High Ion Conducting Polymer Nanocomposite Electrolytes Using Hybrid Nanofillers

There is a growing shift from liquid electrolytes toward solid polymer electrolytes, in energy storage devices, due to the many advantages of the latter such as enhanced safety, flexibility, and manufacturability. The main issue with polymer electrolytes is their lower ionic conductivity compared to that of liquid electrolytes. Nanoscale fillers such as silica and alumina nanoparticles are known to enhance the ionic conductivity of polymer electrolytes. Although carbon nanotubes have been used as fillers for polymers in various applications, they have not yet been used in polymer electrolytes as they are conductive and can pose the risk of electrical shorting. In this study, we show that nanotubes can be packaged within insulating clay layers to form effective 3D nanofillers. We show that such hybrid nanofillers increase the lithium ion conductivity of PEO electrolyte by almost 2 orders of magnitude. Furthermore, significant improvement in mechanical properties were observed where only 5 wt % addition of the filler led to 160% increase in the tensile strength of the polymer. This new approach of embedding conducting–insulating hybrid nanofillers could lead to the development of a new generation of polymer nanocomposite electrolytes with high ion conductivity and improved mechanical properties

Porous Spinel Zn_<i>x</i>Co_3–<i>x</i>O₄ Hollow Polyhedra Templated for High-Rate Lithium-Ion Batteries

Nanostructured metal oxides with both anisotropic texture and hollow structures have attracted considerable attention with respect to improved electrochemical energy storage and enhanced catalytic activity. While synthetic strategies for the preparation of binary metal oxide hollow structures are well-established, the rational design and fabrication of complex ternary metal oxide with nonspherical hollow features is still a challenge. Herein, we report a simple and scalable strategy to fabricate highly symmetric porous ternary Zn_<i>x</i>Co_3–<i>x</i>O₄ hollow polyhedra composed of nanosized building blocks, which involves a morphology-inherited and thermolysis-induced transformation of heterobimetallic zeolitic imidazolate frameworks. When tested as anode materials for lithium-ion batteries, these hollow polyhedra have exhibited excellent electrochemical performance with high reversible capacity, excellent cycling stability, and good rate capability

Intrinsic and Strain-Dependent Properties of Suspended WSe₂ Crystallites toward Next-Generation Nanoelectronics and Quantum-Enabled Sensors

Two-dimensional (2D) layered materials exhibit great potential for high-performance electronics, where knowledge of their thermal and phononic properties is critical toward understanding heat dissipation mechanisms, considered to be a major bottleneck for current generation nanoelectronic, optoelectronic, and quantum-scale devices. In this work, noncontact Raman spectroscopy was used to analyze thermal properties of suspended 2D WSe2 membranes to access the intrinsic properties. Here, the influence of electron–phonon interactions within the parent crystalline WSe2 membranes was deciphered through a comparative analysis of extrinsic substrate-supported WSe2, where heat dissipation mechanisms are intimately tied to the underlying substrate. Moreover, the excitonic states in WSe2 were analyzed by using temperature-dependent photoluminescence spectroscopy, where an enhancement in intensity of the localized excitons in suspended WSe2 was evident. Finally, phononic and electronic properties in suspended WSe2 were examined through nanoscale local strain engineering, where a uniaxial force was induced on the membrane using a Au-coated cantilever within an atomic force microscope. Through the fundamental analysis provided here with temperature and strain-dependent phononic and optoelectronic properties in suspended WSe2 nanosheets, the findings will inform the design of next-generation energy-efficient, high-performance devices based on WSe2 and other 2D materials, including for quantum applications

Marine Corrosion Protective Coatings of Hexagonal Boron Nitride Thin Films on Stainless Steel

Recently, two-dimensional, layered materials such as graphene and hexagonal boron nitride (h-BN) have been identified as interesting materials for a range of applications. Here, we demonstrate the corrosion prevention applications of h-BN in marine coatings. The performance of h-BN/polymer hybrid coatings, applied on stainless steel, were evaluated using electrochemical techniques in simulated seawater media [marine media]. h-BN/polymer coating shows an efficient corrosion protection with a low corrosion current density of 5.14 × 10^–8 A/cm² and corrosion rate of 1.19 × 10^–3 mm/year and it is attributed to the hydrofobic, inert and dielectric nature of boron nitride. The results indicated that the stainless steel with coatings exhibited improved corrosion resistance. Electrochemical impedance spectroscopy and potentiodynamic analysis were used to propose a mechanism for the increased corrosion resistance of h-BN coatings

Optical Power Limiting in Fluorinated Graphene Oxide: An Insight into the Nonlinear Optical Properties

Fluorination of carbon nanomaterials has many advantages due to the unique nature of the carbon–fluorine (C–F) bond. In this work, we report the optical power limiting properties of fluorinated graphene oxide (F–GO) using the optical <i>z</i>-scan technique. In addition, we used the photoacoustic technique to gain insight into the nonlinear processes involved in the optical limiting of samples. The photoacoustic technique enabled us to confirm that optical limiting observed in F–GO at low fluence arises from nonlinear absorption, while that at higher fluence is due to nonlinear scattering. Moreover, we found that F–GO has high nonlinear absorption and nonlinear scattering and its optical limiting threshold is about an order of magnitude better than that of graphene oxide (GO)

Effect of Carrier Localization on Electrical Transport and Noise at Individual Grain Boundaries in Monolayer MoS₂

Despite its importance in the large-scale synthesis of transition metal dichalcogenides (TMDC) molecular layers, the generic quantum effects on electrical transport across individual grain boundaries (GBs) in TMDC monolayers remain unclear. Here we demonstrate that strong carrier localization due to the increased density of defects determines both temperature dependence of electrical transport and low-frequency noise at the GBs of chemical vapor deposition (CVD)-grown MoS₂ layers. Using field effect devices designed to explore transport across individual GBs, we show that the localization length of electrons in the GB region is ∼30–70% lower than that within the grain, even though the room temperature conductance across the GB, oriented perpendicular to the overall flow of current, may be lower or higher than the intragrain region. Remarkably, we find that the stronger localization is accompanied by nearly 5 orders of magnitude enhancement in the low-frequency noise at the GB region, which increases exponentially when the temperature is reduced. The microscopic framework of electrical transport and noise developed in this paper may be readily extended to other strongly localized two-dimensional systems, including other members of the TMDC family

Bottom-up Approach toward Single-Crystalline VO₂‑Graphene Ribbons as Cathodes for Ultrafast Lithium Storage

Although lithium ion batteries have gained commercial success owing to their high energy density, they lack suitable electrodes capable of rapid charging and discharging to enable a high power density critical for broad applications. Here, we demonstrate a simple bottom-up approach toward single crystalline vanadium oxide (VO₂) ribbons with graphene layers. The unique structure of VO₂-graphene ribbons thus provides the right combination of electrode properties and could enable the design of high-power lithium ion batteries. As a consequence, a high reversible capacity and ultrafast charging and discharging capability is achieved with these ribbons as cathodes for lithium storage. A full charge or discharge is capable in 20 s. More remarkably, the resulting electrodes retain more than 90% of the initial capacity after cycling more than 1000 times at an ultrahigh rate of 190C, providing the best reported rate performance for cathodes in lithium ion batteries to date

Graphene Terahertz Technology

During the past two decades, a variety of linear and nonlinear dynamical phenomena, especially in the terahertz (THz) frequency range, have been revealed for charge carriers in graphene, which can be utilized to develop THz devices - i.e., emitters, receivers, and modulators of THz electromagnetic waves. This review discusses various applications of graphene in THz technology, including sensing, spectroscopy, photonics, and communications. First, the basic physics and techniques of THz-wave absorption processes in graphene are discussed. THz wave absorption in graphene can occur both through interband and intraband absorption processes. Such absorption can be readily modulated by an applied gate voltage and can be enhanced by utilizing parallel-plate waveguides or a total internal reflection geometry. Next, the effect of adsorbed molecules on THz emission from graphene is described. This phenomenon can be used to construct a metamaterial-free THz sensor for biointerfaces. The manipulation of THz waves through thermal annealing is also discussed, as well as their enhancement in a graphene-based THz modulator employing metallic ring apertures. Lastly, the review highlights the excitation of propagating surface plasmon polaritons in graphene at THz frequencies, which can play important roles in THz devices for communications, nanophotonics, and imaging

Functionalized Multilayered Graphene Platform for Urea Sensor

Multilayered graphene (MLG) is an interesting material for electrochemical sensing and biosensing because of its very large 2D electrical conductivity and large surface area. We propose a less toxic, reproducible, and easy method for producing functionalized multilayer graphene from multiwalled carbon nanotubes (MWCNTs) in mass scale using only concentrated H₂SO₄/HNO₃. Electron microscopy results show the MLG formation, whereas FTIR and XPS data suggest its carboxylic and hydroxyl-functionalized nature. We utilize this functionalized MLG for the fabrication of a novel amperometric urea biosensor. This biosensor shows linearity of 10–100 mg dL^–1, sensitivity of 5.43 μA mg^–1 dL cm^–2, lower detection limit of 3.9 mg dL^–1, and response time of 10 s. Our results suggest that MLG is a promising material for electrochemical biosensing applications

Photoluminescence Quenching and Charge Transfer in Artificial Heterostacks of Monolayer Transition Metal Dichalcogenides and Few-Layer Black Phosphorus

Transition metal dichalcogenides monolayers and black phosphorus thin crystals are emerging two-dimensional materials that demonstrated extraordinary optoelectronic properties. Exotic properties and physics may arise when atomic layers of different materials are stacked together to form van der Waals solids. Understanding the important interlayer couplings in such heterostructures could provide avenues for control and creation of characteristics in these artificial stacks. Here we systematically investigate the optical and optoelectronic properties of artificial stacks of molybdenum disulfide, tungsten disulfide, and black phosphorus atomic layers. An anomalous photoluminescence quenching was observed in tungsten disulfide–molybdenum disulfide stacks. This was attributed to a direct to indirect band gap transition of tungsten disulfide in such stacks while molybdenum disulfide maintains its monolayer properties by first-principles calculations. On the other hand, due to the strong build-in electric fields in tungsten disulfide–black phosphorus or molybdenum disulfide–black phosphorus stacks, the excitons can be efficiently splitted despite both the component layers having a direct band gap in these stacks. We further examine optoelectronic properties of tungsten disulfide–molybdenum disulfide artificial stacks and demonstrate their great potentials in future optoelectronic applications