Functional palladium tetrapod core of heterogeneous palladium-platinum nanodendrites for enhanced oxygen reduction reaction (original) (raw)
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Nano Research, 2010
In a seed-mediated synthesis, nanocrystal growth is often described by assuming the absence of homogeneous nucleation in the solution. Here we provide new insights into the nucleation and growth mechanisms underlying the formation of bimetallic nanodendrites that are characterized by a dense array of Pt branches anchored to a Pd nanocrystal core. These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K 2 PtCl 4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution. Transmission electron microscopy (TEM) and high-resolution TEM analyses revealed that both homogeneous and heterogeneous nucleation of Pt occurred at the very early stages of the synthesis and the Pt branches grew through oriented attachment of small Pt particles that had been formed via homogeneous nucleation. These new findings contradict the generally accepted mechanism for seeded growth that only involves heterogeneous nucleation and simple growth via atomic addition. We have also investigated the electrocatalytic properties of the Pd-Pt nanodendrites for the oxygen reduction and formic acid oxidation reactions by conducting a comparative study with foam-like Pt nanostructures prepared in the absence of Pd seeds under otherwise identical conditions.
PtPd bimetallic nanodendrites (NDs), with enhanced activities from PtPd over element Pt and unique anisotropic morphology, show potential as catalysts in fuel cell applications. However, the research has been limited to pure materials, and constructing a practical fuel cell catalyst electrode from PtPd NDs still remains as a challenge. In this paper, we demonstrated, for the first time, catalyst electrodes from PtPd NDs for polymer electrolyte fuel cell (PEFC) applications. PtPd NDs are in-situ grown on large-area carbon paper gas diffusion layers (GDLs) and directly employed as cathodes in H2/air PEFCs. The thin catalyst layer with PtPd nanodendrites significantly reduces mass transfer resistance and a higher power performance is achieved than those based on pure Pt nanowires and Pt/C nanoparticle electrocatalysts. The crystal growth mechanisms of this advanced nanostructure on large-area support are also detailed based on the time-dependent experiments and Pd content.
Highly active Pt decorated Pd/C nanocatalysts for oxygen reduction reaction
International Journal of Hydrogen Energy, 2017
This article describes findings of the correlation between the atomic scale surface structure and the electrocatalytic performance of nanoengineered Pt-Pd/C catalysts for oxygen reduction reaction (ORR), aiming at providing a new fundamental insight into the role of the detailed atomic decorated structure of the catalysts in fuel cell reactions. Carbonsupported Pt decorated Pd nanoparticles (donated as Pt-Pd/C), with Pt coverage close to a monolayer, were prepared from a simple galvanic replacement reaction between Pd/C particles and PtCl 4 2À at room temperature. The decorated architecture was confirmed by extensive microstructural characterization techniques, including TEM, XRD, XPS, HAADF-STEM, ICP and HS-LEIS. The catalysts were also examined for their intrinsic kinetic activities towards oxygen reduction reaction. The results have shown that the Pt-Pd/C catalysts are highly active towards molecular oxygen electrocatalytic reduction. These findings have profound implications to the design and nanoengineering of decorated surfaces of catalysts for oxygen reduction reaction.
Applied Catalysis B: Environmental, 2021
A novel self-etched engineering of Pt-Co nanodendrite in nanoframe (Pt-Co ND-NF) synthesized through a simple one-pot approach, for the first-time. The modulation mechanism of Pt-Co ND-NF formation is established by investigating critical factors of adjusting: i) the water amount, ii) the ratio of mixed solvent oleylamine to oleic acid and iii) the amount of surfactant hexadecyl trimethyl ammonium bromide. Besides, the formation process of Pt-Co ND-NF is carefully explored with reaction time progress, further confirming the state of Pt-Co nanoframe blockade on Pt-Co nanodendrite (ND). Pt-Co ND-NF exhibits improved catalytic performance for oxygen reduction reaction (ORR), in which mass activity (0.939 A mg Pt −1) is much higher (∼500 %) than that of commercial Pt/C (0.187 A mg Pt −1), respectively. Furthermore, Pt-Co ND-NF shows enhanced stability during the accelerated durability tests (ADTs) for 50,000 cycles. Pt-Co nanodendrites in nanoframe with Pt skin, create a novel protection with an external nanoframe (NF) and obtain a unique catalytic material Pt-Co ND-NF, which could provide promising ways for highly strengthening catalytic activity.
Electrochimica Acta, 2010
We have established a scale-up synthesis method to produce gram-quantities of Pt monolayer electrocatalysts. The core-shell structure of the Pt/Pd/C electrocatalyst has been verified using the HAADF-STEM Z-contrast images, STEM/EELS, and STEM/EDS line profile analysis. The atomic structure of this electrocatalyst and formation of a Pt monolayer on Pd nanoparticle surfaces were examined using in situ EXAFS. The Pt mass activity of the Pt/Pd/C electrocatalyst for ORR is considerably higher than that of commercial Pt/C electrocatalysts. The results with Pt monolayer electrocatalysts may significantly impact science of electrocatalysis and fuel-cell technology, as they have demonstrated an exceptionally effective way of using Pt that can resolve problems of other approaches, including electrocatalysts' inadequate activity and high Pt content.