Tribological properties of Ta‐C‐N and Ta‐N thin films

The amorphous Ta‐C‐N and Ta‐N thin films were deposited using magnetron sputtering on silicon wafer under the similar condition. The as‐prepared thin films were characterized using scanning electron microscope (SEM), optical profiling system, nano‐indentation and friction test instruments. The results show that, compared with the Ta‐N thin film, the Ta‐C‐N thin film has higher nano‐hardness (9.45 GPa) and elastic modulus (225.71 GPa). Furthermore, the lower friction coefficient and wear rate of the Ta‐C‐N thin film are 0.238 and 5.94×10^–6 mm^–3· N^–1·m^–1, respectively. The wear surface of Ta‐C‐N thin film is smoother than that of the Ta‐N thin film. Therefore, it shows better anti‐wear properties.     

Vertically Aligned Niobium Nanowire Arrays for Fast‐Charging Micro‐Supercapacitors

Planar micro‐supercapacitors are attractive for system on chip technologies and surface mount devices due to their large areal capacitance and energy/power density compared to the traditional oxide‐based capacitors. In the present work, a novel material, niobium nanowires, in form of vertically aligned electrodes for application in high performance planar micro‐supercapacitors is introduced. Specific capacitance of up to 1 kF m^?2 (100 mF cm^?2) with peak energy and power density of 2 kJ m^?2 (6.2 MJ m^?3 or 1.7 mWh cm^?3) and 150 kW m^?2 (480 MW m^?3 or 480 W cm^?3), respectively, is achieved. This remarkable power density, originating from the extremely low equivalent series resistance value of 0.27 Ω (2.49 µΩ m² or 24.9 mΩ cm²) and large specific capacitance, is among the highest for planar micro‐supercapacitors electrodes made of nanomaterials.     

Fully Integrated Design of a Stretchable Solid‐State Lithium‐Ion Full Battery

A solid‐state lithium‐ion battery, in which all components (current collector, anode and cathode, electrolyte, and packaging) are stretchable, is introduced, giving rise to a battery design with mechanical properties that are compliant with flexible electronic devices and elastic wearable systems. By depositing Ag microflakes as a conductive layer on a stretchable carbon–polymer composite, a current collector with a low sheet resistance of ≈2.7 Ω □^?1 at 100% strain is obtained. Stretchable electrodes are fabricated by integrating active materials with the elastic current collector. A polyacrylamide–“water‐in‐salt” electrolyte is developed, offering high ionic conductivity of 10^?3 to 10^?2 S cm^?1 at room temperature and outstanding stretchability up to ≈300% of its original length. Finally, all these components are assembled into a solid‐state lithium‐ion full cell in thin‐film configuration. Thanks to the deformable individual components, the full cell functions when stretched, bent, or even twisted. For example, after stretching the battery to 50%, a reversible capacity of 28 mAh g^?1 and an average energy density of 20 Wh kg^?1 can still be obtained after 50 cycles at 120 mA g^?1, confirming the functionality of the battery under extreme mechanical stress.     

A Hydrogel‐Film Casting to Fabricate Platelet‐Reinforced Polymer Composite Films Exhibiting Superior Mechanical Properties

The fabrication of mechanically superior polymer composite films with controllable shapes on various scales is difficult. Despite recent research on polymer composites consisting of organic matrices and inorganic materials with layered structures, these films suffer from complex preparations and limited mechanical properties that do not have even integration of high strength, stiffness, and toughness. Herein, a hydrogel‐film casting approach to achieve fabrication of simultaneously strong, stiff, and tough polymer composite films with well‐defined microstructure, inspired from a layer‐by‐layer structure of nacre is reported. Ca²⁺‐crosslinked alginate hydrogels incorporated with platelet‐like alumina particles are dried to form composite films composed of horizontally aligned alumina platelets and alginate matrix with uniformly layered microstructure. Alumina platelets are evenly distributed parallel without precipitations and contribute to synergistic enhancements of strength, stiffness and toughness in the resultant film. Consequentially, Ca²⁺‐crosslinked alginate/alumina (Ca²⁺‐Alg/Alu) films show exceptional tensile strength (267 MPa), modulus (17.9 GPa), and toughness (3.60 MJ m⁻³). Furthermore, the hydrogel‐film casting allows facile preparation of polymer composite films with controllable shapes and various scales. The results suggest an alternative approach to design and prepare polymer composites with the layer‐by‐layer structure for superior mechanical properties.     

Using Graphene Oxide to Enhance the Barrier Properties of Poly(lactic acid) Film

The ultra‐thin (polyethyleneimine/graphene oxide)_n [(PEI/GO)_n]multilayer films on poly(lactic acid) (PLA) were constructed via the layer‐by‐layer assembly. Here, the electrostatic interactions between PEI and GO were used to obtain the nanoscale composite membrane of (PEI/GO)_n on the surface of PLA film. With the number of assembling layers increased, the oxygen permeability (PO₂) of PLA film decreased substantially. As a 0.06 wt% GO solution was used with only four layers, the PO₂ decreased from 53.8 to 0.377 × 10^?4 cm³/m²/d/Pa, only 0.7% of the original PLA film. At the same time, the coated PLA film also presented a good transparency and better mechanical properties. It is a novel way to use GO on biodegradable packaging materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Laser‐Assisted Large‐Scale Fabrication of All‐Solid‐State Asymmetrical Micro‐Supercapacitor Array

The micro‐supercapacitors are of great value for portable, flexible, and integrated electronic equipments. Here, the large‐scale and integrated asymmetrical micro‐supercapacitor (AMSC) array is fabricated in virtue of the laser direct writing and electrodeposition technology. The AMSC shows the ideal flexibility, high areal specific capacitance (21.8 mF cm^?2), and good rate capability. Moreover, its energy density reaches 12.16 µW h cm^?2, outperforming most micro‐supercapacitors reported previously. Meanwhile, large‐scale series‐connected AMSCs are integrated on the flexible substrates (e.g., indium tin oxide‐polyethylene terephthalate film), which can power a veriety of the commercial electronics. The combination of AMSCs array, solar cell, and electronic device proves the feasibility for practical application in the portable, flexible, and integrated electronic equipments.     

Superior Toughness and Fast Self‐Healing at Room Temperature Engineered by Transparent Elastomers

The most important properties of self‐healing polymers are efficient recovery at room temperature and prolonged durability. However, these two characteristics are contradictory, making it difficult to optimize them simultaneously. Herein, a transparent and easily processable thermoplastic polyurethane (TPU) with the highest reported tensile strength and toughness (6.8 MPa and 26.9 MJ m^?3, respectively) is prepared. This TPU is superior to reported contemporary room‐temperature self‐healable materials and conveniently heals within 2 h through facile aromatic disulfide metathesis engineered by hard segment embedded aromatic disulfides. After the TPU film is cut in half and respliced, the mechanical properties recover to more than 75% of those of the virgin sample within 2 h. Hard segments with an asymmetric alicyclic structure are more effective than those with symmetric alicyclic, linear aliphatic, and aromatic structures. An asymmetric structure provides the optimal metathesis efficiency for the embedded aromatic disulfide while preserving the remarkable mechanical properties of TPU, as indicated by rheological and surface investigations. The demonstration of a scratch‐detecting electrical sensor coated on a tough TPU film capable of auto‐repair at room temperature suggests that this film has potential applications in the wearable electronics industry.     

A Shape‐Adaptive Thin‐Film‐Based Approach for 50% High‐Efficiency Energy Generation Through Micro‐Grating Sliding Electrification

Effectively harvesting ambient mechanical energy is the key for realizing self‐powered and autonomous electronics, which addresses limitations of batteries and thus has tremendous applications in sensor networks, wireless devices, and wearable/implantable electronics, etc. Here, a thin‐film‐based micro‐grating triboelectric nanogenerator (MG‐TENG) is developed for high‐efficiency power generation through conversion of mechanical energy. The shape‐adaptive MG‐TENG relies on sliding electrification between complementary micro‐sized arrays of linear grating, which offers a unique and straightforward solution in harnessing energy from relative sliding motion between surfaces. Operating at a sliding velocity of 10 m/s, a MG‐TENG of 60 cm² in overall area, 0.2 cm³ in volume and 0.6 g in weight can deliver an average output power of 3 W (power density of 50 mW cm^?2 and 15 W cm^?3) at an overall conversion efficiency of ～50%, making it a sufficient power supply to regular electronics, such as light bulbs. The scalable and cost‐effective MG‐TENG is practically applicable in not only harvesting various mechanical motions but also possibly power generation at a large scale.     

Carbon‐MEMS‐Based Alternating Stacked MoS2@rGO‐CNT Micro‐Supercapacitor with High Capacitance and Energy Density

A novel process to fabricate a carbon‐microelectromechanical‐system‐based alternating stacked MoS₂@rGO–carbon‐nanotube (CNT) micro‐supercapacitor (MSC) is reported. The MSC is fabricated by successively repeated spin‐coating of MoS₂@rGO/photoresist and CNT/photoresist composites twice, followed by photoetching, developing, and pyrolysis. MoS₂@rGO and CNTs are embedded in the carbon microelectrodes, which cooperatively enhance the performance of the MSC. The fabricated MSC exhibits a high areal capacitance of 13.7 mF cm^?2 and an energy density of 1.9 µWh cm^?2 (5.6 mWh cm^?3), which exceed many reported carbon‐ and MoS₂‐based MSCs. The MSC also retains 68% of capacitance at a current density of 2 mA cm^?2 (5.9 A cm^?3) and an outstanding cycling performance (96.6% after 10 000 cycles, at a scan rate of 1 V s^?1). Compared with other MSCs, the MSC in this study is fabricated by a low‐cost and facile process, and it achieves an excellent and stable electrochemical performance. This approach could be highly promising for applications in integration of micro/nanostructures into microdevices/systems.     

A TiN Nanorod Array 3D Hierarchical Composite Electrode for Ultrahigh‐Power‐Density Bromine‐Based Flow Batteries

Bromine‐based flow batteries are well suited for stationary energy storage due to attractive features of high energy density and low cost. However, the bromine‐based flow battery suffers from low power density and large materials consumption due to the relatively high polarization of the Br₂/Br^? couple on the electrodes. Herein, a self‐supporting 3D hierarchical composite electrode based on a TiN nanorod array is designed to improve the activity of the Br₂/Br^? couple and increase the power density of the bromine‐based flow battery. In this design, a carbon felt provides a composite electrode with a 3D electron conductive framework to guarantee high electronic conductivity, while the TiN nanorods possess excellent catalytic activity for the Br₂/Br^? electrochemical reaction to reduce the electrochemical polarization. Moreover, the 3D micro–nano hierarchical nanorod‐array alignment structure contributes to a high electrolyte penetration and a high ion‐transfer rate to reduce diffusion polarization. As a result, a zinc–bromine flow battery with the designed composite electrode can be operated at a current density of up to 160 mA cm^?2, which is the highest current density ever reported. These results exhibit a promising strategy to fabricate electrodes for ultrahigh‐power‐density bromine‐based flow batteries and accelerate the development of bromine‐based flow batteries.     

Bioinspired Nacre‐Like Ceramic with Nickel Inclusions Fabricated by Electroless Plating and Spark Plasma Sintering

Hybrid composites of layered brittle‐ductile constituents assembled in a brick‐and‐mortar architecture are promising for applications requiring high strength and toughness. Mostly, polymer mortars have been considered as the ductile layer in brick‐and‐mortar composites. However, low stiffness of polymers does not efficiently transfer the shear between hard ceramic bricks. Theoretical models point to metals as a more efficient mortar layer. However, infiltration of metals into ceramic scaffold is non‐trivial, given the low wetting between metals and ceramics. The authors report on an alternative approach to fabricate brick‐and‐mortar ceramic‐metal composites by using electroless plating of nickel (Ni) on alumina micro‐platelets, in which Ni‐coated micro‐platelets are subsequently aligned by a magnetic field, taking advantage of ferromagnetic properties of Ni. The assembled Ni‐coated ceramic scaffold is then sintered using spark plasma sintering (SPS) to locally create Ni mortar layers between ceramic platelets, as well as to sinter the ceramic micro‐platelets. The authors report on materials and mechanical properties of the fabricated composite. The results show that this approach is promising toward development of bioinspired ceramic‐metal composites.

     

One‐Step Synthesis of Monodispersed Mesoporous Carbon Nanospheres for High‐Performance Flexible Quasi‐Solid‐State Micro‐Supercapacitors

Cost‐effective synthesis of carbon nanospheres with a desirable mesoporous network for diversified energy storage applications remains a challenge. Herein, a direct templating strategy is developed to fabricate monodispersed N‐doped mesoporous carbon nanospheres (NMCSs) with an average particle size of 100 nm, a pore diameter of 4 nm, and a specific area of 1093 m² g^?1. Hexadecyl trimethyl ammonium bromide and tetraethyl orthosilicate not only play key roles in the evolution of mesopores but also guide the assembly of phenolic resins to generate carbon nanospheres. Benefiting from the high surface area and optimum mesopore structure, NMCSs deliver a large specific capacitance up to 433 F g^?1 in 1 m H₂SO₄. The NMCS electrodes–based symmetric sandwich supercapacitor has an output voltage of 1.4 V in polyvinyl alcohol/H₂SO₄ gel electrolyte and delivers an energy density of 10.9 Wh kg^?1 at a power density of 14014.5 W kg^?1. Notably, NMCSs can be directly applied through the mask‐assisted casting technique by a doctor blade to fabricate micro‐supercapacitors. The micro‐supercapacitors exhibit excellent mechanical flexibility, long‐term stability, and reliable power output.     

High‐Efficiency Solution‐Processed Inorganic Metal Halide Perovskite Light‐Emitting Diodes

This paper reports highly bright and efficient CsPbBr₃ perovskite light‐emitting diodes (PeLEDs) fabricated by simple one‐step spin‐coating of uniform CsPbBr₃ polycrystalline layers on a self‐organized buffer hole injection layer and stoichiometry‐controlled CsPbBr₃ precursor solutions with an optimized concentration. The PeLEDs have maximum current efficiency of 5.39 cd A^?1 and maximum luminance of 13752 cd m^?2. This paper also investigates the origin of current hysteresis, which can be ascribed to migration of Br^? anions. Temperature dependence of the electroluminescence (EL) spectrum is measured and the origins of decreased spectrum area, spectral blue‐shift, and linewidth broadening are analyzed systematically with the activation energies, and are related with Br^? anion migration, thermal dissociation of excitons, thermal expansion, and electron–phonon interaction. This work provides simple ways to improve the efficiency and brightness of all‐inorganic polycrystalline PeLEDs and improves understanding of temperature‐dependent ion migration and EL properties in inorganic PeLEDs.     

Hierarchical Composite of Rose‐Like VS2@S/N‐Doped Carbon with Expanded (001) Planes for Superior Li‐Ion Storage

In the present work, a hierarchical composite of rose‐like VS₂@S/N‐doped carbon (VS₂@SNC) with expanded (001) planes is successfully fabricated through a facile synthetic route. Notably, the d‐spacing of (001) planes is expanded to 0.92 nm, which is proved to dramatically reduce the energy barrier for Li⁺ diffusion in the composite of VS₂@SNC by density functional theory calculation. On the other hand, the S/N‐doped carbon in the composite greatly promotes the electrical conductivity and enhances the structural stability. In addition, the hierarchical structure of VS₂@SNC facilitates rapid electrolyte diffusion and increases the contact area between the electrode and electrolyte simultaneously. Benefiting from the merits mentioned above, the VS₂@SNC electrode exhibits excellent electrochemical properties, such as a large reversible capacity of 971.6 mA h g^?1 at 0.2 A g^?1, an extremely high rate capability of 772.1 mA h g^?1 at 10 A g^?1, and a remarkable cycling stability up to 600 cycles at 8 A g^?1 with a capacity of 684.5 mA h g^?1, making it a promising candidate as an anode material for lithium‐ion batteries.     

Vertically Oriented Graphene Nanoribbon Fibers for High‐Volumetric Energy Density All‐Solid‐State Asymmetric Supercapacitors

Graphene fiber based micro‐supercapacitors (GF micro‐SCs) have attracted great attention for their potential applications in portable and wearable electronics. However, due to strong π–π stacking of nanosheets for graphene fibers, the limited ion accessible surface area and slow ion diffusion rate leads to low specific capacitance and poor rate performance. Here, the authors report a strategy for the synthesis of a vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined‐hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process. As a result, the as‐obtained fiber shows high length specific capacitance of 3.2 mF cm^?1 and volumetric capacitance of 234.8 F cm^?3 at 2 mV s^?1, as well as excellent rate capability and outstanding cycling performance (96% capacitance retention after 10 000 cycles). Moreover, an all‐solid‐state asymmetric supercapacitor based on graphene nanoribbon fiber as negative electrode and MnO₂ coated graphene ribbon fiber as positive electrode, shows high volumetric capacitance and energy density of 12.8 F cm^?3 and 5.7 mWh cm^?3 (normalized to the device volume), respectively, much higher than those of previously reported GF micro‐SCs, as well as a long cycle life with 88% of capacitance retention after 10 000 cycles.     

High‐Performance Microwave‐Derived Multi‐Principal Element Alloy Coatings for Tribological Application

The authors report the development of Al_xCoCrFeNi (x = 0.1 to 3) high entropy alloy (HEA) coatings using a simple and straightforward microwave technique. The microstructure of the developed coatings is composed of a cellular structure and diffused interface with the substrate. The microstructure of the HEA coatings varies as a direct function of Al content. An increase in Al fraction shows structural transformation from FCC to BCC along with the evolution of σ and B₂ as the major secondary phases. The diffusion of Mo from the substrate enhances the mixing entropy and promotes σ‐phase formation. The HEA coatings show significantly high hardness compared to SS316L substrate steel (227 HV) with a maximum value of 726 HV observed for three‐molar composition. The fracture toughness exhibits an inverse correlation with the Al fraction with the highest value of around 49 MPa m^1/2 observed for Al_0.1CoCrFeNi coating. The equimolar coating composition shows lowest erosion rates among all the tested samples due to optimum combination of the mechanical properties. The erosion resistance of the equimolar coating is 2 to 5 times higher than steel substrate and around 1.5 times higher than the non‐equimolar counterparts depending upon the impingement angles.

     

Ultrahigh‐Conductivity Polymer Hydrogels with Arbitrary Structures

A poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) hydrogel is prepared by thermal treatment of a commercial PEDOT:PSS (PH1000) suspension in 0.1 mol L^?1 sulfuric acid followed by partially removing its PSS component with concentrated sulfuric acid. This hydrogel has a low solid content of 4% (by weight) and an extremely high conductivity of 880 S m^?1. It can be fabricated into different shapes such as films, fibers, and columns with arbitrary sizes for practical applications. A highly conductive and mechanically strong porous fiber is prepared by drying PEDOT:PSS hydrogel fiber to fabricate a current‐collector‐free solid‐state flexible supercapacitor. This fiber supercapacitor delivers a volumetric capacitance as high as 202 F cm^?3 at 0.54 A cm^?3 with an extraordinary high‐rate performance. It also shows excellent electrochemical stability and high flexibility, promising for the application as wearable energy‐storage devices.     

Aluminum‐Ion‐Intercalation Supercapacitors with Ultrahigh Areal Capacitance and Highly Enhanced Cycling Stability: Power Supply for Flexible Electrochromic Devices

Electrochemical capacitor systems based on Al ions can offer the possibilities of low cost and high safety, together with a three‐electron redox‐mechanism‐based high capacity, and thus are expected to provide a feasible solution to meet ever‐increasing energy demands. Here, highly efficient Al‐ion intercalation into W₁₈O₄₉ nanowires (W₁₈O₄₉NWs) with wide lattice spacing and layered single‐crystal structure for electrochemical storage is demonstrated. Moreover, a freestanding composite film with a hierarchical porous structure is prepared through vacuum‐assisted filtration of a mixed dispersion containing W₁₈O₄₉NWs and single‐walled carbon nanotubes. The as‐prepared composite electrode exhibits extremely high areal capacitances of 1.11–2.92 F cm^?2 and 459 F cm^?3 at 2 mA cm^?2, enhanced electrochemical stability in the Al³⁺ electrolyte, as well as excellent mechanical properties. An Al‐ion‐based, flexible, asymmetric electrochemical capacitor is assembled that displays a high volumetric energy density of 19.0 mWh cm^?3 at a high power density of 295 mW cm^?3. Finally, the Al‐ion‐based asymmetric supercapacitor is used as the power source for poly(3‐hexylthiophene)‐based electrochromic devices, demonstrating their promising capability in flexible electronic devices.     

Lithium Titanate Cuboid Arrays Grown on Carbon Fiber Cloth for High‐Rate Flexible Lithium‐Ion Batteries

High‐rate performance flexible lithium‐ion batteries are desirable for the realization of wearable electronics. The flexibility of the electrode in the battery is a key requirement for this technology. In the present work, spinel lithium titanate (Li₄Ti₅O₁₂, LTO) cuboid arrays are grown on flexible carbon fiber cloth (CFC) to fabricate a binder‐free composite electrode (LTO@CFC) for flexible lithium‐ion batteries. Experimental results show that the LTO@CFC electrode exhibits a remarkably high‐rate performance with a capacity of 105.8 mAh g^?1 at 50C and an excellent electrochemical stability against cycling (only 2.2% capacity loss after 1000 cycles at 10C). A flexible full cell fabricated with the LTO@CFC as the anode and LiNi_0.5Mn_1.5O₄ coated on Al foil as the cathode displays a reversible capacity of 109.1 mAh g^?1 at 10C, an excellent stability against cycling and a great mechanical stability against bending. The observed high‐rate performance of the LTO@CFC electrode is due to its unique corn‐like architecture with LTO cuboid arrays (corn kernels) grown on CFC (corn cob). This work presents a new approach to preparing LTO‐based composite electrodes with an architecture favorable for ion and electron transport for flexible energy storage devices.     

Aligning Solution‐Derived Carbon Nanotube Film with Full Surface Coverage for High‐Performance Electronics Applications

The main challenge for application of solution‐derived carbon nanotubes (CNTs) in high performance field‐effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution‐derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on‐state current I_on of 290 µA µm^?1 (V_ds = ?1.5 V and V_gs = ?2 V) and peak transconductance g_m of 150 µS µm^?1, which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT‐based electronics.