Effects Of Additives On Sintering And Electrical Properties Of Samarium Doped Ceria

Doped CeO₂?Doped CeO₂,DCO?is a kind of solid electrolyte with high oxygen ion conductivity,and it can be used in solid oxide fuel cells?SOFC?,oxygen sensors,catalysts and other technical fields.However,the widespread use of DCO electrolyte is limited because of its poor sinterability.It is found that the sinterability of DCO can be improved by some additives,and the cost of preparation can be reduced.The effects of additives on electrical properties of DCO,however,are not very clear yet.It is reported that proper additives can scavenge the Si O₂ in grain boundaries of SDC,thereby improving the grain boundary conductivity and the apparent oxygen ion conductivity of the electrolyte.The commonly used additives are Li₂O and some transition metal oxides?TMO?,such as Cu O,Co O,Fe₂O₃.The transition metal elements may be reduced in hydrogen,and as a result,electronic conduction may occur in DCO electrolyte.This will lower the the open circuit voltage of a SOFC and its performances,when DCO contained TMO additives are used as the electrolyte of the SOFC.Therefore,this work focuses on the effects of additives on sintering and electrical properties of samarium doped ceria(Ce_0.8Sm_0.2O_2-?,SDC).Different additives including non-transition metal oxide?non-TMO?and transition metal oxides?TMO?are tested.The effects of different contents and the synergetic effect of composite additives on the properties of SDC are studied.In chapter 1,the reports about SOFC and the electrolyte materials are reviewed.The main points are focused on the influence of additives on sinterability and electrical properties of DCO electrolytes.In chapter 2,the effects of CaO,Al₂O₃,Mg O,SrO and Ba O additives with contents in the range of 0.0001mol%?5mol%on the sintering of SDC,which is prepared via ammonium oxalate coprecipitation,are studied.The relative density and sintering kinetics of the SDC with additives are tested,and mechanisms of the effect of additives on sintering are discussed.The results show that oxide additives consist of cations with larger absolute value of Vegard's Slope and lower valence state can improve the sinterability of SDC,even their contents in SDC are very low.In chapter 3,the different effects of non-TMO and TMO additives on conductivity of SDC under oxidation/reduction atmosphere.The conductivities of SDC contained Cu O,Mg O and SrO are obtained by AC impedance spectra under air/hydrogen atmosphere,respectively.The preliminary results show that Cu O additive may result in more electron conductivity under reduction atmosphere;while the non-TMO additives,such as Mg O,may weaken the problem that the conductivity of SDC increases quickly in hydrogen at high temperatures.In chapter 4,the synergetic effect of composite additives on the properties of SDC are studied.The composite additives,Ba O-SrO or CaO-SrO,are used to change the sinterability and conductivity of SDC electrolyte.The relative densities,sintering behaviors and conductivities of SDC are studied.The results show that the linear shrinkage rate of SDC in different range of temperatures can be changed by adjusting the contents of additives and the ratio of the two additives.As for the electrical properties,although the composite additives used in this work did not improve the oxygen ion conductivity of SDC electrolyte,it can further weaken the problem that the conductivity of SDC increases quickly in hydrogen at high temperatures.