Structure Regulation And Electrolysis Performance Of Sr₂Fe_1.5Mo_0.5O_6-δ Electrode For Solid Oxide Cell

Solid Oxide Electrolysis Cell（SOEC）is a promising new energy technology that can use renewable energy to convert water vapor into hydrogen energy or greenhouse gas CO₂into CO.In addition,the syngas can also be obtained by co-electrolysis of H₂O-CO₂ based on SOEC.Sr₂Fe_1.5Mo_0.5O_6-δ（SFM）oxide was be used as both anode and cathode of SOEC because of its good chemical structure stability.However,its conductivity and catalytic activity need to be further improved.In this thesis,the conductivity and catalytic activity of SFM electrode are improved by Sr deficiency in A-site SFM and in-situ growth of Fe nanoparticles,resulting in high electrochemical performance of steam splitting and H₂O-CO₂ co-electrolysis.The main content and conclusions of this thesis are as follows:（1）Sr_2-xFe_1.5Mo_0.5O_6-δ（SFM）anode with different Sr deficiency was synthesized by GNP method and the effects of Sr deficiency on crystal structure,electrical conductivity and electrochemical properties of Sr₂Fe_1.5Mo_0.5O_6-δanode were systematically investigated.The results show that the introduce of Sr deficiency in Sr-site increases the cell volume and lowers the temperature of oxygen overflow,enhancing the activity of oxygen in the crystal lattice.Sr_1.95Fe_1.5Mo_0.5O_6-δhas a maximum conductivity of 38.4 S cm^-1.The polarization resistances of Sr₂Fe_1.5Mo_0.5O_6-δ,Sr_1.95Fe_1.5Mo_0.5O_6-δand Sr_1.9Fe_1.5Mo_0.5O_6-δsymmetric cell at 800℃are 0.102,0.070 and 0.096Ωcm²,respectively.The current density of Ni O-YSZ（SL）/Ni O-YSZ（FL）/YSZ/SDC/Sr_1.95Fe_1.5Mo_0.5O_6-δcell reaches-1300 m A cm^-2 at 20%H₂O-H₂,800℃and 1.5 V.In addition,the cell exhibits an excellent stability with a decay rate of0.001 V h^-1 under a constant current density of-500 m A cm^-2 during the operation of 110 h.（2）Sr_2-xFe_1.5Mo_0.5O_6-δ（SFM）oxides were further used as SOEC cathode to investigate the effect of in-situ exsolved Fe nanoparticles on the electrochemical performance of CO₂/H₂O electrolysis.X-ray diffractometer（XRD）and scanning electron microscopy（SEM）technologies were applied to study the growth process of Fe nanoparticles.XRD and SEM results show that the precipitation number and size of Fe nanoparticles increase with the increase of reduction temperature,reduction time and hydrogen partial pressure.The electrochemical test of H₂O/CO₂ co-electrolysis shows that the electrochemical performance increases with the increase of temperature and H₂O content.When the water vapor content is 10%,20%and 50%,the current densities of SFM/LDC/LSGM/LSCF-SDC cell at 850℃and 1.5 V are-2830,-2809,-3502 m A cm^-2,respectively.The cell stably operates for 110 h at 50%H₂O-CO₂,800℃and 1.3 V.When the cathode atmosphere is 10%H₂O-H₂,20%H₂O-H₂ and 50%H₂O-H₂,the current densities obtained at 850℃and 1.5 V are-1199,-1885,and-3132 m A cm^-2,respectively.The single cell operates at 50%H₂O-H₂,800℃and1.3 V voltage for 60 h.