Perovskite Oxyfluoride Electrode Enabling Direct Electrolyzing Carbon Dioxide with Excellent Electrochemical Performances

Abstract Solid oxide electrolysis cells (SOECs) can efficiently convert the greenhouse‐gas CO 2 to valuable fuel CO at the cathodes. Herein, fluorine is doped into mixed ionic–electronic conducting Sr 2 Fe 1.5 Mo 0.5 O 6‐δ (SFM), to evaluate its potential use as a cathode for CO 2 reduction reaction (CO 2 ‐RR). SFM retains its cubic structure after doped with fluorine, forming perovskite oxyfluoride Sr 2 Fe 1.5 Mo 0.5 O 6‐δ F 0.1 (F‐SFM). The substitution of oxygen by fluorine increases CO 2 adsorption by a factor of ≈2, bulk oxygen vacancy concentration by 35–37% at 800 °C, and consequently enhances the surface reaction rate constant for CO 2 ‐RR and chemical bulk diffusion coefficient by factors of 2–3. The faster kinetics are also reflected by a lower polarization resistance of 0.656 Ω cm 2 for F‐SFM than 1.130 Ω cm 2 for SFM at 800 °C in symmetrical cells. Furthermore, the single cell with F‐SFM cathode exhibits the best CO 2 electrolysis performance among the reported perovskite electrodes, achieving current density of 1.36 A cm −2 at 1.5 V and excellent stability over 120 h at 800 °C under harsh conditions. The theoretical computations confirm that fluorine doping is energetically favorable to CO 2 adsorption and dissociation. The present work provides a promising strategy for the design of robust cathodes for direct CO 2 electrolysis in SOECs.