Preparation And Properties Study Of Sr Doped Double Perovskite Structure Material La_0.5Gd_0.5Ba_1-xSr_xCo₂O_5+δ

Solid oxide fuel cell（SOFC）,as an efficient green energy conversion device,is of great significance to promote the use of green and clean energy and achieve our"double carbon"goal.However,the high operating temperature（>800 ^oC）of conventional SOFCs has caused many problems such as long start-up time and expensive manufacturing cost,which limit their commercialization.The development of solid oxide fuel cells（IT-SOFC）at low and medium temperatures（500-700 ^oC）is currently the focus of research.But as the temperature decreases,the electrochemical reaction kinetics of the cathode material is slow,which greatly affects the output power of the cell.Therefore,it is necessary to develop novel high-performance cathode materials for IT-SOFC.In recent years,mixed ionic and electronic conductor perovskite oxides LnBaCo₂O_5+δhave attracted attention because of their high oxygen conductivity and excellent oxygen surface exchange coefficient.A large number of monolanthanide LnBaCo₂O_5+δstudies show that different lanthanide ions can lead to large differences in electrical and electrochemical properties,and their comprehensive performance needs to be optimized.It has been shown that partial replacement of the Ba layer element in the A site with Sr element can enhance the electrical conductivity and oxygen catalytic activity of the cathode.To further improve the electrical and electrochemical properties of cathode materials,this paper proposes the introduction of Sr elements to partially replace Ba layer elements on the basis of A site double lanthanide doping,hoping to obtain a new high performance cathode material for IT-SOFC.A series of Sr-doped La_0.5Gd_0.5Ba_1-xSr_xCo₂O_5+δ（LGBCOSr-x）cathode materials were prepared by the solid-phase method to investigate the effects of Sr doping on the phase structure,thermal expansion coefficient（TEC）,thermochemical stability,electrical conductivity and electrochemical properties of the LGBCO materials.The effect of Sr doping on the cathode phase structure was explored by XRD test and refinement method,and the results showed that the pure phase LGBCOSr-x（x=0-0.5）compound was successfully synthesized by calcination at 1150℃in air for 12 h.With the increase of Sr doping,the cathode phase structure gradually changed from a double perovskite structure with P4/mmm space group to a single perovskite structure with Pm-3m space group,meanwhile the unit cell parameters and unit cell volume became smaller.The in-situ high-temperature XRD test shows that LGBCOSr-x can maintain phase structure stability in wet air and at high temperatures,but the cathode was less stable in CO₂ atmosphere,and the addition of Sr reduced the durability of the cathode material against CO₂.In addition,it has good thermochemical compatibility with electrolytes GDC and BZCY at less than 1100℃.The thermal expansion test shows that the addition of small radius Sr²⁺inhibits the physical expansion of the cathode in the low temperature section,thereby improving the thermal expansion coefficient of the material.O₂-TPD tests revealed that the doping of Sr reduced the chemisorption oxygen desorption temperature and improved the cathode’s oxygen adsorption and desorption activity.The conductivity tests showed that the cathode conductivity showed a tendency to increase and then decrease as the temperature increased due to the generation of oxygen vacancies and the reduction of Co ions.Furthermore,the addition of Sr effectively improves the conductivity of the material,with the highest conductivity at the cathode(1042S·cm^-1 at 400℃)at a doping level of 0.5.XPS analysis revealed that the doping of Sr significantly increased the ratio of surface adsorbed oxygen,which was favorable to the cathodic oxygen reduction catalytic activity.The EIS test and DRT analysis showed that the charge transfer process is the main rate-controlling step of the cathode oxygen reduction process.ASR value of the cathode gradually decreased with the increase of Sr doping,the introduction of Sr significantly reduces the resistance of the main velocity control step of the cathode,effectively enhancing the electrochemical properties of the material.The material LGBCOSr-0.5 exhibits the best electrical and electrochemical properties,which is a potential cathode material for IT-SOFC.