Lithium–sulfur batteries (Li–S) have attracted soaring attention due to the particularly high energy density for advanced energy storage system. However, the practical application of Li–S batteries still faces multiple challenges, including the shuttle effect of intermediate polysulfides, the low conductivity of sulfur and the large volume variation of sulfur cathode. To overcome these issues, here we reported a self-templated approach to prepare interconnected carbon nanotubes inserted/wired hollow Co3S4 nanoboxes (CNTs/Co3S4–NBs) as an efficient sulfur host material. Originating from the combination of three-dimensional CNT conductive network and polar Co3S4–NBs, the obtained hybrid nanocomposite of CNTs/Co3S4–NBs can offer ultrahigh charge transfer properties, and efficiently restrain polysulfides in hollow Co3S4–NBs via the synergistic effect of structural confinement and chemical bonding. Benefiting from the above advantages, the S@CNTs/Co3S4–NBs cathode shows a significantly improved electrochemical performance in terms of high reversible capacity, good rate performance, and long-term cyclability. More remarkably, even at an elevated temperature (50 °C), it still exhibits high capacity retention and good rate capacity.

The presence of metallic nanotubes in as-grown single walled carbon nanotubes (SWNTs) is the major bottleneck for their applications in field-effect transistors. Herein, we present a method to synthesize enriched, semiconducting nanotube arrays on quartz substrate. It was discovered that introducing appropriate amounts of water could effectively remove the metallic nanotubes and significantly enhance the density of SWNT arrays. More importantly, we proposed and confirmed that the high growth selectivity originates from the etching effect of water and the difference in the chemical reactivities of metallic and semiconducting nanotubes. Three important rules were summarized for achieving a high selectivity in growing semiconducting nanotubes by systematically investigating the relationship among water concentration, carbon feeding rate, and the percentage of semiconducting nanotubes in the produced SWNT arrays. Furthermore, these three rules can be applied to the growth of random SWNT networks on silicon wafers.

•Te/SnS2/Ag ANLs heterostructure is prepared to catalyze overall water splitting.•The catalyst show impressive H2 and O2 production rate under visible light.•The structure and efficiency of catalyst shows no degradation after 10 days.To produce hydrogen and oxygen from photocatalytic overall splitting of pure water provides a promising green route to directly convert solar energy to clean fuel. However, the design and fabrication of high-efficiency photocatalyst is challenging. Here we present that by connecting different nanostructures together in a rational fashion, components that cannot individually split water into H2 and O2 can work together as efficient photocatalyst with high solar-to-hydrogen (STH) energy conversion efficiency and avoid the use of any sacrificial reagent. Specifically, Te/SnS2/Ag artificial nanoleaves (ANLs) consist of ultrathin SnS2 nanoplates grown on Te nanowires and decorated with numerous Ag nanoparticles. The appropriate band structure of Te/SnS2 p-n junctions and the surface plasmon resonance of Ag nanoparticles synergistically enhance the quantum yield and separation efficiency of electron-hole pairs. As a result, Te/SnS2/Ag ANLs enable visible-light driven overall water-splitting without any sacrificial reagent and exhibit high H2 and O2 production rates of 332.4 and 166.2 μmol h−1, respectively. Well-preserved structure after long-term measurement indicates its high stability. It represents a feasible approach for direct H2 production from only sunlight, pure water, and rationally-designed ANL photocatalysts.Download high-res image (290KB)Download full-size image

The design of electrochemically active materials with appropriate structures and compositions is very important for applications in energy conversion and storage devices. Herein, we demonstrate an effective strategy to prepare microporous heteroatom-doped carbon frameworks derived from naturally-abundant pine needles. The preparation procedure is based on the carbonization of pine needles, followed by KOH activation at a temperature range of 700–1000 °C. The resultant nitrogen-doped carbon consists of abundant micropores and an ultrahigh specific surface area (up to 2433 m2 g−1), leading to high performances in electrocatalytic hydrogen evolution reaction (HER) and supercapacitors. Specifically, when the pine needle-derived carbon (activated at 800 °C) serves as a HER electrocatalyst, it exhibits a low onset potential (∼4 mV), a small Tafel slope (∼45.9 mV dec−1) and a remarkable stability over long-term cycling. When evaluated as an electrode material for supercapacitors, the pine needle-derived carbon (activated at 900 °C) demonstrates high specific capacitance (236 F g−1 at 0.1 A g−1), remarkable rate capability (183 F g−1 at even 20 A g−1) and good long-term stability. Notably, the specific capacitance at 2.0 A g−1 increased from ∼205 to ∼227 F g−1 after cycling for 5000 times, owing to the further activation and wetting of the electrodes. This novel and low-cost biomass-derived carbon material is very promising for many applications, especially in electrocatalytic water splitting and supercapacitors.

Perovskite photovoltaics have attracted remarkable attention recently due to their exceptional power conversion efficiencies (PCE). State-of-the-art perovskite absorbers typically require thermal annealing steps for high film quality. However, the annealing process adds cost and reduces yield for device fabrication and may also hinder application in tandem photovoltaics and flexible/ultra-low-cost optoelectronics. Herein, we report an additive-based room-temperature process for realizing high-quality methylammonium lead iodide films with micron-sized grains (>2 μm) and microsecond-range carrier lifetimes (τ1 = 931.94 ± 89.43 ns; τ2 = 320.41 ± 43.69 ns). Solar cells employing such films demonstrate 18.22% PCE with improved current–voltage hysteresis and stability without encapsulation. Further, we reveal that room-temperature-processed perovskite film grain size strongly depends on the precursor aggregate size in the film-deposition solution and that additive-based tuning of aggregate properties enables enlarging grains to the micron scale. These results offer a new pathway for more versatile, cost-effective perovskite processing.

Perovskite photovoltaics have attracted remarkable attention recently due to their exceptional power conversion efficiencies (PCE). State-of-the-art perovskite absorbers typically require thermal annealing steps for high film quality. However, the annealing process adds cost and reduces yield for device fabrication and may also hinder application in tandem photovoltaics and flexible/ultra-low-cost optoelectronics. Herein, we report an additive-based room-temperature process for realizing high-quality methylammonium lead iodide films with micron-sized grains (>2 μm) and microsecond-range carrier lifetimes (τ1 = 931.94 ± 89.43 ns; τ2 = 320.41 ± 43.69 ns). Solar cells employing such films demonstrate 18.22% PCE with improved current–voltage hysteresis and stability without encapsulation. Further, we reveal that room-temperature-processed perovskite film grain size strongly depends on the precursor aggregate size in the film-deposition solution and that additive-based tuning of aggregate properties enables enlarging grains to the micron scale. These results offer a new pathway for more versatile, cost-effective perovskite processing.

Here we report an effective bottom-up solution-phase process for the preparation of nitrogen-doped porous carbon scaffolds (NPCSs), which can be employed as high-performance anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The as-obtained NPCSs show favorable features for electrochemical energy storage such as high specific surface area, appropriate pore size distribution (3.9 nm in average), large pore volume (1.36 cm3 g−1), nanosheet-like morphology, a certain degree of graphitization, enlarged interlayer distance (0.38 nm), high content of nitrogen (∼5.6 at%) and abundant electrochemically-active sites. Such a unique architecture provides efficient Li+/Na+ reservoirs, and also possesses smooth electron transport pathways and electrolyte access. For LIBs, the anodes based on NPCSs deliver a high reversible capacity of 1275 mA h g−1 after 250 cycles at 0.5 C (1 C = 372 mA g−1), and outstanding cycling stabilities with a capacity of 518 mA h g−1 after 500 cycles at 5 C and 310 mA h g−1 after 1500 cycles even at 10 C. For SIBs, the anodes based on NPCSs display a reversible capacity of 257 mA h g−1 at 50 mA g−1, and superior long-term cycling performance with a capacity of 191 mA h g−1 after 1000 cycles at 200 mA g−1.

Here, novel multifunctional electronic skins (E-skins) based on aligned few-walled carbon nanotube (AFWCNT) polymer composites with a piezoresistive functioning mechanism different from the mostly investigated theory of “tunneling current channels” in randomly dispersed CNT polymer composites are demonstrated. The high performances of as-prepared E-skins originate from the anisotropic conductivity of AFWCNT array embedded in flexible composite and the distinct variation of “tube-to-tube” interfacial resistance responsive to bending or stretching. The polymer/AFWCNT-based flexion-sensitive E-skins exhibit high precision and linearity, together with low power consumption (<10 µW) and good stability (no degradation after 15 000 bending–unbending cycles). Moreover, polymer/AFWCNT composites can also be used for the construction of tensile-sensitive E-skins, which exhibit high sensitivity toward tensile force. The polymer/AFWCNT-based E-skins show remarkable performances when applied to monitor the motions and postures of body joints (such as fingers), a capability that can find wide applications in wearable human–machine communication interfaces, portable motion detectors, and bionic robots.

Despite high theoretical energy density, the practical deployment of lithium–sulfur (Li–S) batteries is still not implemented because of the severe capacity decay caused by polysulfide shuttling and the poor rate capability induced by low electrical conductivity of sulfur. Herein, we report a novel sulfur host material based on “sea urchin”-like cobalt nanoparticle embedded and nitrogen-doped carbon nanotube/nanopolyhedra (Co-NCNT/NP) superstructures for Li–S batteries. The hierarchical micromesopores in Co-NCNT/NP can allow efficient impregnation of sulfur and block diffusion of soluble polysulfides by physical confinement, and the incorporation of embedded Co nanoparticles and nitrogen doping (∼4.6 at. %) can synergistically improve the adsorption of polysulfides, as evidenced by beaker cell tests. Moreover, the conductive networks of Co-NCNT/NP interconnected by nitrogen-doped carbon nanotubes (NCNTs) can facilitate electron transport and electrolyte infiltration. Therefore, the specific capacity, rate capability, and cycle stability of Li–S batteries are significantly enhanced. As a result, the Co-NCNT/NP based cathode (loaded with 80 wt % sulfur) delivers a high discharge capacity of 1240 mAh g–1 after 100 cycles at 0.1 C (based on the weight of sulfur), high rate capacity (755 mAh g–1 at 2.0 C), and ultralong cycling life (a very low capacity decay of 0.026% per cycle over 1500 cycles at 1.0 C). Remarkably, the composite cathode with high areal sulfur loading of 3.2 mg cm–2 shows high rate capacities and stable cycling performance over 200 cycles.Keywords: carbon nanotube/nanopolyhedra superstructures; hierarchical micromesopores; Lithium−sulfur batteries; polysulfide trapping;

Herein, we report a unique thermal synthesis method to prepare a novel two-dimensional (2D) hybrid nanostructure consisting of ultrathin and tiny-sized molybdenum disulfide nanoplatelets homogeneously inlaid in graphene sheets (MoS2/G) with excellent electrocatalytic performance for HER. In this process, molybdenum oleate served as the source of both molybdenum and carbon, while crystalline sodium sulfate (Na2SO4) served as both reaction template and sulfur source. The remarkable integration of MoS2 and graphene in a well-assembled 2D hybrid architecture provided large electrochemically active surface area and a huge number of active sites and also exhibited extraordinary collective properties for electron transport and H+ trapping. The MoS2/G inlaid nanosheets deliver ultrahigh catalytic activity toward HER among the existing electrocatalysts with similar compositions, presenting a low onset overpotential approaching 30 mV, a current density of 10 mA/cm2 at ∼110 mV, and a Tafel slope as small as 67.4 mV/dec. Moreover, the strong bonding between MoS2 nanoplatelets and graphene enabled outstanding long-term electrochemical stability and structural integrity, exhibiting almost 100% activity retention after 1000 cycles and ∼97% after 100 000 s of continuous testing (under static overpotential of −0.15 V). The synthetic strategy is simple, inexpensive, and scalable for large-scale production and also can be extended to diverse inlaid 2D nanoarchitectures with great potential for many other applications.

Diameter control in the synthesis of single-walled carbon nanotube (SWNT) arrays is vital to the control of their properties and their integration into practical devices. Controlling the size of catalyst nanoparticles (NPs) and following a tangential nucleation mode has been shown to be an effective approach to diameter control of SWNTs. The size distribution of SWNTs, however, was much wider than that of the catalyst NPs because of the evolution of catalysts at high growth temperatures. Here, we demonstrate that rhodium (Rh) nanoparticles serve as highly active catalysts for the synthesis of dense and aligned arrays of SWNTs and offer unexpected diameter control via a perpendicular nucleation mode. The diameter distribution of SWNTs grown from the Rh catalysts is much narrower than that from conventional iron and copper catalysts and is independent of the size and shape of the catalyst NPs. More importantly, the Rh catalysts have remarkable catalytic activity at reduced temperatures (<800 °C) and exhibit improved chirality control through a decrease in the growth temperature.

Selective synthesis of single-walled carbon nanotubes (SWNTs) with controlled properties is an important research topic for SWNT studies. Here we report a thiophene-assisted chemical vapor deposition (CVD) method to directly grow highly conductive SWNT thin films on substrates, including transparent ones. By adding low concentration thiophene into the carbon feedstock (ethanol), the as-prepared carbon nanotubes demonstrate an obvious up-shift in the diameter distribution while the single-walled structure is still retained. In the proposed mechanism, the change in the diameter is sourced from the increase in the carbon yield induced by the sulfur-containing compound. Such SWNTs are found to possess high conductivity with 95% SWNTs demonstrating on/off ratios lower than 100 in transistors. More importantly, it is further demonstrated that this method can be used to directly synthesize dense SWNT networks on transparent substrates which can be utilized as transparent conductive films (TCFs) with very high transparency. Such TCFs can be applied to fabricate a light modulating window as a proof-of-concept. The present work provides important insights into the growth mechanism of SWNTs and great potential for the preparation of TCFs with high scalability, easy operation and low cost.

Lithiated transition metal phosphates with large theoretical capacities have emerged as promising cathode materials for rechargeable lithium-ion batteries. However, the poor kinetic properties caused by their low intrinsic electronic and ionic conductivity greatly hinder their practical applications. In this work, we demonstrate a novel strategy to prepare monoclinic lithium vanadium phosphate nanoparticles implanted in carbon nanofibers as the cathodes of Li-ion cells with high capacity, flexibility, long cycle stability and significantly improved high-rate performance. The composite nanofibers were obtained by electrospinning using polyacrylonitrile and Li3V2(PO4)3 nanoparticles, followed by annealing and coating with a thin layer of carbon by plasma enhanced chemical vapor deposition. The Li3V2(PO4)3 nanocrystals with the monoclinic phase were uniformly distributed in the composite nanofibers. The electrochemical performances of the as-prepared binder-free fibrous cathodes were characterized by potentiostatic and galvanostatic tests. At the rate of 0.5 C in the range of 3.0–4.3 V, the composite displayed an initial discharge capacity of 128 mA h g−1 (96.2% of the theoretical capacity). A discharge capacity of 120 mA h g−1 was observed even at a high rate of 10 C, and a capacity retention of 98.9% was maintained after 500 cycles at 5 C, indicating excellent high-rate capability and capacity retention. Compared to the control samples without a carbon outer-layer, the composite nanofibers with carbon coating demonstrated much better electrochemical performances. It indicates that the carbon coating can further protect the structural integrity of nanofabric electrodes during the charge/discharge processes without hindering the Li-ion mobility and also can prevent undesired side reactions with an electrolyte, thus greatly improving the rate performance and cyclic stability of the cathode.

Here, we report a hierarchical Co3ZnC/carbon nanotube-inserted nitrogen-doped carbon concave-polyhedrons synthesized by direct pyrolysis of bimetallic zeolitic imidazolate framework precursors under a flow of Ar/H2 and subsequent calcination for both high-performance rechargeable Li-ion and Na-ion batteries. In this structure, Co3ZnC nanoparticles were homogeneously distributed in in situ growth carbon nanotube-inserted nitrogen-doped carbon concave-polyhedrons. Such a hierarchical structure offers a synergistic effect to withstand the volume variation and inhibit the aggregation of Co3ZnC nanoparticles during long-term cycles. Meanwhile, the nitrogen-doped carbon and carbon nanotubes in the hierarchical Co3ZnC/carbon composite offer fast electron transportation to achieve excellent rate capability. As anode of Li-ion batteries, the electrode delivered a high reversible capacity (∼800 mA h/g at 0.5 A/g), outstanding high-rate capacity (408 mA h/g at 5.0 A/g), and long-term cycling performance (585 mA h/g after 1500 cycles at 2.0 A/g). In Na-ion batteries, the Co3ZnC/carbon composite maintains a stable capacity of 386 mA h/g at 1.0 A/g without obvious decay over 750 cycles and a superior rate capability (∼500, 448, and 415 mA h/g at 0.2, 0.5, and 1.0 A/g, respectively).Keywords: anode materials; lithium storage; metal−organic frameworks; sodium storage; ternary metallic carbides

Polydisperse rhodium nanoparticles have recently shown promise for ultraviolet (UV) plasmonics, but controlling the size and morphology of metal nanoparticles is essential for tuning surface plasmon resonances. Here we report the use of slow-injection polyol methods to synthesize monodisperse Rh nanocubes with unprecedentedly large sizes and slightly concave faces. The associated local surface plasmon resonances (LSPRs) red-shifted with increasing sizes in the UV region from deep UV to around 400 nm, consistent with numerical simulations. UV illumination of p-aminothiophenol attached to the Rh nanocubes generated surface-enhanced Raman spectra and accelerated photo-decomposition, and these enhancements were largest for nanocubes whose LSPR was resonant with the UV laser. The lack of a native oxide coating, the precise control of nanocube size and morphology demonstrated here, and the ability to tune the surface plasmon resonance from the deep UV to near UV spectral region, make rhodium a compelling choice for UV plasmonic applications.

•Self-assembled ultrathin NiCo2S4 nanoflakes grown on Ni foam was fabricated.•NiCo2S4/Ni foam was prepared by directly sulfidation of NiCo-LDH/Ni foam.•NiCo2S4/Ni foam show a significantly improved HER catalytic activity.•Possible mechanism for the enhanced catalytic activity was proposed.Considerable efforts have been devoted on the design and fabrication of non-platinum electrocatalysts with high performance and low cost for hydrogen evolution reaction (HER). However, the catalytic activity of existing electrocatalysts usually subjects to the limited amount of exposed active sites. Herein, we propose that self-assembled ultrathin NiCo2S4 nanoflakes grown on nickel foam (NiCo2S4/Ni foam) can serve as excellent electrocatalyst for HER in alkaline solution with high activity and stability. The NiCo2S4/Ni foam electrodes were prepared by the complete sulfidation of networked ultrathin NiCo-layered double hydroxide nanoflakes grown on Ni foam (NiCo-LDH/Ni foam). The advantages of this unique architecture are that the ultrathin and porous NiCo2S4 nanoflakes can provide a huge number of exposed active sites, the highly-conductive Ni foam can promote the transfer of electrons, and the three-dimensional-networked structure can facilitate the diffusion and penetration of electrolyte. Electrochemical measurements reveal that NiCo2S4/Ni foam electrodes exhibit greatly improved performance than NiCo-LDH/Ni foam for HER in alkaline solution with low onset overpotential (17 mV), small Tafel slope (84.5 mV/dec) and excellent long-duration cycling stability (maintaining an onset overpotential of ~20 mV and an overpotential of 155 mV at 50 mA/cm2 after testing for 100,000 s). In addition, the highly-flexible NiCo2S4/Ni foam electrodes show no obvious catalytic degradation after bending for 200 times, confirming the high flexibility and robustness under severe conditions.

Aligned single-walled carbon nanotubes (SWNTs) synthesized by the chemical vapor deposition (CVD) method have exceptional potential for next-generation nanoelectronics. However, the coexistence of semiconducting (s-) and metallic (m-) SWNTs remains a considerable challenge since the latter causes significant degradation in device performance. Here we demonstrate a facile and effective approach to selectively break all m-SWNTs by stacking two layers of horizontally aligned SWNTs to form crossbars and applying a voltage to the crossed SWNT arrays. The introduction of SWNT junctions amplifies the disparity in resistance between s- and m-pathways, leading to a complete deactivation of m-SWNTs while minimizing the degradation of the semiconducting counterparts. Unlike previous approaches that required an electrostatic gate to achieve selectivity in electrical breakdown, this junction process is gate-free and opens the way for straightforward integration of thin-film s-SWNT devices. Comparison to electrical breakdown in junction-less SWNT devices without gating shows that this junction-based breakdown method yields more than twice the average on-state current retention in the resultant s-SWNT arrays. Systematic studies show that the on/off ratio can reach as high as 1.4 × 106 with a correspondingly high retention of on-state current compared to the initial current value before breakdown. Overall, this method provides important insight into transport at SWNT junctions and a simple route for obtaining pure s-SWNT thin film devices for broad applications.

It is well known that both the structural morphology and chemical doping are important factors that affect the properties of metal hydroxide materials in electrochemical energy storage devices. In this work, an effective method to tailor the morphology and chemical doping of metal hydroxides is developed. It is shown that the morphology and the degree of crystallinity of Ni(OH)2 can be changed by adding glucose in the ethanol-mediated solvothermal synthesis. Ni(OH)2 produced in this manner exhibited an increased specific capacitance, which is partially attributed to its increased surface area. Interestingly, the effect of morphology on cobalt doped-Ni(OH)2 is found to be more effective at low cobalt contents than at high cobalt contents in terms of improving the electrochemical performance. This result reveals the existence of competitive effects between chemical doping and morphology change. These findings will provide important insights to design effective materials for energy storage devices.

A graphical abstract is available for this content

Researchers have demonstrated that the alignment of single-walled carbon nanotubes (SWNTs) on the surface of the single crystal substrate is due to guided growth along either step edges (graphoepitaxial) or certain directions in the atomic lattice (epitaxial), with only one of the two alignment modes predominating in different research systems. For the SWNTs grown on a quartz surface, the growth of a perfectly aligned array and other shapes were induced by the epitaxial effect. Here we report the finding that water vapor introduced during the catalyst annealing process can change the alignment mode of the SWNTs on the quartz surface by modifying the surface status of both the catalyst and the substrate. Zigzag shaped nanotube arrays can be obtained by enabling both alignment modes simultaneously through adjusting the water vapor concentration, changing the oxidation state of the metal catalyst and/or modifying the morphology of the substrate surface. These findings provide important insights into the mechanism of guided growth of complex nanotube shapes, for potential applications including electronics, photodetection, sensing, and in other devices.

A “top-down” and scalable approach for processing carbon fiber cloth (CFC) into flexible and all-carbon electrodes with remarkable areal capacity and cyclic stability was developed. CFC is commercially available in large quantities but its use as an electrode material in supercapacitors is not satisfactory. The approach demonstrated in this work is based on the sequential treatment of CFC with KOH activation and high temperature annealing that can effectively improve its specific surface area to a remarkable 2780 m2 g−1 while at the same time achieving a good electrical conductivity of 320 S m−1 without sacrificing its intrinsic mechanical strength and flexibility. The processed CFC can be directly used as an electrode for supercapacitors without any binders, conductive additives and current collectors while avoiding elaborate electrode processing steps to deliver a specific capacitance of ∼0.5 F cm−2 and ∼197 F g−1 with remarkable rate performance and excellent cyclic stability. The properties of these processed CFCs are comparable or better than graphene and carbon nanotube based electrodes. We further demonstrate symmetric solid-state supercapacitors based on these processed CFCs with very good flexibility. This “top-down” and scalable approach can be readily applied to other types of commercially available carbon materials and therefore can have a substantial significance for high performance supercapacitor devices.

Here we report a new light-responsive and self-healing anticorrosion coating by incorporating hollow nanocontainers with smart molecular switches. The smart coating was obtained by immobilizing photoresponsive azobenzene molecular switches in the nanopores of hollow mesoporous silica nanocontainers. These novel nanocontainers with hollow cavities can encapsulate active molecules under visible light and release them under ultraviolet irradiation. The release of benzotriazole from the hollow nanocontainers can be started and stopped with high controllability, which provides an effective approach to avoid excessive release of active molecules after corrosion healing. The results of scanning vibrating electrode technique demonstrate that the azobenzene molecular switch modified hollow mesoporous silica nanocontainers exhibit excellent continuous photosensitive self-healing performance for improving the long-term performance of aluminium alloy.

Flexible lithium batteries with high energy density have recently received tremendous interest due to their potential applications in flexible electronic devices. Herein, we report a novel method to fabricate highly flexible and robust carbon nanotube–graphene/sulfur (CNTs–RGO/S) composite film as free-standing cathode for flexible Li/S batteries with increased capacity and significantly improved rate capability. The free-standing CNTs–RGO/S cathode was able to deliver a peak capacity of 911.5 mAh g–1sulfur (∼483 mAh g–1electrode) and maintain 771.8 mAh g–1sulfur after 100 charge–discharge cycles at 0.2C, indicating a capacity retention of 84.7%, which were both higher than the cathodes assembled without CNTs. Even after 100 cycles, the cathode showed a high tensile strength of 62.3 MPa. More importantly, the rate capability was improved by introducing CNTs. The CNTs–RGO/S cathode exhibited impressive capacities of 613.1 mAh g–1sulfur at 1C with a capacity recuperability of ∼94% as the current returned to 0.2C. These results demonstrate that the well-designed nanocomposites are of great potential as the cathode for flexible lithium sulfur (Li/S) batteries. Such improved electrochemical properties could be attributed to the unique coaxial architecture of the nanocomposite, in which the evenly dispersed CNTs enable electrodes with improved electrical conductivity and mechanical properties and better ability to avoid the aggregation and ensure the dispersive distribution of the sulfur species during the charge/discharge process.

Graphene fibers are a promising electrode material for wire-shaped supercapacitors (WSSs) that can be woven into textiles for future wearable electronics. However, the main concern is their high linear resistance, which could be effectively decreased by the addition of highly conductive carbon nanotubes (CNTs). During the incorporation process, CNTs are typically preoxidized by acids or dispersed by surfactants, which deteriorates their electrical and mechanical properties. Herein, unfunctionalized few-walled carbon nanotubes (FWNTs) were directly dispersed in graphene oxide (GO) without preoxidation or surfactants, allowing them to maintain their high conductivity and perfect structure, and then used to prepare CNT-reduced GO (RGO) composite fibers by wet-spinning followed by reduction. The pristine FWNTs increased the stress strength of the parent RGO fibers from 193.3 to 385.7 MPa and conductivity from 53.3 to 210.7 S cm–1. The wire-shaped supercapacitors (WSSs) assembled based on these CNT-RGO fibers presented a high volumetric capacitance of 38.8 F cm–3 and energy density of 3.4 mWh cm–3. More importantly, the performance of WSSs was revealed to decrease with increasing length due to increased resistance, revealing a key issue for graphene-based electrodes in WSSs.Keywords: carbon nanotubes; fibers; graphene; solution spinning; supercapacitors; wire;

A core/shell stretchable conductive composite of a few-walled carbon nanotube network coated on a poly(m-phenylene isophthalamide) fiber (FWNT/PMIA) was fabricated by a dip-coating method and an annealing process that greatly enhanced interactions between the FWNT network and PMIA core as well as within the FWNT network. The first strain–conductivity test of the as-prepared FWNT/PMIA fiber showed a stretching-induced alignment of nanotubes in the shell during the deformation process and a good conductivity stability with a slight conductivity drop from 109.63 S/cm to 98.74 S/cm (Δσ/σ0 = 10%) at a strain of ∼150% (2.5 times the original length). More importantly, after the first stretching process, the fiber can be recovered with a slight increase in length but a greatly improved conductivity of 167.41 S/cm through an additional annealing treatment. The recovered fiber displays a similarly superb conductivity stability against stretching, with a decrease of only ∼13 S/cm to 154.49 S/cm (Δσ/σ0 = 8%) at a strain of ∼150%. We believe that this conductivity stability came from the formation and maintaining of aligned nanotube structures during the stretching process, which ensures the good tube–tube contacts and the elongation of the FWNT network without losing its conductivity. Such stable conductivity in stretchable fibers will be important for applications in stretchable electronics.Keywords: core/shell structure; few-walled carbon nanotube; fibers; PMIA; stretchable conductor; stretching-induced alignment;

This study presents a simple method to reproducibly obtain well-aligned vertical ZnO nanowire arrays on silicon oxide (SiOx) substrates using seed crystals made from a mixture of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2) solution. In comparison, high levels of OH− concentration obtained using NaOH or KOH solutions lead to incorporation of Na or K atoms into the seed crystals, destroying the c-axis alignment of the seeds and resulting in the growth of misaligned nanowires. The use of NH4OH eliminates the metallic impurities and ensures aligned nanowire growth in a wide range of OH− concentrations in the seed solution. The difference of crystalline orientations between NH4OH- and NaOH-based seeds is directly observed by lattice-resolved images and electron diffraction patterns using a transmission electron microscope (TEM). This study obviously suggests that metallic impurities incorporated into the ZnO nanocrystal seeds are one of the factors that generates the misaligned ZnO nanowires. This method also enables the use of silicon oxide substrates for the growth of vertically aligned nanowires, making ZnO nanostructures compatible with widely used silicon fabrication technology.

The effect of composition and microstructure of NiO on the electrochemical properties of NiO/reduced graphene oxide-based supercapacitor electrodes prepared by solvothermal methods were investigated systematically. The findings reveal that the influences of reduced graphene oxide (RGO) coating on electrode systems are essentially 2-fold. One is to increase the electrical conductivity of the electrodes, especially when the electrodes are not very conductive. However, this influence is not that obvious when the electrodes are already highly conductive to begin with. The second influence is to improve the mechanical stability of the electrode, thus increasing the cyclability of the electrodes. Moreover, adding glucose during the electrode synthesis reduces the particle size as well as the thickness of deposited active material (NiO) on the substrate under similar mass loading. These thinner but denser NiO structures exhibited much improved electrochemical performance. These understandings will be important in the designing of high performance energy storage devices, especially from materials with limited electrical conductivity.

Single-walled carbon nanotubes (SWNTs) are highly desired for future electronic applications due to the excellent electrical, mechanical, and thermal properties. However, the density and the selectivity in the growth of aligned semiconducting nanotubes do not coexist previously: when the selectivity is high, the density is low and vice versa. In the present work, we found that random carbon nanotubes (CNTs) in the catalyst area block the growth of aligned SWNTs along the lattice structure on the quartz surface, thus significantly reducing the density of nanotubes during growth. More interestingly, it was shown that the random CNTs can be selectively removed through appropriate treatments using water vapor as an in situ etchant while the aligned SWNTs survive even after long-time water vapor treatment. To obtain high-density semiconducting SWNT arrays, we designed an improved multiple-cycle growth method, which included the treatment of SWNTs with water vapor after each growth cycle without cooling the system. Using this method, we have successfully obtained dense semiconducting SWNTs (∼10 SWNTs/μm) over large areas and with high uniformity.Keywords: high density; high selectivity; multiple-cycle growth method; single-walled carbon nanotubes; water vapor

The coexistence of semiconducting and metallic single-walled carbon nanotubes (SWNTs) during synthesis is one of the major bottlenecks that prevent their broad application for the next-generation nanoelectronics. Herein, we present more understanding and demonstration of the growth of highly enriched semiconducting SWNTs (s-SWNTs) with a narrow diameter distribution. An important fact discovered in our experiments is that the selective elimination of metallic SWNTs (m-SWNTs) from the mixed arrays grown on quartz is diameter-dependent. Our method emphasizes controlling the diameter distribution of SWNTs in a narrow range where m-SWNTs can be effectively and selectively etched during growth. In order to achieve narrow diameter distribution, uniform and stable Fe–W nanoclusters were used as the catalyst precursors. About 90% of as-prepared SWNTs fall into the diameter range 2.0–3.2 nm. Electrical measurement results on individual SWNTs confirm that the selectivity of s-SWNTs is ∼95%. The present study provides an effective strategy for increasing the purity of s-SWNTs via controlling the diameter distribution of SWNTs and adjusting the etchant concentration. Furthermore, by carefully comparing the chirality distributions of Fe–W-catalyzed and Fe-catalyzed SWNTs under different water vapor concentrations, the relationship between the diameter-dependent and electronic-type-dependent etching mechanisms was investigated.Keywords: diameter control; Fe−W nanoclusters; selective etching; semiconducting; single-walled carbon nanotubes

In this paper we describe an accumulative approach to move beyond simple incorporation of conductive carbon nanostructures, such as graphene and carbon nanotubes, to improve the performance of metal oxide/hydroxide based electrodes in energy storage applications. In this approach we first synthesize Co–Ni double hydroxides/graphene binary composites through a co-precipitation process. We then assemble these composites into films (∼6 mg cm−2) by integrating with carbon nanotubes that can be used directly as electrodes. Experimental results indicate that the synergistic contributions from nanotubes, graphene and cobalt substitution enabled electrodes with substantially improved energy storage performance metrics. With 50% Co and 50% Ni (i.e. Co0.5Ni0.5(OH)2), the composite exhibited a remarkable maximum specific capacitance of 2360 F g−1 (360 mA h g−1) at 0.5 A g−1 and still maintained a specific capacitance as high as 2030 F g−1 at 20 A g−1 (∼86% retention). More importantly, the double hydroxides exhibited tunable redox behavior that can be controlled by the ratio between cobalt and nickel. These results demonstrate the importance of the rational design of functional composites and the large-scale assembly strategies for fabricating electrodes with improved performance and tunability for energy storage applications.

Long-term instability of Li–S batteries is one of their major disadvantages compare to other secondary batteries. The reasons for the instability include dissolution of polysulfide intermediates and mechanical instability of the electrode film caused by volume changes during charging/discharging cycles. In this paper, we report a novel graphene–sulfur–carbon nanofibers (G-S-CNFs) multilayer and coaxial nanocomposite for the cathode of Li–S batteries with increased capacity and significantly improved long-cycle stability. Electrodes made with such nanocomposites were able to deliver a reversible capacity of 694 mA h g–1 at 0.1C and 313 mA h g–1 at 2C, which are both substantially higher than electrodes assembled without graphene wrapping. More importantly, the long-cycle stability was significantly improved by graphene wrapping. The cathode made with G-S-CNFs with a initial capacity of 745 mA h g–1 was able to maintain ∼273 mA h g–1 even after 1500 charge–discharge cycles at a high rate of 1C, representing an extremely low decay rate (0.043% per cycle after 1500 cycles). In contrast, the capacity of an electrode assembled without graphene wrapping decayed dramatically with a 10 times high rate (∼0.40% per cycle after 200 cycles). These results demonstrate that the coaxial nanocomposites are of great potential as the cathode for high-rate rechargeable Li–S batteries. Such improved rate capability and cycle stability could be attributed to the unique coaxial architecture of the nanocomposite, in which the contributions from graphene and CNFs enable electrodes with improved electrical conductivity, better ability to trap soluble the polysulfides intermediate and accommodate volume expansion/shrinkage of sulfur during repeated charge/discharge cycles.

Supercapacitors with both high energy and high power densities are critical for many practical applications. In this paper, we discuss the design and demonstrate the fabrication of flexible asymmetric supercapacitors based on nanocomposite electrodes of MnO2, activated carbon, carbon nanotubes and graphene. The combined unique properties of each of these components enable highly flexible and mechanically strong films that can serve as electrodes directly without using any current collectors or binders. Using these flexible electrodes and a roll-up approach, asymmetric supercapacitors with 2 V working voltage were successfully fabricated. The fabricated device showed excellent rate capability, with 78% of the original capacitance retained when the scan rate was increased from 2 mV s−1 to 500 mV s−1. Owing to the unique composite structure, these supercapacitors were able to deliver high energy density (24 W h kg−1) under high power density (7.8 kW kg−1) conditions. These features could enable supercapacitor based energy storage systems to be very attractive for a variety of critical applications, such as the power sources in hybrid electric vehicles and the back-up powers for wind and solar energy, where both high energy density and high power density are required.

Flexible and lightweight energy storage systems have received tremendous interest recently due to their potential applications in wearable electronics, roll-up displays, and other devices. To manufacture such systems, flexible electrodes with desired mechanical and electrochemical properties are critical. Herein we present a novel method to fabricate conductive, highly flexible, and robust film supercapacitor electrodes based on graphene/MnO2/CNTs nanocomposites. The synergistic effects from graphene, CNTs, and MnO2 deliver outstanding mechanical properties (tensile strength of 48 MPa) and superior electrochemical activity that were not achieved by any of these components alone. These flexible electrodes allow highly active material loading (71 wt % MnO2), areal density (8.80 mg/cm2), and high specific capacitance (372 F/g) with excellent rate capability for supercapacitors without the need of current collectors and binders. The film can also be wound around 0.5 mm diameter rods for fabricating full cells with high performance, showing significant potential in flexible energy storage devices.

Conductive fillers, such as amorphous carbon, carbon nanotube and graphene etc., are generally mixed with nanostructured metal oxide materials to improve the performance of electrode materials in energy storage devices. However, the conductive framework that provides path for electric conduction does not normally form a well-connected and robust 3-D network to ensure optimized ions transport. Here, we report a convenient, inexpensive and scalable method for synthesizing hybrid carbon and titanium dioxide co-gels and co-aerogels to improve the electrochemical capacity by combining both the lithium insertion and the surface storage mechanisms in Li ion batteries (LIBs) anodes. A monolithic piece of a hybrid C/TiO2 co-aerogel can be directly used as an active electrode without the addition of binders, such as polyvinylidene fluoride (PVDF). As a result, the performance of LIB anodes using the hybrid co-aerogel is significantly improved over current LIBs based on carbon/titanium oxide composites. The reversible discharge capacity was stabilized at ∼400 mAh g−1 at a 168 mA g−1 scan rate and an operating voltage between 3.0 and 0.05 V vs. Li+/Li with excellent cyclic capacity retention. This approach, however, is not limited to only C/TiO2 system but can be extended to other metal oxides to form co-gels with carbon to improve their potential use in numerous electrochemical, photocatalytic, and photoelectronic devices.Highlights► We developed a simple one-pot method for the synthesis of co-gel of carbon and TiO2. ► The co-aerogel of carbon and TiO2 demonstrated superior electrochemcial properties for Li battery. ► We demonstrated the existence of interconnected carbon and metal oxide network in the co-aerogel structures.

We present a bottom-up synthesis, spectroscopic characterization, and ab initio simulations of star-shaped hexagonal zinc oxide (ZnO) nanowires. The ZnO nanostructures were synthesized by a low-temperature hydrothermal growth method. The cross-section of the ZnO nanowires transformed from a hexagon to a hexagram when sulfur dopants from thiourea [SC(NH2)2] were added into the growth solution, but no transformation occurred when urea (OC(NH2)2) was added. Comparison of the X-ray photoemission and photoluminescence spectra of undoped and sulfur-doped ZnO confirmed that sulfur is responsible for the novel morphology. Large-scale theoretical calculations were conducted to understand the role of sulfur doping in the growth process. The ab initio simulations demonstrated that the addition of sulfur causes a local change in charge distribution that is stronger at the vertices than at the edges, leading to the observed transformation from hexagon to hexagram nanostructures. Open image in new window

Double-walled carbon nanotubes (DWNTs) have recently been recognized as important members in the carbon nanotube family because they are expected to have certain unique properties. For example, DWNTs are expected to replace single-walled carbon nanotubes (SWNTs) in biomarker applications and optoelectronics if the observed luminescence from DWNTs can be verified. However, due to unavoidable byproducts, such as SWNTs, optical properties of DWNTs still remain controversial. There is an ongoing debate concerning the ability of DWNTs to exhibit photoluminescence (PL). In this report, we aim to clearly resolve this debate through the study of carefully separated DWNTs. DWNTs were successfully separated from SWNTs using density gradient ultracentrifugation. Here we clearly show that light is emitted from the inner wall of DWNTs; however, the intensity of the emission is significantly quenched. Interestingly, it was found that a very narrow range of diameters of the inner walls of DWNTs is required for PL to be observable. All other diameters led to complete PL quenching in DWNTs. In short, we have shown that both sides of the debate are correct under certain situations. The real answer to the question is that some DWNTs do emit light but most DWNTs do not.

A dense array of parallel single-walled carbon nanotubes (SWNTs) as the device channel can carry higher current, be more robust, and have smaller device-to-device variation, thus is more desirable for and compatible with applications in future highly integrated circuits when compared with single-tube devices. The density of the parallel SWNT arrays and the diameter of SWNTs both are key factors in the determination of the device performance. In this paper, we present a new multiple-cycle chemical vapor deposition (CVD) method to synthesize horizontally aligned arrays of SWNTs with densities of 20−40 SWNT/μm over large area and a diameter distribution of 2.4 ± 0.5 nm on the quartz surface based on a methanol/ethanol CVD method. The high nucleation efficiency of catalyst particles in multiple-cycle CVD processes has been demonstrated to be the main reason for the improvements in the density of SWNT arrays. More interestingly, we confirmed the existence of an etching effect, which strongly affects the final products in the multiple-cycle growth. This etching effect is likely the reason that only large-diameter SWNTs were obtained in the multiple-cycle CVD growth. Using these high-density and large-diameter nanotube arrays, two-terminal devices with back-gates were fabricated. The performances of these devices have been greatly improved in overall resistance and on-state current, which indicates these SWNT arrays have high potential for applications such as interconnects, high-frequency devices, and high-current transistors in future micro- or nanoelectronics.Keywords: high density; horizontally aligned arrays; large diameter; single-crystal quartz; single-walled carbon nanotubes

The environmental and health impacts of nanomaterials are becoming important topics of research in recent years. The unique advantages offered by these nanomaterials in wide range of applications cannot be realized until these concerns are resolved. Among all the nanomaterials, Ag nanoparticles, due to their existing extensive uses in commercial products, demand immediate attention. Since the nanoparticle suspensions will be exposed to environmental conditions different from a research lab setting, many factors, including light, temperature, salinity, etc., are suspected to affect the stability of the nanoparticle and also their toxicity. In this study, we examined the effect of sunlight on the stability and toxicity of 6 and 25 nm Ag nanoparticles coated with gum arabic (GA) and polyvinylpyrrolidone (PVP). Under sunlight irradiation, all of these nanoparticles irreversibly aggregated to different degrees depending on the surface coating. The UV content of the sunlight is identified to be the driving force of nanoparticle aggregation, and the strong oscillating dipole−dipole interaction is believed to be the origin of the destabilization. Toxicity examinations of the nanoparticles to a wetland plant, Lolium multiflorum, indicate that their toxicity is greatly reduced after sunlight irradiation.

For efficient use of metal oxides, such as MnO2 and RuO2, in pseudocapacitors and other electrochemical applications, the poor conductivity of the metal oxide is a major problem. To tackle the problem, we have designed a ternary nanocomposite film composed of metal oxide (MnO2), carbon nanotube (CNT), and conducting polymer (CP). Each component in the MnO2/CNT/CP film provides unique and critical function to achieve optimized electrochemical properties. The electrochemical performance of the film is evaluated by cyclic voltammetry, and constant-current charge/discharge cycling techniques. Specific capacitance (SC) of the ternary composite electrode can reach 427 F/g. Even at high mass loading and high concentration of MnO2 (60%), the film still showed SC value as high as 200 F/g. The electrode also exhibited excellent charge/discharge rate and good cycling stability, retaining over 99% of its initial charge after 1000 cycles. The results demonstrated that MnO2 is effectively utilized with assistance of other components (fFWNTs and poly(3,4-ethylenedioxythiophene)−poly(styrenesulfonate) in the electrode. Such ternary composite is very promising for the next generation high performance electrochemical supercapacitors.

High-density arrays of perfectly aligned single-walled carbon nanotubes (SWNTs) consisting almost exclusively of semiconducting nanotubes were grown on ST-cut single crystal quartz substrates. Raman spectroscopy together with electrical measurements of field effect transistors (FETs) fabricated from the as-grown samples showed that over 95% of the nanotubes in the arrays are semiconducting. The mechanism of selective growth was explored. It is proposed that introducing methanol in the growth process, combined with the interaction between the SWNTs and the quartz lattice, leads to the selective growth of aligned semiconducting nanotubes. Such a high density of horizontally aligned semiconducting SWNTs can be readily used in high current nanoFETs and sensors. This method demonstrates great promise to solve one of the most difficult problems which limits application of carbon nanotubes in nanoelectronics—the coexistence of metallic and semiconducting nanotubes in samples produced by most, if not all, growth methods.

The reported fluorescence from inner shells of double-walled carbon nanotubes (DWCNTs) is an intriguing and potentially useful property. A combination of bulk and single-molecule methods was used to study the spectroscopy, chemical quenching, mechanical rigidity, abundance, density, and TEM images of the near-IR emitters in DWCNT samples. DWCNT inner shell fluorescence is found to be weaker than SWCNT fluorescence by a factor of at least 10 000. Observable near-IR emission from DWCNT samples is attributed to SWCNT impurities.

Carbon nanotubes (CNTs) have attracted attention for their remarkable electrical properties and have being explored as one of the best building blocks in nano-electronics. A key challenge to realize such potential is the control of the nanotube growth directions. Even though both vertical growth and controlled horizontal growth of carbon nanotubes have been realized before, the growth of complex nanotube structures with both vertical and horizontal orientation control on the same substrate has never been achieved. Here, we report a method to grow three-dimensional (3D) complex nanotube structures made of vertical nanotube forests and horizontal nanotube arrays on a single substrate and from the same catalyst pattern by an orthogonally directed nanotube growth method using chemical vapor deposition (CVD). More importantly, such a capability represents a major advance in controlled growth of carbon nanotubes. It enables researchers to control the growth directions of nanotubes by simply changing the reaction conditions. The high degree of control represented in these experiments will surely make the fabrication of complex nanotube devices a possibility.

We present a chemical vapor deposition (CVD) method for the growth of uniform single-walled carbon nanotube (SWNT) arrays on a stable temperature (ST)-cut single crystal quartz substrate using a mixture of methanol and ethanol as carbon source. It is found that introducing methanol during the growth can improve the density and the length of the well-aligned SWNTs in the arrays as well as increase the SWNT/quartz interaction. Obvious “up-shifts” of G-band frequencies in the Raman spectra have been found for the aligned SWNTs. A welldesigned control experiment shows that the G-band “up-shifts” originate from the strong interaction between SWNTs and the quartz substrate. It is believed that exploring this interaction will help to elucidate the growth mechanism; ultimately, this will help realize the promise of controlling the chirality of SWNTs.

We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes (SWNTs) by reviewing recent progress in the surface synthesis of SWNTs. Three effects of catalysts on surface synthesis are studied: type of catalyst, the relationship between the size of catalyst particles and carbon feeding rates, and interactions between catalysts and substrates. Understanding of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate the fabrication of nanotube-based devices.

Compared to single-walled carbon nanotubes (SWNTs) and more defective multiwalled carbon nanotubes (MWNTs), the thin few-walled carbon nanotubes (FWNTs) are believed to have extraordinary mechanical properties. However, the enhancement of mechanical properties in FWNTs-polymer composites has remained elusive. In this study, free-standing carbon nanotubes (CNTs)/polymer composite films were fabricated with three types (SWNTs, FWNTs, MWNTs) of functionalized CNTs. The mechanical properties of composite films have been investigated. It is observed that the Young’s modulus of composite films with only 0.2 wt % functionalized FWNTs shows a remarkable reinforcement value of dY/dVf = 1658 GPa, which is ∼400 GPa higher than the highest value (dY/dVf = 1244 GPa) that was previously reported. In addition, the Young’s modulus increased steadily with the increased concentration of FWNTs. The results indicated that FWNTs are practically the optimum reinforcing filler for the next generation of carbon nanotube-based composite materials.Keywords: FWNTs; PVA; Young’s modulus

Horizontally aligned single-walled carbon nanotubes (SWNTs) are highly desired for SWNT device applications. A large variety of metals including Fe, Co, Ni, Cu, Pt, Pd, Mn, Mo, Cr, Sn, Au, Mg, and Al successfully catalyzed the growth of such tubes on stable temperature (ST)-cut quartz by lattice guidance. In addition, Mg and Al were presented to produce random and aligned SWNTs for the first time. A hypothesis is proposed in which the precipitated carbon shell on the outer surface of the metal catalysts guides the alignment along the crystal lattice but not the catalysts themselves. By elucidating the role of the catalysts, an understanding of the aligned growth mechanism on quartz is further improved. Moreover, a simple “scratch” method by a razor blade such as the carbon steel and tungsten carbide (with 9% cobalt) is presented to pattern the “catalysts” without any complex processing steps such as lithography for the aligned SWNT growth.

Purification of high-quality few-walled carbon nanotubes (fWNTs) was developed by slow but selective oxidation in hydrogen peroxide (H2O2) at room temperature. The purity, nanotubes’ structure, and thermal stability of purified fWNTs were characterized by transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis (TGA), respectively. The results showed that fWNTs could be selectively purified by prolonging the stirring time in 30 wt % H2O2 solution. Highly purified fWNTs were obtained, having a high G/D ratio in Raman spectra and good thermal stability indicating the good quality of the purified fWNTs. The approach provides a simple low cost method for purification that also has higher nanotube yield than other purification methods.Keywords: few-walled carbon nanotubes; high yield; hydrogen peroxide; purification; Raman spectra

Nanoscale devices are expected to provide important advances for a number of applications. While many methods to generate nanoscale patterns exist, their use is confined to a relatively narrow range of materials. To fabricate nanoscale structures of a material with useful properties, the most convenient route is to transfer the geometry of an existing pattern into another material. Methods to achieve this pattern transfer are summarized and organized in this review. Methods to generate the original patterns, as well as applications of the final structure are also described.

A simple method to fabricate parallel and/or crossed networks of ultra-long single-walled carbon nanotube (SWNT) arrays based on carbon monoxide-chemical vapor deposition (CO-CVD) by a “fast-heating” growth process is reported. The catalysts which are water-soluble inorganic molecular clusters containing Fe and Mo atoms can be easily “drawn” on the substrate by an ink pen using the cluster solution as “ink” or transferred by micro-contact printing (μCP) using poly (dimethylsiloxane) (PDMS) elastomer stamp onto substrate. The as-grown SWNTs are millimetres in length with diameters ranging from 0.7 to 2.0 nm and with controllable location and direction. Multi-dimensional crossed-networks of SWNTs can be easily fabricated by multi-step growth processes. Patterning catalysts using water-soluble clusters can be compatible with ink-jet printing techniques for generating large-area well-oriented and precisely-located SWNTs. We have also demonstrated that the ease of patterning and growing aligned nanotube arrays provides a reliable way to fabricate nanotube electronic devices.

•The PM-CNPs possess the advantages of large specific surface area, porous structure, and good conductivity.•The PM-CNP based supercapacitors exhibit excellent specific capacity and superb stability over long-term cycling.•The PM-CNPs also show good ORR electrocatalytic activity and excellent stability towards methanol crossover.Particulate matter (PM) pollution has become a serious environmental problem, especially in developing countries, owing to its severe threat to human health. Particularly, airborne PM2.5 (mean aerodynamic diameter ≤2.5 µm) particles are extremely harmful, because the tiny particles can enter human respiratory system and even penetrate into circulatory system. Herein, we propose an effective strategy to recycle PM2.5 carbon nanoparticles generated by diesel vehicle engine for the applications of clean energy. After thermal treatment and purification, the PM2.5 derived carbon nanoparticles show a diameter distribution between 25 and 40 nm, mesoporous characteristics (with an average pore size of ~3.3 nm), and homogeneous nitrogen incorporation (with N content of ~1.1 at%). The PM2.5 derived N-doped mesoporous carbon nanoparticles were used as an advanced electrode material in supercapacitors, exhibiting excellent specific capacity and superb stability over long-term cycling. Moreover, the recycled PM2.5 carbon nanoparticles show attractive electrocatalytic properties for oxygen reduction reaction, presenting high onset potential and good immunity to methanol crossover. We expect this research can provide inspiration for air pollution control and sustainable energy utilization.

Li-ion batteries have dominated the field of electrochemical energy storage for the last 20 years. It still remains to be one of the most active research fields. However, there are difficult problems still surrounding lithium ion batteries, such as high cost, unsustainable lithium resource and safety issues. Rechargeable batteries base on alternative metal elements (Na, K, Mg, Ca, Zn, Al, etc.) can provide relatively high power density and energy density using abundant, low-cost materials. Therefore, non-lithium ion batteries are regarded as promising candidates to partially replace lithium ion batteries in near future. In recent years, the research on non-lithium rechargeable batteries is progressing rapidly, but many fundamental and technological obstacles remain to be overcome. Here we provide an overview of the current state of non-lithium rechargeable batteries based on monovalent metal ions (Na+ and K+) and multivalent metal ions (Mg2+, Ca2+, Zn2+ and Al3+). The needs and possible choices of superior electrode materials and compatible electrolytes beneficial for ion transport were emphatically discussed in this review.Download high-res image (167KB)Download full-size image

•An approach to solve the matching of the capacitance between the shell and core electrodes is proposed by using multiple thin wire core electrode to fit a tubular shell electrode.•The fully encapsulated single wire devices show a high area-normalized capacitance, comparable to the best cable devices with more exposed structures.A key challenge in wire-shaped energy storage devices is their complete encapsulation for practical applications. Hence it is of great importance to design and fabricate an all-inclusive structure in which inner and outer current collectors, active materials, electrolyte and separator are all enclosed in a single wire structure. However, due to the surface area differences between the shell and core electrodes, the matching of the capacitance on both electrodes become a challenging task. We solved this problem by using multiple thin Ni wires with three-dimensional MnO2-carbon nanotubes (CNTs)-graphene hybrids as the core electrode and a Ni tube as the shell electrode in a coaxial-cable supercapacitors structure. Within the seamless tubular electrode, all the necessary components are included and protected by the metal tube shell. The fully encapsulated single wire devices show a high area-normalized capacitance of 31 mF cm−2 at a current density of 0.29 mA cm−2, comparable to the best cable devices with more exposed structures. Such devices are more suitable for applications by providing more mechanical stability and avoiding exposure and loss of electrolytes during operation.

The presence of metallic nanotubes in as-grown single walled carbon nanotubes (SWNTs) is the major bottleneck for their applications in field-effect transistors. Herein, we present a method to synthesize enriched, semiconducting nanotube arrays on quartz substrate. It was discovered that introducing appropriate amounts of water could effectively remove the metallic nanotubes and significantly enhance the density of SWNT arrays. More importantly, we proposed and confirmed that the high growth selectivity originates from the etching effect of water and the difference in the chemical reactivities of metallic and semiconducting nanotubes. Three important rules were summarized for achieving a high selectivity in growing semiconducting nanotubes by systematically investigating the relationship among water concentration, carbon feeding rate, and the percentage of semiconducting nanotubes in the produced SWNT arrays. Furthermore, these three rules can be applied to the growth of random SWNT networks on silicon wafers.

Researchers have demonstrated that the alignment of single-walled carbon nanotubes (SWNTs) on the surface of the single crystal substrate is due to guided growth along either step edges (graphoepitaxial) or certain directions in the atomic lattice (epitaxial), with only one of the two alignment modes predominating in different research systems. For the SWNTs grown on a quartz surface, the growth of a perfectly aligned array and other shapes were induced by the epitaxial effect. Here we report the finding that water vapor introduced during the catalyst annealing process can change the alignment mode of the SWNTs on the quartz surface by modifying the surface status of both the catalyst and the substrate. Zigzag shaped nanotube arrays can be obtained by enabling both alignment modes simultaneously through adjusting the water vapor concentration, changing the oxidation state of the metal catalyst and/or modifying the morphology of the substrate surface. These findings provide important insights into the mechanism of guided growth of complex nanotube shapes, for potential applications including electronics, photodetection, sensing, and in other devices.

Nanoscale devices are expected to provide important advances for a number of applications. While many methods to generate nanoscale patterns exist, their use is confined to a relatively narrow range of materials. To fabricate nanoscale structures of a material with useful properties, the most convenient route is to transfer the geometry of an existing pattern into another material. Methods to achieve this pattern transfer are summarized and organized in this review. Methods to generate the original patterns, as well as applications of the final structure are also described.

Here we report a new light-responsive and self-healing anticorrosion coating by incorporating hollow nanocontainers with smart molecular switches. The smart coating was obtained by immobilizing photoresponsive azobenzene molecular switches in the nanopores of hollow mesoporous silica nanocontainers. These novel nanocontainers with hollow cavities can encapsulate active molecules under visible light and release them under ultraviolet irradiation. The release of benzotriazole from the hollow nanocontainers can be started and stopped with high controllability, which provides an effective approach to avoid excessive release of active molecules after corrosion healing. The results of scanning vibrating electrode technique demonstrate that the azobenzene molecular switch modified hollow mesoporous silica nanocontainers exhibit excellent continuous photosensitive self-healing performance for improving the long-term performance of aluminium alloy.