Performance Degradation Modeling And Non-coking Anode Design Of Solid Oxide Fuel Cell

As a new energy technology,solid oxide fuel cell(SOFC)can convert the chemical energy of fuel directly to electrical energy.It shows great advantages of high energy efficiency,low pollution and good fuel flexibility,and has a promising future.As SOFC works under high temperature(600～1000℃),the change of cell materials becomes very significant.The resulting lack of long-term stability is a major obstacle to the commercialization of SOFC and has become one of the research hotspots.The experimental method is the basis of SOFC research but limited by its time-consuming and costly features,theoretical calculations and numerical simulations then have gradually become effective supplementary methods.Theoretical calculations and numerical simulations are more efficient and less costly.They can provide in-depth analysis of the relationship between the microstructure and effective properties of cell materials,and examine the effects of changes in microstructure on cell performance.They can also provide detailed information on the performance degradation caused by material structure evolution and help to optimize the material.Numerical simulation can also show the distribution of components,current density,etc.inside the cell,providing support for the design and optimization of the cell structure and working conditions.It is of great value for the development of SOFC technology.The main work of this doctoral dissertation is to study the degradation of SOFC’s long-term performance due to changes in material properties through simulation techniques.The following is a brief introduction to the main contents of each chapter.In the first chapter,the history of the development of solid oxide fuel cell and the prospects for its future are introduced.The advantages and disadvantages of the SOFC technology are pointed out.After that,I introduce the geometry and components of the SOFC in detail.The material selection for each component is performed.Then I give the working mechanism of SOFC,and introduced the material degradation phenomenon of the cell components and its mechanism that affect the long-term stability of SOFC.Finally,the research progress of SOFC simulation and the application of simulation technology in SOFC performance degradation is briefly introduced.In the second chapter,the performance degradations of SOFCs induced by the microstructure evolutions of cell component materials are examined by multi-physics numerical simulations.Explicit considerations are given to the typical material set:Ni-YSZ anode,YSZ electrolyte,and SS430 interconnect.Degradation of the Ni-YSZ anode is attributed to the agglomeration of Ni particles that results in a reduced three-phase-boundary length and a reduced electrical conductivity of the anode.Degradation of the SS430 interconnect is considered based on the growth of its oxide scale.The decreased conductivity of YSZ due to its phase transformation from cubic to tetragonal is the cause of degradation associated with the electrolyte.The simulations provide quantatively the effects of the microstructure evolutions of the cell components on the cell performance.It is concluded that the long-term stability required for the SOFC commercialization can be achieved through an anti-oxidation coating of SS430 and a proper choice of the initial anode compositions.In the third chapter,a multi-physics model coupling the gas transport,chemical and electrochemical reactions,current conduction and heat conductions is described.Using this multi-physics model,I check the anti-coking effect of barrier layer on button SOFC anode and reveal the relationship between the anti-coking effect with the fuel utilization of the cell.In the model,carbon activity which is deduced by an empirical semi-quantitative coking criterion reduces with the rising of fuel utilization.Based on different methane steam reforming equations,I give a new no-coking anode design for CH4 fueled plate solid oxide with detailed working condition limit.Under the suitable working condition,this new kind plate SOFC which utilized Ni-based anodes can work with humidified(3%H20)methane at the 800℃.In the forth chapter,the electrochemical properties of LSCF used as single-phase electrode,composite electrode and nano-impregnated electrode in SOFC are studied.The formulas of effective electrode conductivity and electrochemical reaction area are given.The effective properties of single-phase LSCF electrode and LSCF nano-impregnated electrode are related to the particle radius of LSCF.The smaller the LSCF particle radius,the better the performance of the cell.Afterwards,according to the formula of particle radius increasing rate given by the experimental group,the effect of grain coarsening of the nano-impregnated LSCF electrode on the performance of the cell is calculated.At 600 degrees,the degradation rate was 0.153%/1000 hours,which is good for the application.The fifth chapter is a summary of the whole dissertation.