Novel Perovskite Oxides Electrode For Symmetrical Solid Oxide Fuel Cells-doping And Properties

Solid oxide fuel cell(SOFC)is an all-solid energy conversion device,which has the advantages of high energy conversion efficiency,flexible fuel sources,and high integration degree.In general,SOFC single cells have a cathode-electrolyte-anode asymmetric structure;that is,the cathode and the anode have different structures and materials.In recent years,a symmetric structure SOFC has been widely studied,which uses the same materials as the cathode and anode,usually oxide ceramics.Compared with asymmetric SOFCs,symmetrical SOFCs have apparent advantages:(1)oxide anodes have better resistance to carbon deposition and sulfur poisoning and can be regenerated through the oxidation-reduction cycle,improve the long-term stability of the system.(2)Cathode and anode can be fabricated in one-step,which reduces the production cost.(3)Symmetrical SOFCs can be flexibly switched in the mode of fuel cell and electrolytic cell(SOEC),so that it has a broader application prospect in Power Grid Peak Regulation,Energy Internet Construction,and other aspects.The purpose of this paper is to explore the properties of perovskite oxides and their derivatives as electrodes of symmetrical SOFCs and to optimize their electrochemical properties through doping and surface modification.The first chapter is the introduction part,which introduces the working principle of SOFC,the factors affecting its performance,and its role in the sustainable energy system.The electrolytes,cathode,and anode materials of SOFC and their modification methods were summarized,extracting the main points of the research.Chapter 2 studies the electrochemical properties of La0.5Sr1.5MnO4 with the Ruddlesden-Popper structure(A2BO4).And the La0.5Sr1.5Ni0.1MnO4+? electrode with excessive Ni doping was designed.Ni doping reduced the polarization resistance of the cathode by 26%.Under the reduced atmosphere,Ni exsolves from the parent phase and form Ni nanoparticles on the anode surface,which reduces the polarization resistance of anode by 41%.The overall effect of Ni doping increased the maximum output power density of symmetrical cells by four times.In chapter 3,the influence of Calcium doping on the conductivity and electrochemical performance of Sr2Fe1.5Mo0.5O6(SFM)are researched.Calcium doping increased the conductivity of SFM from 39.85 S cm-1 to 93.07 S cm-1 at 800? in the H2 atmosphere.The maximum output power density of Ca0.25-SFM|LSGM|Ca0.25-SFM symmetrical cell at 80? with H2 as fuel is 709 mW cm-2.Under the SOEC mode,the current density can reach 1183 mA cm-2 when electrolysis water at 1.5 V DC bias.The electrochemical oxidation mechanism of H2 at Ca0.25-SFM anode is analyzed by the three-electrode method.The polarization resistance of Ca0.25-SFM anode is not affected by water pressure and is proportional to PH2-1.Based on the law of mass action and the Butler-Volmer equation,the dynamic model was established and compared with DRT analysis results.The results show that the dissociation adsorption of H2 on the electrode surface contributes most of the polarization resistance and has the maximum activation energy,which is the rate-limiting step of the anode reaction.