Nanowire Templated Semihollow Bicontinuous Graphene Scrolls: Designed Construction, Mechanism, and Enhanced Energy Storage Performance

Vanadium Oxide: Phase Diagrams, Structures, Synthesis, and Applications

Vanadium oxides with multioxidation states and various crystalline structures offer unique electrical, optical, optoelectronic and magnetic properties, which could be manipulated for various applications. For the past 30 years, significant efforts have been made to study the fundamental science and explore the potential for vanadium oxide materials in ion batteries, water splitting, smart windows, supercapacitors, sensors, and so on. This review focuses on the most recent progress in synthesis methods and applications of some thermodynamically stable and metastable vanadium oxides, including but not limited to V₂O₃, V₃O₅, VO₂, V₃O₇, V₂O₅, V₂O₂, V₆O₁₃, and V₄O₉. We begin with a tutorial on the phase diagram of the V-O system. The second part is a detailed review covering the crystal structure, the synthesis protocols, and the applications of each vanadium oxide, especially in batteries, catalysts, smart windows, and supercapacitors. We conclude with a brief perspective on how material and device improvements can address current deficiencies. This comprehensive review could accelerate the development of novel vanadium oxide structures in related applications.

Fibrous MXene Aerogels with Tunable Pore Structures for High-Efficiency Desalination of Contaminated Seawater

The seawater desalination based on solar-driven interfacial evaporation has emerged as a promising technique to alleviate the global crisis on freshwater shortage. However, achieving high desalination performance on actual, oil-contaminated seawater remains a critical challenge, because the transport channels and evaporation interfaces of the current solar evaporators are easily blocked by the oil slicks, resulting in undermined evaporation rate and conversion efficiency. Herein, we propose a facile strategy for fabricating a modularized solar evaporator based on flexible MXene aerogels with arbitrarily tunable, highly ordered cellular/lamellar pore structures for high-efficiency oil interception and desalination. The core design is the creation of 1D fibrous MXenes with sufficiently large aspect ratios, whose superior flexibility and plentiful link forms lay the basis for controllable 3D assembly into more complicated pore structures. The cellular pore structure is responsible for effective contaminants rejection due to the multi-sieving effect achieved by the omnipresent, isotropic wall apertures together with underwater superhydrophobicity, while the lamellar pore structure is favorable for rapid evaporation due to the presence of continuous, large-area evaporation channels. The modularized solar evaporator delivers the best evaporation rate (1.48 kg m-2 h-1) and conversion efficiency (92.08%) among all MXene-based desalination materials on oil-contaminated seawater.

Ordered Van der Waals Hetero-nanoribbon from Pressure-Induced Topochemical Polymerization of Azobenzene

Pressure-induced topochemical polymerization of molecular crystals with various stackings is a promising way to synthesize materials with different co-existing sub-structures. Here, by compressing the azobenzene crystal containing two kinds of intermolecular stacking, we synthesized an ordered van der Waals carbon nanoribbon (CNR) heterostructure in one step. Azobenzene polymerizes via a [4 + 2] hetero-Diels-Alder (HDA) reaction of phenylazo-phenyl in layer A and a para-polymerization reaction of phenyl in layer B at 18 GPa, as evidenced by in situ Raman and IR spectroscopies, X-ray diffraction, as well as gas chromatography-mass spectrometry and the solid-state nuclear magnetic resonance of the recovered products. The theoretical calculation shows that the obtained CNR heterostructure has a type II (staggered) band gap alignment. Our work highlights a high-pressure strategy to synthesize bulk CNR heterostructures.

Metallic phase WSe2 nanoscrolls for the hydrogen evolution reaction

Nanostructured metastable metallic phase transition-metal dichalcogenides (TMDs) have attracted tremendous attention due to their promising practical applications in the hydrogen evolution reaction (HER).

Synthesis Strategy of Metal Oxide Quantum Wires via a Nanoparticle-Induced Graphene Oxide Rolling Procedure

The efficient synthesis of quantum materials is becoming a research hotspot as it determines their successful application in the fields of biomedicine, illumination, energy, sensors, information, and communication. Among the quantum materials, it is still a challenge to synthesize quantum wires (QWs) with surfactants due to the inevitable radial growth of QWs in the soft template method. In this paper, amphipathic graphene oxide (GO) was adopted as a macromolecular surfactant to limit the radial growth instead of the commonly used surfactant. GO could roll up under its electrostatic interaction with a cuprous oxide (Cu₂O) quantum dot (QD) and then form a tubular template for the growth of the Cu₂O QW, which was named herein as the nanoparticle-induced graphene oxide rolling (NIGOR) procedure. The NIGOR procedure was confirmed by the molecular dynamics results by simulating systems consisting of GO and Cu₂O nanoparticles. An intermediate with a necklace morphology corresponding to the simulation result was also observed experimentally during the formation of the QW. Meanwhile, the formation mechanism of the QW was demonstrated rationally. Furthermore, increasing the dosage of the reactant, reaction time, and temperature altered the diameter of the QW from 2 to 4 nm and also changed the morphology of the final products from a QD to a QW and then to a bundle of QWs. This was attributed to the aggregation of materials for the lowest surface energy in the system. Additionally, the universality of NIGOR was manifested via the synthesis of other metal oxides as well. The NIGOR strategy provided an alternative, convenient, and mass production method for synthesizing QWs.

Feature-Rich Geometric and Electronic Properties of Carbon Nanoscrolls

How to form carbon nanoscrolls with non-uniform curvatures is worthy of a detailed investigation. The first-principles method is suitable for studying the combined effects due to the finite-size confinement, the edge-dependent interactions, the interlayer atomic interactions, the mechanical strains, and the magnetic configurations. The complex mechanisms can induce unusual essential properties, e.g., the optimal structures, magnetism, band gaps and energy dispersions. To reach a stable spiral profile, the requirements on the critical nanoribbon width and overlapping length will be thoroughly explored by evaluating the width-dependent scrolling energies. A comparison of formation energy between armchair and zigzag nanoscrolls is useful in understanding the experimental characterizations. The spin-up and spin-down distributions near the zigzag edges are examined for their magnetic environments. This accounts for the conservation or destruction of spin degeneracy. The various curved surfaces on a relaxed nanoscroll will create complicated multi-orbital hybridizations so that the low-lying energy dispersions and energy gaps are expected to be very sensitive to ribbon width, especially for those of armchair systems. Finally, the planar, curved, folded, and scrolled graphene nanoribbons are compared with one another to illustrate the geometry-induced diversity.

The "Yin and Yang" of Immunomodulatory Magnesium-Enriched Graphene Oxide Nanoscrolls Decorated Biomimetic Scaffolds in Promoting Bone Regeneration

Tissue regeneration driven by immunomodulatory agents has emerged as a potential solution for repairing bone defects. However, the therapeutic benefits are compromised by disturbances in the pro- and anti-inflammatory balance. Here, using magnesium nanoparticles (MgNPs) as a template, magnesium-enriched graphene oxide nanoscrolls (MgNPs@GNSs) designed for combinational modulation of the inflammatory response are reported. First, the different effects of graphene oxide (GO) and magnesium ions (Mg²⁺ ) on Raw264.7 macrophage phenotype transformation are screened. The results reveal that GO activates inflammatory M1 macrophages, and that Mg²⁺ facilitates repolarization of M1 macrophages to the pro-healing M2 phenotype. With sustained release of Mg²⁺ , the MgNPs@GNS nanoplatform can orchestrate harmonious type 1 and type 2 inflammatory responses. Mg²⁺ decrease the internalization of GO and downregulate the nuclear factor kappa-B pathway, which is profoundly involved in the inflammatory process. A series of experiments show that the ordered inflammatory response induced by MgNPs@GNSs stimulates in vitro angiogenesis and osteogenesis through chemotactic, mitogenic, and morphogenic actions. Obvious vascularized bone regeneration is achieved in a rat cranial bone defect model via MgNPs@GNS deposited decellularized bone matrix scaffold. Therefore, the potential of using inherently therapeutic nanomedicine to modulate biomaterial-induced immune responses and thus enhance bone regeneration is demonstrated.

VO2 Nanostructures for Batteries and Supercapacitors: A Review

Vanadium dioxide (VO₂ ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO₂ has been extensively used in electrochromic displays and memristors and its VO₂ (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO₂ (B) nanostructures which displayed different energy storage behavior than the bulk VO₂ . The present review provides a systematic overview of the progress in VO₂ nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO₂ nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO₂ nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO₂ nanostructure as potential electrode material for future application.

V6 O13-δ @C Nanoscrolls with Expanded Distances between Adjacent Shells as a High-Performance Cathode for a Knittable Zinc-Ion Battery

Herein, the defective vanadate oxide (V₆ O_13-δ )/C (denoted as DVOC) nanoscrolls with large distance between adjacent shells are constructed as a cathode material for ZIBs. By simultaneously enlarging the distance between adjacent shells and engineering the defective structure for oxide crystal, the DVOC nanoscrolls achieve fast kinetics, high reversibility and good energy storage capability. The formation process of DVOC nanoscrolls is investigated and a self-assembling-rolling sequential mechanism is disclosed. Moreover, the fiber-shaped flexible ZIBs are fabricated based on the DVOC cathode. Their admirable volumetric energy density, good high rate capability and excellent cycling stability demonstrate the superiority of the unique structure. Therefore, this work not only introduces a new strategy to improve the properties of vanadium oxides but also provide a new strategy for the design of knittable power sources for flexible electronics.

A graphene–MnO2 composite supercapacitor material accomplished tactically using liquid–liquid and solid–liquid interface reaction techniques

An exceptional, simplistic, approach is established for preparing a GNS–MnO₂ thin film supercapacitor having a steady and superior performance.

MnO2–GO-scroll–TiO2–ITQ2 as a low-temperature NH3-SCR catalyst with a wide SO2-tolerance temperature range

GO-scroll–TiO₂–ITQ2 improved the steam-resistance and SO₂-resistance of the low-temperature manganese-based NH₃-SCR catalyst.

1D Carbon-Based Nanocomposites for Electrochemical Energy Storage

Electrochemical energy storage (EES) devices have attracted immense research interests as an effective technology for utilizing renewable energy. 1D carbon-based nanostructures are recognized as highly promising materials for EES application, combining the advantages of functional 1D nanostructures and carbon nanomaterials. Here, the recent advances of 1D carbon-based nanomaterials for electrochemical storage devices are considered. First, the different categories of 1D carbon-based nanocomposites, namely, 1D carbon-embedded, carbon-coated, carbon-encapsulated, and carbon-supported nanostructures, and the different synthesis methods are described. Next, the practical applications and optimization effects in electrochemical energy storage devices including Li-ion batteries, Na-ion batteries, Li-S batteries, and supercapacitors are presented. After that, the advanced in situ detection techniques that can be used to investigate the fundamental mechanisms and predict optimization of 1D carbon-based nanocomposites are discussed. Finally, an outlook for the development trend of 1D carbon-based nanocomposites for EES is provided.

Vanadium-based nanowires for sodium-ion batteries

Sodium-ion batteries (SIBs) have received great attention because of the abundance source and low cost. To date, some Na⁺ storage materials have achieved great performance, but the larger Na⁺ radius and more complex Na⁺ storage mechanism compared with Li⁺ still limit the energy density and power density. This review systematically summarizes emerging synthetic technologies of vanadium-based materials from simple nanowires to complicated modified/optimized structures. In addition, vanadium-based nanowire materials are reviewed at both the cathode and anode side, and advantages and drawbacks are proposed to explain the challenges facing application of novel materials. Furthermore, a vanadium-based single-nanowire device is reported to reveal the Na⁺ storage mechanism, which contributes to the understanding of the reaction in SIBs. Finally, this review summarizes the current development challenges of SIBs and looks forward to the future development prospects of vanadium-based nanowires, providing a new direction for further applications of SIBs.

Impact of pH on Regulating Ion Encapsulation of Graphene Oxide Nanoscroll for Pressure Sensing

Recently, graphene oxide nanoscroll (GONS) has attracted much attention due to its excellent properties. Encapsulation of nanomaterials in GONS can greatly enhance its performance while ion encapsulation is still unexplored. Herein, various ions including hydronium ion (H₃O⁺), Fe³⁺, Au³⁺, and Zn²⁺ were encapsulated in GONSs by molecular combing acidic graphene oxide (GO) solution. No GONS was obtained when the pH of the GO solution was greater than 9. A few GONSs without encapsulated ion were obtained at the pH of 5–8. When the pH decreased from 5 to 0.15, high-density GONSs with encapsulated ions were formed and the average height of GONS was increased from ~50 to ~190 nm. These results could be attributed to the varied repulsion between carboxylic acid groups located at the edges of GO nanosheets. Encapsulated metal ions were converted to nanoparticles in GONS after high-temperature annealing. The resistance-type device based on reduced GONS (rGONS) mesh with encapsulated H₃O⁺ showed good response for applied pressure from 600 to 8700 Pa, which manifested much better performance compared with that of a device based on rGONS mesh without H₃O⁺.

The Regulating Role of Carbon Nanotubes and Graphene in Lithium-Ion and Lithium-Sulfur Batteries

The ever-increasing demands for batteries with high energy densities to power the portable electronics with increased power consumption and to advance vehicle electrification and grid energy storage have propelled lithium battery technology to a position of tremendous importance. Carbon nanotubes (CNTs) and graphene, known with many appealing properties, are investigated intensely for improving the performance of lithium-ion (Li-ion) and lithium-sulfur (Li-S) batteries. However, a general and objective understanding of their actual role in Li-ion and Li-S batteries is lacking. It is recognized that CNTs and graphene are not appropriate active lithium storage materials, but are more like a regulator: they do not electrochemically react with lithium ions and electrons, but serve to regulate the lithium storage behavior of a specific electroactive material and increase the range of applications of a lithium battery. First, metrics for the evaluation of lithium batteries are discussed, based on which the regulating role of CNTs and graphene in Li-ion and Li-S batteries is comprehensively considered from fundamental electrochemical reactions to electrode structure and integral cell design. Finally, perspectives on how CNTs and graphene can further contribute to the development of lithium batteries are presented.

Self-Assembly of Hybrid Nanorods for Enhanced Volumetric Performance of Nanoparticles in Li-Ion Batteries

The benefits of nanosize active particles in Li-ion batteries are currently ambiguous. They are acclaimed for enhancing the cyclability of certain electrode materials and for improving rate performance. However, at the same time, nanoparticles are criticized for causing side reactions as well as for their low packing density and, therefore, poor volumetric battery performance. This paper demonstrates for the first time that self-assembly can be used to pack nanoparticles into dense battery electrodes with up to 4-fold higher volumetric capacities. Furthermore, despite the dense packing of the self-assembled electrodes, they retain a higher volumetric capacity than randomly dispersed nanoparticles up to rates of 5 C. Finally, we did not observe substential degradation in capacity after 1000 cycles, and post-mortem analysis indicates that the self-assembled structures are maintained during cycling. Therefore, the proposed self-assembled electrodes profit from the advantages of nanostructured battery materials without compromising the volumetric performance.

MnO2–Graphene-oxide-scroll–TiO2 composite catalyst for low-temperature NH3-SCR of NO with good steam and SO2 resistance obtained by low-temperature carbon-coating and selective atomic layer deposition

Coating GO at low temperature and selectively depositing TiO₂ on oxygen-containing functional groups on GO.

A facile and general approach for production of nanoscrolls with high-yield from two-dimensional nanosheets

Nanoscrolls (NSs) assembled from two-dimensional nanosheets have emerged as a novel type of one-dimensional nanomaterials because of their unique topological features and properties. The scale-up preparation of the NSs is crucial for their foundational and applied research. Herein, we report a general and straightforward approach for efficiently converting two-dimensional nanosheets into the NSs with high yield. We demonstrated the converting process by illustrating the formation of the graphene nanoscrolls through characterizing their morphology and structure using a scanning electron microscope, transmission electron microscope, Raman spectra, and X-ray diffraction spectra. The graphene sheets with a few-lay number were converted immediately and entirely into the graphene nanoscrolls when they mixed with an ethanol solution of silver nitrate at room temperature. The as-prepared graphene nanoscrolls were confirmed to be formed via the layer-by-layer assembly of graphene triggered by silver cyanide formed in site. Also, we extended this approach to construct the nanoscrolls of the hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide, respectively, from their corresponding two-dimensional nanomaterials. In a broader context, this approach paves a significant new way for the large production of the NSs with cost-efficiency.

A High-Rate and Stable Quasi-Solid-State Zinc-Ion Battery with Novel 2D Layered Zinc Orthovanadate Array

Zinc-ion batteries are under current research focus because of their uniqueness in low cost and high safety. However, it is still desirable to improve the rate performance by improving the Zn²⁺ (de)intercalation kinetics and long-cycle stability by eliminating the dendrite formation problem. Herein, the first paradigm of a high-rate and ultrastable flexible quasi-solid-state zinc-ion battery is constructed from a novel 2D ultrathin layered zinc orthovanadate array cathode, a Zn array anode supported by a conductive porous graphene foam, and a gel electrolyte. The nanoarray structure for both electrodes assures the high rate capability and alleviates the dendrite growth. The flexible Zn-ion battery has a depth of discharge of ≈100% for the cathode and 66% for the anode, and delivers an impressive high-rate of 50 C (discharge in 60 s), long-term durability of 2000 cycles at 20 C, and unprecedented energy density ≈115 Wh kg^-1 , together with a peak power density ≈5.1 kW kg^-1 (calculation includes masses of cathode, anode, and current collectors). First principles calculations and quantitative kinetics analysis show that the high-rate and stable properties are correlated with the 2D fast ion-migration pathways and the introduced intercalation pseudocapacitance.

Mechanics of the scrolling and folding of graphene

The competition between the out-of-plane rigidity and the van der Waals interaction leads to the scrolled and folded structural configurations of graphene. These configuration changes, as compared with the initially planar geometry, significantly affect the electronic, optical and mechanical properties of graphene, promising exciting applications in graphene-nanoelectronics. We propose a finite-deformation theoretical model, in which no presumed assumptions on the geometries of deformed configurations are required. Both the predicted deformed profiles and the critical conditions show great agreements with molecular dynamics simulations results when compared with existing studies with simple geometrical assumptions. Moreover, MD simulations are performed to explore the morphology transitions between different configurations. It is observed that the folded configuration is energetically favorable for a short graphene sheet, while a long graphene sheet tends to scroll. Of particular interest, we observe the morphology transition from a Fermat scroll to the Archimedean scroll for the bi-scrolled graphene. These findings are useful for understanding the stability of graphene and may provide guidance to the design of programmable graphene-nanoelectronics.

Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring Behavior of Polysulfides for Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery has been deemed as one of the most promising energy-storage systems owing to its high energy density, low cost, and environmental benignancy. However, the capacity decay and kinetic sluggishness stemming from polysulfide shuttle effects have by far posed a great challenge to practical performance. We herein demonstrate the employment of low-cost, wet-chemistry-derived VO₂ nanobelts as the effective host additives for the graphene-based sulfur cathode. The VO₂ nanobelts displayed an ultrafast anchoring behavior of polysulfides, managing to completely decolor the polysulfide solution in 50 s. Such a fast and strong anchoring ability of VO₂ was further investigated and verified by experimental and theoretical investigations. Benefitting from the synergistic effect exerted by VO₂ in terms of chemical confinement and catalytic conversion of polysulfides, the Li-S batteries incorporating VO₂ and graphene manifested excellent cycling and rate performances. Notably, the batteries delivered an initial discharge capacity of 1405 mAh g^-1 when cycling at 0.2 C, showed an advanced rate performance of ∼830 mAh g^-1 at 2 C, and maintained a stable cycling performance at high current densities of 1, 2, and 5 C over 200 cycles, paving a practical route toward cost-effective and environmentally benign cathode design for high-energy Li-S batteries.

One-Dimensional Hetero-Nanostructures for Rechargeable Batteries

Rechargeable batteries are regarded as one of the most practical electrochemical energy storage devices that are able to convert and store the electrical energy generated from renewable resources, and they function as the key power sources for electric vehicles and portable electronics. The ultimate goals for electrochemical energy storage devices are high power and energy density, long lifetime, and high safety. To achieve the above goals, researchers have tried to apply various morphologies of nanomaterials as the electrodes to enhance the electrochemical performance. Among them, one-dimensional (1D) materials show unique superiorities, such as cross-linked structures for external stress buffering and large draw ratios for internal stress dispersion. However, a homogeneous single-component electrode material can hardly have the characteristics of high electronic/ionic conductivity and high stability in the electrochemical environment simultaneously. Therefore, designing well-defined functional 1D hetero-nanostructures that combine the advantages and overcome the limitations of different electrochemically active materials is of great significance. This Account summarizes fabrication strategies for 1D hetero-nanostructures, including nucleation and growth, deposition, and melt-casting and electrospinning. Besides, the chemical principles for each strategy are discussed. The nucleation and growth strategy is suitable for growing and constructing 1D hetero-nanostructures of partial transition metal compounds, and the experimental conditions for this strategy are relatively accessible. Deposition is a reliable strategy to synthesize 1D hetero-nanostructures by decorating functional layers on 1D substrate materials, on the condition that the preobtained substrate materials must be stable in the following deposition process. The melt-casting strategy, in which 1D hetero-nanostructures are synthesizes via a melting and molding process, is also widely used. Additionally, the main functions of 1D hetero-nanostructures are summarized into four aspects and reviewed in detail. Appropriate surface modification can effectively restrain the structure deterioration and the regeneration of the solid-electrolyte interphase layer caused by the volume change. A porous or semihollow external conducting material coating provides advanced electron/ion bicontinuous transmission. Suitable atomic heterogeneity in the crystal structure is beneficial to the expansion and stabilization of the ion diffusion channels. Multiphase-assisted structural design is also an accessible way for the sulfur electrode material restriction. Moreover, some outlooks about the further industrial production, more effective and cheaper fabrication strategies, and new heterostructures with smaller-scale composition are given in the last part. By providing an overview of fabrication methods and performance-enhancing mechanisms of 1D hetero-nanostructured electrode materials, we hope to pave a new way to facile and efficient construction of 1D hetero-nanostructures with practical utility.

Cellulose Nanocrystal Templated Graphene Nanoscrolls for High Performance Supercapacitors and Hydrogen Storage: An Experimental and Molecular Simulation Study

Graphene nanoscrolls (GNS), due to their remarkably interesting properties, have attracted significant interest with applications in various engineering sectors. However, uncontrolled morphologies, poor yield and low quality GNS produced through traditional routes are major challenges associated. We demonstrate sustainable approach of utilizing bio-derived cellulose nanocrystals (CNCs) as template for fabrication of GNS with tunable morphological dimensions ranging from micron-to-nanoscale(controlled length < 1 μm or >1 μm), alongwith encapsulation of catalytically active metallic-species in scroll interlayers. The surface-modified magnetic CNCs acts as structural-directing agents which provides enough momentum to initiate self-scrolling phenomenon of graphene through van der Waals forces and π-π interactions, mechanism of which is demonstrated through experimental and molecular simulation studies. The proposed approach of GNS fabrication provides flexibility to tune physico-chemical properties of GNS by simply varying interlayer spacing, scrolling density and fraction of encapsulated metallic nanoparticles. The hybrid GNS with confined palladium or platinum nanoparticles (at lower loading ~1 wt.%) shows enhanced hydrogen storage capacity (~0.2 wt.% at~20 bar and ~273 K) and excellent supercapacitance behavior (~223–357 F/g) for prolonged cycles (retention ~93.5–96.4% at ~10000 cycles). The current strategy of utilizing bio-based templates can be further extended to incorporate complex architectures or nanomaterials in GNS core or inter-layers, which will potentially broaden its applications in fabrication of high-performance devices.

Graphene Scroll-Coated α-MnO2 Nanowires as High-Performance Cathode Materials for Aqueous Zn-Ion Battery

The development of manganese dioxide as the cathode for aqueous Zn-ion battery (ZIB) is limited by the rapid capacity fading and material dissolution. Here, a highly reversible aqueous ZIB using graphene scroll-coated α-MnO₂ as the cathode is proposed. The graphene scroll is uniformly coated on the MnO₂ nanowire with an average width of 5 nm, which increases the electrical conductivity of the MnO₂ nanowire and relieves the dissolution of the cathode material during cycling. An energy density of 406.6 Wh kg^-1 (382.2 mA h g^-1 ) at 0.3 A g^-1 can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn-ion battery so far, and good long-term cycling stability with 94% capacity retention after 3000 cycles at 3 A g^-1 are achieved. Meanwhile, a two-step intercalation mechanism that Zn ions first insert into the layers and then the tunnels of MnO₂ framework is proved by in situ X-ray diffraction, galvanostatic intermittent titration technique, and X-ray photoelectron spectroscopy characterizations. The graphene scroll-coated metallic oxide strategy can also bring intensive interests for other energy storage systems.

Rolling up graphene oxide sheets through solvent-induced self-assembly in dispersions

Herein we report a new approach to fabricating nanoscrolls through the self-assembly of graphene oxide (GO) sheets in a dispersion. The assembly process for GO nanosheets was induced by the dropwise addition of an appropriate organic solvent such as N,N-dimethylformamide (DMF) into the aqueous dispersion. The results show that nanoscrolls were gradually formed from the GO sheets by rolling-up in a piece-by-piece manner with the increase of the DMF content. The transmission electron microscopic analysis indicates that for a typical case, the nanoscrolls have an average diameter of 242 ± 102 nm at the central part and the interlayer spacing between adjacent GO layers is 0.58 nm. The scrolls were estimated to have 207 turns and include on average 42 pieces of GO sheets per scroll. By this method, GO sheets with different sizes and oxidation degrees were proved to be able to form GO nanoscrolls in a similar way. Moreover, it is interesting that the diffraction efficiency of surface-relief-gratings photoinduced on the film of azo molecular glass was significantly enhanced by doping the GO nanoscrolls with a very low content (0.5 wt%); this suggests a possible new application for the GO scrolls in optical devices. This facile approach, which is also feasible by using other organic solvents such as ethanol, can be used to fabricate GO nanoscrolls for large scale applications in supercapacitors, sensors and other devices.

Architecting Graphene Oxide Rolled-Up Micromotors: A Simple Paper-Based Manufacturing Technology

A graphene oxide rolled-up tube production process is reported using wax-printed membranes for the fabrication of on-demand engineered micromotors at different levels of oxidation, thickness, and lateral dimensions. The resultant graphene oxide rolled-up tubes can show magnetic and catalytic movement within the addition of magnetic nanoparticles or sputtered platinum in the surface of graphene-oxide-modified wax-printed membranes prior to the scrolling process. As a proof of concept, the as-prepared catalytic graphene oxide rolled-up micromotors are successfully exploited for oil removal from water. This micromotor production technology relies on an easy, operator-friendly, fast, and cost-efficient wax-printed paper-based method and may offer a myriad of hybrid devices and applications.

Structural transformations of carbon and boron nitride nanoscrolls at high impact collisions

The behavior of nanostructures under high strain-rate conditions has been the object of theoretical and experimental investigations in recent years.

Water-Lubricated Intercalation in V2 O5 ·nH2 O for High-Capacity and High-Rate Aqueous Rechargeable Zinc Batteries

Low-cost, environment-friendly aqueous Zn batteries have great potential for large-scale energy storage, but the intercalation of zinc ions in the cathode materials is challenging and complex. Herein, the critical role of structural H₂ O on Zn²⁺ intercalation into bilayer V₂ O₅ ·nH₂ O is demonstrated. The results suggest that the H₂ O-solvated Zn²⁺ possesses largely reduced effective charge and thus reduced electrostatic interactions with the V₂ O₅ framework, effectively promoting its diffusion. Benefited from the "lubricating" effect, the aqueous Zn battery shows a specific energy of ≈144 Wh kg^-1 at 0.3 A g^-1 . Meanwhile, it can maintain an energy density of 90 Wh kg^-1 at a high power density of 6.4 kW kg^-1 (based on the cathode and 200% Zn anode), making it a promising candidate for high-performance, low-cost, safe, and environment-friendly energy-storage devices.

In situ preparation of Fe3O4 in a carbon hybrid of graphene nanoscrolls and carbon nanotubes as high performance anode material for lithium-ion batteries

A new conductive carbon hybrid combining both reduced graphene nanoscrolls and carbon nanotubes (rGNSs-CNTs) is prepared, and used to host Fe₃O₄ nanoparticles through an in situ synthesis method. As an anode material for LIBs, the obtained Fe₃O₄@rGNSs-CNTs shows good electrochemical performance. At a current density of 0.1 A g^-1, the anode material shows a high reversible capacity of 1232.9 mAh g^-1 after 100 cycles. Even at a current density of 1 A g^-1, it still achieves a high reversible capacity of 812.3 mAh g^-1 after 200 cycles. Comparing with bare Fe₃O₄ and Fe₃O₄/rGO composite anode materials without nanoscroll structure, Fe₃O₄@rGNSs-CNTs shows much better rate capability with a reversible capacity of 605.0 and 500.0 mAh g^-1 at 3 and 5 A g^-1, respectively. The excellent electrochemical performance of the Fe₃O₄@rGNSs-CNTs anode material can be ascribed to the hybrid structure of rGNSs-CNTs, and their strong interaction with Fe₃O₄ nanoparticles, which on one hand provides more pathways for lithium ions and electrons, on the other hand effectively relieves the volume change of Fe₃O₄ during the charge-discharge process.

Graphene-Like-Graphite as Fast-Chargeable and High-Capacity Anode Materials for Lithium Ion Batteries

Here we propose the use of a carbon material called graphene-like-graphite (GLG) as anode material of lithium ion batteries that delivers a high capacity of 608 mAh/g and provides superior rate capability. The morphology and crystal structure of GLG are quite similar to those of graphite, which is currently used as the anode material of lithium ion batteries. Therefore, it is expected to be used in the same manner of conventional graphite materials to fabricate the cells. Based on the data obtained from various spectroscopic techniques, we propose a structural GLG model in which nanopores and pairs of C-O-C units are introduced within the carbon layers stacked with three-dimensional regularity. Three types of highly ionic lithium ions are found in fully charged GLG and stored between its layers. The oxygen atoms introduced within the carbon layers seem to play an important role in accommodating a large amount of lithium ions in GLG. Moreover, the large increase in the interlayer spacing observed for fully charged GLG is ascribed to the migration of oxygen atoms within the carbon layer introduced in the state of C-O-C to the interlayer space maintaining one of the C-O bonds.

Direct observation of multiple rotational stacking faults coexisting in freestanding bilayer MoS2

Electronic properties of two-dimensional (2D) MoS₂ semiconductors can be modulated by introducing specific defects. One important type of defect in 2D layered materials is known as rotational stacking fault (RSF), but the coexistence of multiple RSFs with different rotational angles was not directly observed in freestanding 2D MoS₂ before. In this report, we demonstrate the coexistence of three RSFs with three different rotational angles in a freestanding bilayer MoS₂ sheet as directly observed using an aberration-corrected transmission electron microscope (TEM). Our analyses show that these RSFs originate from cracks and dislocations within the bilayer MoS₂. First-principles calculations indicate that RSFs with different rotational angles change the electronic structures of bilayer MoS₂ and produce two new symmetries in their bandgaps and offset crystal momentums. Therefore, employing RSFs and their coexistence is a promising route in defect engineering of MoS₂ to fabricate suitable devices for electronics, optoelectronics, and energy conversion.

Scrolling up graphene oxide nanosheets assisted by self-assembled monolayers of alkanethiols

We report a simple and novel method for the fabrication of high-quality nanoscrolls of graphene oxide (GO) and graphene oxide decorated with silver nanoparticles (GO-Ag) on a gold substrate through a scrolling process assisted by the self-assembly of alkanethiol monolayers. The yield and rate of the scrolling process were highly dependent on the lengths of the alkanethiol molecules, and could be well described by power law functions. Importantly, compared to nanosheets, nanoscrolls of GO and GO-Ag showed superior performance in humidity sensing due to their unique scrolled structures.

Facile synthesis of ultrathin Ni-MOF nanobelts for high-efficiency determination of glucose in human serum

Ultrathin Ni-MOF nanobelts, [Ni₂₀(C₅H₆O₄)₂₀(H₂O)₈]·40H₂O(Ni-MIL-77 NBs), were synthesized by a facile one-pot solution process and can be used as an efficient catalyst electrode for glucose oxidation under alkaline conditions. Electrochemical measurements demonstrate that the NB/GCE, when used as a non-enzymatic glucose sensor, offers superior analytical performances with a wide linear range (from 1 μM to 500 μM), a low detection limit (0.25 μM, signal-to-noise = 3), and a response sensitivity of 1.542 μA mM^-1 cm^-2. Moreover, it can also be applied for glucose detection in human blood serum with the relative standard deviation (RSD) of 7.41%, showing the high precision of the sensor in measuring real samples.

Ultrathin Nanoribbons of in Situ Carbon-Coated V3O7·H2O for High-Energy and Long-Life Li-Ion Batteries: Synthesis, Electrochemical Performance, and Charge-Discharge Behavior

The ever-growing demands of Li-ion batteries (LIBs) for high-energy and long-life applications, such as electrical vehicles, have prompted great research interest. Herein, by applying an interesting one-step high-temperature mixing method under hydrothermal conditions, ultrathin V₃O₇·H₂O@C nanoribbons with good crystallinity and robust configuration are in situ synthesized as promising cathode materials of high-energy, high-power, and long-life LIBs. Their capacity is up to 319 mA h/g at a current density of 100 mA/g. Moreover, the capacity of 262 mA h/g can be delivered at 500 mA/g, and 94% of capacity can be retained after 100 cycles. Even at a large current density of 3000 mA/g, they can still deliver a high capacity of 165 mA h/g, and 119% of the initial capacity can be kept after 600 cycles. Importantly, their energy density is up to 800 Wh/kg, which is 48-60% higher than those of conventional cathode materials (such as LiCoO₂, LiMn₂O₄, and LiFePO₄), and they can maintain an energy density of 355 Wh/kg at a high power density of 8000 W/kg. Furthermore, based on ex situ X-ray diffraction and X-ray photoelectron spectroscopy technology, their exact charge-discharge behavior is reasonably described for the first time. Excitingly, it is found for the first time that the as-synthesized V₃O₇·H₂O@C nanoribbons are also great promising cathode materials for Na-ion batteries.