Preparation And Performance Of Proton Conductive SOFC Co-doped BaCeO₃ Electrolyte

Solid oxide fuel cell（SOFC）is a clean energy device that does not require the combustion of chemical energy and directly converts it into electrical energy.With the continuous exploration of SOFC-related research,the research and preparation technology of SOFC is gradually optimized,but it is also faced with some problems.For example,the high sintering temperature of traditional solid oxide fuel cells.To obtain a high-density electrolyte,it is necessary to sinter the electrolyte at high temperature of 1600°C and above.Excessive sintering temperature may have certain effects on the electrolyte structure.In addition,the traditional SOFC can only reach the temperature condition for battery startup when the operating temperature reaches 800-1000°C.Excessive operating temperature requires high thermal expansion coefficients between the electrochemical components of the battery and the performance of the material itself,and the battery life is reduced.In order to solve the above problems,the core component electrolyte called SOFC"heart"has become the research hotspot.The electrolytes currently studied are mainly divided into the following categories:perovskite-type oxide,layered perovskite structure,niobate structure and pyrochlore structure.The electrolyte materials prepared from perovskite-type oxides have the most excellent overall performance of BaCeO₃-based and Ba Zr O₃-based perovskite structure electrolytes.Due to the superior sintering activity and better electrical conductivity than Ba Zr O₃-based electrolytes,BaCeO₃-based electrolyte materials are currently research hotspot in perovskite structure electrolyte materials.This thesis mainly explores the influence of the rare earth elements and different valence elements co-doped BaCeO₃-based perovskite structure on the overall performance of electrolyte materials.The electrolyte material is modified by doping Sr,Sm,M（Zr,Y,Zn）and other elements on the A site and B site of the BaCeO3 perovskite structure to improve the sintering performance,density and proton conductivity of the electrolyte material and reduce the working temperature of SOFC electrolyte material.In this paper,Ba_0.6Sr_0.4Ce_1-x-yZr_xSm_yO_3-δ（BSCZS-x,y;x,y=0.00,0.05,0.10,0.15,0.20）,Ba_0.6Sr_0.4Ce_0.9-zY_xSm_0.1O_3-δ（BSCYS-z;z=0.00,0.05,0.10,0.15,0.20）and Ba_0.6Sr_0.4Ce_0.9-nZn_nSm_0.1O_3-δ（BSCNS-n;n=0.00,0.05,0.10,0.15,0.20）double-doped electrolyte material were prepared by the preparation process of citric acid combustion.XRD,SEM,electrochemical impedance and electrical conductivity were used to characterize the electrolyte,and the effects of dual-site doping on the crystal structure,microscopic morphology and proton conductivity of BaCeO3-based electrolyte materials were analyzed in detail.The research results of Zr⁴⁺,Sm³⁺doped BSCZS-x,y electrolytes show that double-site co-doped Sr²⁺,Zr⁴⁺,Sm³⁺using citric acid combustion method can prepare stable perovskite structure electrolyte materials with impurity-free second.Doping Zr⁴⁺at the B site of the ABO₃structure significantly improve the sintering performance of the electrolyte material.As the doping amount of different elements increases,the grain size of the electrolyte becomes larger and the number of pores decreases.The incorporation of Sm³⁺does not improve the density of the electrolyte.The co-doping Zr⁴⁺and Sm³⁺greatly increases the proton conductivity of the BSCZS electrolyte.The conductivity increases with the increase of the doping amount.When the doping amount reaches a certain value,the conductivity gradually decreases.When x=0.1 and y=0.1,the highest conductivity is 3.33×10^-3 S/cm（at 700℃）,with lowest activation energy 13.32 k J/mol.Sm³⁺has a better advantage in reducing the overall resistance of the proton conductive electrolyte and increasing the proton conductivity of the electrolyte material.On the basis of the Sm³⁺doping significantly enhance the electrolyte conductivity,we also studied the effect of B-site doping Y³⁺and Sm³⁺on the overall performance of the electrolyte.The research results of BSCYS-z electrolyte show that pure stable single perovskite structure electrolyte can be prepared by the citric acid combustion method at a calcination temperature of 900℃and above.When the sintering temperature is 1250°C,the electrolyte material with good sintering performance and high density can be prepared.And with the increase of Y³⁺doping,the electrolyte crystal grain size gradually increases,the gap between the crystal grains decreases,the density increases significantly compared with the undoped condition,the electrolyte conductivity increases continuously,and the overall resistance decreases.When the doping amount is z=0.20 and the sintering temperature is1250℃,the electrolyte exhibits the most excellent density and sinter-ability,large grain size and uniform distribution,the electrical conductivity reaches 0.158 S/cm and the total electrolyte resistance is 1.23Ω（700℃）,electrolyte activation energy reaches 8.75 k J/mol.Discussion and analysis of the comprehensive performance of BSCNS-n electrolyte and BaCeO3-based electrolyte doped with different valence elements show that Ba_0.6Sr_0.4Ce_0.9-nZn_nSm_0.1O_3-δelectrolyte powders prepared by the citric acid combustion method have single and stable phase structure.The incorporation of Zn significantly improves the sinter-ability and density of the BaCeO₃-based electrolyte.The conductivity of the electrolyte increases first and then decreases with the increase of doping content.When the Zn doping content is n=0.10the conductivity is the highest,which is 1.47×10^-2 S/cm（operating at 700℃）,and the activation energy is 13.19 k J/mol.The Zr⁴⁺,Y³⁺,Zn²⁺doped BaCeO3-based electrolytes have same structure and no impurity peaks generated.Among them,the Zn-doped BSCNS-0.10electrolyte has the best density,the largest grain size,and the best sintering performance.Y³⁺doped BSCYS-0.20 electrolyte has the highest conductivity and the lowest activation energy,respectivelyσ=4.41×10^-2 S/cm,E=8.75 k J/mol（operating at 550℃）.The total resistance value of Y³⁺doped BSCYS-0.20 electrolyte measured at 550℃is only 3.2Ωdifferent from that at 700℃,and the conductivity is 4.41×10^-2 S/cm.In summary,the trivalent Y³⁺doped BaCeO₃-based electrolyte material has the characteristics of stable structure,good sintering performance,high density,and excellent proton conductivity,more suitable for applications in medium and low temperature working environments.