Chemical vapor deposition of uniform bilayer PtS2 flakes for electrocatalytic hydrogen evolution.

Two-dimensional (2D) 1T-PtS2 has been drawing considerable attention due to its highly layer-dependent bandgap, high carrier mobility, superior air stability, etc. However, the growth of 2D PtS2 with uniform thickness and controllable shape remains an immense challenge. Herein, the uniform bilayer (2L) 1T-PtS2 single crystals are controllably grown on mica using chemical vapor deposition for the first time. The variable morphology from triangular to hexagonal can be obtained by regulating growth temperature. Significantly, the 2L PtS2 flakes show a good electrocatalytic hydrogen evolution reaction (HER) property with an overpotential of 184 mV at 10 mA cm-2, Tafel slope of 81 mV dec-1, exchange current density of 43 µA cm-2, and outstanding stability. This work manifests that 2D PtS2 is a promising candidate for HER applications.

Magnetic Skyrmions with Unconventional Helicity Polarization in a Van Der Waals Ferromagnet.

Skyrmion helicity, which defines the spin swirling direction, is a fundamental parameter that may be utilized to encode data bits in future memory devices. Generally, in centrosymmetric ferromagnets, dipole skyrmions with helicity of -π/2 and π/2 are degenerate in energy, leading to equal populations of both helicities. On the other hand, in chiral materials where the Dzyaloshinskii-Moriya interaction (DMI) prevails and the dipolar interaction is negligible, only a preferred helicity is selected by the type of DMI. However, whether there is a rigid boundary between these two regimes remains an open question. Herein, the observation of dipole skyrmions with unconventional helicity polarization in a van der Waals ferromagnet, Fe5- δ GeTe2 , is reported. Combining magnetometry, Lorentz transmission electron microscopy, electrical transport measurements, and micromagnetic simulations, the short-range superstructures in Fe5- δ GeTe2 resulting in a localized DMI contribution, which breaks the degeneracy of the opposite helicities and leads to the helicity polarization, is demonstrated. Therefore, the helicity feature in Fe5- δ GeTe2 is controlled by both the dipolar interaction and DMI that the former leads to Bloch-type skyrmions with helicity of ±π/2 whereas the latter breaks the helicity degeneracy. This work provides new insights into the skyrmion topology in van der Waals materials.

Chiral Helimagnetism and One-Dimensional Magnetic Solitons in a Cr-Intercalated Transition Metal Dichalcogenide.

Chiral magnets endowed with topological spin textures are expected to have promising applications in next-generation magnetic memories. In contrast to the well-studied 2D or 3D magnetic skyrmions, the authors report the discovery of 1D nontrivial magnetic solitons in a transition metal dichalcogenide 2H-TaS2 via precise intercalation of Cr elements. In the synthetic Cr1/3 TaS2 (CTS) single crystal, the coupling of the strong spin-orbit interaction from TaS2 and the chiral arrangement of the magnetic Cr ions evoke a robust Dzyaloshinskii-Moriya interaction. A magnetic helix having a short spatial period of ≈25 nm is observed in CTS via Lorentz transmission electron microscopy. In a magnetic field perpendicular to the helical axis, the helical spin structure transforms into a chiral soliton lattice (CSL) with the spin structure evolution being consistent with the chiral sine-Gordon theory, which opens promising perspectives for the application of CSL to fast-speed nonvolatile magnetic memories. This work introduces a new paradigm to soliton physics and provides an effective strategy for seeking novel 2D magnets.

Gut Escherichia coli expressing Pb2+-adsorption protein reduces lead accumulation in grass carp, Ctenopharyngodon idellus.

Lead (Pb2+) is easy to accumulate in fish which become a major source of Pb2+ exposure to humans. In this study, a recombinant Escherichia coli strain expressing Pb2+-specific surface-binding protein anchored by the ice nucleation protein was introduced into grass carp (Ctenopharyngodon idellus) gut to investigate its protective effect against dietary Pb2+ exposure. Pb2+ mostly precipitated on the surface of the engineered strain through Pb2+-specific surface-binding protein, with a maximum adsorption efficiency of 73% and an adsorption capacity of 163 µmol/g dry cells. The Pb2+ concentration in engineered bacteria-fed grass carp was reduced significantly, and the residual level of Pb2+ in feces was increased by 76%, compared with the control group. Meantime, the engineered bacteria were able to mitigate the oxidative stress and histological alterations of intestines and dysbiosis of gut microbiota induced by Pb2+exposure. Thus, the engineered bacterium that can effectively reduce Pb2+ residue in grass carp might be a useful tool for decontamintion of lead in aquatic organisms.

Porous nanotube networks of SnO2/MoO3@Graphene as anodes for rechargeable lithium-ion batteries.

We successfully fabricated composite porous nanotube networks of SnO2/MoO3@Graphene through electrospinning and used it as lithium-ion battery anodes. When the ratio of SnO2 to MoO3 is 1:1, the composite of SnO2/MoO3 delivers a high capacity of 560 mAh g-1 at 1 A g-1 after 300 cycles. The excellent electrochemical performance was attributed to the unique 3D porous nanotube network structure which could provide more transmission channels for Li+ ions and electrons, and provide more electrochemical reaction sites. The hybrid nanostructure can also weaken local stress and relieve volume expansion which contributes to the attractive cycling stability. Moreover, we added a small amount of graphene in the composite to improve the electrical conductivity, and the SnO2/MoO3@Graphene composite showed favorable electrochemical performance (798 mAh g-1 at 1 A g-1 after 300 cycles). Finally, electrospinning technology is a simple and efficient synthesis strategy, which can promote the preparation of different types of metal oxide composite materials and has good application prospects.

Electric bicycle cost calculation models and analysis based on the social perspective in China.

Electric bicycles (EBs) are increasingly popular around the world. In April 2014, EB ownership in China reached 181 million. While some aspects of the impact of EBs have been studied, most of the literature analyzing the cost of EBs has been conducted from the buyer's point of view and the perspective of social cost has not been covered, which is therefore the focus of this paper. From the consumer's point of view, only the costs paid from purchase until retirement are included in the cost of EBs, i.e., the EB acquisition cost, battery replacement cost, charging cost, and repair and maintenance cost are included. Considered from the perspective of the social cost (including impact on the environment), costs that are not paid directly by consumers should also be included in the cost of EBs, i.e., the lead-acid battery scrap processing cost, the cost of pollution caused by wastewater, and the traffic-related costs. Data are obtained from secondary sources and surveys, and calculations demonstrate that in the life cycle of an EB, the consumer cost is 6386.2 CNY, the social cost is 10,771.2 CNY, and the ratio of consumer to social cost is 1:1.69. By comparison, the ratio for motor vehicles is 1:1.06, so that the share of the life cycle cost of EBs that is not borne by the consumer is much higher than that for motor vehicles, which needs to be addressed.