3D microstructure of solid oxide fuel cell (SOFC) electrodes by a dual-phase infiltration procedure is constructed numerically from a phenomenological standpoint. The present work studies such a dual-phase infiltration procedure, from generation of backbone matrix to infiltration of backbone phase nanoparticles, followed by infiltration of electrocatalytic nanoparticles. Important geometric properties are calculated under various electrocatalytic nanoparticle loadings, including total and percolated surface areas and percolation probability of electrocatalytic nanoparticles, and total and percolated three-phase boundary (TPB) lengths. The effects of backbone nanoparticles, including infiltration loading, particle size and aggregation risk are studied systematically. One important finding is that the infiltration of backbone nanoparticles increases TPB length but shows negligible influence on the surface area of electrocatalytic nanoparticles. It demonstrates that the dual-phase infiltration has little advantage to reduce electrode resistance compared to the catalyst-phase infiltration when electrode reaction is limited to catalytic surface. However, the different influences of dual-phase infiltration on TPB length and surface area of electrocatalytic nanoparticles offers a potential strategy to identify electrode reaction mechanisms. (C) 2013 The Electrochemical Society. All rights reserved.