Preparation And Electrical Properties Characterization Of Yttrium-stabilized Zirconium Solid Oxide Electrolyte

Human demand for energy has accelerated the consumption of fossil fuels,which are non-renewable and cause various environmental damages during their use.Therefore,finding alternative green energy sources is the key to achieving sustainable development of human society.Solid oxide fuel cell（SOFC）has the advantages of high efficiency,green environmental protection and good stability,and is one of the key new energy technologies currently under research and development.The electrolyte,as the core component of SOFC,determines the comprehensive performance of the whole SOFC system.With good high-temperature conductivity and excellent stability,8 mol%Y₂O₃-stabilized ZrO₂（8YSZ）is the most commercially used solid oxide electrolyte at present.However,the further popularization of 8YSZ electrolytes is seriously limited by the tendency of the 8YSZ nanopowders obtained by the existing synthesis methods to agglomerate,the inadequate electrical conductivity of the prepared ceramics,and the high sintering temperature of the ceramics,resulting in high production costs.In response to the above problems,the aim of this thesis is to obtain 8YSZ nanopowders with uniform particle size,good dispersion and high specific surface area,as well as to reduce the sintering temperature and improve the electrical conductivity of 8YSZ ceramics.Firstly,systematic study on the preparation method of 8YSZ powder to obtain 8YSZ nanopowders that meet the above performance requirements.Then,the 8YSZ ceramics were sintered at low temperatures by a cold sintering process to study and analyze the changes in densities,crystal structures,electrical conductivity,and their influence mechanisms.Finally,Sc³⁺ion co-doping was used to reduce the lattice distortion,thus further improving the electrical conductivity of 8YSZ.The main study contents and results are as follows.（1）To explore the optimal conditions for powder preparation.The effects of various process parameters of the homogeneous precipitation-hydrothermal method on the 8YSZ powder were systematically investigated,and 8YSZ powder with pure cubic phase crystal structure,a particle size of about 60 nm,uniform particle size,and high specific surface area was prepared.（2）To study the effect of cold sintering on the densification and electrical conductivity of 8YSZ ceramics.As a comparison,8YSZ ceramics with high densities were prepared by conventional sintering process at 1400℃,and the electrical conductivity measured at 850℃was 0.036 S/cm.Then,Cold sintering process（CSP）technique associated with post-heat-treatment（PHT）was used to prepare 8YSZ ceramics and test their conductivity at 850℃.The results show that cold sintering can improve the initial densities of ceramic blanks,and the relative densities and conductivities of 8YSZ ceramics increase with the increase of PHT temperature.and the relative density reaches～98%at PHT temperature of 1200℃and the conductivity is 0.042 S/cm.When the PHT temperature was increased to 1400℃,the conductivity was as high as 0.080 S/cm,and the grain size was only 300 nm,indicating that the cold sintering technology can achieve high density and fine grain structure of 8YSZ ceramics at a lower sintering temperature,while improving the conductivity.Compared with the conventional sintering method,the 8YSZ ceramics prepared by the CSP-PHT process have lower oxygen vacancy activation energy,which is related to the amorphous phase elimination,the increase in relative density,and the increase in conductive grain boundaries generated by the grain refinement that occurs during the CSP-PHT process.（3）To study the effect of Sc³⁺co-doping on 8YSZ ceramics.Fisrtly,Sc³⁺/Y³⁺co-doped xSc-（8-x）YSZ（x=1,2,3,4）nanopowders were prepared on the basis of 8YSZ using a homogeneous precipitation-hydrothermal method,and the ceramics were prepared at 1200℃using a CSP-PHT process.The results show that the conductivity increases from 0.055 S/cm for 1Sc-7YSZ to 0.083S/cm for 4Sc-4YSZ with the increase of Sc³⁺doping.Meanwhile,the oxygen vacancy activation energy decreases from 1.004 e V to 0.904 e V,which is mainly because the radius of Sc³⁺is close to that of Zr⁴⁺,which leads to the reduction of lattice distortion caused by Y³⁺doping.