The cathodic reaction can simultaneously occur via several competing paths, but here we assume that they can all be represented by a few well-defined reaction rates. For each of the allowed reaction pathways, all of the physical parameters influencing the relevant reactions and transport are incorporated within the framework of kinetic Monte Carlo simulations, including polarization resistance and electrostatic effects. In order to better understand the atomistic behavior of the YSZ cathode model, our simulated predictions of the ionic current density, J (mA/cm2), are divided into three categories, based upon the simulation parameters being investigated:
• Materials independent: oxygen partial pressure (PO2), external applied bias voltage (Vext), and temperature (T)
• Materials dependent: doping levels (i.e., concentration of Y in YSZ) and relative permittivity
• Geometrical parameters: surface area (A) and electrolyte thickness (D)
To identify the influence of each of the parameters in a well-defined manner, we varied each of these parameters independently, while keeping all others fixed during the simulation. Moreover, some parameters (PO2, T, Vext, etc.) are rather easy to control experimentally, whereas other parameters (e.g., impurity segregation, thermally or electrically induced chemical and morphological changes of cathodes/YSZ interfaces), are experimentally ill-defined and a methodical variation and ultimate prediction of these influences is beyond the scope of this study.
Broadly speaking, all of the results obtained with our model are consistent with the experimental findings and previous theoretical predictions. Among the physical parameters that we studied, temperature, dopant fraction of Y2O3, and the relative permittivity of YSZ are found to have the most profound influence on the calculated ionic current density of the fuel cell cathode. Our most recent results from the KMC model include frequency-response analysis, generated from simulations of alternating applied voltages, over a range of frequencies. From these simulations, we can capture the properties of geometric and double-layer capacitance and resistance within the SOFC. Also, recent efforts will be presented that incorporate the anode-side of the SOFC.