Performance of Polymer Electrolyte Fuel Cell Electrodes with Atomically Dispersed (AD) Fe-C-N ORR Catalyst

Activity of (AD)Fe-N-C catalyst with low Fe content is investigated in differential cells prepared by hot pressing anode gas diffusion electrodes (0.2 mg_Pt/cm²) to N211 membrane and brush painting the cathode catalyst ink. Polarization curves obtained in H₂/O₂ show double Tafel slopes which, in conjunction with the redox potential observed in cyclic voltammetry traces, forms the basis for a distributed ORR (oxygen reduction reaction) kinetic model with potential-dependent available sites. Application of this model to polarization data in H₂/air provides the basis for formulating an oxygen transport model and leads to 7.7 ± 0.6 mA/cm² catalyst activity at 0.9 V, 31.5–34.3 mA/cm² cell performance at 0.8 V, and 0.8-2 s/cm O₂ transport resistance. A coupled kinetic, O₂ transport and proton transport illustrates the projected improvements needed in catalyst activity and electrode structure to approach the automotive target of 1000 mW/cm² stack power density while meeting the 1.45 kW/°C heat rejection constraint at 1.5 cathode stoichiometry. The model indicates that we need twelve-fold higher mass activity for reducing the kinetic losses, doubling of active site density and an engineered electrode structure for 50% lower proton transport resistance, as well as a 50% reduction in electrode thickness to limit the O₂ transport losses.