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The trace detection of biomarker molecules in exhaled breaths enables a facile disease diagnosis in early stages. However, the selective detection of each pathognomonic gas was difficult to achieve due to a poor understanding of the selectivity mechanism, which impeded the development of a rational design for practical diagnostics. Herein, we report a systematic study of the explicit roles of noble metal catalysts in modulating the gas selectivity of metal oxides and provide an in-depth mechanistic understanding of the reaction pathways specific to each element. Using a consistent synthetic platform to prepare highly dispersed catalysts on In2O3 nanofibers, we identified that Ru and Pd catalysts showed exceptional selectivity to CH3SH and H2S, respectively, while Pt selectively interacted with CH3COCH3 molecules. Furthermore, we revealed that the element-specific gas adsorption and the ensuing charge transfer form the basis for regulating selective surface reactions of target gases. Altogether, we propose a set of design principles for sensing layers based on the prominent, element-dependent roles of catalysts toward the development of a rational synthesis of sensing materials with optimal sensing performance. These principles can be summarized as follows: controlled chemisorption of oxygen species, selective gas adsorption, and subsequent activation of adsorbed gases. [ABSTRACT FROM AUTHOR]

Although efforts have been made to increase the Ni content in Ni-rich cathodes for Li-ion batteries with high specific capacities, an unstable surface of the cathode and electrolyte remains a significant challenge. To stabilize the surface, various protective layers – such as aluminum oxide (Al2O3) – have been introduced on the surface of Ni-rich cathodes. In this study, we used a facing-target sputtering (FTS) method to avoid the reaction of residual Li and moisture from the precursor for the coating method, and to build a dense, homogeneous, protective, ultrathin Al2O3 layer at the surface of NCM811. It was proven that FTS rules out the presence of the LiOH byproduct of residual Li on the NCM811 during surface modification. Ensuring interface protection by using FTS instead of atomic layer deposition with an H2O-based precursor was identified as a crucial determinant of the NCM811 performance. Our findings present an updated and promising process for stabilizing the surface, demonstrating the need to select a technique to achieve surface passivation of Ni-rich cathodes and improvements in cycling performance. [ABSTRACT FROM AUTHOR]

It is well known that certain gas molecules can serve as specific markers for characterizing the physiological and environmental nature of a subject, such as acetylene gas which can be used for determining a person's smoking status as well as for monitoring air pollution levels. For their reliable detection, gas sensors should be designed with high sensing capabilities in terms of selectivity, sensitivity and low detection limit. In this work, we present a rational design approach for the synthesis of p-type LaFeO3/n-type SnO2 composite nanotubes (NTs) via galvanic replacement reaction (GRR) on electrospun perovskite LaFeO3 NTs for p–n type-converted sensing. The GRR process provides LaFeO3/SnO2 NTs with high surface area (146.6 m2 g−1) by generating SnO2 nanograins (<10 nm), as controlled by varying the reaction time. The abundant heterogeneous p–n junctions formed in LaFeO3/SnO2 NTs contribute to the dramatic improvements in their sensing characteristics. In fact, the LaFeO3/SnO2 NTs exhibited 31.2-fold increased response toward acetylene (5 ppm) with a far improved response speed (16 s) compared to that of pristine LaFeO3 NTs (64 s). Our results demonstrate that the GRR process can be used to engineer the morphology and composition of p-type perovskites to achieve exceptional chemical sensing performances. [ABSTRACT FROM AUTHOR]

The development of high-tap density electrode materials that can simultaneously achieve stable electrochemical performance at high charge/discharge rates is critically in demand. Herein, we propose an innovative material design that can offer high tap density and excellent rate capabilities by using Co3O4 nanograin-interconnected secondary particles (Co3O4 NISPs). By taking advantage of a conversion reaction that forms Co from Co3O4, we demonstrate that Co3O4 NISPs are capable of creating a number of metallic Co sites along with a number of vacant sites in-between nanograins. Electrochemical tests that reveal reduced internal cell resistance and more accessible Li diffusion are achieved for Co3O4 NISPs compared with Co3O4 nanoparticles (NPs). Additionally, in situ X-ray diffraction (XRD) analyses, electron energy loss spectroscopy (EELS), and density functional theory (DFT) calculations reveal that the insulating intermediate product (CoO) is formed less on the Co3O4 NISPs, which can enhance the charge transport. Attributed to the combinatorial effects of Co3O4 nanograins that form metallic Co upon conversion and secondary particles that enable high tap density, Co3O4 NISPs show the most outstanding volumetric capacity (2167.3 mA h cm−3 at a current density of 500 mA g−1) among spinel-type metal oxide electrode materials researched so far. [ABSTRACT FROM AUTHOR]

The disposal of natural wastes has become a global problem and the use of lower-grade gums is very limited owing to their impurities as well as sticky nature. Rather than disposing these wastes, nanoporous carbon (nC) has instead been synthesized by carbonization and exfoliation. The synthesized nC exhibits a substantially high surface area along with abundant micro/mesopores. This desirable and useful nature of nC is well-suited for water-driven effective electrical energy conversion, which enables the fast evaporation of water via a capillary action through nanopores. Under asymmetric wetting in a water container and ambient conditions, the nC-based energy harvesters showed high capability of electricity production and reliable output generation, easily turning on a blue light-emitting diode (2.5 V and 20 mA) using a stored power source. In summary, many energy harvesters can be manufactured for the scale-up of electricity, and the suitability of regenerated carbon nanomaterials for green energy harvesting can contribute toward alleviating chronic environmental issues. [ABSTRACT FROM AUTHOR]

Multi-heterogeneous oxide sensing layers, i.e., NiO/Fe2O3 catalyst loaded SnO2 fiber-in-tube nanostructures (NiO/Fe2O3–FITs), were rationally synthesized from an electrospinning solution containing a bio-inspired chitosan–bimetal complex template. The NiO/Fe2O3–FITs showed remarkably enhanced sensing properties and superior cross-sensitivity toward sub-ppm levels of formaldehyde. [ABSTRACT FROM AUTHOR]

The solid-state Li–O2 battery is considered an ideal candidate for high-performance energy storage because of its high safety, due to use of non-flammable and non-volatile electrolytes, and high specific energy, as it uses Li metal and O2 gas as active materials. We present an original solid-state Li–O2 cell composed of a Li metal anode, a flexible polymer interlayer, a perovskite-structured Al-doped Li–La–Ti–O (A-LLTO) solid electrolyte, and an integrated cathode in which a porous A-LLTO solid electrolyte frame was covered with a carbon layer and CoO nanoparticles as the catalyst for the cyclic oxygen evolution and reduction reactions. The designed solid-state cell operated safely in pure O2 atmosphere at temperatures from 25 °C to 100 °C and delivered the first discharge capacity from 796 mA h gC+CoO−1 to 4035 mA h gC+CoO−1, respectively, at a current density of 0.05 mA cm−2. Notably, at 50 °C, the cell was maintained for 132 cycles under a limited capacity mode of 500 mA h gC+CoO−1 at a high current density of 0.3 mA cm−2, demonstrating the first step of success towards realizing Li batteries with high energy and cyclability, as well as safety. [ABSTRACT FROM AUTHOR]

A new method of graphene oxide (GO) templating is pioneered to prepare highly porous oxide fibers consisting of crumpled two-dimensional (2D) SnO2 nanosheets (NSs). GO flakes, which are functionalized with Sn2+ ions through electrostatic interactions between negatively charged GO and positively charged Sn ions (Sn-loaded GO), are directly electrospun. During electrospinning, Sn-loaded GO flakes undergo self-crumpling on the as-spun polymeric nanofibers. After subsequent pyrolysis, highly porous oxide NFs comprised of crumpled SnO2 NSs are achieved, offering three distinct benefits, i.e., (i) a high surface area and broad pore size distribution stemming from the co-existence of 1D and 2D structures, (ii) formation and effective modulation of the electron depletion region due to the ultrasmall thickness of SnO2 NSs and small crystallite size, and (iii) the enhanced catalytic effect of Pt nanoparticles anchored on porous SnO2 NSs. As a result, under high humidity (95% RH), the Pt-functionalized SnO2 NS-assembled NFs exhibited an exceptionally high acetone response (Rair/Rgas = 79.4@1 ppm), excellent selectivity, fast response speed (∼12.7 s), and outstanding stability at 350 °C. Sensor arrays were further utilized to discriminate simulated diabetic breath from healthy breath via pattern recognition, thus demonstrating potential feasibility for reliable sensing of breath biomarkers. [ABSTRACT FROM AUTHOR]

In this work, highly porous SnO2 fiber-in-tubes (FITs), which are functionalized with perovskite La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) particles as a chemical sensitizer, are used as a superior formaldehyde (CH2O) sensing layer. LSCM-loaded as-spun Sn precursor/polymer composite fibers are rapidly calcined to create a porous FIT SnO2 structure with high surface area. Such unique morphological evolution originates from the Ostwald ripening effect and crystal growth inhibition caused by LSCM particles. Furthermore, LSCM particles with high oxygen vacancy concentration and a large work function significantly promote oxygen spillover and electron depletion on the surface of SnO2 (6.80 eV for LSCM vs. 4.55 eV for SnO2). As a result, LSCM-loaded SnO2 FITs (LSCM@SnO2 FITs) provide remarkably high response to formaldehyde (Rair/Rgas = 26.50 to 5 ppm) and excellent selectivity against interfering gases (H2S, C7H8, NH3, C2H6O, C8H10, CO, and C5H12) even without using noble metal catalysts. These observations demonstrate the potential use of LSCM@SnO2 FITs for real-time monitoring of indoor air quality, especially toward formaldehyde, which has not been accurately detected by using conventional metal oxide based sensors. [ABSTRACT FROM AUTHOR]

Porous Si is considered a potential anode material for next-generation Li-ion batteries (LIBs) because of its high specific capacity, low lithiation/delithiation potential, low cost, and environmental friendliness. In this work, we introduce a simplified Mg-thermal-reduction method for the production of mass-scalable coral-like bulk-Si powder with a high surface area (38 m2 g−1), broad pore-size distribution (2–200 nm), and 3-dimensionally (3D) interconnected Si structure for application in LIBs. The porous, coral-like Si electrode delivered a high reversible capacity of 2451 mA h g−1, corresponding to ∼70% of the theoretical capacity of Si, at a rate of C/10. After 100 cycles, the porous, coral-like Si electrode maintained a capacity of 1956 mA h g−1, corresponding to 79.8% of the initial reversible capacity. Importantly, a reasonably high reversible capacity of 614 mA h g−1 was achieved even at a high rate of 10C. These outstanding results demonstrate that the 3D-networked, porous, coral-like Si powder, synthesized via a NaCl-assisted Mg-thermal-reduction process on a stainless-steel plate over a period of one minute, can be employed as a promising anode material for the next generation of high-energy LIBs. [ABSTRACT FROM AUTHOR]

Huge volume expansion during discharge is always a critical problem of high capacity conversion anodes for next generation lithium-ion (Li-ion) batteries. Although extensive efforts have been devoted to controlling the volume expansion using nanostructuring and surface engineering till now, more simple and facile approaches have to be considered due to the complicated and inefficient synthetic methods. Here, we report a straightforward synthesis of Ag coated ZnCo2O4 porous hollow spheres (ZnCo2O4@Ag HSs): (i) immobilization of metal–organic frameworks (MOFs) including Zn and Co metal nodes onto polystyrene sphere templates, (ii) calcination (∼450 °C) for the removal of core polystyrene sphere templates and oxidation of MOFs to produce a mesoporous ZnCo2O4 HSs, and (iii) a subsequent Ag-mirror reaction for 10 min, resulting in the formation of ZnCo2O4@Ag HSs. This porous hollow morphology not only effectively relieves the strain stemming from the volume expansion of transition metals, but also facilitates the efficient electron transport for Li+ diffusion by shortening the Li-ion diffusion path during a lithiation/delithiation process. Moreover, uniformly decorated Ag nanoparticles are beneficial to the formation of a stable solid electrolyte interface (SEI) layer as well as an increased electrical conductivity of ZnCo2O4. The MOF derived porous ZnCo2O4@Ag HSs exhibited remarkably stable cycling performance (a capacity value of 616 mA h g−1 after 900 cycles at a current density of 1 A g−1) and an excellent capacity retention of 80% at a very high current density of 20.0 A g−1. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2), have been studied intensively in recent years due to wide range of potential applications. TMD gas sensors have been developed and intensively explored for their promising applications. In recent times, it has been reported that edge sites of TMDs can contribute to highly enhanced gas adsorption properties. Herein, superior room temperature gas sensing properties of WS2 edge functionalized carbon nanofibers (CNFs) with multiple tubular pores (WS2@MTCNFs) have been demonstrated. A copolymer-electrospinning route, which uses poly(styrene-acrylonitrile) as sacrificial templates and WS2 precursor containing poly(acrylonitrile) as carbon matrix, offered facile synthesis of CNFs having high gas permeability with single-layered WS2 edge-rich surface. As a result, WS2@MTCNFs based sensors exhibited notable gas response (15% at 1 ppm of NO2) at room temperature compared to pristine CNFs (2% at 1 ppm of NO2), which can be attributed to the synergistic effects that originated from enhanced surface area and open porosity with numerous elongated pore channels of MTCNFs as well as remarkably increased active spots on the surface from WS2 edge sites. [ABSTRACT FROM AUTHOR]

We report on the synthesis of highly porous, 1-D tungsten-doped BiVO4 nanofibers (W:BiVO4 NFs). To facilitate photocatalysis, we introduced nickel nanoparticles (NiOx NPs) as co-catalysts on the surface of W:BiVO4 NFs. The outstanding water oxidation performance of the NiOx NP-functionalized W:BiVO4 NFs was obtained through (i) the control of polymers/precursors to achieve porous W:BiVO4 NFs (for highly increased surface area), (ii) the control of the tungsten-doping level (for fast charge transfer), and (iii) the optimization of the loading amounts of NiOx NPs (for efficient charge pathway suppression of charge recombination). [ABSTRACT FROM AUTHOR]

Poor electrochemical performances of materials in commercial lithium-ion batteries (LIBs) make it difficult to realize battery technologies for future electric power applications such as energy storage systems and electric vehicles. To reach beyond the horizon of state-of-the-art LIBs, the exploration of next generation batteries composed of rationally designed nanomaterials in consideration of the structure, phase and element influencing the battery performance is critical. By virtue of the simple set-up, versatility, size controllability and mass-productivity of electrospinning, one-dimensional (1D) nanofibers (NFs) produced via electrospinning are attractive candidates for the construction of advanced secondary batteries. A comprehensive review of the forefront in the development of electrospun NFs as advanced materials of next generation LIBs, sodium-ion batteries (NIBs), lithium–sulfur batteries and lithium–air batteries with particular emphasis on synthesis and improved energy and power density, and cyclability is presented. In this review, we highlight the recent advancements in electrospun 1D nano-architectures with large surface area to volume ratios and controllable morphologies as anodes, cathodes, separators, electrolytes and even catalytic materials. Furthermore, current challenges and prospects of electrospun NFs in both academia and industry are also discussed. We expect that this review opens up new research activities in a variety of research fields including advanced rechargeable batteries. [ABSTRACT FROM AUTHOR]

Pore-loaded WO3 nanofibers (NFs) functionalized with spherical catalyst films were achieved via electrospinning combined by the sacrificial templating route using layer-by-layer (LbL) catalyst assembled polystyrene (PS) colloids. The catalyst-loaded porous WO3 NFs exhibited significantly improved toluene and acetone detection capability for potential application in exhaled breath analysis. [ABSTRACT FROM AUTHOR]

The detection of nitrogen dioxide, NO2, is currently the subject of extensive scientific and technological research, motivated by its deleterious impact on the environment and on human health and safety. However, detecting trace levels of NO2 gas in a timely, sensitive, and selective manner remains challenging, while the mechanisms governing selective NO2 sensing are still unclear. In this work, a monolayer α-Fe2O3 inverse opal (IO) film with single-crystalline 3-fold rotocenters is firstly synthesized in situ on a substrate using a sacrificial template and evaluated as a sensitive NO2 chemiresistor. Interestingly, the Fe2O3 macroporous film manifests abnormal sensing behavior with reversible transitions from p- to n-type sensing as a function of the NO2 concentration (C) and working temperature (T). Based on more familiar phase diagrams, a binary (T–C) transition diagram has been created in terms of the gas sensing response, which can be directly used to design and control the p–n transitions. Further investigations also show that such abnormal p–n transitions do not occur if a different sensing material (e.g. SnO2 IO) is used, or on exposure to gases other than NO2. The porous Fe2O3 sensor is capable of detecting trace levels of NO2, as low as 10 ppb, and shows good stability. Finally, the mechanisms underlying the unusual NO2 sensing transitions are described based on the nature of the materials and the well-known Lennard-Jones model. Reversible switching from p- to n-type sensing and the associated transition diagram carry great potential for the recognition and sensitive detection of trace levels of NO2. [ABSTRACT FROM AUTHOR]

The core–shell structure of RuO2–Co3O4 fibers comprising the inner region of highly conductive RuO2 and the outer region of catalytic Co3O4 provided a fast and effective transport pathway for holes to O2-evolving sites, leading to a highly efficient water oxidation performance. [ABSTRACT FROM AUTHOR]

Hollow thin walled NiO tubes functionalized by catalytic Pt were synthesized viananofiber templating and multilayered sputter-coating of Pt and NiO thin overlayers followed by heat-treatment at 600 °C. Sandwich Pt–NiO–Pt tube networks exhibited superior C2H5OH sensing response and remarkable selectivity against CO and H2gases. [ABSTRACT FROM AUTHOR]

Microstructural evolution of spinel Zn2SnO4nanofibers was manipulated viaan in situphase separation process of inorganic precursors and a matrix polymer during electrospinning and calcination. Chemiresistive gas sensors using porous Zn2SnO4fibers exhibited superior C2H5OH sensing response. [ABSTRACT FROM AUTHOR]

The selective detection of two different gases, NO2and C2H5OH, has been achieved using a p-type Co3O4-decorated n-type ZnO nanowire (NW) network sensor. The gas selectivity was explained by the catalytic effect of nanocrystalline Co3O4and the extension of the electron depletion layer viathe formation of p–n junctions. [ABSTRACT FROM AUTHOR]

Ultra-fast responding and recovering C2H5OH sensors were prepared using nanoscale SnO2hollow spheres with NiO-functionalized inner walls. The exceptional ultra-fast recovery characteristics were attributed to the catalytic surface reaction assisted by NiO at the inner shell. [ABSTRACT FROM AUTHOR]

Close packed arrays of hollow SnO2hemispheres were prepared using PMMA microspheres as sacrificial templates for subsequent sputter-deposition of SnO2films, leading to a threefold enhancement in gas sensitivity compared to non-templated (flat) films. [ABSTRACT FROM AUTHOR]