Fabricating Black-Phosphorus/Iron-Tetraphosphide Heterostructure via a Solid-Phase Solution-Precipitation Method for High-Performance Nitrogen Reduction.

Although constructing heterostructures is considered as one of the most successful strategies to improve the activity of a catalyst, the heterostructures usually suffer from the cumbersome preparation treatments and low-yield. Inspired by a solid-phase solution-precipitation (SPSP) process, an approach for interface intensive heterostructures with high yield is developed. Herein, a black-phosphorus/iron-tetraphosphide (BP/FeP4 ) heterostructure is prepared mechanochemically with high transient pressure by the solid-phase ball milling approach. The BP/FeP4 heterostructure delivers excellent catalytic performance in the nitrogen reduction reaction (NRR) as exemplified by an NH3 yield of 77.6 µg h-1 mg cat . - 1 \[{\rm{mg}}_{{\rm{cat}}{\rm{.}}}^{{\bm{ - }}1}\] and Faradic efficiency of 62.9% (-0.2 V), which are superior to that of most NRR catalysts recently reported. Experimental investigation and density-functional theory calculation indicate the importance of excess phosphorus in the heterostructures on the NRR activity, which assists the Fe atom to activate N2 via adsorbing the H atom. The results demonstrate the great potential of this new type of heterostructures prepared by the SPSP approach. Benefiting from the simple preparation process and low cost, the heterostructures offer a new insight into the development of highly efficient catalysts.

Carbon Nitride with Rationally Designed π-Conjugated Structure for Bright Blue-Violet Light-Emitting Diodes.

Carbon nitride consisting of the broken π-conjugated structure (bc-CN) is designed as the emitting layer in a blue-violet light emitting diode (LED). The bc-CN is prepared by a metal-oxide (MgO) template-assisted method, in which the low reaction temperature and nano MgO jointly control the degree of polymerization to form cyano groups and broken π-conjugation in the bc-CN nanosheets (bc-CN NS) which emit intense blue-violet photoluminescence at 412 nm. The broken π-conjugated heptazine-ring structure in the bc-CN NS mitigates non-radiation energy loss and promotes the d*-LP transition. As a result, a high quantum efficiency of 73.1% is achieved. The excellent dispersing ability of the bc-CN NS enables solution-based fabrication of the light emitting diode (LED). The LED exhibits intense electroluminescence of 236 cd m-2 at 412 nm with an external quantum efficiency of 0.46%. The broken π-conjugation modulates the optical properties of the polymerized carbon nitride semiconductor giving rise to intense blue-violet electroluminescence, which is very desirable for printable and wide-color-gamut display devices.

Long-Term Antifogging Coating Based on Black Phosphorus Hybrid Super-Hydrophilic Polymer Hetero-Network.

The antifogging coating based on super-hydrophilic polymer is regarded as the most promising strategy to avoid fogging but suffers from short-term effectiveness due to antifogging failure induced by water invasion. In this study, a black phosphorus nanosheets (BPs) hybrid polymer hetero-network coating (PUA/PAHS/BPs HN) was prepared by UV curing for the first time to achieve long-term antifogging performance. The polymer hetero-network (HN) structure was composed of two novel cross-linked acrylic resin and polyurethane acrylate. Different from physical blending, a covalent P-C bond between BPs and polymer is generated by UV initiated free radical reaction, resulting in BPs firmly embedded in the polymer HN structure. The BPs enriched on the coating surface by UV regulating migration prevent permeation of water towards the inside of the coating through its own good water-based lubricity and water absorption capacity. Compared with the nonhybrid polymer HN, PUA/PAHS/BPs HN not only has higher hardness and better friction resistance properties, but also exhibits superior water resistance and longer antifogging duration. Since water invasion was greatly reduced by BPs, the PUA/PAHS/BPs HN coating maintained antifogging duration for 60 min under a 60 °C water vapor test and still maintained long-term antifogging performance after being immersed in water for 5 days.

Silicon monophosphides with controlled size and crystallinity for enhanced lithium anodic performance.

New electrode materials are crucial to high-performance lithium-ion batteries (LIBs). Silicon monophosphides (SiPs), composed of silicon and phosphorus, have a very high theoretical capacity (3060 mA h g-1), which is more than 8 times that of graphite (372 mA h g-1). The two-dimensional structure of SiPs also benefits ion transportation and diffusion. In this work, the chemical vapor transport (CVT) method is employed to synthesize SiPs for LIB anodes, and the lithium storage capacity co-affected by size and crystallinity is investigated using controllably synthesized thin belts and bulk crystals. The SiPs prepared by the high-temperature iodine-assisted CVT method have a belt-like morphology about 72 nm thick. After 200 cycles, the stable capacity is about 615 mA h g-1 at 100 mA g-1, and a reversible capacity of ∼320 mA h g-1 is achieved at a high current density of 5.0 A g-1. In contrast, the micrometer-thick bulk SiP crystals cannot provide efficient lithium ion extraction. Moreover, the smaller and thinner SiPs obtained at a lower temperature show abnormally high mass transport resistance and low lithium ion diffusivity. These results demonstrate that SiPs are promising LIB anode materials, and the size and crystallinity are closely related to the anodic performance. This new knowledge is valuable for the development of high-performance LIBs.

From Octahedron Crystals to 2D Silicon Nanosheets: Facet-Selective Cleavage and Biophotonic Applications.

2D silicon nanosheets (SiNSs) are promising materials for biomedicine but facile synthesis of SiNSs remains a challenge. Herein, by means of a sulfur-iodine co-assisted chemical vapor transport method, octahedron silicon (oct-Si) crystals with fully exposed {111} planes are prepared as precursors for efficient synthesis of SiNSs by facet-selective exfoliation. The 13 nm thick SiNSs have good biocompatibility and the sharp Raman scattering signal facilitates intracellular Raman imaging upon exposure to a near-infrared (NIR) laser. Furthermore, the SiNSs have excellent NIR photothermal characteristics such as a large extinction coefficient of 11.3 L g-1 cm-1 and high photothermal conversion efficiency of 21.4% at 1064 nm. In vitro experiments demonstrate superior NIR-II photothermal therapeutic effects in killing cancer cells. Comparing to conventional methods, the novel facet-selective cleavage strategy is more controllable and environmentally friendly boding well for the fabrication of non-van der Waals 2D materials. The multimodal photonic behavior also suggests large potential of the SiNSs pertaining to integrated multi-NIR biophotonic techniques using single nanomaterials.

Rapid and scalable production of high-quality phosphorene by plasma-liquid technology.

Scalable synthesis of few-layered phosphorene typically relies on liquid ultrasonic/shear exfoliation but this technique suffers from drawbacks such as the long processing time, small sheet size, and poor quality. Herein, a simple and efficient plasma-liquid technique for rapid (∼5 minutes) and scalable production of few-layered high-quality phosphorene has been described. The plasma-exfoliated phosphorene has a tunable thickness less than 10 nanometers and a large size over a micrometer, enabling the fabrication of a macroscopic photodetection device with good photo-response. This plasma-exfoliation method has large potential in the development of phosphorene-related technologies as well as mass production of two-dimensional materials.

Facile mass production of self-supported two-dimensional transition metal oxides for catalytic applications.

We report a novel metal-corrosion route beyond traditional top-down or bottom-up strategies for the mass production of 2D TMOs with a self-supported structure. The self-supported 2D Co3O4, a typical TMO, exhibits excellent electrocatalytic activity and stability in the oxygen evolution reaction surpassing those of commercial precious metal RuO2 catalysts at high currents.

Black Phosphorus/Platinum Heterostructure: A Highly Efficient Photocatalyst for Solar-Driven Chemical Reactions.

A 2D black phosphorus/platinum heterostructure (Pt/BP) is developed as a highly efficient photocatalyst for solar-driven chemical reactions. The heterostructure, synthesized by depositing BP nanosheets with ultrasmall (≈1.1 nm) Pt nanoparticles, shows strong Pt-P interactions and excellent stability. The Pt/BP heterostructure exhibits obvious P-type semiconducting characteristics and efficient absorption of solar energy extending into the infrared region. Furthermore, during light illumination, accelerated charge separation is observed from Pt/BP as manifested by the ultrafast electron migration (0.11 ps) detected by a femtosecond pump-probe microscopic optical system as well as efficient electron accumulation on Pt revealed by in situ X-ray photoelectron spectroscopy. These unique properties result in remarkable performance of Pt/BP in typical hydrogenation and oxidation reactions under simulated solar light illumination, and its efficiency is much higher than that of other common Pt catalysts and even much superior to that of conventional thermal catalysis. The 2D Pt/BP heterostructure has enormous potential in photochemical reactions involving solar light and the results of this study provide insights into the design of next-generation high-efficiency photocatalysts.

In situ growth of all-inorganic perovskite nanocrystals on black phosphorus nanosheets.

This communication describes a novel low-dimensional nanohybrid structure consisting of all-inorganic perovskite nanocrystals (NCs) growing in situ on two-dimensional (2D) black phosphorus (BP) nanosheets. Such a nanohybrid structure promises synergetic properties by combining the respective strengths of perovskite materials and BP, which opens new opportunities for next-generation optoelectronic devices.

Characteristics of microscopic proton current flow distributions in fresh and aged Nafion membranes.

Proton conductance in fresh and aged Nafion ionomer membranes has been studied using current sensing atomic force microscopy which measures the proton current flow from a nanometer-sized tip in contact with the membrane surface to an electrode attached to the other side of the membrane. By scanning the tip across the membrane, the measured conductance maps out the local proton conductance variations, revealing the distributions of ionic domains on the membrane surface. For fresh Nafion membranes, the local proton conductance always displays a single-peaked distribution, while, for membranes after being aged for about three years in an ambient environment, the local proton conductance shows a distribution with two peaks, one at high current corresponding to the variation of contact and the conductive path of proton current and the other at near zero current which corresponds to the appearance of large nonconductive domains on the membranes. A detailed analysis reveals that the aging causes significant changes in the ionic domains or channels exposed on the membranes' surfaces.

Conductance mapping of proton exchange membranes by current sensing atomic force microscopy.

We show that proton conductance variation in Nafion membranes can be mapped using current sensing atomic force microscopy (CSAFM) to reveal and to characterize the heterogeneity in proton transport properties of the membranes. The distribution obtained by using a conventional CSAFM probe tip coated with a catalyst layer on a fresh Nafion membrane under a humid condition always displays a Gaussian-like shape. Such a feature can be explained in terms of the size of the contact area between a CSAFM tip and the membrane in comparison to the size of the tip apex. The conductance of individual proton channels and the density of the channels can be derived from the distribution. The averaged conductance and the density of proton channels derived are found to be consistent with that obtained in a recent simulation work based on the small-angle X-ray scattering (SAXS) data.