A unique network approach has been developed to predict the movement of ions, reactant gas, and water both in the pore and ionomer phase inside a catalyst layer of PEMFC under various operating conditions. Separate networks for each of the catalyst layer reactive transport paths have been generated in the model and transport equations are applied therein. The simulation results provide insight into the coupling between overall PEMFC performance and local phenomena for different catalyst layer properties (porosity, ionomer to carbon ratio, ionomer volume fraction, catalyst loading, etc.), which can work as a guideline for the premanufacturing of catalyst layers and post-manufacturing testing tool.