Inefficient usage of expensive platinum catalyst has plagued the design of PEM fuel cells and contributed to the limited production and use of fuel cell systems. Here, it is shown that hierarchical optimization can increase platinum utilization 30-fold over existing catalyst layer designs while maintaining power densities over 0.35 W/cm(2). The cathode catalyst layer microstructure is optimized with respect to platinum utilization (measured as kilowatts of electricity produced per gram of platinum). A one-dimensional agglomerate model that accounts for liquid water saturation is used in this study. The cathode catalyst layer microstructure is optimized by manipulating the platinum loading (m(Pt)), platinum-to-carbon ratio (Pt vertical bar C), and catalyst layer void fraction (epsilon(ct)(V)). The resulting catalyst layer microstructure features ultra low platinum loadings of roughly 0.01 mg/cm(2). (C) 2013 Elsevier Ltd. All rights reserved.