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.

Two-dimensional (2D) heterostructured Ni/graphene nanocomposites were constructed via electrostatic-induced spread by following in situ-reduction growth process for magnetically recyclable catalysis of p-nitrophenol to p-aminophenol. The heterostructures with large 2D surface and moderate inflexibility enable the superior catalytic activity and selectivity toward hydrogenation reaction for p-nitrophenol. On the basis of high-efficiency utilization of Ni Nps catalysis activity and electron-enhanced effect from graphene, the coupling effect of Ni/graphene magnetic nanocomposites can lead to highly catalytic activity for the hydrogenation reaction of p-nitrophenol with the pseudo-first-order rate constants of 11.7 × 10–3 s–1, which is over 2-fold compared to Ni Nps (5.45 × 10–3 s–1) and higher than reported noble metal nanocomposites. Complete conversion of p-nitrophenol was achieved with selectivity to p-aminophenol as high as 90% under atmosphere and room temperature. Additionally, this heterostructured ma...

Ni/graphene Nanostructure and Its Electron-Enhanced Catalytic Action for Hydrogenation Reaction of Nitrophenol

Recent advances in liquid-phase chemical hydrogen storage

Nickel nanoparticles immobilized on three-dimensional nitrogen-doped graphene-based frameworks (NiNPs@3D-(N)GFs) were synthesized and examined for hydrogen generation from the hydrolytic dehydrogenation of ammonia borane. The high dispersion of NiNPs over the 3D-(N)GFs and consolidated interaction between the 3D-(N)GFs and NiNPs catalyzes the dissociation of hydrogen molecules and the subsequent migration of hydrogen atoms on the 3D-(N)GFs. Due to the unique properties of the as-prepared material such as porous structure and existence of nitrogen and nickel to have interaction with molecular hydrogen, it has high potential to be employed in hydrogen storage. The as-prepared catalyst is an ideal candidate for developing highly efficient portable hydrogen generation, which can be useful for various applications such as fuel cells, metal/air batteries, etc.

Nickel nanoparticles immobilized on three-dimensional nitrogen-doped graphene as a superb catalyst for the generation of hydrogen from the hydrolysis of ammonia borane

Well dispersed magnetically recyclable trimetallic core–shell Ag@CoNi nanoparticles (NPs) supported on graphene have been synthesized via a facile one-step in situ procedure using methylamine borane (MeAB) as the reducing agent. The as-synthesized NPs exhibit much higher catalytic activities for hydrolytic dehydrogenation of ammonia borane (AB) than the monometallic, bimetallic, trimetallic alloy (AgCoNi/graphene), and graphene free (Ag@CoNi) counterparts. Moreover, compared with NaBH4 and AB, the weaker reducing agent MeAB has much better control during the synthesis of the graphene supported Ag@CoNi NPs, which resulted in the highest catalytic activity. Kinetic studies indicate that the catalytic hydrolysis of AB by the Ag@CoNi/graphene NPs is first order, with the activation energy measured to be 36.15 kJ mol−1. Furthermore, the as-prepared NPs exert good catalytic activities and recycle stabilities towards the hydrolysis of AB and MeAB. Hence, this general method indicates that MeAB can be used as both a potential hydrogen storage material and an efficient reducing agent, and can be easily extended to facile preparation of other graphene supported multi-metal NPs.

In situ synthesis of graphene supported Ag@CoNi core–shell nanoparticles as highly efficient catalysts for hydrogen generation from hydrolysis of ammonia borane and methylamine borane

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 C-isolated Ag–C–Co sandwich sphere nanostructures have been fabricated through a synchronous growth and assembly process, in which the outer Co sphere-shells assemble around the surface of synchronously grown Ag–C sphere-cores. Raman and UV-vis absorption spectroscopy studies show that the covering of Co shell on Ag–C sphere cores weakens the surface-enhanced Raman scattering (SERS) and surface plasmon resonance (SPR) of Ag–C sphere cores. Owing to its ferromagnetic behaviour, the as-prepared C-isolated Ag–C–Co sandwich nanospheres can be easily separated and recycled by an external magnet field for application. Compared with Ag–Co, C–Co, and Co nanospheres of the same size, the resultant magnetic Ag–C–Co sandwich nanospheres exhibit markedly high catalytic activity toward ammonia borane hydrolytic dehydrogenation at atmospheric pressure and room temperature, which is induced by SPR from C-isolated sandwich structural and electronic synergistic effects.

C-isolated Ag–C–Co sandwich sphere-nanostructures and their high activity catalysis induced by surface plasmon resonance

An approach has been explored to highly improve the catalytic activity and stability for methanol oxidation reaction (MOR) by using dominant α-(NiCu)3Pd phase-structural NiCuPd nanoparticles (NPs) as anode catalysts. The NiCuPd alloy NPs are monodispersed with the diameter of ∼10 nm and have been prepared by the reduction of Pd(acac)2, Ni(acac)2, and Cu(acac)2 following alloying growth process. In the Ni–Cu–Pd alloy system, Ni atoms fused in Cu3Pd phase to form α-(NiCu)3Pd phase together with NiCuPd solid solution phase. As Ni concentration gradually enriched, the crystallinity of α-(NiCu)3Pd became higher, while its percentage decreased by one degree. Owing to the synergistic effect between components and facet atom arrangement, the catalytic activity and stability of NiCuPd NPs can be adjusted toward the MOR in alkaline media. The maximized crystallinity of α-(NiCu)3Pd results in the largest catalytic activity. Compared with commercial Pd/C with (111) facets, α-(NiCu)3Pd phase with (117) facets afforded...

Novel-Phase Structural High-Efficiency Anode Catalyst for Methanol Fuel Cells: α-(NiCu)3Pd Nanoalloy

Power system transient security assessment based on multi-channel time series data mining

With the proposal of the dual-carbon goal, the new generation of “source-network-vehicle-storage” integrated power supply systems for electrified railways has received widespread attention. The source-network-vehicle-storage system is a low-inertia and weak-damping system with multitype and multiquantity converters, which easily causes system oscillation and is not conducive to the stable operation of electrified railways. To evaluate and analyze the potential risk and key influencing factors of small signal instability of the “source-network-vehicle-storage” system, a complete impedance model of the “source-network-vehicle-storage” system with multiple converters is established in this paper. On this basis, the influence of different circuit/control parameters on stability is analyzed by this analysis method. Finally, the validity and accuracy of the theoretical analysis are verified by time-domain simulation.

Bo Zhou

Papers

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

C-isolated Ag–C–Co sandwich sphere-nanostructures and their high activity catalysis induced by surface plasmon resonance

Novel-Phase Structural High-Efficiency Anode Catalyst for Methanol Fuel Cells: α-(NiCu)3Pd Nanoalloy

Power system transient security assessment based on multi-channel time series data mining

Small-Signal Stability of a “Source-Network-Train-Storage” System for Electric Railways based on Impedance Sensitivity