Modeling Competing Diffusion and Conductivity Effects in Infiltrated Solid Oxide Fuel Cells

Due to the steadily increasing energy demands of the world, and the steadily dwindling resources of our primary energy source, fossil fuels, there is a need to investigate new energy sources, with a focus on clearer, more efficient ways to exploit our limited resources. Fuel cells are an emerging technology that represent a promising avenue of research. This research focuses on Solid Oxide Fuel Cells (SOFCs), electrochemical devices that use a ceramic electrolyte to directly oxidize fuel, producing electricity at a high efficiency with few emissions. Fuel cell operation and performance is based on the intersection of four key characteristics: porosity to allow fuel to move through the cell, electron conductivity to transport electrons away from the reaction site, oxygen ion conductivity to transport the oxidizing agent to the fuel, and the presence of three phase boundary (TPB) sites, which enable the reaction. TPB sites occur at the intersection of electrical conductor, oxygen ion conductor, and empty space such that an electrochemical reaction including electrons, oxidizing agent, and fuel may occur. SOFCs may be prepared in a variety of ways, but this research focuses specifically on infiltrated SOFCs, in which electron conducting, catalytic material is deposited onto a network of oxygen ion conducting ceramic particles. This production method has many advantages over other methods, including increased efficiency and decreased conductor material required. However, many production parameters may be changed to impact the performance of the produced SOFC, so modeling techniques are critical for predicting SOFC properties.

In this work, we show a model for the design process of a SOFC and the corresponding determination of electrical conductivity, oxygen ion conductivity, and fuel diffusivity. The model uses a mechanistic approach which mimics the physical production steps of a SOFC: slurry formation, pore former combustion, ceramic sintering, and electron conducting material infiltration. The impact of porosity, ceramic particle size, pore former particle size, and infiltrate loading on each conductivity are demonstrated. Tradeoffs between each conductivity will also be discussed.