Interface Manipulation And Electrochemical Characteristics Of Ni/YSZ Electrode For High Termperature Solid State Cells

The high temperature solid state cell consists of a solid oxide electrolytic cell?SOEC?and a solid oxide fuel cell?SOFC?.SOEC can electrolyze CO₂ at high temperatures and use excess waste heat and electricity to electrolyze CO₂ into CO,convert energy into fuel which is easy to store and transport.And SOFC can convert fuel into electric energy.As a new energy transform technology,SOEC and SOFC have many advantages in the process of high temperature,such as producing higher conversion efficiency.So they have a good development prospect.Ni/YSZ has been widely used as an anode for solid oxide cells?SOCs?due to its excellent catalytic activity,thermal matching of electrolytes and high ionic and electrical conductivity.However,the main factors of restricting their efficient application were low catalytic performance and easy to produce carbon deposition.In the study,CeO₂ can store and release oxygen.Transition metal doping CeO₂ not only can improve the ability to store oxygen,but also can make it have good catalytic activity.Therefore,this dissertation chooses Ni/YSZ electrode which was impregnated the transition metal doping CeO₂ to solve the problem of carbon deposition and enhance its electrocatalytic activity.The impregnated liquid was prepared into a powder by combustion method and characterized by physical methods such as XRD.It is proved that the powder owns stable structure and no metal precipitation under high temperature oxidation and reducing atmosphere.And the doping results meet our requirements.Ni/YSZ electrode modified by impregnation with Fe,Co,Ni and Mn doped with CeO₂ was prepared as SOFC.After the discharge performance test in H2,it was found that the SOFC discharge power density was greatly improved after impregnation modification.The electrochemical performance of SOFC doped with Mn-doped CeO₂ was the best compared to others,and the discharge power density reached 780 mW·cm-2 at 800 ? in all tested cells.However,the discharge power density under the same conditions of SOFCs with no impregnation modification was only 510 mW·cm-2.And the rate of improvement reached up to 52.9 %.The open-circuit polarization impedance of the SOFC was also reduced from 1.28 ?·cm2 to 0.25 ?·cm2.The extent of the reduction was very obvious.The order of the electrocatalytic performance of the four transition mental dopants to the electrode was Ce-Mn,Ce-Co,Ce-Ni,Ce-Fe,and untreated electrode.The SOEC was prepared by using different transition metal doping Ce O₂ to modify cathode.And the electrolytic performance was more significant than that of traditional SOEC.The electrolytic current density of SOEC modified by Ce-Ni immersion at 2.0 V was 2.60 A·cm-2 in all SOECs.However,traditional SOEC under the same conditions was only 0.47 A·cm-2.The former performance increased by 5.33 times than the latter's.The polarization resistance of SOEC was also reduced to a great extent with the increase of the applied voltage.In addition,the SOEC electrolysis performance of Ni or Mn-doped CeO₂ was not very different,but it was much better than the SOEC which was impregnated by Fe and Co doping CeO₂.The long-term stability of SOEC and carbon deposition mechanism were studied by SEM,EDS and EIS.The results showed that the performance of traditional SOEC had serious attenuation in the long run process.The decay rate reached 42.2 %.And SOEC current fluctuated greatly,the stability was very poor.Besides,the carbon content grew significantly during the long-term test.However,the SOEC was modified by impregnation treatment during the long-term operation.And the performance was almost no attenuation and the carbon content on the electrode surface was only a small increase.In summary,the Ni/YSZ electrode which was by impregnating transition metal doping CeO₂ at high temperature.And the electrode catalytic performance had been greatly improved.When electrolysis of CO₂,SOEC has a large current density,high efficiency and good stability.The performance did not occur significant performance attenuation in long-term operation.And its carbon resistance ability was also significantly improved.Therefore,the research of this dissertation provides reliable evidence for the practical and efficient application of SOEC regarding CO₂.