Assessment of LaM0.25Mn0.75O3-δ (M = Fe, Co, Ni, Cu) as promising cathode materials for intermediate-temperature solid oxide fuel cells

Abstract

A series of novel perovskites LaM0.25Mn0.75O3−δ (M=Fe, Co, Ni, Cu) are considered as promising cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Polycrystalline powders of LaM0.25Mn0.75O3−δ are synthesized by a modified Pechini method. Powder X-ray Rietveld refinements reveal that LaM0.25Mn0.75O3−δ series are in the orthorhombic perovskite structure within Pnma (no. 62) space group at room temperature. In situ high temperature X-ray diffractions indicate the existence of phase transformation from the orthorhombic Pnma phase to a higher symmetrical rhombohedral phase at elevated temperatures without any second phase formation for all these compounds. Multivalent states of M (Fe, Co, Ni and Cu) and Mn ions are testified by X-ray photoelectron spectroscopy measurement (XPS). The electrical conductivity are measured to be 39.6, 85.3 and 48.1, 99.4Scm−1 for M=Fe, Co, Ni and Cu, respectively and the corresponding impedance are 0.131, 0.106, 0.107 and 0.0634Ωcm2 at 850°C. Among these compounds, LaCu0.25Mn0.75O3−δ exhibits the highest electrical conductivity and the lowest electrode polarization resistances, which is consistent with its calculated smallest band gap and lowest oxygen vacancy formation energy. Moreover, they all exhibit excellent chemical compatibility with prototypical electrolyte Ce0.8Sm0.2O2−δ (SDC). While the overall electrochemical properties of LaM0.25Mn0.75O3−δ (M=Fe, Co, Ni) are high enough to fulfill the practical applications. Thus, these LaM0.25Mn0.75O3−δ (M=Fe, Co, Ni, Cu) compounds are potential cathode materials for IT-SOFCs.