Photo/Electrocatalytic Hydrogen Peroxide Production by Manganese and Iron Porphyrin/Molybdenum Disulfide Nanoensembles.

The oxygen reduction reaction (ORR) 2e- pathway provides an alternative and green route for industrial hydrogen peroxide (H2 O2 ) production. Herein, the ORR photo/electrocatalytic activity in the alkaline electrolyte of manganese and iron porphyrin (MnP and FeP, respectively) electrostatically associated with modified 1T/2H MoS2 nanosheets is reported. The best performing catalyst, MnP/MoS2 , exhibits excellent electrocatalytic performance towards selective H2 O2 formation, with a low overpotential of 20 mV for the 2e- ORR pathway (Eons  = 680 mV vs RHE) and an H2 O2 yield up to 99%. Upon visible light irradiation, MnP/MoS2 catalyst shows significant activity enhancement along with good stability. Electrochemical impedance spectroscopy assays suggest a reduced charge transfer resistance value at the interface with the electrolyte, indicating an efficient intra-ensemble transfer process of the photo-excited electrons through the formation of a type II heterojunction or Schottky contact, and therefore justifies the boosted electrochemical activities in the presence of light. Overall, this work is expected to inspire the design of novel advanced photo/electrocatalysts, paving the way for sustainable industrial H2 O2 production.

Large-Scale 1T'-Phase Tungsten Disulfide Atomic Layers Grown by Gas-Source Chemical Vapor Deposition.

The control of crystal polymorphism and exploration of metastable, two-dimensional, 1T'-phase, transition-metal dichalcogenides (TMDs) have received considerable research attention. 1T'-phase TMDs are expected to offer various opportunities for the study of basic condensed matter physics and for its use in important applications, such as devices with topological states for quantum computing, low-resistance contact for semiconducting TMDs, energy storage devices, and as hydrogen evolution catalysts. However, due to the high energy difference and phase change barrier between 1T' and the more stable 2H-phase, there are few methods that can be used to obtain monolayer 1T'-phase TMDs. Here, we report on the chemical vapor deposition (CVD) growth of 1T'-phase WS2 atomic layers from gaseous precursors, i.e., H2S and WF6, with alkali metal assistance. The gaseous nature of the precursors, reducing properties of H2S, and presence of Na+, which acts as a countercation, provided an optimal environment for the growth of 1T'-phase WS2, resulting in the formation of high-quality submillimeter-sized crystals. The crystal structure was characterized by atomic-resolution scanning transmission electron microscopy, and the zigzag chain structure of W atoms, which is characteristic of the 1T' structure, was clearly observed. Furthermore, the grown 1T'-phase WS2 showed superconductivity with the transition temperature in the 2.8-3.4 K range and large upper critical field anisotropy. Thus, alkali metal assisted gas-source CVD growth is useful for realizing large-scale, high-quality, phase-engineered TMD atomic layers via a bottom-up synthesis.

Fabricating Dual-Atom Iron Catalysts for Efficient Oxygen Evolution Reaction: A Heteroatom Modulator Approach.

Understanding the thermal aggregation behavior of metal atoms is important for the synthesis of supported metal clusters. Here, derived from a metal-organic framework encapsulating a trinuclear FeIII 2 FeII complex (denoted as Fe3 ) within the channels, a well-defined nitrogen-doped carbon layer is fabricated as an ideal support for stabilizing the generated iron nanoclusters. Atomic replacement of FeII by other metal(II) ions (e.g., ZnII /CoII ) via synthesizing isostructural trinuclear-complex precursors (Fe2 Zn/Fe2 Co), namely the "heteroatom modulator approach", is inhibiting the aggregation of Fe atoms toward nanoclusters with formation of a stable iron dimer in an optimal metal-nitrogen moiety, clearly identified by direct transmission electron microscopy and X-ray absorption fine structure analysis. The supported iron dimer, serving as cooperative metal-metal site, acts as efficient oxygen evolution catalyst. Our findings offer an atomic insight to guide the future design of ultrasmall metal clusters bearing outstanding catalytic capabilities.

Nickel clusters embedded in carbon nanotubes as high performance magnets.

Ensembles of fcc nickel nanowires have been synthesized with defined mean sizes in the interior of single-wall carbon nanotubes. The method allows the intrinsic nature of single-domain magnets to emerge with large coercivity as their size becomes as small as the exchange length of nickel. By means of X-ray magnetic circular dichroism we probe electronic interactions at nickel-carbon interfaces where nickel exhibit no hysteresis and size-dependent spin magnetic moment. A manifestation of the interacting two subsystems on a bulk scale is traced in the nanotube's magnetoresistance as explained within the framework of weak localization.

Characterization of graphene grown on bulk and thin film nickel.

We report on graphene films grown by atmospheric pressure chemical vapor deposition on bulk and thin film nickel. Carbon precipitation on the polycrystalline grains is controlled by the methane concentration and substrate cooling rate. It is found that graphene grows over multiple grains, with edges terminating along the grain boundaries and with dimensions directly correlated to the size of the underlying grains. This greatly restricts the resulting graphene size (<10 µm) in the thin film growth, whereas monolayer graphene with linear dimensions of hundreds of micrometers takes up the great majority of the surface overlayers on the bulk nickel (>50%). In addition, the number of layers can be better controlled in the bulk growth. Characterizations of the graphene sheets using transmission electron microscopy, Raman spectroscopy, and transport measurements in the field-effect configuration are also discussed.

Iron and ruthenium nanoparticles in carbon prepared by thermolysis of buckymetallocenes.

Thermolysis of fullerene iron and ruthenium complexes (buckymetallocene M(C(60)R(5))Cp (M = Fe; R = Ph (1) and Me (2), M = Ru; R = Ph (3), Me (4)) under a nitrogen atmosphere produced metal nanoparticles dispersed in carbon materials. The thermal degradation processes of the buckymetallocenes were studied by TG-DTA, TEM with a heating sample stage, and VT-XRD. Variation of the thermolysis temperature led to a change in the size of the nanoparticles and the morphology of the carbon materials. Thermolysis of buckyferrocene at 700 degrees C gave highly dispersed iron nanoparticles (average diameter of 7.4 nm). After thermal treatment at 900 degrees C, graphite structures such as carbon nanocapsules and carbon nanotubes formed because of the catalytic activity of the iron nanoparticles. Ruthenium nanoparticles prepared from buckyruthenocene were much smaller than the iron counterparts, and did not catalyze the formation of graphite structures. When buckyruthenocene absorbed on silica gel was heated at 500 degrees C under a hydrogen atmosphere, the resulting ruthenium nanoparticles showed high activity in catalytic hydrogenation.