Geometrical modeling of microstructure of solid oxide fuel cell composite electrodes

A model based on random packing of electron and ion conductor particles is developed to study the microstructure performance relationship of solid oxide fuel cell electrodes. This three-dimensional model takes into account special variations of triple phase boundary (TPB) by keeping track of all particles in the packing. Porosity of the media can be controlled and is set to 30%. Effect of particle size, electrode thickness, electrode composition and particle size ratio on the length of TPB line has been studied. The study shows that unlike what models based on percolation theory suggest, the electrode media is not homogeneous for electrochemical reaction. While increasing the thickness increases the length of the TPB to some extent, beyond that little or no improvement was observed. The study also revealed that adding a current collector layer made of electron conductors can increase the TPB line by at least 4%. While for particles of the same size maximum length of TPB was observed at equal volume percent of electron and ion conductor particles, for size ratio of particles other than one the maximum TPB tends to occur above or below 50% depending on the size ratio.