Tailoring high-temperature stability and electrical conductivity of high entropy lanthanum manganite for solid oxide fuel cell cathodes

Abstract

High entropy perovskite oxides (HEPOs) have been proposed to serve as improved cathode materials for solid oxide fuel cells (SOFCs); however, the larger compositional design space introduced by HEPOs urges for a better understanding of the correlation among the composition, phase stability and resulting properties of HEPO cathodes. In this work, a series of LaMnO₃ based HEPOs (HEALMOs) were designed systematically to investigate the effect of the A site high entropy composition on the structure and thermochemical/electrical properties of HEALMO materials. The results show that the high entropy effect manifests itself on top of the conventional doping effect. First of all, neither the Goldschmidt tolerance factor nor the cation size difference can be used simply to predict the formation ability of single-phase HEALMOs. Meanwhile, HEALMOs may exhibit higher crystallographic symmetry with much higher cation size differences and at Goldschmidt tolerance factor values deviating more largely from 1. Secondly, while high-temperature stability including both resistance to elemental segregation and chemical compatibility with 8YSZ is affected by the A site cation size difference in a similar way to that of conventional perovskite oxides, HEALMOs show much enhanced stability at larger A site cation size differences. Finally, high entropy contributes to the maintenance of electrical conductivity in the high temperature range. The optimum HEALMO with the composition of (La_0.2Nd_0.2Sm_0.2Ca_0.2Sr_0.2)MnO₃ exhibits a combination of excellent high-temperature stability and good electrical conductivity, highlighting its great potential as a promising cathode material for SOFCs.