Phase Engineering of Metastable Transition Metal Dichalcogenides via Ionic Liquid Assisted Synthesis.

Metallic group VIB transition metal dichalcogenides (1T-TMDs) have attracted great interest because of their outstanding performance in electrocatalysis, supercapacitors, batteries, and so on, whereas the strict fabrication conditions and thermodynamical metastability of 1T-TMDs greatly restrict their extensive applications. Therefore, it is significant to obtain stable and high-concentration 1T-TMDs in a simple and large-scale strategy. Herein, we report a facile and large-scale synthesis of high-concentration 1T-TMDs via an ionic liquid (IL) assisted hydrothermal strategy, including 1T-MoS2 (the obtained MoS2 sample was denoted as MoS2-IL), 1T-WS2, 1T-MoSe2, and 1T-WSe2. More importantly, we found that IL can adsorb on the surface of 1T-MoS2, where the steric hindrance, π-π stacking, and hydrogen bonds of ionic liquid collectively induce the formation of the 1T-MoS2. In addition, DFT calculation reveals that electrons are transferred from [BMIM]SCN (1-butyl-3-methylimidazolium thiocyanate) to 1T-MoS2 layers by hydrogen bonds, which enhances the stability of 1T-MoS2, so the MoS2-IL performs with high stability for 180 days at room temperature without obvious change. Furthermore, the MoS2-IL exhibits excellent HER performance with an overpotential of 196 mV at 10 mA cm-2 in acid conditions.

Spectroscopic observation and structure-insensitivity of hydroxyls on gold.

The O-H stretching vibration of surface hydroxyls remained at 3691 cm-1 for gold structures ranging in size from clusters to nanoparticles, to non-flat bulk surfaces. In contrast, this vibration was not observed on flat gold surfaces. Therefore, this vibration can serve as an indicator of the roughness of the gold surface and associated functional properties, such as catalytic activity.

Controllable Synthesis of a Loofah-Like Cobalt-Nickel Selenide Network as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

The rational design and construction of noble metal-free electrocatalysts featuring high efficiency and low cost are important for the hydrogen evolution reaction (HER). A significant development in the synthesis of a loofah-like Co0.6Ni0.4Se2 architecture (expressed as Co0.6Ni0.4Se2-LN) electrocatalyst on carbon cloth through a three-step method is reported. Both the ionic liquid 1-dodecyl-3-methylimidazolium acetate (IL, [C12MIm]Ac) and the molar ratio of Co to Ni play a pivotal role in the synthesis of Co0.6Ni0.4Se2-LN with 3D hierarchical architecture. Co0.6Ni0.4Se2-LN exposes abundant active sites and provides hierarchical and stable transfer channels for both electrolyte ions and electrons, which results in outstanding HER performance. Impressively, Co0.6Ni0.4Se2-LN shows a low overpotential of 163 mV at 10 mA cm-2, a small Tafel slope of 40 mV dec-1, and superior stability to continuously catalyze the generation of H2 for 40 h. This study offers a new perspective to the synthesis of high-efficiency inexpensive electrocatalysts for HER and also presents a good example for investigating the potential application of ILs in the synthesis of functional materials.

Catalytic Platinum Nanoparticles Decorated with Subnanometer Molybdenum Clusters for Biomass Processing.

The development of improved technologies for biomass processing into transportation fuels and industrial chemicals is hindered due to a lack of efficient catalysts for selective oxygen removal. Here we report that platinum nanoparticles decorated with subnanometer molybdenum clusters can efficiently catalyze hydrodeoxygenation of acetic acid, which serves as a model biomass compound. In contrast with monometallic Mo catalysts that are inactive and monometallic Pt catalysts that have low activities and selectivities, bimetallic Pt-Mo catalysts exhibit synergistic effects with high activities and selectivities. The maximum activity occurs at a Pt to Mo molar ratio of three. Although Mo atoms themselves are catalytically inactive, they serve as preferential binding anchors for oxygen atoms while a catalytic transformation proceeds on neighboring surface Pt atoms. Beyond biomass processing, Pt-Mo nanoparticles are promising catalysts for a wide variety of reactions that require a transformation of molecules with an oxygen atom and, more broadly, in other fields of science and technology that require tuning of surface-oxygen interactions.

Design and Synthesis of a Reduced Graphene Oxide/Patronite Composite with Enhanced Lithium-Ion Storage Performance.

The construction of graphene-based composites is a novel electrode material design strategy and has become a promising field in new energy material research. However, the rational design principle is still poorly understood, and the synthetic technology urgently needs to be expanded. Here, a novel strategy for the synthesis of a reduced graphene oxide (rGO)/VS4 nanoparticle (NP) composite is reported using an ionic liquid (IL)-assisted hydrothermal method. The synergistic effects of graphene and IL, which include the π-cation/anion interactions of graphene, the capping agent effect of IL, and their π-π stacking interaction, are responsible for the synthesis of the composite, achieving delicate tailoring of VS4 NPs as well as their homogeneous dispersal on the surface of rGO nanosheets. The superior nanostructure of the composite results in enhanced lithium-ion storage performance, such as improved cyclic stability (1009 mA h g-1 at 0.1 A g-1 after 150 cycles and 788 mA h g-1 after 240 cycles even at 1 A g-1) and rate capability (1540 and 621 mA h g-1 at 0.1 and 2 A g-1, respectively). This strategy provides an effective new approach for designing graphene composites and is expected to be applicable in the design of other rGO/transition-metal sulfide composites for energy storage.

Catalysis. Identification of molybdenum oxide nanostructures on zeolites for natural gas conversion.

Direct methane conversion into aromatic hydrocarbons over catalysts with molybdenum (Mo) nanostructures supported on shape-selective zeolites is a promising technology for natural gas liquefaction. We determined the identity and anchoring sites of the initial Mo structures in such catalysts as isolated oxide species with a single Mo atom on aluminum sites in the zeolite framework and on silicon sites on the zeolite external surface. During the reaction, the initial isolated Mo oxide species agglomerate and convert into carbided Mo nanoparticles. This process is reversible, and the initial isolated Mo oxide species can be restored by a treatment with gas-phase oxygen. Furthermore, the distribution of the Mo nanostructures can be controlled and catalytic performance can be fully restored, even enhanced, by adjusting the oxygen treatment.