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

摘要

Solid oxide electrolysis cells (SOECs) can efficiently convert the greenhouse-gas CO2 to valuable fuel CO at the cathodes. Herein, fluorine is doped into mixed ionic-electronic conducting Sr2Fe1.5Mo0.5O6-delta (SFM), to evaluate its potential use as a cathode for CO2 reduction reaction (CO2-RR). SFM retains its cubic structure after doped with fluorine, forming perovskite oxyfluoride Sr2Fe1.5Mo0.5O6-delta F0.1 (F-SFM). The substitution of oxygen by fluorine increases CO2 adsorption by a factor of approximate to 2, bulk oxygen vacancy concentration by 35-37% at 800 degrees C, and consequently enhances the surface reaction rate constant for CO2-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 omega cm(2) for F-SFM than 1.130 omega cm(2) for SFM at 800 degrees C in symmetrical cells. Furthermore, the single cell with F-SFM cathode exhibits the best CO2 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 degrees C under harsh conditions. The theoretical computations confirm that fluorine doping is energetically favorable to CO2 adsorption and dissociation. The present work provides a promising strategy for the design of robust cathodes for direct CO2 electrolysis in SOECs.