Simultaneously synthesizing and structuring atomically thick or ultrathin 2D non-precious metal nanocrystal may offer a new class of materials to replace the state-of-art noble-metal electrocatalysts; however, the synthetic strategy is the bottleneck which should be urgently solved. Here we report the synthesis of an ultrathin nickel nanosheet array (Ni-NSA) through in situ topotactic reduction from Ni(OH)2 array precursors. The Ni nanosheets showed a single-crystalline lamellar structure with only ten atomic layers in thickness and an exposed (111) facet. Combined with a superaerophobic (low bubble adhesive) arrayed structure the Ni-NSAs exhibited a dramatic enhancement on both activity and stability towards the hydrazine-oxidation reaction (HzOR) relative to platinum. Furthermore, the partial oxidization of Ni-NSAs in ambient atmosphere resulted in effective water-splitting electrocatalysts for the hydrogen-evolution reaction (HER).

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Single‐Crystalline Ultrathin Nickel Nanosheets Array from In Situ Topotactic Reduction for Active and Stable Electrocatalysis

Solvothermal synthesis of metal nanocrystals and their applications

Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz–Slyozov–Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Follow...

Direct observation of aggregative nanoparticle growth: kinetic modeling of the size distribution and growth rate.

Well-dispersed magnetically recyclable core–shell Ag@M (M = Co, Ni, Fe) nanoparticles (NPs) supported on graphene have been synthesized via a facile in situ one-step procedure, using methylamine borane (MeAB) as a reducing agent under ambient condition. Their catalytic activity toward hydrolysis of ammonia borane (AB) were studied. Although the Ag@Fe/graphene NPs are almost inactive, the as-prepared Ag@Co/graphene NPs are the most reactive catalysts, followed by Ag@Ni/graphene NPs. Compared with AB and NaBH4, the as-synthesized Ag@Co/graphene catalysts which reduced by MeAB exert the highest catalytic activity. Additionally, the Ag@Co NPs supported on graphene exhibit higher catalytic activity than the catalysts with other conventional supports, such as the SiO2, carbon black, and γ-Al2O3. The as-synthesized Ag@Co/graphene NPs exert satisfied catalytic activity, with the turnover frequency (TOF) value of 102.4 (mol H2 min–1 (mol Ag)−1), and the activation energy Ea value of 20.03 kJ/mol. Furthermore, the ...

Graphene-supported Ag-based core-shell nanoparticles for hydrogen generation in hydrolysis of ammonia borane and methylamine borane.

NiCo-Based Electrocatalysts for the Alkaline Oxygen Evolution Reaction: A Review

New dimensional NiCo alloy icosahedral nanocrystals with controllable size have been first reported and synthesized through an Ostwald ripening process in a template-absent solvothermal reaction system. The proposed synthesis is corroborated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The as-obtained NiCo icosahedral nanocrystals exhibit the size- and component-dependent magnetic behaviors. The coercivity (Hc) depends on both the magnetocrystalline and structure anisotropy, and the saturation magnetizations (Ms) decided by the content of Co. Hc decreases from 189.02 to 147.95 Oe with the increase of the icosahedral NCs size from 200 to 850 nm. Especially, the Hc of the icosahedral NCs at 157.38 Oe is higher than that of nanospheres at 104.02 Oe. In addition, Ms and Hc increased with the increasing Co content. It can be an ideal building block for appl...

Solvothermal synthesis of NiCo alloy icosahedral nanocrystals.

Double-shelled Ag/C/Ni nanocables have been synthesized through a deposition covering process of Ni nanoparticles (NPs) onto Ag/C pentagonal prism nanowires (NWs). The proposed synthesis mechanism is corroborated by scanning electron microscopy, transition electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy. The resulting Ag/C/Ni nanocables with an average diameter of ∼270 nm are made up of Ag NW core (∼200 nm diameter) with internal amorphous C layer (∼10 nm thickness) and outer Ni shell (∼25 nm thickness). The UV-vis absorption spectroscopy analysis indicates that the covering of the Ni shell on the Ag/C nanowire can dampen the surface plasmon resonance (SPR) of Ag wire core and lead to a red-shifted SPR absorption peak. In particular, compared with Ni NPs, the resultant double-shelled Ag/C/Ni magnetic nanocables exhibits higher catalytic activity for the dehydrogenation toward aqueous ammonia borane under ambient atmosphere, and its calculated activation energy is lower than those of many bimetallic catalysts.

Controllable assembly of Ag/C/Ni magnetic nanocables and its low activation energy dehydrogenation catalysis

Magnetic double-shelled Ag@C@Co pentagonalprism nanocables are fabricated using a synchronous growth and oriented assembly process, in which the second shell of Co is arranged along the edges of Ag@C pentagonalprism nanowires (NWs). The resulting Ag@C@Co pentagonalprism nanocables exhibit an average diameter of ≈400 nm and consist of Ag core NWs with diameter of ≈200 nm and C middle layers with a thickness of ≈10 nm as well as outer Co shells with a thickness of ≈100 nm. UV-vis absorption spectroscopy shows that the Co shell on Ag@C NWs can damp the surface plasmon resonance (SPR) of the Ag core wires and lead to a red-shifted SPR absorption peak. Additionally, the Ag@C@Co nanocables have the ferromagnetic behavior, which can be controlled by modulating the shell density. The resulting magnetic Ag@C@Co nanocables exert excellent selected catalytic activity along the edges toward the dehydrogenation of ammonia borane aqueous under ambient conditions at room temperature.

Oriented Growth and Assembly of Ag@C@Co Pentagonalprism Nanocables and their Highly Active Selected Catalysis Along the Edges for Dehydrogenation

Newly designed magnetic-alloy/noble-metal FeCo/Pt nanorods have been first reported and fabricated through a length-controllable catalyzing-synthesis process in which the growth of FeCo nanorods was induced on Pt nanotips. The length of FeCo/Pt nanorods depends on the number of platinum nanotips. The proposed synthesis mechanism was corroborated by scanning electron microscopy, transition electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. With the decrease of Fe content in FexCo96–x/Pt4 nanoalloys from 77 to 15, the morphology changes from nanorods with different lengths to nanoparticles. The analysis of the magnetic hysteresis loops indicated that the magnetic saturation and coercivity were strongly dependent on the length of the nanorods in which maximum saturation magnetization and minimum coercivity were obtained for Fe77Co19/Pt4 nanorods with the length of ∼2.5 μm. In particular, FeCo/Pt exhibited length-dependent reactivity towards 1,1...

Length-controllable catalyzing-synthesis and length-corresponding properties of FeCo/Pt nanorods.

Newly designed magnetic FeNi-Pt match-like heterostructured nanorods were synthesized by means of induced growth of FeNi nanorods on Pt nanotips. The proposed synthesis mechanism is corroborated by SEM, TEM, XRD and XPS. The magnetic behavior shows that the magnetic saturation and coercivity are strongly dependent on both the shape and the alloy composition. The saturation magnetizations (Ms) and the coercivity (Hc) of nanorods synthesized are larger than those of nanoparticles because of the relatively large anisotropy of nanorods. Maximum saturation magnetization is obtained for Fe(82) Ni(15) -Pt(3) at 226.6 emu g(-1), whereas maximum coercivity is obtained for Fe(20)Ni(77)-Pt(3) at 136.8 Oe. Shape-dependent reactivity toward the reduction of chlorinated solvents was observed for the FeNi-Pt heterostructured nanomaterials. In particular, the Fe(82)Ni(15)-Pt(3) nanorods are highly reactive in the dechlorination process of 1,1,2,2-tetrachloroethane.

Baolei Sun

Papers

Solvothermal synthesis of NiCo alloy icosahedral nanocrystals.

Controllable assembly of Ag/C/Ni magnetic nanocables and its low activation energy dehydrogenation catalysis

Oriented Growth and Assembly of Ag@C@Co Pentagonalprism Nanocables and their Highly Active Selected Catalysis Along the Edges for Dehydrogenation

Length-controllable catalyzing-synthesis and length-corresponding properties of FeCo/Pt nanorods.

Inducing Growth of FeNi–Pt Match‐Like Magnetic Nanoheterostructures on Pt Nanotips and Dechlorination of Hydrochloric Ether