Medium-entropy oxide (Ce0.25Sm0.25La0.25Gd0.25)2O3-δ as promising electrolyte for low-temperature solid oxide fuel cells

The development of high-performance electrolyte is crucial for low-temperature solid oxide fuel cells (LT-SOFCs). Traditional ceria-based materials such as Gd0.1Ce0.9O2-δ (GDC) are promising electrolytes in intermediate-temperature range but their performance drop rapidly with decreasing temperature. Recent advances proposed a new concept for SOFC materials design in terms of entropy, indicative of enormous potential. Herein, a medium-entropy ceria-based oxide (Ce0.25Sm0.25La0.25Gd0.25)2O3-δ (CSLG25) is developed via entropy engineering and evaluated as potential electrolyte for LT-SOFCs by comparing with low-entropy electrolyte GDC. The effects of configuration entropy on crystal structure, oxygen vacancy, electrochemical performance, and proton transport characteristic of the materials are systematically investigated. It is found the CSLG25 cell device exhibits a remarkable power density of 747 mW cm−2 at 520 °C, along with a superionic conductivity of 0.1534 S cm−1. Further study via XPS and Raman technology reveals that the higher entropy of CSLG25 creates more oxygen vacancies and contributes to fast proton transport, which leads to promising fuel cell performance at 430–520 °C. The CSLG25 cell device also delivers the 55.5 h durability performance at 520 °C. This study thus provides a novel electrolyte material for LT-SOFCs and points out a feasible entropy engineering strategy for developing ionic conductors.