Noble-metal Nanocrytals Synthesis And Performance Research

As a new alternative energy conversion instead of traditional fossil fuels, commercializationof Fuel Cells is a dream to be realized globally. Until now, Platinum (Pt) is still acknowledged asthe most the most effective electrocatalyst for fuel (including hydrogen, methanol, ethanol, andformic acid) oxidation reaction and oxygen reduction reaction. However, its low resistance toCO poisoning and high cost restrain its wide application. As a promising route, Pt-M (M=Pd, Au,Co, Ni, Fe, Au, Cu, etc.) bimetallic electrocatalysts, which often show electronic and chemicalproperties that are distinct from those of their parent metals owing to the synergetic effect of thesecond metal, which offer the opportunity to obtain new electrocatalysts with enhancedselectivity, activity, and stability. For instance, as a pioneering work of Pt-M bimetallicelectrocatalysts, Pd@Pt was first prepared by Xia’s group, core/shell structures have attractedmuch attention. Tremendous efforts have been focused on the solution-phase synthesis for thepreparation of core/shell Pt-M bimetallic electrocatalysts. However, it is really difficult inpreparation core-shell bimetallic structure than its monometallic counterparts owing to thecomplicated synthetic conditions caused by the difference in the reduction rate of metal salts andthe different tendencies of structural directing agents for interaction with metal surfaces.Furthermore, the influence of structural directing agent is also an important problem whichcauses increasing attention. Structural directing agent such as poly(vinylpyrrolidone)(PVP),fatty acids, fatty amine and halide ions, ect, are very essential and indispensable agents in thepreparation process of nanocrystals, which usually assist in shape-control synthesis ofnanocrystals with different morphologies by preferential adsorption on specific crystal facets, oretching particular crystal planes, or accelerating/inhibiting certain crystal growth direction. Thesestructural directing agents are often strongly adsorbed and effectively cap the surfaces of metalnanocrystals, and are very difficult to remove, which leads to an apparent reduction of thecatalytic activity.To solve the above problem, the urgent method to develop a simple and feasible, synthesizeto metal catalyst with high-performance without any structural inducer. Herein, we attempt tochallenge this problem and produce Pt nano-flower and Pd@Pt core-shell nanoparticles by asimple light induced synthesis approach using methanol as a reducing agent. Without using any structural directing agent, the core/shell nanoparticles exhibit clean surface, high specific surfacearea and excellent electrocatalytic activity.Shape controlled Au nanoparticles were prepared at room temperature by using glucose asreducing agent. In order to prevent aggregation and achieve monodispersed Au nanoparticles,various surfactants were attempted. The results showed that addition of non-ionic surfactantoleate-400can obtain spherical monodispersed Au NPs with5-10nm. It is expected to becomeas Au seeds to synthesize other bi-metal or multi-metal catalysts.Pt flower-like nanostructures were successfully prepared by a simple, easy light inducedsynthesis approach using methanol as a reducing agent without any structural inducer, which theprepared catalysis exhibited a better methanol oxidation activity. Under ultraviolet lightirradiation, a amount of H2PtCl6solution was reduced to Pt nano-flowers with methanol solution.Through we adjusted the ratio of methanol and water, methanol alternative, the light intensityparameters, and the concentration of precursor optimal experimental parameters, which researchthe optimum experimental conditions. Moreover, Pt nano-flower formation mechanism also beresearched by the evolution of morphology with time changing. Pt nano-flowers exhibited abetter methanol oxidation activity than the commercial Pt/C and Pt black catalyst: which is3.9times and2.3times higher than that of commercial Pt black and Pt/C catalysts for the MOR massactivity in acid medium; which is5times and2.8times higher than that of commercial Pt blackand Pt/C catalysts for the MOR mass activity in alkaline medium.Based on Pt nano-flowers discussed, we further investigate Pd@Pt bimetallic catalysts andcatalytic properties of methanol performance. The optimum conditions of Pd seeds would beobtained firstly, which is as the bimetallic core. Pd@Pt bimetallic was prepared by the similarconditions, including the morphology impact of the amount of precursor and the evolution ofmorphology with time changing. Further XPS was analyzed the valence on the catalyst surfaceand element distribution. The optimum conditions Pd@Pt nanoparticles has better excellentcatalytic performance: which is2.7times,10.5times and6.4times higher than that of the Ptnanoflowers, commercial Pt black and Pt/C catalysts for the MOR mass activity in acid medium;which is2.5times,12.5times and7.1times higher than that of the Pt nanoflowers, commercialPt black and Pt/C catalysts for the MOR mass activity in alkaline medium.