Key Materials For Proton-conducting Solid Oxide Fuel Cells With In-situ Ethylene Production

Ethylene is one of the largest chemical products in the world.Ethylene industry is the core of petrochemical industry.Ethylene products account for more than 75%of petrochemical products,and its global demand increases significantly every year.However,there are some technical difficulties in the production process of ethylene,such as high energy consumption,heavy emission,low conversion rate and poor selectivity.Therefore,it is of great significance to develop a green and efficient ethylene production technology.Solid oxide fuel cell（SOFC）is an electrochemical device which can convert the chemical energy of hydrocarbons into electrical energy efficiently and environmentally friendly.When ethane fuel is dehydrogenated in the anode of proton conductor SOFC（H-SOFC）to produce ethylene and hydrogen,it becomes an H-SOFC reactor that produces ethylene and consumes hydrogen to generate electricity.However,due to the lack of research on anode materials with catalytic dehydrogenation ability,there is still a contradiction between the theoretical and experimental phenomena to explain the proton transport mechanism in the electrolyte,and there is also a phenomenon that cannot be explained from the macro experimental perspective in the modification experiment of cathode materials.Therefore,the catalysts for ethane dehydrogenation,electrolytes and cathode materials in H-SOFC reactor are studied in this paper.The main research contents and results are as follows:（1）In the research of H-SOFC reactor,the first goal is to develop catalyst materials with the ability of anti carbon deposition and ethane dehydrogenation.For this reason,A-site deficient and Ni-doped perovskite materials La_0.9Mn_0.8Ni_0.2O_3-δ（LMN）,La_0.9Cr_0.85Ni_0.15O_3-δ（LCN）,La_0.8Sr_0.1Cr_0.85Ni_0.15O_3-δ（LSCN81）and La_0.6Sr_0.3Cr_0.85Ni_0.15O_3-δ（LSCN63）are prepared.All the catalysts are reduced to prepare R-LMN,R-LCN,R-LSCN81 and R-LSCN63 and ER-LMN,for evaluation as catalysts for C₂H₆dehydrogenation to co-produce C₂H₄and H₂.The 1 h reduction causes the formation of Ni nanoparticles embedded in a perovskite substrate,but the excessive reduction for 6 h causes LMN decomposition to La₂O₃,Mn O and Ni nanoparticles.The performance of the catalysts increases with increasing temperature and the performance of LMN-based catalysts are better than other catalysts.The doping of Sr makes the particles of LCN based catalyst materials slightly smaller from about 350 nm to about 280 nm.With a higher ratio of Sr doping,the substrate particles of R-LSCN63 are smoother than that of R-LSCN81.It can be inferred that the higher ratio of Sr doping makes the base particles dissolve in the same reducing atmosphere,thus more Ni particles are precipitated.R-LMN demonstrates the highest performance among the LMN-based catalysts,with 41.6%C₂H₆conversion and 98.0%C₂H₄selectivity at 750℃;ER-LMN exhibits the lowest catalytic performance because of LMN decomposition.The performance of R-LMN is essentially stable during a 50 h test;and the slow growth of Ni nanoparticles slightly increases C₂H₆conversion and decreases C₂H₄selectivity due to the increase of the surface area of the Ni nanoparticles.（2）In recent years,the research on H-SOFC electrolyte materials shows that B-site doped Ba Ce O₃and Ba Zr O₃show high proton conductivity.It is generally believed that the doping of B-site elements causes a large number of oxygen vacancies in these materials,which can improve their proton conductivity.In order to explore the mechanism of proton transport in these materials,ideal Ba Ce O₃（BCO）and Ba Zr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δwithout and with an oxygen vacancy（BZCYYb and BZCYYb＿V）are studied at the microscopic level by the first-principles approach.Two forms of proton transfer,that is,the H ion-form and OH group-form,in addition,the OH group-forms are divided into R-type（O-H bond rotation）and S-type（O-H bond translation）,are investigated in the aspects of proton transport path,energy barrier along the path,differential charge density,electrostatic potential,the distance between H and O atoms at the transition state of saddle point as well as the distance between adjacent O atoms.The results indicate that S-type（the direction of OH bond is perpendicular to the transfer path）OH-form in BZCYYb＿V is the most favorable realistic mode for proton transfer,which indicates that protons migrate in the form of OH in the presence of oxygen vacancies.;doping of Zr,Y and Yb reduces the electrostatic potential barrier for proton transport,which makes proton transfer much easier in BZCYYb than in BCO.In addition,the doping of these three elements makes the valence band top of BZCYYb exceed the Fermi level,thus greatly improving the electronic conductivity of the material;and the introduction of an oxygen vacancy further reduces the electrostatic potential barrier for H-form proton transfer in BZCYYb＿V.（3）The study of SOFC cathode shows that the Sr doped La Mn O₃（LSM）has good conductivity,structural stability and high electrocatalytic activity for oxygen reduction reaction（ORR）.The composite of LSM and materials with proton conductivity can also be used as cathode materials of H-SOFC.However,the catalytic activity of LSM decreased significantly in the middle temperature range.In order to improve the electrochemical activity of LSM cathode,Pd O was used to modify the LSM,but under the condition of polarization,the poor stability of nano PDO particles limited its application in SOFC.The results show that the thermal stability and catalytic activity of Pd O can be improved by doping 20%Zr.In order to investigate the influence of Zr doping on the stability and its catalytic activity for ORR reaction of Pd O material,the oxygen reduction reaction properties on the Pd O and Zr-doped Pd O surfaces,and the relative stability of the concerned surfaces have been studied by the first-principles calculations.The results demonstrate that the doped Zr element plays an important role in the stabilization of the Pd O surfaces and the enhancement of the oxygen reduction activities on these surfaces.The Zr atoms prefer to replace the cus-Pd atoms on the Pd O（101）surface,which is more stable than Zr doped Pd O（001）surface.The interaction between Pd and Zr could strengthen the hybridization between the adsorbed O 2p and Pd 4d states,thus lower the adsorption energy,improving the O₂adsorption performance.The adsorbed O₂molecules tend to be dissociated on the Pd O（101）surface.It is also discovered that the increase of Zr doping concentration can also enhance the O₂adsorption properties and facilitate the subsequent dissociation.