Parametric Modeling Study of PEM Fuel Cell with Platinum Group Metal -Free Cathode Catalyst Layer

Abstract

Polymer electrolyte fuel cells offer zero-emissions energy conversion but are commercially limited by cost and durability. Stack cost can be reduced by using platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR). PGM-free catalysts have lower volumetric activity relative to PGM catalysts and consequently require thicker catalyst layers. Thicker catalyst layers result in increased oxygen transport resistance and flooding in the cathode, which must be considered to accurately model PGM-free fuel cells and quantify the distinct transport resistance. For this purpose, we have developed a well validated model to elucidate relative contributions to oxygen transport resistance. This two-phase, transient, non-isothermal, channel-to-channel model contains cathode catalyst layer morphology informed by plasma-focused ion beam (P-FIB) SEM. Furthermore, the model includes agglomerate treatment of volumetrically active catalyst primary particles coated by ionomer. The structure of the agglomerate model is well suited for describing the catalyst layers containing metal organic framework (MOF) derived metal-nitrogen-carbon catalysts that are roughly spherical and volumetrically active for ORR. The MOF-derived Fe-N-C catalyst used in this study’s experiments contains atomically dispersed active sites and uniform, tunable primary particle size. In this presentation, we will report on our investigation of the performance sensitivity to a wide variety of operating conditions and MEA design specificiation, including cell temperature, gas pressures, cathode thickness, hydrophobic pore fractions and wettability, catalyst primary particle size, ionomer content, and ionomer equivalent weight. Non-dimensional characteristic parameter analysis on the model results is used to distinguish the transition between proton conductivity limited and oxygen transport limited performance, and indicate critical values that affect the the through plane ultilization of the catalyst. This information and studies on the impact of active site density help us set catalyst-specific targets for meeting fuel cell performance goals. With highly active PGM-free catalysts, we can model the impact of parameter changes on transport with experimental validation.DOE ACKNOWLEDGEMENTThis material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under award number DE-EE0008076. The authors gratefully acknowledge research support from the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under contract number DEEE0008076.