Meso-micro Multiscale Study On The Mechanical And Thermal Properties Of SOFC Electrolyte And Interface Of Composite Anode

As a new power generation technology,fuel cells have attracted attention due to its advantages of high energy conversion and low pollution.Specifically,the solid oxide fuel cell(SOFC)has become one of the most promising fuel cells due to its low material cost,highest energy conversion,and wide fuel adaptability.In SOFC,the strength of the electrolyte layer and the strength of the metal-ceramic interface in the functional anode layer are often key factors that affect its service life.In addition,the metal-ceramic interface in the anode layer has a large specific surface area,making it significantly affect the overall mechanical and thermal properties of the anode structure.Although traditional experim ental and simulation methods can measure and calculate the mechanical and thermal properties of SOFC electrolytes,they are powerless to cope with the changes in material properties caused by complex chemical reactions during their work.In addition,it is also difficult to experimentally measure the mechanical and thermal properties of the metal-ceramic interface in the anode.In this study,molecular dynamics(MD)simulations,micro/nano mechanical experiments,and multiscale simulations were used to study the mechanical and thermal properties of the yttrium stabilized zirconia(YSZ)electrolyte and the interfaces between nickel(Ni)and YSZ.The effects of high temperatures and chemical reactions on the mechanical and thermal properties of the electrolyte and Ni-YSZ interface were systematically analyzed.The main research contents are as follows:In terms of the mechanical properties,the mechanical properties of YSZ under uniaxial tension were studied by reactive force-field MD simulations.The simulation results are in good agreement with experimental results.On this basis,the effects of doping concentration and temperature on the mechanical properties of different crystal orientations were further studied.By fitting the results of MD simulations,a prediction equation that can predict the mechanical properties of YSZ at different temperatures and doping concentrations was obtained.In addition,the effect of high-temperature and chemical reactions on the mechanical properties of YSZ with different crystal orientations was explored by simulating the high-temperature and chemical reaction environment as the actual operation of SOFC.The mechanism of the influence of chemical reactions on the mechanical properties of YSZ was analyzed through analyzing the structural changes of different crystal faces during the simulation process.These research results not only contribute to a further understanding of the microstructure evolution of YSZ electrolyte during SOFC operation,but also provide theoretical guida nce for designing stable and reliable electrolyte materials.The mechanical properties and deformation behaviors of single-crystal and polycrystalline YSZ were studied by combining nanoindentation experiments and MD simulations.By comparing the experimental and simulation results,the accuracy of the simulation method in studying the mechanical properties such as the Young’s modulus and hardness of YSZ was verified.The different deformation behaviors of polycrystalline YSZ and single-crystal YSZ due to the presence of grains and grain boundaries were revealed.The effects of temperature and grain size on the Young’s modulus and hardness of polycrystalline YSZ were studied.Meanwhile,reasons for the differences in mechanical properties and deformation behaviors of polycrystalline YSZ with different grain sizes were explored.This study has a theoretical guiding significance for deeply understanding the differences in mechanical properties between single-crystal and polycrystalline YSZ.The effect of interface on the mechanical properties of metal-ceramic(Ni-YSZ)systems in anodes was studied using a combination of nanoindentation experiments and MD simulations.It is found that the interface can strengthen Ni but weaken YSZ near the interface.The reason for this phenomenon was explained by analyzing the different deformation behaviors of Ni and YSZ near the interface observed in MD simulations.Based on the MD simulation results,an interface potential barrier model and a mechanical model considering the structural flexibility were proposed.By fitting to the experimental results,analytical expressions for the hardness and elastic modulus of materials near the interface were obtained.The results can provide parameters for the mechanical properties of materials near the interface in the continuum mechanical model of Ni-YSZ structure,thus further improving the accuracy of the mesoscopic and macroscopic models of Ni-YSZ structure.In the aspect of thermal properties,the thermal resistance of various interfacial combinations was studied by MD simulations and transient thermal reflection experiments.The results of thermal resistance obtained from MD simulations were modified by using the two-temperature model.It is found that the modified results were consistent with the experimental results,proving the reliability of the simulation results.On this basis,the effects of temperature and chemical reaction on the interfacial thermal resistance of different types of interfaces were studied.The difference of the interfacial thermal resistance in different hydrogen concentration environments was explored.The mechanism of the changes in the interfacial thermal resistance caused by chemical reactions and hydrogen concentration was analyzed.The above results provide a theoretical explanation for the changes in the thermal resistance of the functional anode interface during the operation of SOFC,and also provide a theoretical guidance for designing composite anodes with better thermal performance.By combining Reax FF MD simulation results with finite element simulations,a cross-scale interfacial heat transfer model was constructed.Based on this model,the effect of interface on the heat transfer of functional anode was studied.Meanwhile,the impacts of different interface structures,temperatures,and chemical reactions on interface heat transfer were also revealed.Based on these results,a microstructural finite element model of a real functional anode was established through three-dimensional reconstruction.The difference in the heat transfer behavior of the real composite anode with or without interfacial thermal resistance was studied using this model.The interfacial thermal resistance effect on the heat transfer in the real functional anode was also discussed.The obtained results have theoretical guiding significance for further understanding the heat transfer mechanism in SOFC functional anodes.The proposed cross-scale simulation method combining MD simulations and microstructural e finite element method provides a technical route for a more accurate prediction of the heat t ransfer of SOFC functional anodes.