Transport of electrons, protons, and oxygen are necessary for the cathode reactions in polymer electrolyte membrane fuel cells, and achieving the optimum structure of the electrode catalyst layer and the efficient transport of reactants is an effective avenue to reduce the use of platinum catalyst. This study applied three-phase boundary and cathode catalyst layer models to understand details of optimally efficient structures for the transport of reaction components. The factors dominating the effects of the catalyst layer structure and the properties identified in this manner are investigated using the models. Additionally, equations of evaluation are developed to evaluate the effects of the structure and the properties on the cell performance, and the effectiveness of the developed equations is confirmed by a comparison of the results calculated by the equations with the model simulations. From these results, the structure of the porosity, the catalyst layer, and the polymer electrolyte thicknesses, that are optimum for the gas transport and proton conduction, are determined. It is found that the solubility of oxygen in the polymer is one of the dominant factors in the processes of the cathode catalyst layer, and that increasing the solubility is highly effective to reduce the need for platinum. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3624606] All rights reserved.