Evaluating a Dual-Ion Battery with an Antimony-Carbon Composite Anode.

Dual-ion batteries (DIBs) are attracting attention due to their high operating voltage and promise in stationary energy storage applications. Among various anode materials, elements that alloy and dealloy with lithium are assumed to be prospective in bringing higher capacities and increasing the energy density of DIBs. In this work, antimony in the form of a composite with carbon (Sb-C) is evaluated as an anode material for DIB full cells for the first time. The behaviour of graphite||Sb-C cells is assessed in highly concentrated electrolytes in the absence and presence of an electrolyte additive (1 % vinylene carbonate) and in two cell voltage windows (2-4.5 V and 2-4.8 V). Sb-C full cells possess maximum estimated specific energies of 290 Wh/kg (based on electrode masses) and 154 Wh/kg (based on the combined mass of electrodes and active salt). The work expands the knowledge on the operation of DIBs with non-graphitic anodes.

Synthesis of Black Phosphorene Quantum Dots from Red Phosphorus.

Black phosphorene quantum dots (BPQDs) are most commonly derived from high-cost black phosphorus, while previous syntheses from the low-cost red phosphorus (Pred ) allotrope are highly oxidised. Herein, we present an intrinsically scalable method to produce high quality BPQDs, by first ball-milling Pred to create nanocrystalline Pblack and subsequent reductive etching using lithium electride solvated in liquid ammonia. The resultant ~25 nm BPQDs are crystalline with low oxygen content, and spontaneously soluble as individualized monolayers in tertiary amide solvents, as directly imaged by liquid-phase transmission electron microscopy. This new method presents a scalable route to producing quantities of high quality BPQDs for academic and industrial applications.

Advanced Dual-Ion Batteries with High-Capacity Negative Electrodes Incorporating Black Phosphorus.

Dual-graphite batteries (DGBs), being an all-graphite-electrode variation of dual-ion batteries (DIBs), have attracted great attention in recent years as a possible low-cost technology for stationary energy storage due to the utilization of inexpensive graphite as a positive electrode (cathode) material. However, DGBs suffer from a low specific energy limited by the capacity of both electrode materials. In this work, a composite of black phosphorus with carbon (BP-C) is introduced as negative electrode (anode) material for DIB full-cells for the first time. The electrochemical behavior of the graphite || BP-C DIB cells is then discussed in the context of DGBs and DIBs using alloying anodes. Mechanistic studies confirm the staging behavior for anion storage in the graphite positive electrode and the formation of lithiated phosphorus alloys in the negative electrode. BP-C containing full-cells demonstrate promising electrochemical performance with specific energies of up to 319 Wh kg-1 (related to masses of both electrode active materials) or 155 Wh kg-1 (related to masses of electrode active materials and active salt), and high Coulombic efficiency. This work provides highly relevant insights for the development of advanced high-energy and safe DIBs incorporating BP-C and other high-capacity alloying materials in their anodes.

Mechanochemistry: A force in disguise and conditional effects towards chemical reactions.

Mechanochemistry refers to unusual chemical reactions induced by mechanical energy at room temperatures. It has attracted increased attention because of advantages, such as being a solution-free, energy saving, high-productivity and low-temperature process. However, there is limited understanding of the mechanochemical process because mechanochemistry is often conducted using closed milling devices, which are often regarded as a black box. This feature article shows that mechanochemical reactions can be controlled by varying milling parameters, such as the mechanical force, milling intensity, time and atmosphere. New nanomaterials with doped and functionalized structures can be produced under controlled conditions, which provide a critical insight for understanding mechanochemistry. A fundamental mechanism investigation using force microscopy is discussed.

Facile Solution Processing of Stable MXene Dispersions towards Conductive Composite Fibers.

2D transition metal carbides and nitrides called "MXene" are recent exciting additions to the 2D nanomaterials family. The high electrical conductivity, specific capacitance, and hydrophilic nature of MXenes rival many other 2D nanosheets and have made MXenes excellent candidates for diverse applications including energy storage, electromagnetic shielding, water purification, and photocatalysis. However, MXene nanosheets degrade relatively quickly in the presence of water and oxygen, imposing great processing challenges for various applications. Here, a facile solvent exchange (SE) processing route is introduced to produce nonoxidized and highly delaminated Ti3C2T x MXene dispersions. A wide range of organic solvents including methanol, ethanol, isopropanol, butanol, acetone, dimethylformamide, dimethyl sulfoxide, chloroform, dichloromethane, toluene, and n-hexane is used. Compared to known processing approaches, the SE approach is straightforward, sonication-free, and highly versatile as multiple solvent transfers can be carried out in sequence to yield MXene in a wide range of solvents. Conductive MXene polymer composite fibers are achieved by using MXene processed via the solvent exchange (SE) approach, while the traditional redispersion approach has proven ineffective for fiber processing. This study offers a new processing route for the development of novel MXene-based architectures, devices, and applications.

Plasmonic substrates for surface enhanced Raman scattering.

As an advanced analytical tool, surface-enhanced Raman scattering (SERS) has broad applications in identification of colorants in paints and glazes, hazard detection to ensure food safety, biomedicine and diagnosis, environmental monitoring, detection of explosives and forensic science. In this review, main types of plasmonic substrates, which include solid substrate with metallic nanostructures and chemically synthesized noble metal colloids, and their fabrication methods are reviewed. The design principles for fabrication of ultrasensitive plasmonic substrates for SERS are presented on the basis of published literature. Finally, various applications of SERS substrates are described, indicating the potential of this technique in practical applications. As an ultrasensitive detection method, SERS is at the core of a rapidly expanding research field.

Nanocrystalline SnS2 coated onto reduced graphene oxide: demonstrating the feasibility of a non-graphitic anode with sulfide chemistry for potassium-ion batteries.

An anode material incorporating a sulfide is reported. SnS2 nanoparticles anchored onto reduced graphene oxide are produced via a chemical route and demonstrate an impressive capacity of 350 mA h g-1, exceeding the capacity of graphite. These results open the door for a new class of high capacity anode materials (based on sulfide chemistry) for potassium-ion batteries.

K-ion and Na-ion storage performances of Co3O4-Fe2O3 nanoparticle-decorated super P carbon black prepared by a ball milling process.

The hybridisation of Co3O4 and Fe2O3 nanoparticles dispersed in a super P carbon matrix is proposed as a favourable approach to improve the electrochemical performance (reversible capacity, cycling stability and rate capability) of the metal oxide electrodes in metal-ion batteries. Hybrid Co3O4-Fe2O3/C is prepared by a simple, cheap and easily scalable molten salt method combined with ball-milling and used in sodium-ion and potassium-ion batteries for the first time. The electrode exhibits excellent cycling stability and superior rate capability in sodium-ion cells with a capacity recovery of 440 mA h g-1 (93% retention) after 180 long-term cycles at 50-1000 mA g-1 and back to 50 mA g-1. In contrast, Co3O4-Fe2O3, Co3O4 and Fe2O3 electrodes display unsatisfactory electrochemical performance. The hybrid Co3O4-Fe2O3/C is also reactive with potassium and capable of delivering a reversible capacity of 220 mA h g-1 at 50 mA g-1 which is comparable with the most reported anode materials for potassium-ion batteries. The obtained results broaden the range of transition metal oxide-based hybrids as potential anodes for K-ion and Na-ion batteries, and suggest that further studies of these materials with potassium and sodium are worthwhile.

Two-Dimensional Metal Oxide Nanoflower-Like Architectures: A General Growth Method and Their Applications in Energy Storage and as Model Materials for Nanofabrication.

Nanoflower-like architectures represent a unique type of nanomaterials in which thin 2D nanosheets are self-organised into interconnected structures. Lack of restacking between nanosheets and significant internal porosity are the particular advantages of such nanoscale architectures. A general method for the preparation of nanoflowers of a range of oxides (e.g., FeTiO3 , TiO2 , Mn2 O3 ) through a two-step procedure of ball milling and subsequent hydrothermal treatment is outlined. Importantly, the synthetic method is valid not only for a single oxide, but is extendable to a family of oxide materials. It is established that the formation of the nanoflowers from ball-milled powders follows a dissolution-precipitation mechanism; this is confirmed by inductively coupled plasma time of flight mass spectrometry measurements. Additional information on the X-ray photoelectron spectroscopy characterisation and intermediate stage of growth of the nanostructures is included. Furthermore, two applications of Mn2 O3 nanostructures are briefly investigated. Firstly, their properties for energy storage in the electrodes of electrochemical supercapacitors are presented. A capacitive response in the potential window of -0.1-0.9 V versus an Ag/AgCl reference electrode is observed, with an associated increase of the capacitance values over cycling. Secondly, the use of Mn2 O3 nanoflowers as model systems for the development of novel nanofabrication techniques (such as nanopatterning with a He+ beam) is investigated.

Lithium Germanate (Li2 GeO3 ): A High-Performance Anode Material for Lithium-Ion Batteries.

A simple, cost-effective, and easily scalable molten salt method for the preparation of Li2 GeO3 as a new type of high-performance anode for lithium-ion batteries is reported. The Li2 GeO3 exhibits a unique porous architecture consisting of micrometer-sized clusters (secondary particles) composed of numerous nanoparticles (primary particles) and can be used directly without further carbon coating which is a common exercise for most electrode materials. The new anode displays superior cycling stability with a retained charge capacity of 725 mAh g-1 after 300 cycles at 50 mA g-1 . The electrode also offers excellent rate capability with a capacity recovery of 810 mAh g-1 (94 % retention) after 35 cycles of ascending steps of current in the range of 25-800 mA g-1 and finally back to 25 mA g-1 . This work emphasizes the importance of exploring new electrode materials without carbon coating as carbon-coated materials demonstrate several drawbacks in full devices. Therefore, this study provides a method and a new type of anode with high reversibility and long cycle stability.

Size and Composition Effects in Sb-Carbon Nanocomposites for Sodium-Ion Batteries.

Sodium-ion batteries are in the spotlight as viable alternatives to lithium-ion batteries in stationary storage and power grid applications. Among possible anode materials, Sb is one of the interesting candidates due to a combination of battery-type potential plateaus in the charge-discharge profiles, high capacity (theoretical capacity of 660 mAh g-1), and demonstrated good cyclic stability. The influence of Sb particle size (particularly at the nanoscale range) and the composition of Sb-carbon composites on the electrode performance, stability, and charge storage mechanism is systematically evaluated here for the first time. A range of Sb-carbon nanocomposites with varied Sb particle size (between 50 and ∼1 nm) are studied. The control of the particle size is achieved via varying the carbon and Sb weight ratio in the precursors. The shape of charge-discharge profiles, hysteresis, and the difference in cyclic stabilities and rate performance are analyzed. The nanocomposite with the smallest particle size (∼1 nm) and the largest carbon content provides the most stable cyclic behavior and a better rate capability but suffers from an increased hysteresis between charge and discharge curves. In situ synchrotron X-ray diffraction experiments indicate that the storage mechanism in the Sb-carbon nanocomposites containing Sb nanoparticles is different from the electrodes with bulkier, micron-sized Sb particles, and the electrochemical reaction proceeds through a number of crystalline intermediates.

Tin-based composite anodes for potassium-ion batteries.

The electrochemical behaviour of a Sn-based anode in a potassium cell is reported for the first time. The material is active at low potentials vs. K/K(+), and encouraging capacities of around 150 mA h g(-1) are recorded. Experimental evidence shows that Sn is capable of alloying/de-alloying with potassium in a reversible manner.

Understanding Structure-Function Relationship in Hybrid Co3O4-Fe2O3/C Lithium-Ion Battery Electrodes.

A range of high-capacity Li-ion anode materials (conversion reactions with lithium) suffer from poor cycling stability and limited high-rate performance. These issues can be addressed through hybridization of multiple nanostructured components in an electrode. Using a Co3O4-Fe2O3/C system as an example, we demonstrate that the cycling stability and rate performance are improved in a hybrid electrode. The hybrid Co3O4-Fe2O3/C electrode exhibits long-term cycling stability (300 cycles) at a moderate current rate with a retained capacity of approximately 700 mAh g(-1). The reversible capacity of the Co3O4-Fe2O3/C electrode is still about 400 mAh g(-1) (above the theoretical capacity of graphite) at a high current rate of ca. 3 A g(-1), whereas Co3O4-Fe2O3, Fe2O3/C, and Co3O4/C electrodes (used as controls) are unable to operate as effectively under identical testing conditions. To understand the structure-function relationship in the hybrid electrode and the reasons for the enhanced cycling stability, we employed a combination of ex situ and in situ techniques. Our results indicate that the improvements in the hybrid electrode originate from the combination of sequential electrochemical activity of the transition metal oxides with an enhanced electronic conductivity provided by percolating carbon chains.

Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer Helium Ion Beam.

We report subnanometer modification enabled by an ultrafine helium ion beam. By adjusting ion dose and the beam profile, structural defects were controllably introduced in a few-layer molybdenum disulfide (MoS2) sample and its stoichiometry was modified by preferential sputtering of sulfur at a few-nanometer scale. Localized tuning of the resistivity of MoS2 was demonstrated and semiconducting, metallic-like, or insulating material was obtained by irradiation with different doses of He(+). Amorphous MoSx with metallic behavior has been demonstrated for the first time. Fabrication of MoS2 nanostructures with 7 nm dimensions and pristine crystal structure was also achieved. The damage at the edges of these nanostructures was typically confined to within 1 nm. Nanoribbons with widths as small as 1 nm were reproducibly fabricated. This nanoscale modification technique is a generalized approach that can be applied to various two-dimensional (2D) materials to produce a new range of 2D metamaterials.

High-efficient production of boron nitride nanosheets via an optimized ball milling process for lubrication in oil.

Although tailored wet ball milling can be an efficient method to produce a large quantity of two-dimensional nanomaterials, such as boron nitride (BN) nanosheets, milling parameters including milling speed, ball-to-powder ratio, milling ball size and milling agent, are important for optimization of exfoliation efficiency and production yield. In this report, we systematically investigate the effects of different milling parameters on the production of BN nanosheets with benzyl benzoate being used as the milling agent. It is found that small balls of 0.1-0.2 mm in diameter are much more effective in exfoliating BN particles to BN nanosheets. Under the optimum condition, the production yield can be as high as 13.8% and the BN nanosheets are 0.5-1.5 µm in diameter and a few nanometers thick and of relative high crystallinity and chemical purity. The lubrication properties of the BN nanosheets in base oil have also been studied. The tribological tests show that the BN nanosheets can greatly reduce the friction coefficient and wear scar diameter of the base oil.

Electrochemical investigation of sodium reactivity with nanostructured Co3O4 for sodium-ion batteries.

The electrochemical behaviour of Co3O4 with sodium is reported here. Upon cycling in the voltage window of 0.01-3.0 V, Co3O4 undergoes a conversion reaction and exhibits a reversible capacity of 447 mA h g(-1) after 50 cycles. Therefore, nanostructured Co3O4 presents feasible electrochemical sodium storage, offering possibilities to develop new anode materials for sodium-ion batteries.

Self-assembly of core-satellite gold nanoparticles for colorimetric detection of copper ions.

Molecule-coated nanoparticles are hybrid materials which can be engineered with novel properties. The molecular coating of metal nanoparticles can provide chemical functionality, enabling assembly of the nanoparticles that are important for applications, such as biosensing devices. Herein, we report a new self-assembly of core-satellite gold nanoparticles linked by a simple amino acid l-Cysteine for biosensing of Cu(2+). The plasmonic properties of core-satellite nano-assemblies were investigated, a new red shifted absorbance peak from about 600 to 800 nm was found, with specific wavelength depending on ratios with assembly of large and small gold nanoparticles. The spectral features obtained using surface-enhanced Raman spectroscopy (SERS) provided strong evidence for the assembly of the Cu(2+) ions to the L-Cysteine molecules leading to the successful formation of the core-satellite Cu(l-Cysteine) complex on the gold surfaces. In addition, a linear relationship between the concentration of mediating Cu(2+) and absorbance of self-assembled gold nanoparticles (GNPs) at 680 nm was obtained. These results strongly address the potential strategy for applying the functionalized GNPs as novel biosensing tools in trace detections of certain metal ions.

Clusters of α-LiFeO2 nanoparticles incorporated into multi-walled carbon nanotubes: a lithium-ion battery cathode with enhanced lithium storage properties.

We report the preparation of a novel nanocomposite architecture of α-LiFeO2-MWCNT based on clusters of α-LiFeO2 nanoparticles incorporated into multiwalled carbon nanotubes (MWCNTs). The composite represents a promising cathode material for lithium-ion batteries. The preparation of the nanocomposite is achieved by combining a molten salt precipitation process and a radio frequency oxygen plasma for the first time. We demonstrate that clusters of α-LiFeO2 nanoparticles incorporated into MWCNTs are capable of delivering a stable and high reversible capacity of 147 mA h g(-1) at 1 C after 100 cycles with the first cycle Coulombic efficiency of ~95%. The rate capability of the composite is significantly improved and its reversible capacity is measured to be 101 mA h g(-1) at a high current rate of 10 C. Both rate capability and cycling stability are not simply a result of introduction of functionalized MWCNTs but most likely originate from the unique composite structure of clusters of α-LiFeO2 nanoparticles integrated into a network of MWCNTs. The excellent electrochemical performance of this new nanocomposite opens up new opportunities in the development of high-performance electrode materials for energy storage application using the radio frequency oxygen plasma technique.

Ball milling: a green mechanochemical approach for synthesis of nitrogen doped carbon nanoparticles.

Technological and scientific challenges coupled with environmental considerations have attracted a search for robust, green and energy-efficient synthesis and processing routes for advanced functional nanomaterials. In this article, we demonstrate a high-energy ball milling technique for large-scale synthesis of nitrogen doped carbon nanoparticles, which can be used as an electro-catalyst for oxygen reduction reactions after a structural refinement with controlled thermal annealing. The resulting carbon nanoparticles exhibited competitive catalytic activity (5.2 mA cm(-2) kinetic-limiting current density compared with 7.6 mA cm(-2) on Pt/C reference) and excellent methanol tolerance compared to a commercial Pt/C catalyst. The proposed synthesis route by ball milling and annealing is an effective process for carbon nanoparticle production and efficient nitrogen doping, providing a large-scale production method for the development of highly efficient and practical electrocatalysts.

Crystal phase engineered quantum wells in ZnO nanowires.

We report the fabrication of quantum wells in ZnO nanowires (NWs) by a crystal phase engineering approach. Basal plane stacking faults (BSFs) in the wurtzite structure can be considered as a minimal segment of zinc blende. Due to the existing band offsets at the wurtzite (WZ)/zinc blende (ZB) material interface, incorporation of a high density of BSFs into ZnO NWs results in type II band alignment. Thus, the BSF structure acts as a quantum well for electrons and a potential barrier for holes in the valence band. We have studied the photoluminescence properties of ZnO NWs containing high concentrations of BSFs in comparison to high-quality ZnO NWs of pure wurtzite structure. It is revealed that BSFs form quantum wells in WZ ZnO nanowires, providing an additional luminescence peak at 3.329 eV at 4 K. The luminescence mechanism is explained as an indirect exciton transition due to the recombination of electrons in the QW conduction band with holes localized near the BSF. The binding energy of electrons is found to be around 100 meV, while the excitons are localized with the binding energy of holes of ∼5 meV, due to the coupling of BSFs, which form QW-like structures.