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 ℃, 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 h without visible degradation, demonstrating that LCFMN is a suitable cathode choice for H-SOFCs that combining high performance and good stability.

A La_0.5Ba_0.5MnO_3−δ oxide was prepared using the sol–gel technique. Instead of a pure phase, La_0.5Ba_0.5MnO_3−δ was discovered to be a combination of La_0.7Ba_0.3MnO_3−δ and BaMnO₃. The in-situ production of La_0.7Ba_0.3MnO_3−δ+BaMnO₃ nanocomposites enhanced the oxygen vacancy (V_O) formation compared to single-phase La_0.7Ba_0.3MnO_3−δ or BaMnO₃, providing potential benefits as a cathode for fuel cells. Subsequently, La_0.7Ba_0.3MnO_3−δ+BaMnO₃ nanocomposites were utilized as the cathode for proton-conducting solid oxide fuel cells (H-SOFCs), which significantly improved cell performance. At 700 ℃, H-SOFC with a La_0.7Ba_0.3MnO_3−δ+BaMnO₃ nanocomposite cathode achieved the highest power density (1504 mW·cm⁻²) yet recorded for H-SOFCs with manganate cathodes. This performance was much greater than that of single-phase La_0.7Ba_0.3MnO_3−δ or BaMnO₃ cathode cells. In addition, the cell demonstrated excellent working stability. First-principles calculations indicated that the La_0.7Ba_0.3MnO_3−δ/BaMnO₃ interface was crucial for the enhanced cathode performance. The oxygen reduction reaction (ORR) free energy barrier was significantly lower at the La_0.7Ba_0.3MnO_3−δ/BaMnO₃ interface than that at the La_0.7Ba_0.3MnO_3−δ or BaMnO₃ surfaces, which explained the origin of high performance and gave a guide for the construction of novel cathodes for H-SOFCs.