A model for the description of transport and electrochemical processes in solid oxide fuel cell (SPEC) electrodes is presented in this study. Effective transport and reaction properties are evaluated using a Monte Carlo random walk method on electrodes numerically reconstructed with a packing algorithm. This approach overcomes limitations of typical micro-modeling studies on SOFCs, wherein effective microstructural properties are estimated using empirical correlations or fitted on experimental data. Throughout the entire modeling framework in this study, no fitted or empirical parameters are used. Effective properties as a function of porosity and particle size are calculated and reported in dimensionless form to provide generality in their application. A good agreement with independent experimental data for both gas and solid phases is achieved. The model predictions can be used to improve the design of composite electrodes for solid oxide fuel cells. In particular, simulation results show that porosity lower than 0.20 and particle size smaller than 0.2 mu m should be avoided in the design of SOFC composite cathodes because, under these conditions, Knudsen effects limit the mass transport with a significant reduction in the electrode performance. (C) 2013 Published by Elsevier Ltd.