Overgrowth Versus Galvanic Replacement: Mechanistic Roles of Pd Seeds during the Deposition of Pd-Pt.

Here, a systematic study of the roles played by Pd seeds during seed-mediated coreduction of Pd-Pt is presented. Either nanoparticles with porous, hollow architectures or concave nanocubes were achieved, depending on whether the synthesis conditions favored galvanic replacement or overgrowth. Prior works have shown that the galvanic replacement reaction between seeds and a precursor can be suppressed by introducing a faster, parallel reaction that removes one of the reagents (e.g., adatom generation in solution rather than surface-catalyzed precursor reduction). Here, we show that the galvanic replacement reaction depends on the size and concentration of the Pd seeds; the former of which can be manipulated during the course of the reaction through the use of a secondary reducing agent. This insight will guide future syntheses of multimetallic nanostructures by seeded methods, allowing for a range of nanocrystals to be precisely engineered for a variety of applications.

Manipulating the architecture of Pd@Pt nanostructures through metal-selective capping agent interactions.

Pluronic F127 and NaBr were used during co-reduction of Pd and Pt precursors to achieve octopodal and dendritic Pd@Pt nanoparticles selectively through preferential capping interactions. Our findings demonstrate that two capping agents can be used to independently manipulate the growth regimes of metals in the synthesis of bimetallic nanostructures.

Mesoporous Trimetallic PtPdRu Spheres as Superior Electrocatalysts.

Mesoporous Trimetallic PtPdRu Spheres with well-defined spherical morphology and uniformly sized pores were synthesized in an aqueous solution using ascorbic acid as the reducing agent and triblock copolymer F127 as the pore directing agent. These mesoporous PtPdRu spheres exhibited enhanced electrocatalytic activity compared to commercial Pt black, resulting in a ∼4.9 times improvement in mass activity for the methanol oxidation reaction. The excellent electrocatalytic activity and stability are due to the unique mesoporous architecture and electronic landscape between different elements.

Nanoarchitectures for Mesoporous Metals.

The field of mesoporous metal nanoarchitectonics offers several advantages which cannot be found elsewhere. These materials have been showcasing impressive enhancements of their electrochemical properties for further implementation, compared to their micro- and macroporous counterparts. Since the last few decades, various methods have been developed to achieve narrow pore size distribution with a tunable porosity and particle morphology. While hard templates offer a reliable and intuitive approach to synthesize mesoporous metals, the complexity of the technique and the use of harmful chemicals pushed several research groups to focus in other directions. For example, soft templates (e.g., lyotropic crystals, micelles assemblies) and solution phase methods (requiring to control reduction reactions) offer more and more possibilities in terms of available compositions and morphologies. Indeed, various metal (Pt, Pd, Au, Ru, etc.) can now be synthesized as dendritic, core@shell, hollow or polyhedral nanoparticles, with single- or multicomponents, alloyed or not, with unprecedented electrochemical activity.

All-metal mesoporous nanocolloids: solution-phase synthesis of core-shell Pd@Pt nanoparticles with a designed concave surface.

Colloidal Pd@Pt nanoparticles with uniform mesopores can be synthesized in one step by a facile solution-phase method involving slow reduction of metal species in strong acidic media. In this system, F127 micelles can directly act as a template to form the mesopores in the product, and the greater reducibility of the Pd species leads to the desired core-shell Pd@Pt nanocolloids.

Synthesis of mesoporous Pt-Ru alloy particles with uniform sizes by sophisticated hard-templating method.

Team work: Mesoporous Pt-Ru alloy particles with uniform sizes are synthesized by controlled chemical reduction with ascorbic acid using mesoporous silica as a hard template. Elemental mapping shows uniform distribution of Pt and Ru particles. The electrochemical activity and stability of the alloys towards methanol oxidation much higher than that of mesoporous Pt and commercial Pt catalyst.

Mesoporous metallic cells: design of uniformly sized hollow mesoporous Pt-Ru particles with tunable shell thicknesses.

A new class of hollow mesoporous Pt-Ru and Pt particles with uniform size, named 'mesoporous metallic cells', are synthesized through a dual-templating approach using colloidal silica particles and non-ionic surfactants. To realize the full potential of mesoporous metals as electrocatalysts, the shell thicknesses, compositions, and hollow cavity sizes are precisely controlled.

Pt nanoworms: creation of a bumpy surface on one-dimensional (1D) Pt nanowires with the assistance of surfactants embedded in mesochannels.

A new type of platinum nanowire with a bumpy surface "Pt nanoworm" is electrochemically synthesized in mesochannels of mesoporous silica films with the assistance of a nonionic surfactant (C(16)EO(8)).

Rational synthesis of Pt spheres with hollow interior and nanosponge shell using silica particles as template.

Here we report a facile and efficient method to prepare Pt spheres with hollow interior and nanosponge shell with high surface area. Such a unique Pt nanostructure can effectively improve the electrocatalytic performance of Pt catalysts by facilitating the access of electroactive species to the full-extent Pt surface.

Electrochemical design of two-dimensional Au nanocone arrays using porous anodic alumina membranes with conical holes.

We report step-by-step electrochemical design of two-dimensional (2D) Au nanocone arrays by using novel porous anodic alumina membranes with conical holes. The cones with desirable aspect ratios can be fabricated by using the PAA templates with different aspect ratios. The Au nanocone arrays show high potentials as SERS (Surface Enhanced Raman Scattering)-active substrates and Au electrodes with high surface area.

Block copolymer assisted synthesis of bimetallic colloids with Au core and nanodendritic Pt shell.

We report block copolymer assisted synthesis of a Au metal core coated with a nanodendritic Pt shell (Au@Pt). Herein, a rapid, one-step and efficient wet-chemical route is proposed to straightforwardly synthesize Au@Pt with high yield (approximately 100%), which was mediated by Pluronic F127 block copolymer from the reduction of Pt and Au complexes by ascorbic acid (AA).