Tailoring the structural durability and proton conductivity of electrolytes for highly fuel-flexible and reversible ceramic cells

A durable and high ionic conducting electrolyte is critical for achieving fuel-flexible and reversible protonic ceramic cells (PCCs) at reduced temperatures since the developed electrolyte materials are vulnerable to steam, CO₂, or coking deterioration. Here, we report a fast-conducting electrolyte material BaZr_0.06Ce_0.7Y_0.06Yb_0.06Hf_0.06Gd_0.06O_3−δ (BZCYYbHG), demonstrating excellent durability against CO₂ and H₂O under the realistic electrolysis operations, and a high conductivity of 0.017 S cm⁻¹ at 550 °C for lowering the PCC operating temperature. Density functional theory calculations indicate that the higher configurational entropy of mixing at the B-site cations slightly reduces the hydrogen adsorption energy, suggesting a higher incorporation rate of protons or hydrogen atoms into the electrolyte bulk. Ultimately, single cells with the BZCYYbHG electrolyte deliver peak power densities of 1.39, 1.12, and 0.7 W cm⁻² in H₂, NH₃, and wet CH₄ at 550 °C with promising durability. In addition, the PCCs achieve a current density of −1.61 A cm⁻² at 1.3 V and 550 °C with a high faradaic efficiency of 91.3% at −0.5 A cm⁻², enabling stable operations in steam electrolysis mode under humid air (30% H₂O), wet air containing CO₂ (up to 10%), and reversible cycling.