Elucidation of the Transport Properties of Calcium-Doped High Entropy Rare Earth Aluminates for Solid Oxide Fuel Cell Applications

Solid oxide fuel cells (SOFCs) are paving the way to clean energy conversion, relying on efficient oxygen-ion conductors with high ionic conductivity coupled with a negligible electronic contribution. Doped rare earth aluminates are promising candidates for SOFC electrolytes due to their high ionic conductivity. However, they often suffer from p-type electronic conductivity at operating temperatures above 500 degrees C under oxidizing conditions caused by the incorporation of oxygen into the lattice. High entropy materials are a new class of materials conceptualized to be stable at higher temperatures due to their high configurational entropy. Introducing this concept to rare earth aluminates can be a promising approach to stabilize the lattice by shifting the stoichiometric point of the oxides to higher oxygen activities, and thereby, reducing the p-type electronic conductivity in the relevant oxygen partial pressure range. In this study, the high entropy oxide (Gd,La,Nd,Pr,Sm)AlO3 is synthesized and doped with Ca. The Ca-doped (Gd,La,Nd,Pr,Sm)AlO3 compounds exhibit a higher ionic conductivity than most of the corresponding Ca-doped rare earth aluminates accompanied by a reduction of the p-type electronic conductivity contribution typically observed under oxidizing conditions. In light of these findings, this study introduces high entropy aluminates as a promising candidate for SOFC electrolytes. Doped rare earth aluminates (R1-xMxAlO3) exhibit p-type conduction in oxidizing atmospheres at higher temperatures. The high entropy concept is introduced into R1-xMxAlO3 to counteract the p-type conduction. A single-phase, chemically homogenous perovskite-type high entropy oxide (HEO) is synthesized. The HEO shows a suppressed p-type conduction usually observed in the R1-xMxAlO3 with lower activation energies for ions than electrons. image