Study On The Electrochemical Properties And Thermal Stress Of Planar SOFC Under Multiphysics Coupling

Solid oxide fuel cell(SOFC)has been considering as a highly efficient device to convert chemical fuels directly into electrical power.Compared with traditional energy conversion technologies,SOFC has many significant advantages,including high efficiency,high volumetric and gravimetric,low pollutant emission and noise,easy-fabrication,as well as no re-charge duration.However,SOFC operate at high temperature.There are many factors that affect the performance and structural integrity of SOFCs.Predicting and optimizing the structure and performance of SOFCs with considering all these factors comprehensively are an urgent problem,which are need to be solved.In this paper,through theoretical analysis,the SOFC theoretical model of electrochemical reaction,mass transfer,fluid flow,heat transfer and solid mechanics is established,and the three-dimensional finite element modeling of planar solid oxide fuel cell is realized by COMSOL Multiphysics.The distribution of gas mole fraction,current density,temperature and thermal stress in the working stage of the cell is study.The failure probability was calculated by Weibull method.The effects of SOFC geometry parameters,process parameters and anode structure on the electrochemical performance and thermal stress were discussed.The main conclusions are listed as follows:(1)The peak value of electrolyte current density appears at the air inlet,and the maximum value is 6233 A/m~2.There is a large temperature gradient at both ends of the cell,especially at the contact position between cathode and interconnect,and the maximum temperature gradient is 2.96×10~5 K/m,and the internal thermal stress is the result of temperature and temperature gradient.The cathode failure probability can reach 0.079 in the working stage of the cell,and attention should be paid to the cathode failure risk during the operation of the cell.(2)The effects of rectangular,triangular,trapezoidal,circular channels and the gas flow direction arrangement of the co-flow,counter-flow and cross-flow on the electrochemical performance and thermal stress of SOFC were discussed.The SOFC with rectangular channel design is more conducive to the diffusion of gas in the electrode,which improves the electrochemical performance of the cell,but also leads to the increase of the temperature of SOFC,which makes the first principal stress and failure probability of the anode-electrolyte-negative(PEN)structure in SOFC with rectangular channel design larger than those with circular,trapezoidal and triangular channel design.The co-flow arrangement has smaller temperature gradient,thermal stress and failure probability than cross-flow and counter-flow arrangement;The thermal stress of SOFC with multi-channel arrangements is higher in the middle and lower on both sides.(3)The temperature,temperature gradient,electrolyte current density,thermal stress and PEN failure probability all show an increasing trend with the decrease of the working voltage.When the air inlet rate increased from 1.0 m/s to 2.5 m/s,the maximum output power increased by 34.9%,but the failure probability of electrolyte and cathode increased by 34.9%and 4.3%respectively.(4)The peak output power of SOFC designed by gradient porosity anode can reach2835.6w/m~2,which is 18.2%,8.3%and 3.5%higher than that of 0.2,0.3 and 0.4 respectively.The SOFC with gradient porosity anode can significantly reduce the first principal stress of PEN structure.Compared with uniform porosity anode SOFC,the failure probability of electrolyte and cathode electrode of gradient porosity anode SOFC can be reduced by at least17.5%and 33.2%,which indicates that gradient porosity anode design can effectively adjust the thermo mechanical matching between anode and electrolyte in PEN structure.