Synthesis and oxygen reduction activity of shape-controlled Pt(3)Ni nanopolyhedra

Pt nanoparticles residing in the pores of porous LaNiO₃ nanocubes as high-efficiency electrocatalyst for direct methanol fuel cells

Pt-filled porous LaNiO₃ cubes are prepared through a facile route. The characterizations reveal that large numbers of pores (9-10 nm) are distributed homogeneously in porous LaNiO₃ cubes. The Pt nanoparticles residing in the pores of porous LaNiO₃ cubes are about 5 nm in size. The investigation on the electrocatalytic activity reveals that electrocatalytic activity of the obtained Pt loaded porous LaNiO₃ nanocubes exhibit a significantly improved electrochemical active surface area (EASA) and a remarkably enhanced electrocatalytic performance toward methanol oxidation. The results are significant for improving the efficiency of Pt-based catalysts for DMFCs as well as the applications of perovskite compounds.

Icosahedral platinum alloy nanocrystals with enhanced electrocatalytic activities

This communication describes the synthesis of Pt-M (M = Au, Ni, Pd) icosahedral nanocrystals based on the gas reducing agent in liquid solution method. Both CO gas and organic surface capping agents play critical roles in stabilizing the icosahedral shape with {111} surfaces. Among the Pt-M alloy icosahedral nanocrystals generated, Pt(3)Ni had an impressive ORR specific activity of 1.83 mA/cm(2)(Pt) and 0.62 A/mg(Pt). Our results further show that the area-specific activity of icosahedral Pt(3)Ni catalysts was about 50% higher than that of the octahedral Pt(3)Ni catalysts (1.26 mA/cm(2)(Pt)), even though both shapes are bound by {111} facets. Density functional theory calculations and molecular dynamics simulations indicate that this improvement may arise from strain-induced electronic effects.

Synthesis, shape control, and methanol electro-oxidation properties of Pt-Zn alloy and Pt3Zn intermetallic nanocrystals

We report the first synthesis of highly monodisperse Pt(3)Zn nanocrystals (NCs). Shape-controlled synthesis generates cubic and spherical Pt-Zn NCs. Reaction temperature is the key to incorporate Zn into Pt, even in the absence of a strong reducing agent. The Pt-Zn NCs are active toward methanol oxidation, with the spherical NCs exhibiting higher activity than the cubic NCs. The Pt-Zn alloy phase can be transformed into the Pt(3)Zn intermetallic phase, upon annealing. The intermetallic Pt(3)Zn shows better performance than the alloy phase Pt-Zn. Besides the activity toward methanol oxidation, Pt-Zn NCs show excellent poisoning tolerance. With activities comparable to the commercial Pt catalyst, enhanced poisoning tolerance and lower cost, Pt-Zn and Pt(3)Zn NCs are a promising new family of catalysts for direct methanol fuel cells.

Syntheses of water-soluble octahedral, truncated octahedral, and cubic Pt-Ni nanocrystals and their structure-activity study in model hydrogenation reactions

We developed a facile strategy to synthesize a series of water-soluble Pt, Pt(x)Ni(1-x) (0 < x < 1), and Ni nanocrystals. The octahedral, truncated octahedral, and cubic shapes were uniformly controlled by varying crystal growth inhibition agents such as benzoic acid, aniline, and carbon monoxide. The compositions of the Pt(x)Ni(1-x) nanocrystals were effectively controlled by choice of ratios between the Pt and Ni precursors. In a preliminary study to probe their structure-activity dependence, we found that the shapes, compositions, and capping agents strongly influence the catalyst performances in three model heterogeneous hydrogenation reactions.

Solvothermal synthesis of platinum alloy nanoparticles for oxygen reduction electrocatalysis

Platinum alloy nanoparticles show great promise as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. We report here on the use of N,N-dimethylformamide (DMF) as both solvent and reductant in the solvothermal synthesis of Pt alloy nanoparticles (NPs), with a particular focus on Pt-Ni alloys. Well-faceted alloy nanocrystals were generated with this method, including predominantly cubic and cuboctahedral nanocrystals of Pt(3)Ni, and octahedral and truncated octahedral nanocrystals of PtNi. X-ray diffraction (XRD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), coupled with energy dispersive spectroscopy (EDS), were used to characterize crystallite morphology and composition. ORR activities of the alloy nanoparticles were measured with a rotating disk electrode (RDE) technique. While some Pt(3)Ni alloy nanoparticle catalysts showed specific activities greater than 1000 μA/cm(2)(Pt), alloy catalysts prepared with a nominal composition of PtNi displayed activities close to 3000 μA/cm(2)(Pt), or almost 15 times that of a state-of-the-art Pt/carbon catalyst. XRD and EDS confirmed the presence of two NP compositions in this catalyst. HAADF-STEM examination of the PtNi nanoparticle catalyst after RDE testing revealed the development of hollows in a number of the nanoparticles due to nickel dissolution. Continued voltage cycling caused further nickel dissolution and void formation, but significant activity remained even after 20,000 cycles.

Structure/processing/properties relationships in nanoporous nanoparticles as applied to catalysis of the cathodic oxygen reduction reaction

We present a comprehensive experimental study of the formation and activity of dealloyed nanoporous Ni/Pt alloy nanoparticles for the cathodic oxygen reduction reaction. By addressing the kinetics of nucleation during solvothermal synthesis we developed a method to control the size and composition of Ni/Pt alloy nanoparticles over a broad range while maintaining an adequate size distribution. Electrochemical dealloying of these size-controlled nanoparticles was used to explore conditions in which hierarchical nanoporosity within nanoparticles can evolve. Our results show that in order to evolve fully formed porosity, particles must have a minimum diameter of ∼15 nm, a result consistent with the surface kinetic processes occurring during dealloying. Nanoporous nanoparticles possess ligaments and voids with diameters of approximately 2 nm, high surface area/mass ratios usually associated with much smaller particles, and a composition consistent with a Pt-skeleton covering a Ni/Pt alloy core. Electrochemical measurements show that the mass activity for the oxygen reduction reaction using carbon-supported nanoporous Ni/Pt nanoparticles is nearly four times that of commercial Pt/C catalyst and even exceeds that of comparable nonporous Pt-skeleton Ni/Pt alloy nanoparticles.

Solvothermal synthesis of Pt-Pd alloys with selective shapes and their enhanced electrocatalytic activities

Pt-Pd bimetallic alloy nanostructures with highly selective morphologies such as cube, bar, flower, concave cube, and dendrite have been achieved through a facile one-pot solvothermal synthesis. The effects of shape-controllers (sodium dodecyl sulfate (SDS), ethylenediamine-tetraacetic acid disodium salt (EDTA-2Na), NaI) and solvents (water/DMF) on the morphologies were systematically investigated. The electrocatalytic activities of these Pt-Pd alloy nanostructures toward formic acid oxidation were tested. The results indicated that these alloy nanocrystals exhibited enhanced and shape-dependent electrocatalytic activity toward formic acid oxidation compared to commercial Pt black and Pt/C catalysts.

Controlled synthesis of Pd-Pt alloy hollow nanostructures with enhanced catalytic activities for oxygen reduction

Pd-Pt alloy nanocrystals (NCs) with hollow structures such as nanocages with porous walls and dendritic hollow structures and Pd@Pt core-shell dendritic NCs could be selectively synthesized by a galvanic replacement method with uniform Pd octahedral and cubic NCs as sacrificial templates. Fine control over the degree of galvanic replacement of Pd with Pt allowed the production of Pd-Pt NCs with distinctly different morphologies. The synthesized hollow NCs exhibited considerably enhanced oxygen reduction activities compared to those of Pd@Pt core-shell NCs and a commercial Pt/C catalyst, and their electrocatalytic activities were highly dependent on their morphologies. The Pd-Pt nanocages prepared from octahedral Pd NC templates exhibited the largest improvement in catalytic performance. We expect that the present work will provide a promising strategy for the development of efficient oxygen reduction electrocatalysts and can also be extended to the preparation of other hybrid or hetero-nanostructures with desirable morphologies and functions.

Recent progress in the synthesis of inorganic nanoparticles

Nanoparticles probably constitute the largest class of nanomaterials. Nanoparticles of several inorganic materials have been prepared by employing a variety of synthetic strategies. Besides synthesizing nanoparticles, there has been considerable effort to selectively prepare nanoparticles of different shapes. In view of the great interest in inorganic nanoparticles evinced in the last few years, we have prepared this perspective on the present status of the synthesis of inorganic nanoparticles. This article includes a brief discussion of methods followed by reports on the synthesis of nanoparticles of various classes of inorganic materials such as metals, alloys, oxides chalcogenides and pnictides. A brief section on core-shell nanoparticles is also included.

Small adsorbate-assisted shape control of Pd and Pt nanocrystals

The shape control of noble metal nanocrystals is crucial to their optical properties and catalysis applications. In this Progress Report, the recent progress of shape-controlled synthesis of Pd and Pt nanostructures assisted by small adsorbates is summarized. The use of small strong adsorbates (e.g., I(-) , CO, amines) makes it possible to fabricate Pd and Pt nanostructures with not only well-defined surface structure but also morphologies that have not been achieved by other synthetic strategies. The roles of small adsorbates in shape control of Pd and Pt nanocrystals are discussed in the Report. Also presented in the Report are unique optical and catalytic properties of several Pd and Pt nanostructures (e.g., ultrathin Pd nanosheets, concave Pt octapod, concave Pd tetrahedra), as well as their bioapplications, to demonstrate the power of using small strong adsorbates in the shape control of Pt and Pd nanostructures.

FePt nanoparticles assembled on graphene as enhanced catalyst for oxygen reduction reaction

Seven-nanometer FePt nanoparticles (NPs) were synthesized and assembled on graphene (G) by a solution-phase self-assembly method. These G/FePt NPs were a more active and durable catalyst for oxygen reduction reaction (ORR) in 0.1 M HClO(4) than the same NPs or commercial Pt NPs deposited on conventional carbon support. The G/FePt NPs annealed at 100 °C for 1 h under Ar + 5% H(2) exhibited specific ORR activities of 1.6 mA/cm(2) at 0.512 V and 0.616 mA/cm(2) at 0.557 V (vs Ag/AgCl). As a comparison, the commercial Pt NPs (2-3 nm) had specific activities of 0.271 and 0.07 mA/cm(2) at the same potentials. The G/FePt NPs were also much more stable in the ORR condition and showed nearly no activity change after 10 000 potential sweeps. The work demonstrates that G is indeed a promising support to improve NP activity and durability for practical catalytic applications.

Quantitative analysis of the role played by poly(vinylpyrrolidone) in seed-mediated growth of Ag nanocrystals

This article presents a quantitative analysis of the role played by poly(vinylpyrrolidone) (PVP) in seed-mediated growth of Ag nanocrystals. Starting from Ag nanocubes encased by {100} facets as the seeds, the resultant nanocrystals could take different shapes depending on the concentration of PVP in the solution. If the concentration was above a critical value, the seeds simply grew into larger cubes still enclosed by {100} facets. When the concentration fell below a critical value, the seeds would evolve into cuboctahedrons enclosed by a mix of {100} and {111} facets and eventually octahedrons completely covered by {111} facets. We derived the coverage density of PVP on Ag(100) surface by combining the results from two measurements: (i) cubic seeds were followed to grow at a fixed initial concentration of PVP to find out when {111} facets started to appear on the surface, and (ii) cubic seeds were allowed to grow at reduced initial concentrations of PVP to see at which concentration {111} facets started to appear from the very beginning. We could calculate the coverage density of PVP from the differences in PVP concentration and the total surface area of Ag nanocubes between these two samples. The coverage density was found to be 140 and 30 repeating units per nm(2) for PVP of 55,000 and 10,000 g/mol in molecular weight, respectively, for cubic seeds of 40 nm in edge length. These values dropped slightly to 100 and 20 repeating units per nm(2), respectively, when 100 nm Ag cubes were used as the seeds.