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Lithium–sulfur batteries (LSBs) have shown great potential for application in high-density energy storage systems. However, the performance of LSBs is severely hindered by the shuttle effect and the sluggish reaction kinetics of lithium polysulfides (LiPSs). Here, a Janus Fe3C/N-CNF@RGO electrode consisting of a 1D Fe3C-decorated N-doped carbon nanofibers (Fe3C/N-CNFs) side and a 2D reduced graphene oxide (RGO) side was applied as a free-standing carrier for the Li2S6 catholyte to improve the overall electrochemical performance of LSBs. The Fe3C/N-CNF layer endows the cathode with strong chemisorption abilities for LiPSs and accelerated the redox kinetics via catalyzing the conversion of LiPSs. The 2D RGO sheets serve as a microscopic physical barrier and further resist the shuttling of LiPSs. Like a hunter's trap, behind the trap lies a net. Moreover, the 3D hierarchical conductive network based on 1D N-CNF and 2D RGO sheets enables fast electron transfer. Based on the synergetic effects of chemical immobilization, catalytic abilities, and a physical barrier in a 3D conductive network, LSBs with optimal Fe3C/N-CNF@RGO electrodes exhibit robust long-term cycling stability (a decay rate of only 0.0089% per cycle at 0.5C for 300 cycles), superior rate capabilities (821.7 mA h g−1 at 2.0C), and stable cycling performance at high sulfur loading (6.29 mg cm−2). This work defines an emerging viewpoint relating to the design of novel sulfur carriers with multiple synergistic effects for application in LSBs.

In recent years, it is urgent and challenging to fabricate highly sensitive and selective gas sensors for breath analyses. In this work, Sr-doped cubic In2O3/rhombohedral In2O3 homojunction nanowir...

As a promising cathode material for high-power lithium-ion batteries, LiFePO4 (LFP) suffers from low lithium-ion diffusivity and poor electronic conductivity. In this work, hierarchically porous Ti3C2Tx MXene decorated LFP@C (LFP@C/MXene) composite was successfully synthesized by a facile and efficient electrostatic self-assemble method at room temperature with the help of CTAB to regulate charge state. The introduction of MXene sheets realized the formation of hierarchically porous structure and “dot-to-surface” conductive network, enabling the fast ion and electrons transfer for redox reactions, meanwhile, MXene will be partially oxidized into TiO2 and carbon during cycling, which further improved the diffusion of lithium-ion. Together with the optimized structure of LFP@C nanoplates, the resulting LFP@C/MXene exhibits robust high-rate capability (139 mAh·g−1 at 20 C) as well as a long-life cycling stability (156.6 mAh·g−1 at 1 C with superior capacity retention of 94.8% for 500 cycles). This ingenious design highlights the great potential of 2D MXene for facilely constructing multifunctional electrode materials for application in high-rate Li-ion batteries.

Poor cyclability and rate performance are two key problems hindering the practical application of In2O3 in high power lithium-ion batteries. Herein, we report a phase transition strategy to fabricate novel In1−xZnxOy heterogeneous nanofibers with mixed phases of cubic bixbyite-type In2O3 and rhombohedral corundunm-type In2O3 to enhance the lithium ion storage ability. The one-dimensional structure shortens the path for lithium ion diffusion and electron transfer, and accommodates the large volume changes upon cycling. The introduction of rhombohedral corundunm-type In2O3 can favorably improve the electrical conductivity, provide more pathways for lithium ion diffusion, and optimize the interface interplay. The optimal In0.5Zn0.5O1.25 heterogeneous nanofibers exhibit superior cyclic stability and outstanding high-rate performance, which can be ascribed to the synergistic effects of excellent electrical conductivity, more pathways for lithium ion diffusion, and the coupling effect of heterogeneous interface. This new phase-transition induced formation of heterostructure nanofibers is enlightening in design high performance electrode materials for lithium ion batteries.

It is a challenge to effectively detect the components of a gas mixture using metal oxide sensors which are easily fabricated and inexpensive. In this work, heterostructured SnO2/MOx (i.e. M = Zn, Ga and W) nanotubes (NTs) and nanofibers (NFs) are synthesized via a one-step electrospinning technology and subsequent calcination for use in gas sensors. In specific, compared with pure SnO2 NTs, SnO2/ZnO NTs show an enhanced response to 100 ppm ethanol and acetone, while SnO2/Ga2O3 NTs show an obviously higher response to 100 ppm ethanol and SnO2/WO3 NFs show an optimal response to 100 ppm xylene. All these sensors are selective in the presence of typically interfering gases such as formaldehyde, benzene and toluene. As a proof-of-concept, sensor arrays constructed using these three sensors precisely detected the gas mixtures of ethanol, acetone and xylene by means of matrix manipulation, delivering a superior accuracy of

In recent years, it is urgent and challenging to fabricate highly sensitive and selective gas sensors for breath analyses. In this work, Sr-doped cubic In

High concentration ozone can damage greatly to the respiratory, cardiovascular systems, and fertility of people, and catalytic decomposition is an important strategy to reduce its harm. However, it remains a challenge to develop efficient ozone decomposition catalysts with high efficiency. In this study, p- and n-type silicon nanowires (Si NWs) are fabricated by wet chemical etching method and are firstly applied to catalytic decompose ozone at room temperature. The p-type Si NWs exhibit 90% ozone (20 ppm O3/air) decomposition efficiency with great stability, which is much better than that of n-type Si NWs (50%) with same crystal orientation, similar diameter and specific surface area. The catalytic property difference is mainly attributed to the more delocalization holes in the p-type Si NWs, which can accelerate the desorption of ozone decomposition intermediates (i.e., adsorbed oxygen species).

Although In2O3 nanofibers (NFs) are well-known candidates as active materials for next-generation, low-cost electronics, these NF based devices still suffer from high leakage current, insufficient on–off current ratios (Ion/Ioff), and large, negative threshold voltages (VTH), leading to poor device performance, parasitic energy consumption, and rather complicated circuit design. Here, instead of the conventional surface modification of In2O3 NFs, we present a one-step electrospinning process (i.e., without hot-press) to obtain controllable Mg-doped In2O3 NF networks to achieve high-performance enhancement-mode thin-film transistors (TFTs). By simply adjusting the Mg doping concentration, the device performance can be manipulated precisely. For the optimal doping concentration of 2 mol%, the devices exhibit a small VTH (3.2 V), high saturation current (1.1 × 10–4 A), large on/off current ratio (>108), and respectable peak carrier mobility (2.04 cm2/(V·s)), corresponding to one of the best device performances among all 1D metal-oxide NFs based devices reported so far. When high-κ HfOx thin films are employed as the gate dielectric, their electron mobility and VTH can be further improved to 5.30 cm2/(V·s) and 0.9 V, respectively, which demonstrates the promising prospect of these Mg-doped In2O3 NF networks for highperformance, large-scale, and low-power electronics.

Lithium-sulfur batteries (LSBs) have been regarded as the most promising technology for next generation energy storage systems owing to their high energy density and low cost. However, the undesirable shuttle effect and low utilization of sulfur caused by dissolution and migration of polysulfide intermediates greatly restrict their practical application. Herein, we report a functional separator modified with novel ultrathin hollow carbon spheres (UHCSs) to improve the overall performance of LSBs and demonstrate for the first time that nonporous hollow structured carbon materials are ideal candidates for modifying the separator due to their unique properties. The ultrathin and nonporous shell of the coated UHCSs can act as a physical and a chemical barrier to effectively entrap lithium polysulfides owing to fewer diffusion sites. The UHCSs can also enhance the electron transfer for sulfur and accommodate the large volume change of sulfur as upper current collectors. When applying such UHCSs functionalized separators, the LSBs achieved a significantly improved electrochemical performance including a high capacity of 1346.3 mA h g−1 at 0.2C and high rate capability with a discharge capacity of 458 mA h g−1 even at 5C upon 1000 cycles.

Because of their unique physical and chemical properties, one-dimensional (1-D) metal-oxide nanostructures have been extensively applied in the areas of gas sensors, electrochromic devices, nanogenerators, and so on. Solar water-splitting has attracted extensive research interest because hydrogen generated from solar-driven water splitting is a clean, sustainable, and abundant energy source that not only solves the energy crisis, but also protects the environment. In this comprehensive review, the main synthesis methods, properties, and especially prominent applications in solar water splitting of 1-D metal-oxides, including titanium dioxide (TiO2), zinc oxide (ZnO), tungsten trioxide (WO3), iron oxide (Fe2O3), and copper oxide (CuO) are fully discussed.

Hybrid inorganic–organic heterojunction solar cells (HHSCs) are successfully fabricated using Sb2S3 as a light-absorbing semiconductor, TiO2 nanorods (NRs) as an electron-transport layer, and poly-3 (hexylthiophene) (P3HT) as both a hole conductor and light absorber. The enhanced photo-to-electric conversion performance is expected to (1) enhance optical absorption in the visible light region by Sb2S3 and (2) photo-generate highly efficient charge carrier separation at TiO2/Sb2S3 and Sb2S3/P3HT heterojunction interfaces. The power conversion efficiency (PCE) of HHSCs improves approximately fourfold by inserting the Sb2S3 layer, which can be further enhanced about four more times by optimizing the length of TiO2 nanorod arrays (NRAs). Finally, the mechanism to illustrate the effect of the length of TiO2 NRs on the PCE is discussed. This leads to a theory for achieving high-efficiency inorganic–organic solar cells.

Highlights 3D hierarchical conductive Sn quantum dots encapsulated in N,S co-doped carbon nanofibers sheathed within rGO scrolls (Sn/NS-CNFs@rGO) were prepared through an electrospinning process.Flexible Sn/NS-CNFs@rGO electrode exhibits superior long-term cycling stability and high-rate capability in sodium-ion batteries. Electronic supplementary material The online version of this article (10.1007/s40820-019-0294-9) contains supplementary material, which is available to authorized users., Metallic Sn has provoked tremendous progress as an anode material for sodium-ion batteries (SIBs). However, Sn anodes suffer from a dramatic capacity fading, owing to pulverization induced by drastic volume expansion during cycling. Herein, a flexible three-dimensional (3D) hierarchical conductive network electrode is designed by constructing Sn quantum dots (QDs) encapsulated in one-dimensional N,S co-doped carbon nanofibers (NS-CNFs) sheathed within two-dimensional (2D) reduced graphene oxide (rGO) scrolls. In this ingenious strategy, 1D NS-CNFs are regarded as building blocks to prevent the aggregation and pulverization of Sn QDs during sodiation/desodiation, 2D rGO acts as electrical roads and “bridges” among NS-CNFs to improve the conductivity of the electrode and enlarge the contact area with electrolyte. Because of the unique structural merits, the flexible 3D hierarchical conductive network was directly used as binder- and current collector-free anode for SIBs, exhibiting ultra-long cycling life (373 mAh g−1 after 5000 cycles at 1 A g−1), and excellent high-rate capability (189 mAh g−1 at 10 A g−1). This work provides a facile and efficient engineering method to construct 3D hierarchical conductive electrodes for other flexible energy storage devices. Electronic supplementary material The online version of this article (10.1007/s40820-019-0294-9) contains supplementary material, which is available to authorized users.

Although significant developments have been made in the low-concentration formaldehyde monitoring in indoor air by using gas sensors, they still suffer from insufficient performance for achieving ppb-level detection. In this work, oriented Si nanowires (SiNWs) with high specific surface area were prepared via metal-assisted chemical etching method (MACE), and then were uniformly coated with graphene oxide (GO) followed by the subsequent reductive process in H2/Ar atmosphere at 800 °C to obtain reduced graphene oxide (RGO). The RGO coating (RGO@n-SiNWs) obviously enhances SiNWs sensitivity to low-concentration formaldehyde, benefiting from the increased specific surface area, the sensitization effect of RGO, and the formation of p-n junction between SiNWs and RGO. Specifically, RGO@n-SiNWs exhibits a high response of 6.4 to 10 ppm formaldehyde at 300 °C, which is about 2.6 times higher than that of pristine SiNWs (~ 2.5). Furthermore, the RGO@n-SiNWs show a high response of 2.4 to 0.1 ppm formaldehyde which is the largest permissive concentration in indoor air, a low detection limit of 35 ppb obtained by non-linear fitting, and fast response/recovery times of 30 and 10 s. In the meanwhile, the sensor also shows high selectivity over other typical interfering gases such as ethanol, acetone, ammonia, methanol, xylene, and toluene, and shows a high stability over a measurement period of 6 days. These results enable the highly sensitive, selective, and stable detection of low-concentration formaldehyde to guarantee safety of indoor environment. Electronic supplementary material The online version of this article (10.1186/s11671-019-2921-2) contains supplementary material, which is available to authorized users.

Figure S1. (a) and (b) Scraping n-SiNWs and p-SiNWs, respectively. Figure S2. (a) TEM images of p-SiNWs. (b) HRTEM image of p-SiNWs together with the corresponding FFT. Table S1. XPS data including the peak position, peak area, surface atomic ratio. (DOC 1938 kb)

The research presented here was supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No: CRF-2015-2634-CRG4 and CRF-2016-2996-CRG5. J. H. H. thanks the financial support from City University of Hong Kong.

Lithium-sulfur batteries (LSBs) are considered as one of the most promising energy storage devices owing to the high theoretical specific capacity and high theoretical specific energy, as well as natural abundance of sulfur. However, the soluble lithium polysulfide intermediates (LPSs) in electrolyte cause undesirable shuttle effect, resulting in the loss of sulfur and poor cycling stability. Herein, a novel tungsten oxide-decorated N, S co-doped carbon nanofibers (WO3@NS-CNFs) functional interlayer is applied to restrain the shuttle effect and enhance the cycling performance of LSBs. On the one hand, the uniformly distributed WO3 can provide strong chemical anchoring sites for binding the LPSs and enhance the redox reaction kinetics. On the other hand, the NS-CNFs can also serve as the polysulfide trappers and enhance the electronic conductivity of sulfur electrodes. Therefore, benefiting from the synergy effect of WO3 and NS-CNFs, the LSBs exhibit excellent cycling performance with a high initial capacity of 1444 mA h g−1 and reversible capacity of 1080 mA h g−1 after 100 cycles at 0.2 C, and superior rate capability of 946 mA h g−1 at 2 C.

Although Si nanowires (NWs) arrays are superior candidates for visible light photocatalysis, reports about the photodegradation activity of various crystal-orientated Si NWs are still insufficient. Here, light-doped hydrogen-terminated Si NWs arrays with different crystal orientations were prepared via a metal-assisted chemical etching method (MACE), which simply modulated the concentration of the oxidizer, H2O2. Their dye photodegradation activities were systematically and comprehensively investigated. When compared with Si NWs arrays with crystal orientations of (110) and (111), Si NWs arrays with (100) crystal orientation exhibit a superior photodegradation activity and stability due to the anisotropy of optical and physical properties. The n-type Si NWs arrays exhibit better photodegradation activity than the p-type Si NWs arrays of the same crystal orientation and similar length. The results provide a further understanding of the synthesis of Si NWs arrays with various orientations, and the relationships between photodegradation activity/stability and crystal orientations.

Although significant progress has been made towards using ZnO nanofibers (NFs) in future high-performance and low-cost electronics, they still suffer from insufficient device performance caused by substantial surface roughness (i.e., irregularity) and granular structure of the obtained NFs. Here, a simple one-step electrospinning process (i.e., without hot-press) is presented to obtain controllable ZnO NF networks to achieve high-performance, large-scale, and low-operating-power thin-film transistors. By precisely manipulating annealing temperature during NF fabrication, their crystallinity, grain size distribution, surface morphology, and corresponding device performance can be regulated reliably for enhanced transistor performances. For the optimal annealing temperature of 500 degrees C, the device exhibits impressive electrical characteristics, including a small positive threshold voltage (V-th) of approximate to 0.9 V, a low leakage current of approximate to 10(-12) A, and a superior on/off current ratio of approximate to 10(6), corresponding to one of the best-performed ZnO NF devices reported to date. When high- AlOx thin films are employed as gate dielectrics, the source/drain voltage (V-DS) can be substantially reduced by 10x to a range of only 0-3 V, along with a 10x improvement in mobility to a respectable value of 0.2 cm(2) V-1 s(-1). These results indicate the potential of these nanofibers for use in next-generation low-power devices.