Metal decoration of exfoliated graphite nanoplatelets (xGnP) for fuel cell application.

摘要

The synthesis and characterization of metal particles at nanometer length scale has been the object of much research in modern nanotechnology due to their great impact on new nanoscale scientific and technological applications. Nanoscale metal particles possess unique optical, thermal, electronic, magnetic properties and chemical reactivity since the size of the resulting materials is on the same order as the fundamental interaction distances that give rise to physical properties and thus shows the quantum size effect which is not observed in their bulky status. Therefore, an effective synthetic method is required to obtain uniform small metal powders with controlled size and a narrow size distribution and also to produce nanocomposites consisting of either metals or metal oxides supported on carbons or metals dispersed on metal oxides for a variety of applications in chemical industries, automobiles, energy and power generating devices, hydrogen economy as well as for sensors.;On the other hand, although their excellent mechanical, thermal and electrical conductivity, excellent corrosion and oxidation resistance, and low impurity levels which are required as a breakthrough material to increase performance of next generation energy devices, exfoliated graphite nanoplatelet (xGnP) has not been studied as deeply as recent new nano structured carbon materials such as single wall carbon nanotubes (SWNT), multi-wall carbon nanotubes (MWNT), carbon nanohorn (CNH), graphite nanofiber (GNF), and fullerenes. In addition, xGnP is much cost-effective compared to other carbon nanostructures. Hence, it is interesting to evaluate the applicability of xGnP as a support material for fuel cell which is one of promising energy devices for the future.;In this research, a new simple, efficient and economic way is presented for the synthesis of noble metal nanoparticles such as Pt, Ru, Pd, etc and their deposition on various carbon supports and metal oxides via microwave heating in the presence of various types of room temperature ionic liquids (RTIL). The resulting metal nanocrystals were characterized by means of UV-vis spectroscopy, transmission electron microscopy (TEM), powder x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry measurement. Homogeneous metal nanocrystals with sizes of 0.9∼3nm were synthesized and deposited on various carbon and metal oxide support materials through the reduction of the corresponding metal precursors. The size of metal nanocrystals could be easily and finely tuned by simply controlling experimental factors such as the concentration of RTIL.;xGnP-supported Pt based catalysts were prepared and tested for utilization in a direct methanol fuel cell. They showed much higher catalytic activity compared to commercial carbon black supported catalysts. Excellent activity of the xGnP-supported catalysts over the commercial catalysts originates from the morphology of xGnP facilitating contact between the reactant and catalytically active phase as well as the improved interaction between xGnP and metallic phases. This result proves the potential of xGnP as a support to replace carbon black. xGnP nanocomposites with metal nanocrystals may find potential applications as catalysts for other chemical reactions.