Formation of Pt-Based Alloy Nanoparticles Assisted by Molybdenum Hexacarbonyl

We report on an optimized, scalable solution-phase synthetic procedure for the fabrication of fine-tuned monodisperse nanostructures (Pt(NiCo), PtNi and PtCo). The influence of different solute metal precursors and surfactants on the morphological evolution of homogeneous alloy nanoparticles (NPs) has been investigated. Molybdenum hexacarbonyl (Mo(CO)6) was used as the reductant. We demonstrate that this solution-based strategy results in uniform-sized NPs, the morphology of which can be manipulated by appropriate selection of surfactants and solute metal precursors. Co-surfactants (oleylamine, OAm, and hexadecylamine, HDA) enabled the development of a variety of high-index faceted NP morphologies with varying degrees of curvatures while pure OAm selectively produced octahedral NP morphologies. This Mo(CO)6-based synthetic protocol offers new avenues for the fabrication of multi-structured alloy NPs as high-performance electrocatalysts

Solution-grown dendritic pt-based ternary nanostructures for enhanced oxygen reduction reaction functionality

Nanoalloys with anisotropic morphologies of branched and porous internal structures show great promise in many applications as high performance materials. Reported synthetic approaches for branched alloy nanostructures are, however, limited by the synthesis using a seed-growth process. Here, we demonstrate a conveniently fast and one-pot solution-phase thermal reduction strategy yielding nanoalloys of Pt with various solute feed ratios, exhibiting hyperbranched morphologies and good dispersity. When Pt was alloyed with transition metals (Ni, Co, Fe), we observed well-defined dendritic nanostructures in PtNi, PtCo and Pt(NiCo), but not in PtFe, Pt(FeNi) or Pt(FeCo) due to the steric hindrance of the trivalent Fe(acac)3precursor used during synthesis. In the case of Pt-based nanoalloys containing Ni and Co, the dendritic morphological evolution observed was insensitive to large variations in solute concentration. The functionality of these nanoalloys towards the oxygen reduction reaction (ORR); however, was observed to be dependent on the composition, increasing with increasing solute content. Pt3(NiCo)2exhibited superior catalytic activity, affording about a five-and 10-fold enhancement in area-specific and mass-specific catalytic activities, respectively, compared to the standard Pt/C nanocatalyst. This solution-based synthetic route offers a new approach for constructing dendritic Pt-based nanostructures with excellent product yield, monodispersity and high crystallinity

Topographical and compositional engineering of core-shell Ni@Pt ORR electro-catalysts

© 2020 The Royal Society of Chemistry. Complex faceted geometries and compositional anisotropy in alloy nanoparticles (NPs) can enhance catalytic performance. We report on the preparation of binary PtNi NPs via a co-thermolytic approach in which we optimize the synthesis variables, which results in significantly improved catalytic performance. We used scanning transmission electron microscopy to characterise the range of morphologies produced, which included spherical and concave cuboidal core-shell structures. Electrocatalytic activity was evaluated using a rotating disc electrode (1600 rpm) in 0.1 M HClO4; the electrocatalytic performance of these Ni@Pt NPs showed significant (∼11-fold) improvement compared to a commercial Pt/C catalyst. Extended cycling revealed that electrochemical surface area was retained by cuboidal PtNi NPs post 5000 electrochemical cycles (0.05-1.00 V, vs. SHE). This is attributed to the enclosure of Ni atoms by a thick Pt shell, thus limiting Ni dissolution from the alloy structures. The novel synthetic strategy presented here results in a high yield of Ni@Pt NPs which show excellent electro-catalytic activity and useful durability

High-Index Core-Shell Ni-Pt Nanoparticles as Oxygen Reduction Electrocatalysts

© 2020 American Chemical Society. Developing solid solution nanoparticles with complex faceted geometries and unusual composition sectoral zoning can enhance their catalytic performance. In a solution-phase synthesis of PtNi nanoparticles, we show that a mixture of surfactants results in surface functionalization, which in turn controls the morphological evolution of nanoparticles. The nanoparticles exhibited complex chemical growth zoning, rich in Pt geometric topologies, which varied as a function of surfactant mixture. Compositional mapping, using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with energy dispersive X-ray spectroscopy (EDS), highlights core-shell structures (∼1 nm Pt coating thickness) with edge-vertex Pt-enrichment and Ni-rich faces. These core-shell Ni-Pt nanoparticles demonstrated enhanced activities toward the oxygen reduction reaction (ORR) compared to commercial Pt/C, even after extended potential cycles (5000). Our synthetic approach, which utilizes the surfactants\u27 array of distinct functional groups, offers new avenues toward the formation of concentric core-shell structures with multifaceted topologies. These materials show considerable promise as electrocatalysts