We developed a hydrogen arc discharge exfoliation method for the synthesis of graphene sheets (GSs) with excellent electrical conductivity and good thermal stability from graphite oxide (GO), in combination with solution-phase dispersion and centrifugation techniques. It was found that efficient exfoliation and considerable deoxygenation of GO, and defect elimination and healing of exfoliated graphite can be simultaneously achieved during the hydrogen arc discharge exfoliation process. The GSs obtained by hydrogen arc discharge exfoliation exhibit a high electrical conductivity of ϳ2 ؋ 10 3 S/cm and high thermal stability with oxidization resistance temperature of 601 °C, which are much better than those prepared by argon arc discharge exfoliation (ϳ2 ؋ 10 2 S/cm, 525 °C) and by conventional thermal exfoliation (ϳ80 S/cm, 507 °C) with the same starting GO. These results demonstrate that this hydrogen arc discharge exfoliation method is a good approach for the preparation of GSs with a good quality.

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a mean diameter of 1.6 nm were synthesized on a large scale by using oxygen-assisted floating catalyst chemical vapor deposition. The oxygen introduced can selectively etch metallic SWCNTs in situ, while the sulfur growth promoter functions in promoting the growth of SWCNTs with a large diameter. The electronic properties of the SWCNTs were characterized by laser Raman spectroscopy, absorption spectroscopy, and field effect transistor measurements. It was found that the content of s-SWCNTs in the samples was highly sensitive to the amount of oxygen introduced. Under optimum synthesis conditions, enriched s-SWCNTs can be obtained in milligram quantities per batch.

The freezing behavior of gold nanoclusters was studied by employing molecular dynamics simulations based on the semiempirical embedded-atom method. Investigations of the gold nanoclusters revealed that, just after freezing, ordered nanosurfaces with a fivefold symmetry were formed with interior atoms remaining in the disordered state. Further lowering of temperatures induced nanocrystallization of the interior atoms that proceeded from the surface towards the core region, finally leading to an icosahedral structure. These dynamic processes explain why the icosahedral cluster structure is dominantly formed in spite of its energetic metastability.

Developing cost-effective, high-performance nitrogen reduction reaction (NRR) electrocatalysts is required for the production of green and low-cost ammonia under ambient conditions. Here, a strategy is proposed to adjust the reaction preference of noble metals by tuning the size and local chemical environment of the active sites. This proof-of-concept model is realized by single ruthenium atoms distributed in a matrix of graphitic carbon nitride (Ru SAs/g-C 3 N 4 ). This model is compared, in terms of the NRR activity, to bulk Ru. The as-synthesized Ru SAs/g-C 3 N 4 exhibits excellent catalytic activity and selectivity with an NH 3 yield rate of 23.0 µg mg cat −1 h −1 and a Faradaic efficiency as high as 8.3% at a low overpotential (0.05 V vs the reversible hydrogen electrode), which is far better than that of the bulk Ru counterpart. Moreover, the Ru SAs/g-C 3 N 4 displays a high stability during five recycling tests and a 12 h potentiostatic test. Density functional theory calculations reveal that compared to bulk Ru surfaces, Ru SAs/g-C 3 N 4 has more facile reaction thermodynamics, and the enhanced NRR performance of Ru SAs/g-C 3 N 4 originates from a tuning of the d-electron energies from that of the bulk to a single-atom, causing an up-shift of the d-band center toward the Fermi level.can maximize metal utilization. Since SACs have unique catalytic sites, they usually exhibit a distinct catalytic selectivity as compared to their nanoclusters or nanoparticle counterparts. [2] For example, single atomic Pt immobilized in the surface of Ni nanocrystals shows a higher activity and chemoselectivity toward the hydrogenation of 3-nitrostyrene. [3] Isolated Co single-site catalysts anchored on a N-doped porous carbon nanobelt exhibits an excellent catalytic performance for oxidation of ethylbenzene with 98% conversion and 99% selectivity, whereas the Co nanoparticles are essentially inert. [4] Moreover, atomic Ni-anchored covalent triazine framework has a remarkable selectivity for the conversion of CO 2 to CO, with a Faradaic efficiency (FE) of > 90% over the range of −0.6 to −0.9 V versus the reversible hydrogen electrode (RHE). [5] In view of these reported works, it is evident that the size of metal particles is a key factor in determining their catalytic performance, and decreasing the size offers an intriguing opportunity to alter the activity and selectivity of these metal catalysts. SACs, as the limit of size reduction, hold great potential to achieve high activity and selectivity in catalytic reactions.Recently, the electrocatalytic N 2 reduction reaction (NRR) in aqueous electrolytes for synthesizing ammonia at ambient

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HIGHLIGHTS • Molybdenum aluminum boride single crystals as layered ternary borides were firstly applied for the electrochemical N 2 reduction reaction under ambient conditions and in alkaline media, displaying excellent electrocatalytic performances at the low overpotential. • Through the combination of the strong interaction of Al/B band and N orbitals and the special crystal structure exposing more active sites, synergistic effect of the elements was verified to achieve the enhancement of N 2 reduction reaction process and the limitation of hydrogen evolution reaction.

High-quality single-walled carbon nanotubes (SWNTs) with tunable diameters were synthesized by an improved H(2)/CH(4)-based floating catalyst method. Transmission electron microscopy observations and Raman results demonstrated the overall quality of the as-synthesized samples with finely tailored large diameters at 1.28, 1.62, 1.72, 1.91, and 2.13 nm, depending on the experimental conditions. In addition, Raman analysis revealed that the abundance of specific (n, m) SWNTs could be selectively enriched simultaneously along with the diameter modulation. It was found that the selective etching effects of high hydrogen flow stabilized the decomposition of ultralow CH(4) flow and considerably suppressed the deposition of amorphous carbon and small nanotubes, leading to very pure samples with high structural homogeneity suitable for further applications in practical electronic systems.

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