Percolation theory in SOFC composite electrodes: Effects of porosity and particle size distribution on effective properties

Abstract

A percolation model, accounting for polydispersion of powders and presence of pore formers (i.e. porosity), is presented to predict effective properties of composite electrodes for solid oxide fuel cells, such as the three-phase boundary length and the mean hydraulic radius. Porosity affects both numbers of contacts (so probabilities of connection) and number of particles per unit volume. Both these effects, together with granulometric distribution, are accounted for the estimation of effective properties. As a consequence, the theory can predict numbers of contacts, coordination numbers and therefore effective properties of the electrode for multicomponent polydisperse mixtures. Model simulations show that the three-phase boundary length sharply decreases as porosity increases while the effects of polydispersion of powders are less pronounced, although significant, suggesting that these features should be considered in SOFC electrode models.