Preparation Of A New Ceramic Cathode And Study On The CO₂/H₂O Co-electrolysis Performance Of Solid Oxide Electrolysis Cell

Solid Oxide Electrolysis Cell（SOEC）is a technology that efficiently converts electrical energy into chemical energy.It can use excess electricity from renewable energy sources such as wind or solar energy.The principle is based on the reverse process of Solid Oxide Fuel Cell（SOFC）that has been widely studied.It has the characteristics of cleanliness and high efficiency.The solid oxide electrolysis single cell is mainly composed of three parts:cathode（fuel electrode）,anode（oxygen electrode）and electrolyte.Among them,the cathode is used as a place for fuel gas electrolysis/co-electrolysis,and its performance significantly affects the efficiency of electrolysis.For the cathode of the solid oxide electrolysis cell,in addition to meeting the general requirements for electrode materials,it must also have the ability to maintain good electrocatalytic activity in a high temperature and high humidity environment.At present,the researches on SOEC cathodes at home and abroad mostly refer to the commonly used SOFC anodes,and there is a lack of systematic analysis of the influence of electrolysis atmosphere and applied external potential on materials.In this paper,two new perovskite ceramic materials with different characteristics,La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ（LSCM）and La_0.3Sr_0.7Ti O3+δ（LST）are used as the research objects of cathode materials,aiming at the preparation and characterization of solid oxide electrolysis cell cathode and reveal the process and its performance under the conditions of electrolysis of steam,carbon dioxide and co-electrolysis to comprehensively analyze the material properties.The specific contents and conclusions of the study are as follows:Three synthesis methods of solid state,liquid state and combustion were used to synthesize LSCM powders.The performance of the powders under different synthesis methods was compared.The conductivity of LSCM reached 16S·cm^-1 at 800°C in air,and the material shows good stability under different atmospheres.Under the electrolysis potential,both the symmetrical electrolysis cell and the electrolyte-supported SOEC full battery can effectively electrolyze steam and carbon dioxide.The current density of the electrolysis cell at the same voltage decreases with the increase concentration of steam and increases with the increase concentration of carbon dioxide.In co-electrolysis of 60%H₂O+40%CO₂,the current density of the electrolysis cell reaches 0.21A·cm^-2 under the applied voltage of 2V.Considering the influence of the doping ratio of La and Sr on the performance of La_1-xSr_xTi O3+δpowders,powders with different doping ratios were synthesized by soild state method with x=0.5,0.6,0.7,0.8,and the selection was determined by comprehensively comparing the properties of the powders.x=0.7 is the best doping ratio.The conductivity of LST at 800℃under hydrogen atmosphere is 9S·cm^-1.The material shows obvious performance difference in oxidation and reduction states,but the material can still maintain good stability under different atmospheres.At the electrolysis potential,the symmetrical electrolysis cell can be used to directly electrolyze steam,but it lacks the ability to catalyze the reaction to carbon dioxide.The current density of the electrolysis cell at the same voltage increases with the increase of water vapor concentration,and with the increase of carbon dioxide concentration.The current density of the electrolysis cell reaches 0.17A·cm^-2 under a2V loading voltage under the co-electrolysis atmosphere of 60%H₂O+40%CO₂.The anode-supported of the electrolysis cell was synthesized by the tape-casting method and tested by assembling the electrolysis cell with LSCM and LST as the cathode.Due to the extremely low electrolyte thickness,the electrolysis performance was greatly improved,and the corresponding ohmic impedance was much smaller than that of the electrolysis cell supported by the electrolyte.In the co-electrolysis atmosphere of 60%H₂O+40%CO₂,the current density of the LSCM electrolysis cell reaches 0.55A·cm^-2 and the polarization resistance is only 0.15Ω·cm² under the loading voltage of 2V;the current density of the LST electrolysis cell reaches 0.51A·cm^-2and the polarization impedance is only 0.45Ω·cm².The cell made by tape-casting with LSCM and LST as cathode showed better performance in co-electrolysis than the single electrolysis atmosphere of steam or carbon dioxide,which proves the effectiveness of co-electrolysis.