Nanostructured Catalyst Layer Allowing Production of Ultralow Loading Electrodes for Polymer Electrolyte Membrane...

This study introduces a simple method to produce ultralow loading catalyst-coated membrane electrodes, with an integrated carbon "nanoporous layer", for use in polymer electrolyte membrane fuel cells or other electrochemical devices. This approach allows fabrication of electrodes with loadings down to 5.2 μg_Pt cm^-2 on the anode and cathode (total 10.4 μg_Pt cm^-2, Pt₃Zn/C catalyst) in a controlled, uniform, and reproducible manner. These layers achieve high utilization of the catalyst as measured through electrochemical surface area and mass specific activities. Electrodes composed of Pt/C, PtNi/C, Pt₃Co/C, and Pt₃Zn/C catalysts containing 5.2-7.1 μg_Pt cm^-2 have been fabricated and tested. These electrodes showed an impressive performance of 111 ± 8 A mg_Pt^-1 at 0.65 V on Pt₃Co/C with a power density of 31 ± 2 kW g_Pt,total^-1, about double that of the best previous literature electrodes under the same operating conditions. The performance appears apparently mass transport free and dominated by electrokinetics over a very wide potential range, and thus, these are ideal systems to study oxygen electrokinetics within the fuel cell environment. The improved performance is associated with reduced "contact resistance" and more specifically a reduction in the resistance to lateral current flow in the catalyst layer. Analytical expressions for the effect illuminate approaches to improve electrode design for electrochemical devices in which catalyst utilization is key.