Development of palladium-based nanocatalysts on carbon support for oxygen reduction reaction.

摘要

Direct methanol fuel cell (DMFC) promises to be a power source for space application, transportation and portable devices. However, platinum catalysts, the methanol crossover and the sluggish kinetics of the oxygen reduction reaction (ORR) limit their commercialization.;DMFC has the challenge to find a catalyst with high methanol tolerance and simple synthesis methodology. We proposed the development of palladium-based nanostructures on carbon supports as electrocatalyst for the oxygen reduction reaction. The working hypothesis is that the use of different methodologies and carbon supports will lead the formation of different palladium catalytic nanostructures with high methanol tolerance.;A new single source approach was used to synthesize Pd-Co nanostructures on a highly ordered pyrolytic graphite (HOPG) surface using a bimetallic molecular precursor. Then, synthesis of palladium and palladium-cobalt nanoparticles on Vulcan XC-72R by chemical and thermal reduction using organometallic complexes as precursors was done. The palladium thin films and nanoshells were synthesized on HOPG and carbon cloth using sputtering deposition and electrospinning techniques.;The morphology and composition were characterized by surface analysis techniques, such as: atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscope with energy-dispersive X-ray fluorescence spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), among others. ORR electrocatalytic activity and methanol tolerance was determined for the Pd/C, Pd2Co/C and PdCo 2/C catalysts. The rotating ring-disk electrode technique was used to determine the ORR mechanism and kinetics.;Pd2Co nanorings were formed on a HOPG surface by self-assembly with humidity control. Also, a single precursor was used for the synthesis of palladium-cobalt nanocatalysts on carbon supports by thermal reduction with ORR electrocatalytic activity and higher methanol tolerance than a Pt/C catalyst. Palladium thin films and nanoshell structures have been successfully synthesized on HOPG surfaces. We also demonstrated that sputtering and electrospinning techniques can be used together as a simple and fast method for the synthesis of catalysts directly on the gas diffusion layer for the fuel cells. The results suggest that these novel methodologies can be used for the synthesis of palladium-based nanocatalysts on carbon supports for fuel cell systems.