Study On Sr₂MoFeO_6-δ-based Electrode Materials For CO₂ Electrolysis In Solid Oxide Electrolytic Cell

The high temperature solid oxide electrolytic cell（SOEC）is an advanced,highly efficient electrolysis device that provides an attractive co-electrolysis route to enable efficient energy storage,conversion and facilitation of renewable energy.Based on electricity from renewable energy sources,SOEC can electrolyze CO₂to prepare high-value chemicals such as CO,while converting electrical energy into chemical energy storage.Conventional Ni-based cathodes suffer from oxidation,carbon accumulation and agglomeration growth in high concentration CO₂atmosphere.To avoid these problems,the development and research of highly reactive cathode materials is a key step in electrochemical reduction of CO₂.Studies have shown that perovskite oxides with mixed ion-electron conductivity（MIEC）exhibit excellent redox stability,making them potential cathode candidates for SOEC.Perovskite oxides has higher structural stability under reducing and inert environment.Better interaction can generate between perovskite and the matrix,due to in-situ precipitation of perovskite,which can alleviate carbon accumulation issues accordingly.Perovskite related oxides,such as Sr₂Mo Fe O_6-δ-based,have attracted considerable interest as new choices for SOEC cathode materials due to their high redox stability,excellent carbon resistance,and considerable ionic and electronic conductivity.In this paper,perovskite Sr₂Mo_0.6Fe_1.4O_6-δ（SMF）with adjustable oxygen vacancy characteristics was prepared,and synthesized perovskite Sr₂Mo_0.6Fe_1.3Cu_0.1O_6-δ（SMFC）by doping SMFO_6-δ-based perovskite with Cu ions of similar radius to Fe ions,and used both catalysts as cathodes in SOEC cells for the electrolysis of CO₂,thereby increasing the electrolysis rate and faraday efficiency.1.The CO₂ electrolysis performance of a symmetric single cell SMF-SDC/SDC/YSZ/SDC/SMF-SDC with oxygen ion-conducting material yttrium-stabilized zirconia（YSZ）as the electrolyte,Sm_0.2Ce_0.8O_1.9（SDC）as the electrolyte barrier layer,and Sr₂Mo_0.6Fe_1.4O_6-δ（SMF）perovskite as the fuel electrode was investigated.850 ^oC,with H₂as fuel,the peak power density（PPD）of the single cell was 0.436 W cm^-2,the ohmic impedance（R_o）was 0.308Ωcm^-2,and the polarization impedance（R_P）was0.298Ωcm^-2,SMF exhibits excellent electrochemical performance for power generation.The current density of the electrolyzed CO₂was 1.57 A cm^-2at 850 ^oC with 1.8 V applied;the cell was tested at 850 ^oC with 1.2 V applied for the long-term operational stability of the cell was tested at 1.2 V applied at 850 ^oC.After 100 h of testing,the current density of electrolytic CO₂slightly decayed,and the main reason for the performance decay may be the formation of Sr Mo O₄with poor conductivity after continuous exposure of the cathode material to CO₂.2.The CO₂ electrolysis performance of symmetric single cell SMFC-SDC/SDC/YSZ/SDC/SMFC-SDC with oxygen ion-conducting perovskite material YSZ as the electrolyte,SDC as the electrolyte barrier layer,and SMFC perovskite as the fuel electrode was investigated.SMF has weak high-temperature chemisorption capacity for CO₂molecules and poor electrocatalytic stability.The doping of Cu ions with similar radius to Fe ions at the B-site on the basis of SMF can effectively modulate the physicochemical properties,especially the electrochemical properties of perovskites.At850 ^oC,with H₂as fuel,the PPD of the single cell is 0.655 W cm^-2,R_ois 0.295Ωcm^-2,and R_Pis 0.265Ωcm^-2,which is an improvement in the electrochemical performance of power generation over the SMF single cell under the same conditions.The current density of CO₂electrolysis was 1.975 A cm^-2at 850 ^oC with 1.8 V applied,which is 26.12%higher than that of single cell with SMF as cathode.The long-term operational stability of the cell was tested at 850 ^oC with 1.2 V applied.After 100 h of operation,the current density remained almost constant,showing excellent catalytic stability.The maximum rate of CO production and faraday efficiency were 6.34 m L min^-1cm^-2and 91.84%at 850 ^oC and 1.6V,respectively,which were significantly higher than those of SMF.It indicates that the doping of Cu on the B-site of SMF improves the stability of the material,enhances the electrocatalytic activity of the material and improves the electrode kinetics.In summary,SOEC is an advanced electrolysis device for efficient storage of renewable energy;SMF and SMFC have good reactivity for electrolysis of CO₂,and this work also provides an effective strategy for the design of catalyst materials for future development of SOEC for electrolysis of CO₂.