High-entropy design in sintering aids for proton-conducting electrolytes of solid oxide fuel cells

Abstract

Sintering aids are commonly used to improve the sinterability of proton-conducting oxides, whereas the sintering aid elements are being used alone in previous research. In this study, a high-entropy design method for the BaCe0.4Zr0.4Y0.2O3 (BCZY) proton-conducting oxides sintering aid is proposed. In contrast to the use of sintering aids such as Ni, Fe, Cu, Co, and Zn alone, the high-entropy design allows for the simultaneous use of all five elements, resulting in the new composition BaCe0.4Zr0.4Y0.15Ni0.01Cu0.01Co0.01Fe0.01Zn0.01O3 (HE-BCZY). Compared to conventional BaCe0.4Zr0.4Y0.15M0.05O3 (BCZYM, M = Ni, Cu, Co, Fe, Zn) materials, the sinterability of the new HE-BCZY material is significantly greater than that of BCZYM, despite the fact that the concentration of sintering aids is the same. Following sintering at 1300 °C, the HE-BCZY electrolyte membrane is completely dense. In addition, the HE-BCZY electrolyte has a higher conductivity than BCZYM. The low sintering temperature allows the successful preparation of proton ceramic fuel cells (PCFCs) with the HE-BCZY electrolyte, and the fuel cell reaches a high peak power density of 1218 mW cm−2 at 700 °C, which is much higher than that of PCFCs using BCZY-based electrolytes. In addition, the excellent chemical stability of HE-BCZY is maintained under both H2O and CO2 conditions. Consequently, a fuel cell employing the HE-BCZY electrolyte operates without detectable degradation for 200 h. This study demonstrates that although the high-entropy design is seldom used for sintering aids of proton-conducting oxides, it is an intriguing and promising strategy for creating high-performance electrolyte materials with good sinterability, high conductivity, and excellent stability.