Simulating The Ionic Conduction Of Doped Ceria-carbonate Composite Electrolyte Via A Random Resistor Network Model

To lower the operating temperature of solid oxide fuel cell(SOFC), a series of functional two-phase oxide-salts composite materials were exploited. And among them, doped ceria(DCO)-carbonate composite electrolyte is the most studied and the most promising one. The simultaneous conduction of H+ and O2- in the DCO-carbonate composite electrolyte brings excellent performances of corresponding single cells. However, up to now, there still exist different opinions about the ionic conduction mechanism of the composite electrolytes. Numerical simulation is an effective approach to investigate conductivities of composite materials, which will play an important instructive role in the preparation of DCO-carbonate composite electrolytes.For the first time, the structure of doped ceria-carbonate composite electrolytes is modeled by a two phase random lattice, which is then converted into a random resistor network to calculate the ionic conductivity of the composite electrolytes. Based on different ionic conduction mechanisms, two different conditions are discussed. When the two phases interface has no influence on ionic conduction, the dependence of ionic conductivities on the volume fraction of carbonate, the grain size of doped ceria and temperature is simulated. The simulation results are compared with experimentally obtained conductivities of samarium doped ceria-carbonate composite electrolytes. The simulation and experimental results are found to be in good agreement. And when the two phases interface can enhance ionic conduction, except for the carbonate volume fraction and particle size of two phases, we also investigate the influence of two phases interface on the conductivities of composite electrolytes. The simulation results show that the conductivity of the compoites electrolyte increased at first and then decreased with the increase of carbonate content. And the smaller of the grain size and the more homogeneous of two phases distribution, the better conduction performance of the composites. Furthermore, the obtained results of simulation are in general agreement with the experimental data. All the results show that the resistor network model is an effective method to calculate the conductivities of DCO-carbonate composite electrolytes.