A novel high-entropy perovskite electrolyte with improved proton conductivity and stability for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) are emerging as highly efficient energy conversion devices, operating below 650 °C. The primary challenge in advancing R-PCECs lies in developing efficient and stable proton-conducting electrolytes capable of withstanding the chemical instability caused by common contaminants like CO${}_2$ and H${}_2$O. Herein, a novel high-entropy perovskite oxide (HEPO) material is introduced, incorporating six equimolar B-site cations (BaHf${}_{1/6}$Sn${}_{1/6}$Zr${}_{1/6}$Ce${}_{1/6}$Y${}_{1/6}$Yb${}_{1/6}$O${}_{3-\delta }$, BHSZCYYb). The total conductivity of BHSZCYYb outperforms that of the examined HEPO electrolytes and other reported HEPO variants. Additionally, superior chemical stability of BHSZCYYb is observed when exposed to CO${}_2$. Utilizing the microwave-assisted sintering method, an R-PCEC with BHSZCYYb electrolyte is successfully fabricated. This cell exhibits a maximum power density of 1.151 W cm${}^{-2}$ (650 °C) in fuel cell mode and a current density of 2.326 A cm${}^{-2}$ at 1.3 V (650 °C) in electrolysis cell mode. These results represent the highest-reported values for R-PCECs employing HEPO electrolytes to date and provide valuable insights into the development and advancement of HEPOs, holding great promise for achieving high-performance R-PCECs. (© 2023 Wiley‐VCH GmbH)