Penglei Cui

Alloy Cu3Pt nanoframes through the structure evolution in Cu-Pt nanoparticles with a core-shell construction

Noble metal nanoparticles with hollow interiors and customizable shell compositions have immense potential for catalysis. Herein, we present an unique structure transformation phenomenon for the fabrication of alloy Cu3Pt nanoframes with polyhedral morphology. This strategy starts with the preparation of polyhedral Cu-Pt nanoparticles with a core-shell construction upon the anisotropic growth of Pt on multiply twinned Cu seed particles, which are subsequently transformed into alloy Cu3Pt nanoframes due to the Kirkendall effect between the Cu core and Pt shell. The as-prepared alloy Cu3Pt nanoframes possess the rhombic dodecahedral morphology of their core-shell parents after the structural evolution. In particular, the resulting alloy Cu3Pt nanoframes are more effective for oxygen reduction reaction but ineffective for methanol oxidation reaction in comparison with their original Cu-Pt core-shell precursors.

Noble metal-based composite nanomaterials fabricated via solution-based approaches

One of the key frontiers in nanomaterial fabrication is the integration of different materials within the same structure to increase functionality. In particular, interactions between nanoscale materials with distinctly different physical and chemical properties can greatly improve the overall application performance of the nanocomposites and can even generate new synergetic properties. Within the last decade, the development of wet-chemistry methods has led to the development of research in to composite nanomaterials. The efforts of many leading research groups have led to a rich variety of composite nanomaterials. However, the design and synthesis of composite nanomaterials with controlled properties remain a significant challenge. We devote this review for summarizing the solution-based methods used for the preparation of noble metal-based nanocomposites, their characterization and their potential applications in diverse areas to provide readers with a systematic and coherent overview of the field.

Gold-catalyzed formation of core-shell gold-palladium nanoparticles with palladium shells up to three atomic layers

Ultrathin metal layers formed on seed particles with different lattice parameters usually exhibit enhanced catalytic performance for a given chemical reaction due to the sufficient lattice strain effect induced by the core region. Herein, we report a gold-catalyzed strategy for the synthesis of core–shell gold–palladium nanoparticles with subnanometer-thick palladium shells towards oxygen reduction reaction. In this approach, owing to the catalysis of gold particles, the reduction of palladium precursors would only occur on the surface of gold cores, preventing the newly formed palladium atoms from self-nucleation. The deposition of palladium atoms gradually changes the surface property of gold seeds, and in particular, the catalytic reduction of palladium ions ceases when 3 palladium atomic layers are deposited on the gold cores. In comparison with the commercial palladium catalysts, the core–shell gold–palladium nanoparticles with subnanometer-thick palladium shells display superior activity and durability in catalyzing the oxygen reduction reaction, mainly due to the lattice tensile effect in palladium shells induced by the gold cores, which sufficiently balances the bond-breaking and bond-making steps of the oxygen reduction reaction process.

Carbon-supported hollow palladium nanoparticles with enhanced electrocatalytic performance

Carbon-supported palladium nanoparticles (NPs) with hollow interiors (hPdNPs/C) are fabricated via a facile approach. In this strategy, core–shell NPs with an Ag core and an Ag–Pd alloy shell (Ag@Ag–Pd) are first synthesized in oleylamine by a galvanic replacement reaction between Ag seed particles and Pd2+ ion precursors. Then the core–shell Ag@Ag–Pd NPs are loaded on the XC-72 carbon supports and refluxed in acetic acid to remove the original organic surfactant. The carbon-supported core–shell Ag@Ag–Pd NPs are subsequently agitated in saturated Na2S or NaCl solution for 24 h to eliminate the Ag component from the core and shell regions, leading to the formation of hPdNPs/C. Specifically, the hPdNPs/C generated by NaCl treatment exhibit superior catalytic activity and durability for formic acid oxidation reaction (FAOR) and oxygen reduction reaction (ORR), compared with the commercial Pd/C catalysts from Johnson Matthey, mainly due to the high electrochemically active surface areas (ECSAs) of the hollow structure, whereas the hPdNPs/C obtained by Na2S treatment display very poor catalytic performance due to the serious poisoning induced by S2− adsorption.

Nanoscale noble metals with a hollow interior formed through inside-out diffusion of silver in solid-state core- shell nanoparticles

Noble metal nanoparticles with hollow interiors and customizable shell compositions have immense potential for a wide variety of applications. Herein, we present a facile, general, and cost-effective strategy for the synthesis of noble metal nanoparticles with hollow structures, which is based on the inside-out diffusion of Ag in solid-state core-shell nanoparticles. This approach starts with the preparation of core-shell nanoparticles with Ag residing in the core region, which are then loaded on a solid substrate and aged in air to allow the inside-out diffusion of Ag from the core region, leading to the formation of monometallic or alloy noble metal nanoparticles with a hollow interior. The synthesis was carried out at room temperature and could be achieved on different solid substrates. In particular, the inside-out diffusion of Ag calls for specific concern with respect to the evaluation of the catalytic performance of the Ag-based core-shell nanoparticles since it may potentially interfere with the physical and chemical properties of the core-shell particles.

Formation of composite dimers consisting of Ag2S and hollow structured Pd nanoparticles

Understanding the mechanism for the production of composite dimers, which often exhibit new properties not present in their individual components due to the electron transfer across the nanometer contact at the interface, is undoubtedly important. Herein, with the assistance of a small amount of [AD]PO4, an organic soluble ionic liquid, core–shell Ag@Ag–Pd nanoparticles with an average size of 28.2 nm are successfully prepared, which serve as templates for the subsequent synthesis of dimeric nanocomposites consisting of Ag2S and hollow structured Pd nanoparticles (Ag2S–hPd) by converting the Ag component in the core–shell particles into Ag2S with elemental sulfur. Specifically, the large size of the core–shell nanoparticles allow us to observe clearly the ripening of Ag2S to a single site on the surface of the remnant hollow structured Pd nanoparticles, which elucidates the mechanism accounting for the formation of Ag2S–hPd composite dimers instead of core–shell nanostructures with a hollow Pd core and a continuous Ag2S shell, although the transformation from Ag to Ag2S occurred uniformly on the surface of the remnant hollow Pd particles. Electrochemical measurements demonstrate that the dimeric Ag2S–hPd nanocomposites display better electrocatalytic behavior for formic acid oxidation than commercial Pd/C catalysts due to the strong electronic coupling between the semiconductor and noble metal domains in the nanocomposites.

A 1-dodecanethiol-based phase transfer protocol for the highly efficient extraction of noble metal ions from aqueous phase

A 1-dodecanethiol-based phase-transfer protocol is developed for the extraction of noble metal ions from aqueous solution to a hydrocarbon phase, which calls for first mixing the aqueous metal ion solution with an ethanolic solution of 1-dodecanethiol, and then extracting the coordination compounds formed between noble metal ions and 1-dodecanethiol into a non-polar organic solvent. A number of characterization techniques, including inductively coupled plasma atomic emission spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis demonstrate that this protocol could be applied to extract a wide variety of noble metal ions from water to dichloromethane with an efficiency of >96%, and has high selectivity for the separation of the noble metal ions from other transition metals. It is therefore an attractive alternative for the extraction of noble metals from water, soil, or waste printed circuit boards.

Uniformly dispersed platinum-cobalt alloy nanoparticles with stable compositions on carbon substrates for methanol oxidation reaction

Alloying platinum (Pt) with suitable transition metals is effective way to enhance their catalytic performance for methanol oxidation reaction, and reduce their cost at mean time. Herein, we report our investigation on the synthesis of bimetallic platinum-cobalt (PtCo) alloy nanoparticles, their activation, as well as the catalytic evaluation for methanol oxidation reaction. The strategy starts with the synthesis of PtCo alloy nanoparticles in an organic medium, followed by loading on carbon substrates. We then remove the capping agent by refluxing the carbon-supported PtCo particles in acetic acid before electrochemical measurements. We emphasize the change in composition of the alloys during refluxing process, and the initial PtCo alloys with Pt/Co ratio of 1/2 turns into stable alloys with Pt/Co ratio of 3/1. The final Pt3Co particles have uniform distribution on carbon substrates, and exhibit activity with 2.4 and 1.5 times of that for commercial Pt/C and PtRu/C for methanol oxidation reaction.