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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 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]

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]

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]