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 CO₂ and H₂O. Herein, a novel high-entropy perovskite oxide (HEPO) material is introduced, incorporating six equimolar B-site cations (BaHf_1/6Sn_1/6Zr_1/6Ce_1/6Y_1/6Yb_1/6O_3-δ, 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 CO₂. 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.