The 2(n) full factorial design was applied to identify the key parameters of the active layer affecting the performance of a proton exchange membrane (PEM) fuel cell. Three main selected parameters were considered: carbon-type (Vulcan XC 72R and Black Pearls 2000 conducting furnace blacks, Cabot Corporation Boston, MA), Pt loading (0.1 and 0.5 mg/cm(2)), and Nafion (TM) sulfonic acid fluoropolymer (Du Pont de Nemours, Wilmington, DE) ionomer content (10% and 60%) for variables A, B, and C, respectively. The results from full factorial analysis indicated that the key factors affecting the exchange current density or activation loss were Pt loading whereas the key factors controlling the resistance due to ohmic loss were Nafion content and carbon type. In addition, there are the interactions between these parameters controlling the thin-film active layer performance, especially the interaction of carbon type and Nafion content. From cyclic voltammograms and cell performance testing, a Nafion content of 30% in a catalyst layer consisting of 0.5 mg/cm(2) Pt on Vulcan XC 72R is optimal. (c) 2008 Elsevier Ltd. All rights reserved.