The Performance Of In,Ta And Y-doped BaCeO₃ Proton-conducting Solid Oxide Fuel Cells

Over the past few decades,the studies on the proton-conducting solid oxide fuel cells（H-SOFCs）have attracted much attention due to their excellent performance in H-SOFCs.However,the BaCeO₃-based electrolytes,as the typical representative of H-SOFCs,have poor chemical stability during working,which limited the application and development of H-SOFCs in some degree.In this dissertation,the effects of the doping of In,Ta,Y and other elements on the stability,sintering activity and electrical conductivity of BaCe O₃-based electrolytes were firstly studied.Then,the composition of electrolytes with well performance was determined.Finally,the stability,sintering activity and electrochemical performance of the single cells with above electrolytes were further studied.The contents of each chapter are the followingIn chapter I,the concept and working principle of the solid oxide fuel cell（SOFCs）are comprehensively introduced.In addition,the current research status and significance of H-SOFCs are briefly reviewed.In chapter II,the experimental details,such as the chemical reagents,sample preparation,characterization and testing methods etc.,are shown.In chapter III,the effects of the doping of In,Ta,Y and other elements on the chemical stability,sintering activity and conductivity of BaCeO₃-based electrolytes are systematically studied.After exposure in 100%CO₂ and boiled water for 6 h,the XRD diffraction peaks of the BaCeO₃ phase can be remained well for both the BaCe_0.7Ta_0.2Y_0.1O_3-δ（BCTY）and BaCe_0.7In_0.1Ta_0.1Y_0.1O_3-δ（BCITY）electrolytes,which indicates that both BCTY and BCITY have well chemical stability.For the BaCe_0.7In_0.2Y_0.1O_3-δ（BCIY）electrolyte,it is relatively stable under boiled water,but poor stability under 100%CO₂ atmosphere was observed.The poorest stability was found for the BaCe_0.7Y_0.3O_3-δ（BCY）among all investigated electrolytes.Some secondary phases in addition to the BaCeO₃ perovskite phase were observed in the XRD pattern of the BCY exposed in 100%CO₂.Moreover,the XRD diffraction peaks of the BaCeO₃ perovskite phase were absent for the BCY exposed in boiled water.The above results show that the doping of In and Ta elements can apparently improve the chemical stability of BCY electrolytes;furthermore,the role of Ta on the improvement of the stability of the electrolytes is some greater than that of In.The sintering activity of electrolytes was characterized by the shrinkage of the sample diameter.The results show that the BCIY has the best sintering activity among all electrolytes.Its sintering temperature can be decreased to 1250℃,while it is 1350,1450,and 1450℃for BCITY,BCTY,and BCY,respectively.Hence,the doping of In can apparently improve the sintering activity of the electrolytes.The conductivities of BCY,BCIY,BCTY,and BCITY at 600°C in wet H₂ are 10,3.8,2,and 2.5×10^-3S?cm^-1,respectively,which indicates that the doping of In and Ta can apparently decrease the conductivity of BCY electrolytes.In Chapter IV,preparation and performance testing of single cells.A modified BaCe_0.7In_0.15Ta_0.05Y_0.1O_3-δ(BCI₁₅T₅Y)proton-conducting electrolyte was prepared by a modified citrate method.The sintering temperature of the electrolytes is 1350℃.The BCI₁₅T₅Y electrolyte exhibits good chemical stability in both 100%CO₂ and boiled water environment.Using BCI₁₅T₅Y electrolyte,the single cells were prepared with NiO-BCI₁₅T₅Y composite anode and La_0.7Sr_0.3FeO_3-δ-BaZr_0.1Ce_0.7Y_0.2O_3-δ（LSF-BZCY）composite cathode.The results show that the maximum power densities of 116,200,274,303,and 315 mW/cm² with the open circuit voltage values of 1.080,1.063,1.036,0.999,and 0.965 V were obtained at 550,600,650,700,and 750℃,respectively.In addition,the proton conductivity of the BCI₁₅T₅Y electrolyte can reach 2.7×10^-3 S/cm at 600℃.In all,the BCI₁₅T₅Y with good stability,sintering activity and relatively high conductivity should be one of the excellent proton conductor electrolytes,which provides a useful reference for the development of novel H-SOFCs.In Chapter V,the results are summarized.In addition,the development of proton conductor solid oxide fuel cells in the future is briefly forecasted.