, TP-XRD, temperature programmed reduction TPR, thermogravimetric oxidation and reduction analysis, TGA) to deeply study the phase transition between the m-PBM and the l-PBM. m-PBM sample was prepared by an auto-combustion based citrate procedure [3] and exposed to consecutive oxidation and reduction cycles at high temperature to understand the effect of oxidizing and reducing atmospheres on structural changes and stabilization of the layered double perovskite. By in situ XRD analysis we discovered the existence of a metastable cubic structure (c-PBM), which is formed from the direct oxidation of l-PBM at SOFCs operating temperatures (750 °C). Furthermore, we demonstrated the reversibility of transition from c-PBM to l-PBM during several oxidation and reduction cycles. TPR results confirmed the c-PBM to l-PBM reversibility, and the TGA characterization showed a fast transition between l-PBM to c-PBM. The oxidation of l-PBM to c-PBM seems pivotal for the stabilization of the layered structure. The results are discussed in view of a controlled exsolution of metal phase when the B site of m-PBM is doped with Co, Ni and/or Fe and in the perspective to develop versatile electrodes for SOE/SOFC applications.