One- and two-parameter numerical optimization analyses of the cathode catalyst layer of the PEM fuel cell were investigated with the objective of optimizing the current density of the catalyst layer at a given electrode potential. Catalyst design parameters, such as Nafion content, platinum loading, catalyst layer thickness and porosity, were considered. Numerical analysis shows that there is a global, optimal solution for each one-parameter optimization. A global, optimal solution also exists for two-parameter optimizations. The optimal solution and the surface of the local current density as a function of two design parameters are given for each two-parameter optimization. The numerical analyses provided here are useful in the design of cathode catalyst layers. Crown Copyright (C) 2003 Published by Elsevier B.V. All rights reserved.