Structure And Properties Of Sn And Ni Doped BaCeO₃-based Proton-conducting Electrolytes

Solid oxide fuel cells(SOFC)have a promising future in energy applications due to their high efficiency,low pollution and rich fuel selectivity.Currently more mature SOFC need to operate at 800?1000?.High temperature leads to the choice of materials and cost of the traditional SOFC commercialization has been a great obstacle.SOFC is developing towards the lower temperature of 400??800?.Electrolyte,as the core component of SOFC,affects the temperature range and energy conversion efficiency of the battery,and also determines the selection of electrode materials and corresponding preparation technology.Compared with oxygen ion conductor,proton conductor electrolyte has obvious advantages between 400? and600?,such as higher ionic conductivity and lower activation energy,the generation of water at the cathode side to avoid dilution of fuel and higher theoretical energy conversion efficiency.In this paper,the structure,sinterability and electrical properties of BaCe_0.7Zr_0.1Y_0.2-xSn_xO_3-?(x=0,0.05,0.1)and BaCe_0.7-xNi_xSn_0.1Y_0.2O_3-?(x=0,0.05,0.1)are studied.This paper focuses on analyzing the influence of doping elements on conductivity from the perspective of phase structure and sintering performance.In the first chapter,the development of SOFC,electrochemical and thermodynamic principles and structural components are briefly introduced.We also summarize some oxygen ion conductors and proton conductors and the development of these solid electrolyte.In next chapter,we study the structure,sintering and electrical properties of protic conductor electrolyte BaCe_0.7Zr_0.1Y_0.2-xSn_xO_3-?(x=0,0.05,0.1).XRD refinement results show that is the orthogonal structure of space group Pbnm.The synergistic test of thermal expansion and Raman shows that Sn doping improves the symmetry of BZCY.Sn as dopant hardly improves the sintering of BZCY.Compared with BZCY and BZCYS0.1,BZCYS0.05 shows the highest conductivity.We believe that excessive Sn doping leads to the reduction of theoretical oxygen vacancy,and the reduction of free volume leading to the decline of electrical performance,but the increase of symmetry contributes to the improvement of conductivity.The single cell prepared with BZCYS0.05 electrolyte achieves a power density of 206 mW cm^-2in a wet hydrogen atmosphere at 650?.In chapter three,we use Ni with smaller ionic radius as dopant to adjust symmetry and optimize sintering property,and prepare proton conductor BaCe_0.7-xNi_xSn_0.1Y_0.2O_3-?(x=0,0.05,0.1)and study its structural characteristics,sintering property and electrical properties.XRD is refined to determine the phase structure and Raman shows that Ni doping improves the symmetry.What's more,we use ECS and DRT to analysis electrochemical impedance spectroscopy.In addition,we point out some difficulties in the calculation of free volume in the process of analyzing the phase structure,and propose the idea of dividing the effective charge region and the free region by the density of electron cloud.The reduction of the free region has a negative contribution to the conductivity.BaCe_0.65Ni_0.05Sn_0.1Y_0.2O_3-?achieves the highest conductivity of 12.1 mScm^-1at 600?and corresponding single cell achieves the power density of 192 mW cm^-2.In chapter four,the work of chapter two and chapter three is summarized,and the prospect of developing proton conductor electrolyte is discussed.