Nanofiber, Planar and Ideal Fiber Models of a Polymer Electrolyte Membrane Fuel Cell Dennis O. Dever Advisor: Dr. Yossef Elabd Co-­‐Advisor: Dr. Richard Cairncross Abstract The main objective of this research is to numerically model features in the cathode catalyst layer of a proton exchange membrane fuel cell that have been recently discovered but that have not been incorporated in existing models. These features are included in the new Nanofiber Model. In addition to this, two proton exchange membrane fuel cell models, the Planar Cathode Catalyst Layer Model and the Ideal Fiber Model, were developed to evaluate alternate model geometries. The cathode catalyst layer in a proton exchange membrane fuel cell is now known to contain ionomer nanofibers and experiments have demonstrated a fuel cell performance increase of ca. 10% due to those nanofibers. Experiments demonstrate that ionomer nanofibers have proton conductivities that exceed those of the bulk form of the ionomer by more than an order of magnitude. A new model, the Nanofiber Model, is presented here that predicts the effect of nanofibers on fuel cell performance in terms of the enhanced nanofiber proton conductivity and other relevant variables. The model peak cell power density is ca. 7% greater for the case with 10% of the cathode catalyst layer ionomer in nanofiber form versus the same case without nanofibers. This difference is consistent with trends observed in previously published experimental results. These results are significant as they suggest alternative methods to optimize performance and reduce platinum utilization.