Explore the vast range of titles available.

Developing efficient and stable electrocatalysts is crucial for the electrochemical production of pure and clean hydrogen. For practical applications, an economical and facile method of producing catalysts for the hydrogen evolution reaction (HER) is essential. Here, we report ruthenium (Ru) nanoparticles uniformly deposited on multi-walled carbon nanotubes (MWCNTs) as an efficient HER catalyst. The catalyst exhibits the small overpotentials of 13 and 17 mV at a current density of 10 mA cm –2 in 0.5 M aq. H 2 SO 4 and 1.0 M aq. KOH, respectively, surpassing the commercial Pt/C (16 mV and 33 mV). Moreover, the catalyst has excellent stability in both media, showing almost “zeroloss” during cycling. In a real device, the catalyst produces 15.4% more hydrogen per power consumed, and shows a higher Faradaic efficiency (92.28%) than the benchmark Pt/C (85.97%). Density functional theory calculations suggest that Ru–C bonding is the most plausible active site for the HER. To efficiently produce pure and clean H 2 through electrochemical processes, an efficient and durable catalyst is essential. Here, authors report ruthenium nanoparticles anchored on multi-walled carbon nanotubes as an efficient catalyst for H 2 evolution in both acidic and alkaline media.

Ammonia, one of the most important synthetic feedstocks, is mainly produced by the Haber–Bosch process at 400–500 °C and above 100 bar. The process cannot be performed under ambient conditions for kinetic reasons. Here, we demonstrate that ammonia can be synthesized at 45 °C and 1 bar via a mechanochemical method using an iron-based catalyst. With this process the ammonia final concentration reached 82.5 vol%, which is higher than state-of-the-art ammonia synthesis under high temperature and pressure (25 vol%, 450 °C, 200 bar). The mechanochemically induced high defect density and violent impact on the iron catalyst were responsible for the mild synthesis conditions. The ammonia was synthesized under ambient conditions via a mechanochemical method, reaching a final concentration of 82.5 vol%.

Hydrogen adsorption/desorption behavior plays a key role in hydrogen evolution reaction (HER) catalysis. The HER reaction rate is a trade-off between hydrogen adsorption and desorption on the catalyst surface. Herein, we report the rational balancing of hydrogen adsorption/desorption by orbital modulation using introduced environmental electronegative carbon/nitrogen (C/N) atoms. Theoretical calculations reveal that the empty d orbitals of iridium (Ir) sites can be reduced by interactions between the environmental electronegative C/N and Ir atoms. This balances the hydrogen adsorption/desorption around the Ir sites, accelerating the related HER process. Remarkably, by anchoring a small amount of Ir nanoparticles (7.16 wt%) in nitrogenated carbon matrixes, the resulting catalyst exhibits significantly enhanced HER performance. This includs the smallest reported overpotential at 10 mA cm −2 (4.5 mV), the highest mass activity at 10 mV (1.12 A mg Ir −1 ) and turnover frequency at 25 mV (4.21 H 2 s −1 ) by far, outperforming Ir nanoparticles and commercial Pt/C. Hydrogen adsorption/desorption behavior plays a key role in hydrogen evolution reaction catalysis. Here, the authors demonstrate the rational balancing of hydrogen adsorption/desorption by orbital modulation for significantly enhanced hydrogen evolution performance.

Identification of active sites is one of the main obstacles to rational design of catalysts for diverse applications. Fundamental insight into the identification of the structure of active sites and structural contributions for catalytic performance are still lacking. Recently, X-ray absorption spectroscopy (XAS) and density functional theory (DFT) provide important tools to disclose the electronic, geometric and catalytic natures of active sites. Herein, we demonstrate the structural identification of Zn-N 2 active sites with both experimental/theoretical X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. Further DFT calculations reveal that the oxygen species activation on Zn-N 2 active sites is significantly enhanced, which can accelerate the reduction of oxygen with high selectivity, according well with the experimental results. This work highlights the identification and investigation of Zn-N 2 active sites, providing a regular principle to obtain deep insight into the nature of catalysts for various catalytic applications. Identification of active sites is one of the main obstacles to rational design of catalysts for scientific and industrial applications. Here, the authors demonstrate the synthesis and structural identification of Zn based active sites, as well as the related structural activation for oxygen species.

Hyperbranched macromolecules (HMs, also called hyperbranched polymers) are highly branched three-dimensional (3D) structures in which all bonds converge to a focal point or core, and which have a multiplicity of reactive chain-ends. This review summarizes major types of synthetic strategies exploited to produce HMs, including the step-growth polycondensation, the self-condensing vinyl polymerization and ring opening polymerization. Compared to linear analogues, the globular and dendritic architectures of HMs endow new characteristics, such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility. After discussing the general concepts, synthesis, and properties, various applications of HMs are also covered. HMs continue being materials for topical interest, and thus this review offers both concise summary for those new to the topic and for those with more experience in the field of HMs.

Planar two-dimensional (2D) layered materials such as graphene, metal-organic frameworks, and covalent-organic frameworks are attracting enormous interest in the scientific community because of their unique properties and potential applications. One common feature of these materials is that their building blocks (monomers) are flat and lie in planar 2D structures, with interlayer π–π stacking, parallel to the stacking direction. Due to layer-to-layer confinement, their segmental motion is very restricted, which affects their sorption/desorption kinetics when used as sorbent materials. Here, to minimize this confinement, a vertical 2D layered material was designed and synthesized, with a robust fused aromatic ladder (FAL) structure. Because of its unique structural nature, the vertical 2D layered FAL structure has excellent gas uptake performance under both low and high pressures, and also a high iodine (I 2 ) uptake capacity with unusually fast kinetics, the fastest among reported porous organic materials to date. Stacking of planar layers composed of flat building blocks in two dimensional materials results in restriction of segmental motion which affects their typical properties, such as sorption or desorption. Here, the authors minimize this confinement using a vertically-stacked fused aromatic ladder structure and demonstrate excellent gas uptake under low and high pressure.

Origami, known as paper folding has become a fascinating research topic recently. Origami-inspired materials often establish mechanical properties that are difficult to achieve in conventional materials. However, the materials based on origami tessellation at the molecular level have been significantly underexplored. Herein, we report a two-dimensional (2D) porphyrinic metal-organic framework (MOF), self-assembled from Zn nodes and flexible porphyrin linkers, displaying folding motions based on origami tessellation. A combined experimental and theoretical investigation demonstrated the origami mechanism of the 2D porphyrinic MOF, whereby the flexible linker acts as a pivoting point. The discovery of the 2D tessellation hidden in the 2D MOF unveils origami mechanics at the molecular level. This work introduces a 2D porphyrinic metal-organic framework based on DCS origami tessellation, displaying unique folding behavior inspired by origami mechanics. This breakthrough paves the way for MOFs toward mechanical metamaterials.

Developing efficient and cost‐effective electrocatalysts to replace expensive carbon‐supported platinum nanoparticles for the alkaline hydrogen evolution reaction remains an important challenge. Recently, an innovative catalyst, composed of ruthenium single atoms (Ru1) integrated with small Ru nanoclusters (RuNC), has attracted considerable attention from the scientific community. However, because of its complexity, this catalyst remains a topic of some debate. Here, a method is reported of precisely controlling the ratios of Ru1 to RuNC on a nitrogenated carbon (NC)‐based porous organic framework to produce Ru/NC catalysts, by using different amounts (0, 5, 10 wt.%) of reducing agent. The Ru/NC–10 catalyst, formed with 10 wt.% reducing agent, delivered the best performance under alkaline conditions, indicating that RuNC played a significant role in actual alkaline hydrogen evolution reaction (HER). An anion exchange membrane water electrolyzer (AEMWE) system using the Ru/NC–10 catalyst required a significantly lower operating voltage (1.72 V) than the commercial Pt/C catalyst (1.95 V) to achieve 500 mA cm−2. Moreover, the system can be operated at 100 mA cm−2 without notable performance decay for over 180 h. Theoretical calculations supported these experimental findings that Ru1 contributed to the water dissociation process, while RuNC is more actively associated with the hydrogen recombination process. High‐performance ruthenium on nitrogenated carbon (Ru/NC) catalysts are synthesized with precisely controlled ratios of Ru single atoms (Ru1) and nanoclusters (RuNC). Ru1 facilitated water dissociation, while RuNC enhanced hydrogen recombination. The Ru/NC–10 catalyst, formed with a 10% reducing agent, outperformed commercial Pt/C, demonstrating superior efficiency and durability in alkaline hydrogen evolution reaction (HER) and anion exchange membrane water electrolzyer (AEMWE) systems. A higher ratio of RuNC to Ru1 is crucial for improved water‐splitting performance.

Ordered two-dimensional covalent organic frameworks (COFs) have generally been synthesized using reversible reactions. It has been difficult to synthesize a similar degree of ordered COFs using irreversible reactions. Developing COFs with a fused aromatic ring system via an irreversible reaction is highly desirable but has remained a significant challenge. Here we demonstrate a COF that can be synthesized from organic building blocks via irreversible condensation (aromatization). The as-synthesized robust fused aromatic COF (F-COF) exhibits high crystallinity. Its lattice structure is characterized by scanning tunneling microscopy and X-ray diffraction pattern. Because of its fused aromatic ring system, the F-COF structure possesses high physiochemical stability, due to the absence of hydrolysable weak covalent bonds. Two-dimensional covalent organic frameworks (2D COFs) are commonly synthesised through dynamic covalent chemistry, as it allows for thermodynamic ‘error correction' which enhances crystallinity. Here a crystalline 2D COF with amine and hydroxyl functional groups within the pores is synthesised through kinetically-controlled reactions.

As a new filler, neohexene graphitic nanoplatelets (NeHGNs), is prepared firstly by using ball milling with solid graphite and liquid neohexene. The characteristics of NeHGNs are confirmed using a variety of analytic techniques. Due to the exceptional dispersion in organic solvents ( e.g. xylene) and the good affinity with low-density polyethylene (LDPE), the NeHGN/LDPE_X (NeHGNs content (X) = 0.5, 1, or 2) nanocomposites are made easily through a solution procedure. Thus, the NeHGNs play as a competent filler for LDPE due to its outstanding properties and a chemical affinity between neohexene-functional groups and LDPE. In result, the NeHGN/LDPE_X nanocomposites show significantly improved mechanical properties ( i.e., tensile strength and Young’s modulus) and thermal stability compared to the pure LDPE. Thus, considering excellent performances and competitive price, the NeHGNs are recognized as a new prospective reinforcing filler for a variety of polyolefins.