Fuel Cell Membrane Electrode Assemblies Fabricated by Layer‐by‐Layer Electrostatic Self‐Assembly Techniques

High activity, carbon supported Pt electrocatalysts were synthesized using a supercritical fluid method and a selective heterogeneous nucleation reaction to disperse Pt onto single walled carbon nanotube and carbon fiber supports. These nanocomposite materials were then incorporated into catalyst and gas diffusion layers consisting of polyelectrolytes, i.e., Nafion, polyaniline, and polyethyleneimine using layer‐by‐layer (LBL) assembly techniques. Due to the ultrathin nature and excellent homogeneity characteristics of LBL materials, the LBL nanocomposite catalyst layers (LNCLs) yielded much higher Pt utilizations, 3,198 mW mg_Pt^?1, than membrane electrode assemblies produced using conventional methods (～800 mW mg_Pt^?1). Thinner membranes (100 bilayers) can further improve the performance of the LNCLs and these layers can function as catalyzed gas diffusion layers for the anode and cathode of a polymer electrolyte membrane fuel cell.