Study On Modification Of Intermediate-temperature Solid Oxide Fuel Cell Cathode Materials

As an energy conversion device,solid oxide fuel cell（SOFC）has been widely concerned due to its high energy conversion efficiency,low emissions and pollution-free characteristics.However,the operating temperature of SOFC has always been the main limitation of SOFC’s application in the market,more and more researches are focused on intermediate-temperature solid oxide fuel cells（IT-SOFC）.Therefore,it is very important to develop high-performance IT-SOFC cathode materials.Double perovskite oxide Ln Ba Co₂O_5+δ（Ln=La,Nd）have excellent electrochemical performance at intermediate temperature due to its unique structure,but its high thermal expansion coefficient leads to mismatch with electrolyte materials at high temperature.Therefore,this paper aims to reduce the thermal expansion coefficient of IT-SOFC cathode materials and improve electrochemical performance,a series of modification studies have been carried out on the parent materials La_0.5Ba_0.5Co O_3-δand NdBaCo₂O_5+δ.First,La_0.5Ba_0.5Co_1-xCu_xO_3-δ（LBCC-x,x=0,0.1,0.2,0.3,0.4）cathode materials were prepared by sol-gel method,the electrochemical properties of LBCC-x cathode materials were also studied.Abundant oxygen vacancies were introduced into La_0.5Ba_0.5Co O_3-δby Cu partial substitution of Co to facilitate the electrochemical activity of oxygen reduction reaction.The results show that all the LBCC-x cathode materials have formed pure single perovskite structure,and all samples still maintain sufficient conductivity at intermediate temperature.The polarization resistance of the samples decrease first and then increase with the increase of Cu content,La_0.5Ba_0.5Co_0.7Cu_0.3O_3-δhas the best electrochemical performance in LBCC-x,and its polarization impedance at 750°C is 0.043Ωcm²,exhibiting a 65%decrease in comparison to that of the La_0.5Ba_0.5Co O_3-δcathode.Secondly,NdBaCo₂O_5+δ（NBC）and NdMn O_3-δ（NM）were prepared by sol gel method and solid state reaction method respectively.The NBC-NM-x（x wt%=0,10,20,30,40 wt%）composite cathodes were obtained by mechanical mixing of NBC and NM according to the mass ratio of 9:1,8:2,7:3 and 6:4 respectively.The experimental results show that NBC and NM have good chemical compatibility at high temperature,and the conductivity of NBC-NM-x composite cathodes decrease with the increase of NM content.At the test temperature range of 600～850°C,the polarization resistance of the samples first increase and then decrease with the increase of NM content.NBC-NM-20 shows the best electrochemical performance in all samples,and its polarization resistance at 750°C is 0.043Ωcm²,compared with the original NBC,the polarization impedance is greatly improved.NdBaCo₂O_5+δ-x Gd_0.1Ce_0.9O_1.95（NBC-x GDC,x=0,5,8,10 wt%）were synthesized by one-pot method in order to overcome the disadvantage of uneven two-phase distribution of cathode materials compounded by mechanical mixing.The experimental results show that NBC and GDC have good chemical compatibility at high temperature,and the conductivity of NBC-x GDC（x=0,5,8,10 wt%）composite cathodes decrease with the increase of GDC content.The polarization resistance of NBC-x GDC（x=0,5,8,10 wt%）decrease first and then increase with the increase of GDC content.Compared with the original NBC,the polarization resistance of NBC-x GDC（x=5,8,10 wt%）are improved to some extent.NBC-5GDC shows the best electrochemical performance in all the samples,and its polarization resistance is 0.031Ωcm²at 750°C,which is significantly lower than the original NBC cathode,compared with other composite cathodes prepared by mechanical mixing under the same conditions,the polarization resistance has obvious advantages too.