Controllable Synthesis Of Pt-based Bimetallic Nanocrystals For Methanol Oxidation

Direct methanol fuel cell (DMFC) is one of the most promising commercial proton exchange membrane fuel cells, due to its low polluter emission, high energy density and energy conversion efficiency. Pt-based bimetallic nanocrystals are considered as ideal anode catalysts for DMFC. Designing and tailoring the composition, morphology and structure of Pt-based bimetallic nanocrystals play a key role in improving the electro-catalytic activities of methanol oxidation.In this dissertation, we have developed a solution phase method to the synthesis of Pt-based bimetallic nanocrystals with well-defined morphologies, including Ru-decorated Pt cubes and icosahedra, PtCu3 alloy hexapod nanocrystals and PtCu3 alloy hollow nanocrystals. We have also investigated the formation mechanism and evaluated the methanol oxidation electro-catalytic activities of the above Pt-based nanocrystals. The main innovative results are displayed as follows:(1) Ru decorated Pt cubes faceted with{100} have been prepared in a mixed solution of N,N-dimethylmethanamide (DMF) and oleylamine in a one-pot synthesis. The cubic morphology were formed possibly due to the selective adsorption of CO on Pt{100} arising from the decomposition of DMF catalyzed by Ru salt precursor. When hexadecane was added into the aforementioned solvent, the synthesis became two-phase interfacial reaction due to their large difference in polarity, thereby retarding the reaction kinetics and promoting the formation of the icosahedra faceted with{111}. The Ru decorated Pt bimetallic nanocrystals with similar composition but different exposed facets (i.e.,{100} vs.{111} facets) provide a promising platform for investigating the structure sensitivity towards methanol oxidation reaction (MOR). Both the Ru-decorated Pt bimetallic nanocrystals exhibited the higher specific and mass activity relative to the Pt7Ru/C. Moreover, the Ru-decorated Pt icosahedra showed higher specific and mass activity for MOR than the Ru-decorated Pt cubes.(2) PtCu3 alloy hexapod nanocrystals and PtCu3 alloy hollow nanocrystals have been synthesised by a facial solution phase approach. The use of DMF and Cl" ions played an important role in the morphology formation process. Compared with hexapod nanocrystals, PtCu3 hollow nanocrystals were prepared at a lower temperature. Both PtCu3 alloy nanocrystals exhibited enhanced electrocatalytic properties for MOR relative to the commercial Pt/C. The specific and mass activity of hexapod nanocrystals were 12.9 and 13.2 times as high as those of commercial Pt/C, respectively. In addition, the specific and mass activity of PtCu3 alloy hollow nanocrystals were 11.0 and 24.2 times as high as those of commercial Pt/C, respectively. Both PtCu3 alloy nanocrystals exhibited enhanced durability and CO poison tolerance for MOR relative to the commercial Pt/C.