2D Heterolayer-Structured MoSe2-Carbon with Fast Kinetics for Sodium-Ion Capacitors.

Two-dimensional (2D) layered MoSe2 has been demonstrated to be a promising electrode material for new energy storage systems. However, its nature of poor conductivity and the undesirable interlayer spacing hinder its further application. In this paper, a general and simple plasma-enhanced chemical vapor deposition method is proposed to produce 2D heterolayer-structured MoSe2-carbon (MoSe2/C) with carbon atoms inserted in the MoSe2 layers. After morphology optimization, when applying flat-type MoSe2/C-200 nanosheets with an enlarged interlayer spacing of 0.79 nm as the anode and activated carbon as the cathode, the assembled sodium-ion hybrid capacitors can reach a maximum energy/power density of 116.5 W h kg-1/107.5 W kg-1 and exhibit superior cycling durability (91.3% capacitance retention after 4000 cycles at 1 A g-1). The good electrochemical property can be ascribed to the enlarged interlayer spacing that can offer fast diffusion channels for Na ions, and the carbon layer sandwiched in the MoSe2 layer can not only enhance the electron transfer, accelerating the reaction kinetics, but also alleviate the volume change of MoSe2, ensuring the good stability of the electrode. The proposed approach can also be extended to other 2D transition metal chalcogenide (TMC) materials for constructing the TMC/C heterostructures for the application in energy storage systems.

Effect of Oxide Particles on Microstructure and Mechanical Properties of the 45 Carbon Structural Steel.

Striking difference in density between the oxide and the steel results in difficulty in preparing oxide dispersion strengthened steel with large size parts or materials. In this research, Al2O3 and TiO2 particles were initially milled with the 20 steel, and then the mixture was heated to a molten state to form a master alloy, which was used as a raw material for further preparation of the object steel. It was found that homogeneous distribution of the oxide particles was obtained in the mass production of the steel. Moreover, the obtained 45 carbon structural steel presents fine microstructures, together with improved mechanical properties, especially the impact ductility. This should be attributable to the transformation from the introduced micro-size oxide particles to the nano ones, which act as heterogeneous nucleants that play an important role in grain refinement and dispersion strengthening for the steel, during the remelting of the master alloy.

A highly flexible and multifunctional strain sensor based on a network-structured MXene/polyurethane mat with ultra-high sensitivity and a broad sensing range.

Flexible and multifunctional strain sensors with superior properties including high sensitivity, low detection limits, and a wide sensing range are always in high demand for wearable electronics. However, it remains a big challenge to fully satisfy the aforementioned requirements. In particular, there is always a trade-off between high sensitivity and wide sensing range. Here, we developed a multifunctional strain sensor based on a network-structured MXene/polyurethane mat (network-M/P mat) and well balanced the relationship between the sensitivity and sensing range by rationally designing the morphology and microstructures of the sensing device. The network-structured polyurethane mat (network-P mat) was fabricated through a facile and scalable electrospinning technique. The highly conductive MXene sheets were decorated onto the network-P mat through hydrogen bonding or electrostatic interactions. The obtained highly flexible and stretchable network-M/P mat exhibited a superior comprehensive sensing performance that was characterized by high sensitivity (gauge factor up to 228), a low limit of detection (0.1%), a large and tunable sensing range (up to 150%), excellent stability (over 3200 cycles), and multiple functions (lateral strain, vertical pressure, bending and subtle vibration). Based on its superior performance, the network-M/P mat-based strain sensor can detect a full range of body actions and subtle physiological signals (e.g. respirations and pulse waves), demonstrating great potential for applications in artificial electronic skin and wearable health detectors.

Bioinspired Pretextured Reduced Graphene Oxide Patterns with Multiscale Topographies for High-Performance Mechanosensors.

Highly sensitive mechanical sensing is vital for the emerging field of skin mimicry and wearable healthcare systems. To date, it remains a big challenge to fabricate mechanosensors with both high sensitivity and a wide sensing range. In nature, slit sensilla are crack-shaped sensory organs of arachnids, which are highly sensitive to tiny external mechanical stimuli. Here, inspired by the geometry of slit sensilla, a concept is developed that pretextures reduced graphene oxide (RGO) nanocoating into multiscale topographies with agminated crumples and interlaced cracks (crumpled & cracked RGO) through an efficient and scalable mechanically driven process. Both the sensitivity and the workable range can be facilely tuned by adjusting the crack density. The resulting mechanosensor exhibits a comprehensive superior performance including high sensitivity (a gauge factor of 205 to 3256), a wide and tunable sensing range (from 0-40 to 0-180%), long-term stability (over 5000 cycles), and multiple sensing functions. Based on its excellent performances, the mechanosensor can be used as a wearable electronic to in situ monitor subtle physiological signals and vigorous body actions. The rationally designed crumpled & cracked RGO provides a promising platform for artificial electronic skin and portable healthcare systems.

Strengthening of the Fe-Ni Invar Alloy Through Chromium.

Invar alloys with both high strength and low thermal expansion are urgently needed in fields such as overhead power transmission, aero-molds, and so on. In this paper, Cr was introduced as a cost-efficient alloying element into the Fe-36Ni binary invar alloy to increase its mechanical strength. Our results confirmed that fine Cr7C3 precipitants, together with some Fe3C, in the invar alloy aged at 425 °C could be obtained with a short aging time. Those precipitants then grew and aggregated at grain or sub-grain boundaries with an increase in aging time. Simultaneously, mechanical strength and coefficient of thermal expansion (CTE) parabolically varied with the increase in aging time. The sample aged at 425 °C for 7 h presented a maximum strength of 644.4 MPa, together with a minimum coefficient of thermal expansion of 3.30 × 10-6 K-1 in the temperature range of 20-100 °C. This optimized result should be primarily attributed to the precipitation of the nanoscaled Cr7C3.

Highly Sensitive, Selective, and Flexible NO2 Chemiresistors Based on Multilevel Structured Three-Dimensional Reduced Graphene Oxide Fiber Scaffold Modified with Aminoanthroquinone Moieties and Ag Nanoparticles.

Highly sensitive, selective, and room-temperature-performing gas sensors have always been the pursuit in the sensing field for practical applications. However, the existing gas sensors can seldom satisfy the aforementioned requirements. Here, we integrate zero-dimensional Ag nanoparticles (AgNPs), one-dimensional polymer fibers, and two-dimensional aminoanthroquinone-functionalized reduced graphene oxide (AQRGO) sheets into a three-dimensional sensing scaffold (AgNP-3D-AQRGO) for high-performance NO2 sensing. The AQ moieties and AgNPs are decorated onto the RGO sheets through a wet chemical route. Electrospinning and self-assembly techniques are employed to assemble the polymer fibers and the functional RGO sheets into a three-dimensional scaffold. The resulting AgNP-3D-AQRGO-based gas sensor can perform at room temperature and exhibits excellent sensing performance for NO2, including an ultrahigh sensitivity (10.3 ppm-1), an ultralow limit of detection (0.6 ppb), and an extremely remarkable selectivity to solely NO2 molecules. Furthermore, the sensor is also highly flexible, demonstrating great potential for portable and real-time monitoring of toxic gas in personal mobile electronics.

Percolating Film of Pillared Graphene Layer Integrated with Silver Nanowire Network for Transparent and Flexible Supercapacitors.

Transparent and flexible supercapacitors (TFSCs) are viable power sources for next-generation wearable electronics. The ingenious design of the transparent electrode determines the performance of TFSCs. A percolating film of a pillared graphene layer integrated with a silver nanowire network as the transparent electrode was prepared, by which TFSC devices exhibit a significantly improved performance contrastively. Under the condition of the same transmittance, about 27-72% improvement in the areal capacitance can be achieved. On the one hand, the pillars of carbon nanotube (CNT) were distributed in the graphene layer uniformly, enlarging the inner distance of adjacent graphene layers and providing an open structure for extra ion transport and storage of TFSCs. On the other hand, the introduced CNT could facilitate the electron transport at the direction perpendicular to the graphene basal plane, enhancing the electronic conductivity of the graphene layer. More importantly, the formed percolating film ensures an efficient transport of electron along with the silver nanowire when it encounters the obstacle within the graphene layer, resulting in a highly conductive electrode. The TFSC device with a good compatibility indicates a reliable practicability, which provides a facile route toward the design of high-performance TFSCs.

High-Performance and Multifunctional Skinlike Strain Sensors Based on Graphene/Springlike Mesh Network.

The development of skinlike strain sensors that are integrated with multiple sensing functions has attracted tremendous attention in recent years. To mimic human skin, strain sensors should have the abilities to detect various deformations such as pressing, stretching, bending, and even subtle vibrations. Here, we developed a facile, cost-effective, and scalable method for fabrication of high-performance strain sensors based on a graphene-coated springlike mesh network. This composite-based sensor exhibits an incorporation of low detection limit (LOD) for minute deformation (LOD of 1.38 Pa for pressure, 0.1% for tensile strain, and 10 µm for vibration), multiple sensing functions, long-term stability, and wide maximal sensing range (up to 80 kPa for pressure and 110% for tensile strain). On the basis of its superior performance, it can be applied for in situ monitoring of human motions ranging from subtle physiological signals (e.g., pulse, respiration, and phonation) to substantial movements (e.g., finger bending).

Synthesis of a Flexible Freestanding Sulfur/Polyacrylonitrile/Graphene Oxide as the Cathode for Lithium/Sulfur Batteries.

Rechargeable lithium/sulfur (Li/S) batteries have received quite significant attention over the years because of their high theoretical specific capacity (1672 mAh·g-1) and energy density (2600 mAh·g-1) which has led to more efforts for improvement in their electrochemical performance. Herein, the synthesis of a flexible freestanding sulfur/polyacrylonitrile/graphene oxide (S/PAN/GO) as the cathode for Li/S batteries by simple method via vacuum filtration is reported. The S/PAN/GO hybrid binder-free electrode is considered as one of the most promising cathodes for Li/S batteries. Graphene oxide (GO) slice structure provides effective ion conductivity channels and increases structural stability of the ternary system, resulting in excellent electrochemical properties of the freestanding S/PAN/GO cathode. Additionally, graphene oxide (GO) membrane was able to minimize the polysulfides' dissolution and their shuttle, which was attributed to the electrostatic interactions between the negatively-charged species and the oxygen functional groups on GO. Furthermore, these oxygen-containing functional groups including carboxyl, epoxide and hydroxyl groups provide active sites for coordination with inorganic materials (such as sulfur). It exhibits the initial reversible specific capacity of 1379 mAh·g-1 at a constant current rate of 0.2 C and maintains 1205 mAh·g-1 over 100 cycles (~87% retention). In addition, the freestanding S/PAN/GO cathode displays excellent coulombic efficiency (~100%) and rate capability, delivering up to 685 mAh·g-1 capacity at 2 C.