(576b) Nanoporous, Conducting, Electrocatalytically Active, 10nm Thick Core-Shell Au@Pt Nanoparticle Bilayer Architectures for PEM Fuel Cell

The main challenge facing the development of Proton exchange membrane fuel cells (PEMFC) currently is to fabricate a catalyst layer with minimum loading of precious platinum nanoparticles, maximum availability of eletrocatalytically active area, and high durability of the catalyst layer in presence of poisonous CO species and corrosive electrochemical atmosphere. The different approaches reported in literature to prepare catalyst layers can be broadly divided into two types: 1) where the platinum nanoparticles are physisorbed on carbon substrates like carbon nanotubes, buckypaper, xerogels etc., and 2) where thin films of white gold leaf are dealloyed and electroplated with a thin platinum layer to form the electrocatalytically active catalyst membrane. In our group, we are developing a novel bottom-up approach, wherein self-assembled monolayers of alkanethiol-coated, monodispersed Au@Pt core shell nanoparticles are stacked to fabricate the catalyst layer. Herein, results on bilayer membranes of Au@Pt core shell nanoparticles will be reported. Initially, the bilayers were electrocatalytically inactive, and had a high sheet resistance of the order of GΩ, due to the presence of organic ligands. The bilayers were then treated to room temperature RF plasma in an argon environment. The results of electrical, spectroscopic and microscopic characterization show that argon plasma exposure removes the alkanethiol ligand coating and leads to coalescence of neighbouring nanoparticles, thereby rendering the bilayer electrocatalytically active and electronically conducting. After an optimized time of exposure, the individual nanoparticles in the bilayer stacked laterally coalesce together to form electrically continuous, nanoporous metallic film with sheet resistances that are eight orders of magnitude lower than the ligand-coated bilayer array. We will present the results of our studies on the electrocatalytic activity and conductivity of membranes prepared with different Pt/Au ratios, and for different durations of argon plasma exposure. The activity of these bilayer membranes towards methanol oxidation and CO oxidation will also be reported.