Study On Preparation And Properties Of Neodymium Perovskite Oxide Cathode Materials For Solid Oxide Fuel Cell

Energy promotes the development of human society.Human society has long been highly dependent on traditional energy,and the resulting problems such as environmental pollution and carbon emissions have worsened the natural environment.In recent years,environmental pollution has been effectively curbed,and the impact of excessive carbon emissions on the environment can not be ignored.In order to change this situation,China plans to achieve carbon neutrality in 2060,so we will vigorously develop new energy.Among them,hydrogen energy,as a kind of clean energy without carbon emissions,has a good application prospect in the field of energy saving and emission reduction.Fuel cell is one of the direct utilization ways of hydrogen energy,in which solid oxide fuel cell（SOFC）has attracted wide attention because of its high energy conversion rate and high fuel flexibility.However,the higher working temperature（～1000℃）limits the application of SOFC,and the decrease of working temperature will lead to the decline of cathode performance,which will affect the performance release of the whole SOFC.Therefore,the search for cathode materials with high electrochemical performance at medium and low temperature has become the main research direction in this field.In this thesis,three kinds of Nd-based Co and Fe-based perovskite oxides were obtained by doping Nd-based perovskite oxides with good thermal expansion coefficient and electrochemical properties.Furthermore,the related properties are tested,and the feasibility of using it as SOFC cathode material is explored.The main contents are as follows:（1）Nd_0.8-xSr_0.2Ca_xCo O_3-δ（x=0,0.05,0.1,0.15,0.2）cathode powders were synthesized by sol-gel method.Through XRD test,it is found that the second phase Nd Ca Co O4+δis formed when the amount of Ca doping is higher than 0.1.The test of thermal expansion coefficient shows that the increase of Ca content can inhibit the thermal expansion of the material.The conductivity test shows that with the increase of Ca content,the conductivity increases at first and then decreases,and the highest value is 443 S cm^-1 at 800℃when the Ca doping content is0.1.At the same time,through electrochemical impedance spectroscopy（EIS）,it is found that Nd_0.6Sr_0.4Co_0.9Cu_0.1O_3-δshows the lowest area specific resistance（ASR）.The output power test of single cell shows that the maximum power density of Nd_0.7Sr_0.2Ca_0.1Co O_3-δis 409.31 m W cm^-2 at 800℃,which is slightly higher than that without Ca doping.This shows that compared with the undoped samples,Nd_0.7Sr_0.2Ca_0.1Co O_3-δreduces the TEC while maintaining good electrochemical performance,so it can be used as an IT-SOFC cathode material.（2）Nd_0.6Sr_0.4Co_1-xCu_xO_3-δ（x=0,0.05,0.1,0.15,0.2）cathode materials were synthesized by sol-gel method.The XRD results show that the lattice shrinks with the increase of Cu content,and an unknown second phase is formed when the Cu content is more than 0.10.At the same time,the addition of Cu significantly reduced the coefficient of thermal expansion of the material.In terms of performance test,Nd_0.6Sr_0.4Co_0.9Cu_0.1O_3-δshows good electrochemical performance,and its conductivity is 541 S cm^-1 at 800℃.The impedance test shows that the ion transport ability of the material is enhanced with the introduction of appropriate amount of Cu,and the ASR value decreases obviously compared with the undoped sample.The peak output power of the anode-supported single cell with this material as cathode is 444.87 m W cm^-2 at800℃,which is slightly higher than that without doping.It is proved that proper Cu doping can improve the structural stability on the premise of electrochemical performance.（3）Nd_0.6Sr_0.4Fe_1-xZn_xO_3-δ（x=0.02,0.04,0.06,0.08,0.1）cathode materials were prepared by solid state method.With the addition of Zn,Nd_0.6Sr_0.4Fe_1-xZn_xO_3-δis a single phase in the doping range.However,the test of the coefficient of thermal expansion shows that the inhibition of the thermal expansion property of the original structure is limited by the addition of Zn.When x=0.1,the average CTE value at 35℃ to 800℃ is 15.9279×10^-6 K.In terms of performance test,Nd_0.6Sr_0.4Fe_0.96Zn_0.04O_3-δshows the highest electrical conductivity,which is108.78 S cm^-1 at 700℃.EIS test results show that appropriate amount of Zn doping can improve the oxygen transport capacity of the materials.At the same time,the peak output power density of the single cell with this material as cathode is 306.37 m W cm^-2 at 800℃,which proves that the introduction of appropriate amount of Zn can improve the electrochemical performance of the material.In summary,through the preparation and exploration of Nd_0.8-xSr_0.2Ca_xCo O_3-δ,Nd_0.6Sr_0.4Co_1-xCu_xO_3-δand Nd_0.6Sr_0.4Fe_1-xZn_xO_3-δ,we found that appropriate amounts of Ca,Cu and Zn can improve the stability of the materials.According to the above study on neodymium perovskite oxides,these materials have application value in the field of SOFCs and can be used even at low and medium temperatures as SOFC cathodes.