A series of well-dispersed bimetallic Pd@Pt nanodendrites uniformly supported on XC-72 carbon black are fabricated by using different capping agents. These capping agents are essential for the branched morphology control. However, the surfactant adsorbed on the nanodendrites surface blocks the access of reactant molecules to the active surface sites, and the catalytic activities of these bimetallic nanodendrites are significantly restricted. Herein, a facile reflux procedure to effectively remove the capping agent molecules without significantly affecting their sizes is reported for activating supported nanocatalysts. More significantly, the structure and morphology of the nanodendrites can also be retained, enhancing the numbers of active surface sites, catalytic activity and stability toward methanol and ethanol electro-oxidation reactions. The as-obtained hot water reflux-treated Pd@Pt/C catalyst manifests superior catalytic activity and stability both in terms of surface and mass specific activities, as compared to the untreated catalysts and the commercial Pt/C and Pd/C catalysts. We anticipate that this effective and facile removal method has more general applicability to highly active nanocatalysts prepared with various surfactants, and should lead to improvements in environmental protection and energy production.
A liquid-phase reducing method of synthesizing Pt nanocrystals was demonstrated, and dendrite-, cube-, and cuboctahedron-shaped Pt nanocrystals (NCs) with well-defined monomorphic were successfully synthesized through iodine ions mediated with the CTAB agent. When the KI concentration was increased to thirty times of K 2 PtCl 4 at the nucleation stage, the high-quality Pt nanodendrites could be obtained. However, no matter how many KI were added at the growth age, only cube- and cuboctahedron-shaped Pt nanocrystals formed. The results of high-resolution TEM, EDX, and XRD indicated that the size and shape of Pt NCs could be turned by changing the concentration and time of KI. In the nucleation stage, it might be due to that some iodine ions adsorb on the surfaces of Pt NCs, which probably cause the rapid growth process resulting in the formation of Pt nanodendrites. In the growth stage, although high concentrations of I − ions could contribute to the shape control and generate bigger particles of Pt NCs, small Pt particles do not grow into dendrites. The insight into the role of I − ions in synthesis of Pt NCs reported here provided a viewpoint for clearly understanding the formation mechanism of anisotropic platinum nanostructures.
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