This paper presents a numerical study of the inhomogeneous platinum loading within the catalyst layer (CL) and porosity inside the gas diffusion layer (GDL) at the cathode of a proton exchange membrane fuel cell. Their distributions along the in-plane (longitudinal) direction and the effect of their interactions on the cell performance and current density uniformity are investigated. The mathematic model is validated by a series of experimental results at various conditions. A strong interaction of platinum loading and GDL porosity on performance is revealed, and a significant impact of GDL porosity on the optimal platinum gradients exists, due to the correlations between the electrochemical reaction rate and species transport rate. When the initial platinum loading and GDL porosity are high at the cathode inlet, individually increasing the platinum loading near the outlet cannot improve the cell performance and current density uniformity. Systematically controlling the gradients of platinum loading and GDL porosity achieves a more uniform distribution of current density within the membrane electrode assembly. (C) 2018 Elsevier Ltd. All rights reserved.