Effective debundling of carbon nanotubes and simultaneous synthesis of Pt nanoparticles by Nafion® induced emulsions

Abstract

Carbon nanostructures and, in particular, Single Wall Carbon Nanotubes (SWNT) or Multi Wall Carbon Nanotubes (MWNT) provide unique properties, notably outstanding chemical stability and electronic conductivity. Therefore they can be seen as a potential replacement for carbon black, which is frequently used as support material for polymer electrolyte membrane fuel cell (PEMFC) catalysts. This paper describes a new synthesis method to deposit platinum nanoparticles on carbon by using MWNT/Nafion® emulsions in the reduction reaction of hexachloroplatinate with ethylene glycol and butyl acetate. In contrast to other syntheses described in the literature, the formation of an emulsion allows effective debundling and a good dispersion of MWNTs in the solvent. This strategy helps to maintain a narrow Pt particle size distribution of 3nm±0.5nm and a homogeneous dispersion of the nanoparticles on the support even at loadings of up to 50wt%. It furthermore reduces agglomeration of the MWNTs during electrode manufacturing, so that an airbrush technique can be used, and enhances the ionic conductivity of the electrode layer. Catalyst morphology and distribution are investigated by transmission electron microscopy, X-ray diffraction and scanning electron microscopy. Electrodes are produced by a conventional airbrush technique on Nafion® membranes (Nafion® 117 and Nafion® NRE 212) and tested in a fuel cell test bench.