Study On The Properties Of Double Perovskite Structure SOFC Cathode Material LnBaCo₂O_5+δ

Solid oxide fuel cell（SOFC）is an energy conversion device with a wide range of fuel choices and high conversion efficiency.The intermediate temperature（600-800℃,IGT）SOFC,has attracted much attention due to its advantages such as low cost of material selection and long service life.Therefore,the development of new IT-SOFC cathode material has important value.Based on the double perovskite material Ln Ba Co₂O_5+δ（Ln BC）,the structure,conductivity and electrochemical catalytic performance were optimized through doping and composite strategies to explore excellent electrode materials for IT-SOFC.（1）The structural characteristics,surface states and electrochemical properties of Ln BC（Ln=La,Pr,Nd and Sm）cathode materials were systematically studied.With the decrease of Ln ion radius,the structure symmetry is distorted,the oxygen content of oxides decreases gradually from Ln=La to Sm,and the conductivity and thermal expansion coefficient of the cathode material decrease gradually.X-ray photoelectron spectroscopy further revealed that the oxygen vacancy concentration on the surface of Ln BC sample decreased with the decrease of the Ln³⁺ion radius.With the decrease of Ln³⁺radius,the Ln-O bond energy and oxygen loss temperature increased,and the electrochemical performance of Ln BC electrode deteriorated,which were closely related to the oxygen vacancy concentration both on the surface and in bulk.The results showed that surface exchange and oxygen ion diffusion played important roles in the electrochemical behavior of Ln BC cathode materials.（2）The physical and chemical properties of layered perovskite oxide Pr Ba_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ（PBSCF）were studied comprehensively,and the relationship between structure,surface state and oxygen reduction reaction（ORR）performance was obtained.The PBSCF cathode with tetragonal structure maintain good structural stability at working temperature.X-ray photoelectron spectroscopy（XPS）showed that the mixed oxidation states of（Co,Fe）and Pr could increase the ORR rate by creating oxygen vacancies on the surface.M spectra confirmed that the contents of Fe³⁺and Fe⁴⁺in the oxide were 79.1%and 20.9%,respectively.In air,the polarization resistance impedance of PBSCF at 800℃is 0.067Ωcm².Oxygen ion diffusion acts as a rate-limiting step in electrode reduction.The power density of a single cell with PBSCF cathode at 800℃is 590 m W/cm².These results show that PBSCF is a potential cathode material for IT-SOFC.（3）The compatibility,conductivity and electrocatalytic activity of PBC-SDC composite cathode were studied.The results show that PBC and SDC can maintain good chemical compatibility up to 1000℃.At the same temperature,the conductivity of the composite electrode decreases with the increase SDC content.The ORR activation energy of the composite cathode was the lowest when the SDC content was20 wt%.PBC-SDC|LSGM|PBC-SDC symmetric cell in 800℃when the polarization impedance of the lowest 0.044Ωcm².