Future generations require more efficient and localized processes for energy conversion and chemical synthesis. The continuous on-site production of hydrogen peroxide would provide an attractive alternative to the present state-of-the-art, which is based on the complex anthraquinone process. The electrochemical reduction of oxygen to hydrogen peroxide is a particularly promising means of achieving this aim. However, it would require active, selective and stable materials to catalyse the reaction. Although progress has been made in this respect, further improvements through the development of new electrocatalysts are needed. Using density functional theory calculations, we identify Pt-Hg as a promising candidate. Electrochemical measurements on Pt-Hg nanoparticles show more than an order of magnitude improvement in mass activity, that is, A g(-1) precious metal, for H2O2 production, over the best performing catalysts in the literature.

The direct electrochemical synthesis of hydrogen peroxide is a promising alternative to currently used batch synthesis methods. Its industrial viability is dependent on the effective catalysis of the reduction of oxygen at the cathode. Herein, we study the factors controlling activity and selectivity for H2O2 production on metal surfaces. Using this approach, we discover two new catalysts for the reaction, Ag–Hg and Pd–Hg, with unique electrocatalytic properties both of which exhibit performance that far exceeds the current state-of-the art.

Low-temperature fuel cells are limited by the oxygen reduction reaction, and their widespread implementation in automotive vehicles is hindered by the cost of platinum, currently the best-known catalyst for reducing oxygen in terms of both activity and stability. One solution is to decrease the amount of platinum required, for example by alloying, but without detrimentally affecting its properties. The alloy PtxY is known to be active and stable, but its synthesis in nanoparticulate form has proved challenging, which limits its further study. Herein we demonstrate the synthesis, characterization and catalyst testing of model PtxY nanoparticles prepared through the gas-aggregation technique. The catalysts reported here are highly active, with a mass activity of up to 3.05 A mgPt(-1) at 0.9 V versus a reversible hydrogen electrode. Using a variety of characterization techniques, we show that the enhanced activity of PtxY over elemental platinum results exclusively from a compressive strain exerted on the platinum surface atoms by the alloy core.

Well-defined mass-selected Ru and RuO2 nanoparticles exhibit an order of magnitude improvement in the oxygen evolution activity, relative to the state-of-the-art, with a maximum at around 3–5 nm.

Toward the large-area deposition of MoS 2 layers, we employ metal−organic precursors of Mo and S for a facile and reproducible van der Waals epitaxy on c-plane sapphire. Exposing c-sapphire substrates to alkali metal halide salts such as KI or NaCl together with the Mo precursor prior to the start of the growth process results in increasing the lateral dimensions of single crystalline domains by more than 2 orders of magnitude. The MoS 2 grown this way exhibits high crystallinity and optoelectronic quality comparable to singlecrystal MoS 2 produced by conventional chemical vapor deposition methods. The presence of alkali metal halides suppresses the nucleation and enhances enlargement of domains while resulting in chemically pure MoS 2 after transfer. Field-effect measurements in polymer electrolyte-gated devices result in promising electron mobility values close to 100 cm 2 V −1 s −1 at cryogenic temperatures. KEYWORDS: Chemical vapor deposition, two-dimensional transition metal dichalcogenides, nucleation and growth, microstructure engineering, FET devices T he chemical vapor deposition of two-dimensional materials is a highly promising method to produce atomically thin layers at a large scale for harnessing their attractive properties. Monolayer MoS 2 is a model 2D semiconductor that can be used to realize field-effect transistors with high current on/off ratios. 1 It is a naturally occurring material with a good chemical stability that exhibits a wide range of attractive properties such as a spin−orbit couplinginduced band splitting, 2,3 a mechanically tunable bandgap, 4−8 and a low temperature superconductivity. 9−13 Toward the large-scale synthesis of MoS 2 thin films, a conventional chemical vapor deposition method of producing MoS 2 monolayers typically involves low vapor pressure solid powder precursors such as MoO 3 and sulfur. It has been investigated for centimeter-scale deposition of polycrystalline monolayer MoS 2 with grain sizes of nanometer to micrometer and with controllable coverage. 14,15 However, low vapor pressures of the solid precursors require them to be loaded inside a heated zone of the reactor chamber leading to a limited control over the vapor phase composition and deposition rate. Thus, this synthesis approach heavily undermines the ability to control the nucleation density, thickness, and coverage.Here, we aim to address this issue by employing well-known metal−organic precursors of molybdenum, Mo(CO) 6 , which is a high vapor pressure solid, and of sulfur, H 2 S in gas phase. 16−19 This metal-organic chemical vapor deposition (MOCVD) approach allows reliably setting the concentration of precursor gases within the gaseous mixture that is transported to the substrate by controlling the evaporation rates of the solid precursor and mass flow rates. An extensive vapor phase thermodynamics study performed by Kumar et al. 19 has shown that growth temperatures above 850°C at atmospheric pressure lead to layer-by-layer growth of MoS 2 without extraneous deposition of carbon ...

Employing rationally designed model systems with precise atom-by-atom particle size control, we demonstrate by means of combining noninvasive in situ indirect nanoplasmonic sensing and ex situ scanning transmission electron microscopy that monomodal size-selected platinum cluster catalysts on different supports exhibit remarkable intrinsic sintering resistance even under reaction conditions. The observed stability is related to suppression of Ostwald ripening by elimination of its main driving force via size-selection. This study thus constitutes a general blueprint for the rational design of sintering resistant catalyst systems and for efficient experimental strategies to determine sintering mechanisms. Moreover, this is the first systematic experimental investigation of sintering processes in nanoparticle systems with an initially perfectly monomodal size distribution under ambient conditions.

No abstract

A long-standing problem in the application of solidstate nanopores is the lack of the precise control over the geometry of artificially formed pores compared to the well-defined geometry in their biological counterpart, that is, protein nanopores. To date, experimentally investigated solid-state nanopores have been shown to adopt an approximately circular shape. In this Letter, we investigate the geometrical effect of the nanopore shape on ionic blockage induced by DNA translocation using triangular h-BN nanopores and approximately circular molybdenum disulfide (MoS 2 ) nanopores. We observe a striking geometrydependent ion scattering effect, which is further corroborated by a modified ionic blockage model. The well-acknowledged ionic blockage model is derived from uniform ion permeability through the 2D nanopore plane and hemisphere like access region in the nanopore vicinity. On the basis of our experimental results, we propose a modified ionic blockage model, which is highly related to the ionic profile caused by geometrical variations. Our findings shed light on the rational design of 2D nanopores and should be applicable to arbitrary nanopore shapes.