Accelerating bulk proton transfer in Sr₂Fe_1.5Mo_0.5O_6-δ perovskite oxide for efficient oxygen electrode in protonic ceramic electrolysis cells

Protonic ceramic electrolysis cells (PCECs) have attracted significant attention as a promising technology for green hydrogen production and conversion. However, traditional PCECs oxygen electrodes exhibit poor electrochemical performance because of their limited hydration ability and lack of intrinsic protonic conductivity. In this study, a W-doped perovskite oxide, Sr₂Fe_1.5Mo_0.4W_0.1O_6-δ (SFMW), with a strong hydration capacity and an accelerated proton mobility, was designed to serve as the oxygen electrode in PCECs. The results indicate that W doping enhances the concentration of oxygen vacancies in Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) and facilitates the adsorption of H₂O onto the oxygen electrode, thereby significantly accelerating proton mobility. The bulk diffusion coefficient of protons (D_H) in SFMW, estimated through electrical conductivity relaxation measurement, can reach up to 2.86 × 10⁻⁵ cm∙s⁻¹ at 750 °C, which is significantly higher than that of SFM (7.96 × 10⁻⁶ cm∙s⁻¹). Consequently, SFMW exhibited impressive electrochemical performance, as evidenced by its lower polarization resistance (0.072 Ω⋅cm², 700 °C in air) and higher current density (945 mA/cm² with a voltage of 1.3 V at 650 °C) in PCECs. These results suggest that accelerating bulk proton transfer by W doping is highly feasible and holds great potential for the development of oxygen electrodes for high-activity PCECs.