Enhancing proton mobility through radius-matched Ta⁵⁺ doping in Sr₂Fe_1.5Mo_0.5O_6-δ triple-conducting oxide for high-efficiency protonic ceramic electrolysis cells

Protonic ceramic electrolysis cells (PCECs) are promising for energy conversion and hydrogen production. Developing air electrodes with high reaction kinetics and durability is crucial for their broad applications. In this study, a novel triple-conducting oxide air electrode is developed by incorporating Ta⁵⁺ ions into the Sr₂Fe_1.5Mo_0.5O_6-δ substrate. This modification ensures the lattice matching due to compatible ionic radii, while simultaneously modulating oxygen vacancy concentration. The hydration capacity of SFMTa material is enhanced, leading to an increase in proton defects and improving proton mobility. When tested in air with 3 vol% H₂O at 1.3 V and 700 °C, the Sr₂Fe_1.5Mo_0.4Ta_0.1O_6-δ single cell demonstrates a relatively high current density of 2.17 A/cm². Furthermore, the cell exhibits stable operation for 120 h without significant degradation, indicating the chemical stability of the material. The ionic radius matching strategy offers a practical approach for the development of highly efficient and durable air electrodes for PCECs.