Two-dimensional Hybrid Materials Research Articles

Toughening two-dimensional hybrid materials by integrating carbon nanotubes

Graphene (Gr) has ultra-high intrinsic strength and elastic modulus, but it is fragile and has low fracture toughness. It is extremely difficult to evaluate the mechanical properties of two-dimensional (2D) materials because of brittleness. Contrary to expectation, a high fracture toughness of 2D hybrid materials with effective crack deflection is therefore established here by regularly integrating carbon nanotubes (CNTs). Our combined finite element theory and molecular dynamics simulations confirm that embedded CNTs divert and bridge the propagating crack and provide a different toughening effect for the different region of 2D hybrid material. "Toughening zone effect" explain the asymmetric edge elastic properties at the crack tip and edge swapping during crack propagation. The preparation of 2D hybrid materials with CNTs opens up a new idea for other 2D materials, and can be mechanically customized according to the application requirements of its flexible equipment.

Enhanced solar-driven hydrogen evolution over ultrathin g-C3N4/ReSe2 heterojunction-like nanosheets with surface selenium vacancies

The design of composite photocatalytic materials is essential for efficient photocatalytic hydrogen production. In the present work, we have successfully designed a simple synthetic process to ultrathin ReSe2 nanosheets using an ultrasound-assisted liquid-phase synthetic route through self-assembling ReSe2 onto g-C3N4 (shortened as g-C3N4/ReSe2 nanosheets) to improve photocatalytic performance. Based on density functional theory (DFT) estimation along with experimental characterization, it is found that the integrated heterojunction-like ultrathin g-C3N4/ReSe2 nanosheets possess more edge active sites, enhanced electron transfer efficiency and conductivities, which significantly accelerates the dissociation and migration of photogenerated electron-hole pairs. Meanwhile, selenium vacancies could be introduced into nanosheets via controlling the synthetic procedure with a reduced Se source that will favor to enhance the photocatalytic efficiency. The ultrathin g-C3N4/ReSe2 heterojunction with Se vacancies performed highly improved photocatalytic hydrogen production. In typical, the H2 production of the g-C3N4/ReSe2 nanosheets under visible light is 1055.50 μmol g−1 h−1, which is 21 times higher than that of bare g-C3N4, indicating that it overcomes the high charge complexation rate of g-C3N4. These results do not only provide insight into the application of two-dimensional ReSe2 nanosheets in photocatalysis, but also open up new avenues for the rational design of two-dimensional hybrid materials in solar energy conversion.

Topographic signatures and manipulations of Fe atoms, CO molecules and NaCl islands on superconducting Pb(111).

Topological superconductivity emerging in one- or two-dimensional hybrid materials is predicted as a key ingredient for quantum computing. However, not only the design of complex heterostructures is primordial for future applications but also the characterization of their electronic and structural properties at the atomic scale using the most advanced scanning probe microscopy techniques with functionalized tips. We report on the topographic signatures observed by scanning tunneling microscopy (STM) of carbon monoxide (CO) molecules, iron (Fe) atoms and sodium chloride (NaCl) islands deposited on superconducting Pb(111). For the CO adsorption a comparison with the Pb(110) substrate is demonstrated. We show a general propensity of these adsorbates to diffuse at low temperature under gentle scanning conditions. Our findings provide new insights into high-resolution probe microscopy imaging with terminated tips, decoupling atoms and molecules by NaCl islands or tip-induced lateral manipulation of iron atoms on top of the prototypical Pb(111) superconducting surface.

Synthesis and characterization of rhenium disulfide nanosheets decorated rGO as electrode towards hydrogen generation in different media

Herein, we synthesized the rhenium disulfide (ReS2) and ReS2/reduced graphene oxide (rGO) two-dimensional hybrid materials by a modified hydrothermal method. The composite showed a significant interaction between rGO and ReS2. The electrocatalytic activity of electrodes for the hydrogen evolution reaction (HER) was investigated in different pH media. The catalyst showed higher performance in acidic media due to faster HER kinetics and better coverage of the catalyst surface with H-adsorption. The ReS2/rGO electrode showed an excellent HER activity and showed a low onset overpotential of − 120 mV, a Tafel slope of 47 mV dec−1, and the current density of 10 mA cm−2 in overpotential of − 180 mV at acidic media. The high surface area and conductivity of rGO, the existence of edge sites and porosity in the catalyst, and the synergistic effect between ReS2 and rGO can support the excellent HER activity of ReS2/rGO electrode.

PtSe2/graphene hetero-multilayer: gate-tunable Schottky barrier height and contact type

Graphene-based two-dimensional hybrid materials are attracting significant attention because they can preserve novel characteristics of Dirac cone. Here, based on first-principles methods, we focus on the electronic characteristics of PtSe2/graphene hetero-multilayer. The negative binding energies indicate that the hybrid materials can be fabricated easily in practice. Also, the n-type Schottky contact is formed and its barrier height is robust to the number of graphene layer. Moreover, the gate-voltage can effectively induce the Schottky barrier transformation from n-type to p-type and contact type transformation from Schottky to Ohmic in the PtSe2/graphene hetero-multilayer. Thus, the work demonstrates that the graphene stacking configuration and gate-voltage will tune the electronic characteristics of PtSe2/graphene-based nanodevices.

Two-dimensional hybrid materials: MoS2-RGO nanocomposites enhanced the barrier properties of epoxy coating

By the way of hydrothermal reaction, the MoS2 nanoparticles were loaded on the surface of GO sheets uniformly. Then, the MoS2-RGO composites were modified with γ-(2,3-epoxypropoxy)propytrimethoxysilane (KH560), and followed by preparing the MoS2-RGO/epoxy composite coatings. The morphology and structure of MoS2-RGO were characterized though SEM, TEM, FT-IR and XPS. Besides, the corrosion resistance properties of the as-prepared MoS2-RGO/epoxy composite coatings were characterized by means of electrochemical impedance spectroscopy (EIS) and polarization curves analysis, and then the thermal stability and water permeability resistance of coatings were characterized. The results showed that the MoS2 could be loaded on the surface of GO uniformly when the ratio between MoS2 and GO is 1:1. The anti-corrosion property and permeability resistance of the MoS2-RGO/epoxy composites coating was enhanced significantly due to its excellent barrier property. Besides, the thermal property analysis exhibits that the lamellar structure of MoS2, GO and MoS2-RGO can effectively block the escape of the pyrolysis products, resulting in the maximum thermal weightlessness reduced.

Large-size and high performance visible-light photodetectors based on two-dimensional hybrid materials SnS/RGO.

We report a facile solvothermal method to synthesize two-dimensional hybrid materials consisting of layered SnS nanosheets and reduced graphene oxide (SnS/RGO). Large-size photodetectors with a channel length/width = 2 mm/7 mm are fabricated on Si/SiO2 substrates, showing an excellent photoresponsivity of 0.18 A W−1 under visible-light illumination with a detectivity of 4.18 × 1010 Jones, as well as fast rise and decay times (τrise = τdecay = 0.4 s). SnS/RGO hybrids are therefore promising candidates for potential applications in optoelectronics and low cost, high performance, and reliable photodetectors.

Heterostructures of MXenes and N-doped graphene as highly active bifunctional electrocatalysts.

MXenes with versatile chemistry and superior electrical conductivity are prevalent candidate materials for energy storage and catalysts. Inspired by recent experiments of hybridizing MXenes with carbon materials, here we theoretically design a series of heterostructures of N-doped graphene supported by MXene monolayers as bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Our first-principles calculations show that the graphitic sheet on V2C and Mo2C MXenes are highly active with an ORR overpotential down to 0.36 V and reaction free energies for the HER approaching zero, both with low kinetic barriers. Such outstanding catalytic activities originate from the electronic coupling between the graphitic sheet and the MXene, and can be correlated with the pz band center of surface carbon atoms and the work function of the heterostructures. Our findings screen a novel form of highly active electrocatalysts by taking advantage of the fast charge transfer kinetics and strong interfacial coupling of MXenes, and illuminate a universal mechanism for modulating the catalytic properties of two-dimensional hybrid materials.

Electrical detection of nucleotides via nanopores in a hybrid graphene/h-BN sheet.

Designing the next generation of solid-state biosensors requires developing detectors which can operate with high precision at the single-molecule level. Nano-scaled architectures created in two-dimensional hybrid materials offer unprecedented advantages in this regard. Here, we propose and explore a novel system comprising a nanopore formed within a hybrid sheet composed of a graphene nanoroad embedded in a sheet of hexagonal boron nitride (h-BN). The sensitive element of this setup is comprised of an electrically conducting carbon chain forming one edge of the nanopore. This design allows detection of DNA nucleotides translocating through the nanopore based on the current modulation signatures induced in the carbon chain. In order to assess whether this approach is feasible to distinguish the four different nucleotides electrically, we have employed density functional theory combined with the non-equilibrium Green's function method. Our findings show that the current localized in the carbon chain running between the nanopore and h-BN is characteristically modulated by the unique dipole moment of each molecule upon insertion into the pore. Through the analysis of a simple model based on the dipole properties of the hydrogen fluoride molecule we are able to explain the obtained findings.

Chemically Integrated Inorganic-Graphene Two-Dimensional Hybrid Materials for Flexible Energy Storage Devices.

State-of-the-art energy storage devices are capable of delivering reasonably high energy density (lithium ion batteries) or high power density (supercapacitors). There is an increasing need for these power sources with not only superior electrochemical performance, but also exceptional flexibility. Graphene has come on to the scene and advancements are being made in integration of various electrochemically active compounds onto graphene or its derivatives so as to utilize their flexibility. Many innovative synthesis techniques have led to novel graphene-based hybrid two-dimensional nanostructures. Here, the chemically integrated inorganic-graphene hybrid two-dimensional materials and their applications for energy storage devices are examined. First, the synthesis and characterization of different kinds of inorganic-graphene hybrid nanostructures are summarized, and then the most relevant applications of inorganic-graphene hybrid materials in flexible energy storage devices are reviewed. The general design rules of using graphene-based hybrid 2D materials for energy storage devices and their current limitations and future potential to advance energy storage technologies are also discussed.

(Invited) Designing Two-Dimensional Hybrid Materials for Electrochemical Energy Storage

Two-dimensional materials represent a promising material platform for next-generation energy storage and conversion devices. Owing to their advantageous features of large surface area, widely open ion transport pathway within 2D layers, and mechanical flexibility, graphene and other transition-metal oxides and phosphates based nanosheet materials show great promise in next-generation high-density energy storage devices. Here we will present examples on inorganic 2D materials and their hybrids for advanced energy storage devices including alkali-ion batteries and supercapacitors. The first set of examples is inorganic VOPO4 ultrathin nanosheets for ultraflexible solid-state supercapacitors, as well as for both Li-ion and Na-ion storage. And we will also discuss a novel synthetic strategy towards controlled synthesis of porous inorganic nanosheet materials as a promising class of alkali-ion battery electrodes with high capacity and rate capability.

Interface-induced warping in hybrid two-dimensional materials

Two-dimensional hybrid materials consisting of heterogeneous domains have been of great interest. Using empirical molecular dynamical simulation, we show that the morphology of such hybrid 2D materials can extend into the third dimension via strong warping intrinsic to the interfaces between the domains. The interface warping stems from the compressive stress in the domain with a larger lattice constant and even penetrates into the stretched domain. Based on classic plate theory, we analytically quantify the amplitude, wave length and penetration depth of the interface warping as functions of the lattice mismatch, achieving good agreement with the simulations. Moreover, we propose that periodically placing pentagon-heptagon dislocations along the interface can eliminate the warping in the 2D material and such defective interface can be more favorable than the warped one over a critical domain size, which is consistent with recent experimental observations. Our results suggest that the interface warping in 2D hybrid materials should be considered in further exploring their promising properties.

Negative infrared photocurrent response in layered WS2/reduced graphene oxide hybrids

We report high performance IR photocurrent response of two-dimensional hybrid materials consisting of layered WS2 nanosheets and reduced graphene oxide (RGO). Comparative photocurrent response studies of WS2 nanosheets, RGO, and WS2/RGO hybrids were carried out by performing current-voltage (I-V) and time-dependent current measurements with a laser excitation source having a wavelength of 808 nm. The experimental investigations indicate that WS2/RGO hybrids show negative photocurrent response, whereas WS2 and RGO show positive photocurrent response. The negative photocurrent response of the WS2/RGO hybrids is explained using a band alignment diagram and attributed to a charge transfer mechanism between WS2 and RGO. This analysis is further corroborated by first-principles density functional calculations. The fabricated device based on WS2/RGO hybrids shows a photosensitivity Rλ of about 6 AW−1 and a quantum efficiency η of ∼924%, which demonstrates high sensitivity of the hybrid material towards IR detection. WS2/RGO hybrids are therefore promising candidates for potential applications in optoelectronic circuits and low cost, high performance, and reliable photodetectors.