Synergistic effect of sodium content for tuning Sm₂O₃ as a stable electrolyte in proton ceramic fuel cells

Samarium oxide (Sm₂O₃), a rare earth sesquioxide, shows that a great potential in proton-conducting fuel cells. However, the stability of Sm₂O₃ based cell remains a challenge. Herein we reported a facile method for enhancing the stability via the incorporation of sodium content into Sm₂O₃. This study discloses that the existence of sodium induces phase transition of Sm₂O₃ from monoclinic to cubic phase beneficial for fast proton transportation. Further mechanism investigation reveals that the cubic phase structure of Sm₂O₃ is stabilized resulting from substitution of sodium. Compared with commercial Sm₂O₃ (CSM), the fuel cell employing Na–Sm₂O₃ (NSM) as electrolyte delivers an improved peak power density of 570 mW cm⁻² and the extended stability over 100 h under 130 mWcm⁻² at 520 °C. In this study, NSM is successfully developed as a stable electrolyte material for proton conduct fuel cells, expanding its application in electrochemical devices.