Entropy engineering design of high-performing lithiated oxide cathodes for proton-conducting solid oxide fuel cells

Abstract

A new medium entropy material LiCo_0.25Fe_0.25Mn_0.25Ni_0.25O₂ (LCFMN) is proposed as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs). Unlike traditional LiXO₂ (X=Co, Fe, Mn, Ni) lithiated oxides, which have issues like phase impurity, poor chemical compatibility, or poor fuel cell performance, the new LCFMN material mitigates these problems, allowing for the successful preparation of pure phase LCFMN with good chemical and thermal compatibility to the electrolyte. Furthermore, the entropy engineering strategy is found to weaken the covalence bond between the metal and oxygen in the LCFMN lattice, favoring the creation of oxygen vacancies and increasing cathode activity. As a result, the H-SOFC with the LCFMN cathode achieves an unprecedented fuel cell output of 1803 mW cm^-2 at 700 ^oC, the highest ever reported for H-SOFCs with lithiated oxide cathodes. In addition to high fuel cell performance, the LCFMN cathode permits stable fuel cell operation for more than 450 hours without visible degradation, demonstrating that LCFMN is a suitable cathode choice for H-SOFCs that combines high performance and good stability.