Abstract ：

The rational design of efficient bimetallic nanoparticle (NP) catalysts is challenging due to the lack of theoretical understanding of active components and insights into the mechanisms of a specific reaction. Here, we report the rational design of nanoreactors comprising hollow carbon sphere-confined PtNi bimetallic NPs (PtNi@HCS) as highly efficient catalysts for hydrogen generation via ammonia borane hydrolysis in water. Using both density functional theory calculations and molecular dynamics simulations, the effects of an active PtNi combination and the critical synergistic role of a hollow carbon shell on the molecule diffusion adsorption behaviors are explored. Kinetic isotope effects and theoretical calculations allow the clarification of the mechanism, with oxidative addition of an O-H bond of water to the catalyst surface being the rate-determining step. The remarkable catalytic activity of the PtNi@HCS nanoreactor was also utilized for successful tandem catalytic hydrogenation reactions, using in situ-generated H2 from ammonia borane with high efficiency. The concerted design, theoretical calculations, and experimental work presented here shed light on the rational elaboration of efficient nanocatalysts and contribute to the establishment of a circular carbon economy using green hydrogen.

Keyword ：

ammonia borane nanoreactor hydrogen solid catalyst nanoalloy

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Production of hydrogen (H-2) from H(2 )storage materials is very attractive as a source of sustainable energy. We report that AuNi@ZIF-8 alloys are very efficient nanocatalysts for H2 evolution upon ammonia borane hydrolysis under visible-light illumination with turnover frequency 3.4 times higher than with the monometallic Ni catalyst in the dark. This improvement is attributed to dramatic volcano-type positive synergy optimized in Au0.5Ni0.5 @ZIF-8, for which ZIF-8 is by far the superior support, as well as to the localized surface plasmon resonance induced between 450 and 620 nm. Infrared spectra analysis and tandem reaction confirm the origin of the hydrogen atoms, reveal the reaction mechanism, and suggest how the cleavage of the B-H and O-H bonds proceeds in this reaction. Deuteration experiments with D2O including primary kinetic isotope effects and density functional theory calculation under both dark and visible light conditions show that activation of H2O always is the rate-determining step.

Keyword ：

Ammonia borane hydrolysis Volcano -type effect Plasmonic acceleration Hydrogen production Gold nanoalloy

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Bonding interface quality is crucial for power electronic packaging, while the alloyed Ag nanoparticle sintered joint has lower crack resistance at the interface. In this work, a sandwich structure nanoparticle film consisting of an Ag transition layer, nanoalloy layer, and Ag transition layer was developed for interface-enhanced lowtemperature bonding. The optimized sandwich structure increased the shear strength of Ag-based nanoalloy sintered joints, reaching 5.6 times for Ag10Cu and 2.0 times for Ag10Pd, respectively. The low-temperature spreadability of the Ag transition layer provided a micro-nano structure and further driving force for nanoalloy sintering on the substrate. Both experimental and molecular dynamics simulation results revealed that these nanoalloy particles spread easier and realized a higher effective bonding area. This interface-enhancing strategy enables the Ag-based nanoalloy a high-reliability die-attach material with low-temperature bondability.

Keyword ：

Laser deposition Sintering Electronic packaging Nanoalloy Interface structure

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Nano-Ag sintering can realize superior thermal, electrical, and mechanical properties for power electronic packaging, while it suffers from unstable microstructure and electrochemical migration. In this work, a super-saturated Ag2.8 wt%Cu nanoalloy film has been developed using pulsed laser deposition, which can be sintered at 250 degrees C in air for electronic packaging without sacrificing bondability. It was surprisingly found that both thermal stability and electrochemical migration resistance were significantly improved when alloying the Ag with 2.8 wt% Cu. The in situ formed Cu2O/CuO from Ag-Cu nanoalloy existed on the pore surface and along the grain boundaries of Ag/Ag-Cu nanoalloy, which stabilized the microstructure of bondline from 400 h to 1400 h at 300 degrees C. The synergistic effect of Ag-Cu nanoalloy and Cu oxides realized an obvious protective effect in the process of anodic dissolution, exhibiting a short-circuit time 2.4 times of the pure Ag electrode. The die attach process is compatible with most commercial equipment and Si/SiC dies with improved performance, enabling the supersaturated Ag-Cu nanoalloy to be a promising material for high reliability power electronic packaging.

Keyword ：

Power electronic packaging Thermal and electrochemical stability Low temperature sintering Ag-Cu nanoalloy

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Exploring the transformation/interconversion pathways of catalytic active metal species (single atoms, clusters, nanoparticles) on a support is crucial for the fabrication of high efficiency catalysts, the investigation of how catalysts are deactivated, and the regeneration of spent catalysts. Sintering and redispersion represent the two main transformation modes for metal active components in heterogeneous catalysts. Herein, we established a novel solid-state atomic replacement transformation for metal catalysts, through which metal atoms exchanged between single atoms and nanoalloys to form a new set of nanoalloys and single atoms. Specifically, we found that the Ni of the PtNi nanoalloy and the Zn of the ZIF-8-derived Zn1 on nitrogen-doped carbon (Zn1-CN) experienced metal interchange to produce PtZn nanocrystals and Ni single atoms (Ni1-CN) at high temperature. The elemental migration and chemical bond evolution during the atomic replacement displayed a Ni and Zn mutual migration feature. Density functional theory calculations revealed that the atomic replacement was realized by endothermically stretching Zn from the CN support into the nanoalloy and exothermically trapping Ni with defects on the CN support. Owing to the synergistic effect of the PtZn nanocrystal and Ni1-CN, the obtained (PtZn)n/Ni1-CN multisite catalyst showed a lower energy barrier of CO2 protonation and CO desorption than that of the reference catalysts in the CO2 reduction reaction (CO2RR), resulting in a much enhanced CO2RR catalytic performance. This unique atomic replacement transformation was also applicable to other metal alloys such as PtPd.

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Surface segregation constitutes an efficient approach to enhance the alkaline hydrogen evolution reaction (HER) activity of bimetallic PtxNiy nanoalloys. Herein, a new strategy is proposed by utilizing the small gas molecule of H-2 as the structure directing agent (SDA) to in situ induce Pt surface segregations over a series of PtNi5-n samples with extremely low Pt doping (Pt/Ni = 0.2). Impressively, the sample of PtNi5-0.3 synthesized under 0.3 MPa H-2 delivers an extremely low overpotential of 26.8 mV (-10 mA cm(-2)) and Tafel slope of 19.2 mV dec(-1), which is superior to most of the previously reported PtxNiy electrocatalysts. This is substantially related to the strong H-2 in situ inducing effect to generate Pt-rich@Ni-rich core-shell nanostructure of PtNi5-0.3 with an ultrahigh Pt surface content of 46%. The specific mechanistic effects of H-2 during the PtNi5-n synthesis process are well illustrated based on the combined experimental and theoretical studies. The density functional theory mechanism simulations further unravel that the evolved active site of PtNi5-n can efficiently reduce the reaction Gibbs free energies; especially for the scenario of PtNi5-0.3, the downward-shifted d band center of the Pt active site significantly reduces the Pt-H bond strength, eventually resulting in the lowest absolute value of Delta G(H).

Keyword ：

H PtNi alkaline hydrogen evolution reaction (2) structure directing agent (5) nanoalloy Pt surface segregation DFT calculation

Cite：

Copy from the list or Export to your reference management。