The Effect Of Grain Boundary On Self-diffusion And Conductivity Of Oxygen Ions In Cerium Dioxide

Solid oxide fuel cell(Solid Oxide Fuel Cell,referred to as SOFC)is a solid-state chemical power generation device that directly reacts with oxidants under low and medium temperature conditions and environmentally friendly converts chemical energy stored in fuel directly into electrical energy.The all-solid oxide fuel cell has the advantages of wide fuel adaptability,high energy conversion efficiency,easy storage of all solid state,modular production and assembly,and zero chemical pollution.Therefore,it has received extensive attention and has broad application prospects.However,due to the low diffusion and release rate of oxygen ions in the all-solid oxide electrolyte,the ion conductivity needs to be improved,resulting in the development and application of solid fuel cells being limited.In response to the above problems,this paper studies the diffusion of oxygen ions in the solid electrolyte material ceria and its ion conductive properties through the first principles and molecular dynamics methods to reverse the grain boundary defects,coherent twin boundary defects and grain size Impact.The calculation results show that the oxygen ion diffusion rates in the ceria polycrystalline structure model with grain sizes of 2nm,3nm,4nm,and 5nm are 53.7%,16.9%,6.3%,and 3.1% higher than the ceria single crystal structure,respectively.At a temperature of 1200 K,the ionic conductivity in the cerium oxide polycrystalline structure model with grain sizes of 2nm,3nm,4nm and 5nm is 39.8%,25.5%,11.4% and 2.5%higher than that of the cerium oxide single crystal structure.The diffusion activation energy of oxygen ions in the polycrystalline structure model of cerium dioxide with grain sizes of 2nm,3nm,4nm and 5nm is lower than that of the single crystal structure model by22.7%,10.2%,5.6% and 3.8%,respectively.For the ceria ?5 twisted grain boundary model,twisted grain boundary defects can provide energy for the migration of oxygen ions and reduce the diffusion and migration energy barrier of oxygen atoms.The diffusion activation energy barrier of oxygen ions in the ?5 twisted grain boundary is 12.3% lower than that of the single crystal structure,and the ion conductivity is increased by 34.7%.For the cerium dioxide ?5(210)[001] inclined grain boundary model,the grain boundarydefects can also provide energy for the migration of oxygen ions and reduce the diffusion and migration energy barrier of oxygen atoms.The diffusion activation energy barrier of oxygen ions in the slanted grain boundary structure of ?5(210)[001] is 7.59% lower than that of the single crystal structure,and the ion conductivity is increased by 21.0%.Therefore,we can think that the grain boundary defects can be used as channels for the rapid diffusion of oxygen ions in ceria.The doping of phosphorus atoms creates new oxygen vacancy defects in the polycrystalline structure model of ceria.The doping concentration of phosphorus element with a doping concentration of 1.04% increases the oxygen ion conductivity in ceria by 52.1%.