Safe and long cycle life electrode materials for lithium‐ion batteries are significantly important to meet the increasing demands of rechargeable batteries. Niobium pentoxide (Nb2O5) is one of the ...highly promising candidates for stable electrodes due to its safety and minimal volume expansion. Nevertheless, pulverization and low conductivity of Nb2O5 have remained as inherent challenges for its practical use as viable electrodes. A highly facile method is proposed to improve the overall cycle retention of Nb2O5 microparticles by ammonia (NH3) gas‐driven nitridation. After nitridation, an ultrathin surficial layer (2 nm) is formed on the Nb2O5, acting as a bifunctional nanolayer that allows facile lithium (Li)‐ion transport (10–100 times higher Li diffusivity compared with pristine Nb2O5 microparticles) and further prevents the pulverization of Nb2O5. With the subsequent decoration of silver (Ag) nanoparticles (NPs), the low electric conductivity of nitridated Nb2O5 is also significantly improved. Cycle retention is greatly improved for nitridated Nb2O5 (96.7%) compared with Nb2O5 (64.7%) for 500 cycles. Ag‐decorated, nitridated Nb2O5 microparticles and nitridated Nb2O5 microparticles exhibit ultrastable cycling for 3000 cycles at high current density (3000 mA g−1), which highlights the importance of the surficial nanolayer in improving overall electrochemical performances, in addition to conductive NPs.
A surficial bifunctional nanolayer is adopted on Nb2O5 microparticles by a simple nitridation process, where it results in higher ionic transport and further prevents the pulverizaton of Nb2O5. Upon decoration of Ag nanoparticles, electric conductivity of Nb2O5 is further improved, resulting in ultralong cycle retention at high current density (3000 mA g−1).
Hierarchical SnO2 fibers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying flow rates during electrospinning ...and a subsequent heat treatment. The inner and outer SnO2 tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fiber direction, enabling fast transport of gas molecules to the entire thin‐walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO2 layers. Highly porous SnO2 fibers synthesized at a high flow rate show five‐fold higher acetone responses than densely packed SnO2 fibers synthesized at a low flow rate. Interestingly, thin‐wall assembled SnO2 fibers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un‐doped SnO2 fibers, even at low acetone concentrations. Moreover, Pt‐decorated SnO2 fibers significantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin‐wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer.
Electrospun fibers with wrinkled SnO2 walls composed of a number of elongated openings and pores are synthesized by a microphase separation controlled by the variation of flow rates. The unique structure enables superior acetone sensing performance due to the open pore structure, which provides fast transport and penetration of exhaled gases into the entire sensing layers.
Thin-walled WO3 hemitubes and catalytic Pt-functionalized WO3 hemitubes were synthesized via a polymeric fiber-templating route and used as exhaled breath sensing layers for potential diagnosis of ...halitosis and diabetes through the detection of H2S and CH3COCH3, respectively. Pt-functionalized WO3 hemitubes with wall thickness of 60 nm exhibited superior acetone sensitivity (R air/R gas = 4.11 at 2 ppm) with negligible H2S response, and pristine WO3 hemitubes showed a 4.90-fold sensitivity toward H2S with minimal acetone-sensing characteristics. The detection limit (R air/R gas) of the fabricated sensors with Pt-functionalized WO3 hemitubes was 1.31 for acetone of 120 ppb, and pristine WO3 hemitubes showed a gas response of 1.23 at 120 ppb of H2S. Long-term stability tests revealed that the remarkable selectivity has been maintained after aging for 7 months in air. The superior cross-sensitivity and response to H2S and acetone gas offer a potential platform for application in diabetes and halitosis diagnosis.
The combination of high-capacity and long-term cyclability has always been regarded as the first priority for next generation anode materials in lithium-ion batteries (LIBs). To meet these ...requirements, the Ag nanoparticle decorated mesoporous SnO2/NiO nanotube (m-SNT) anodes were synthesized via an electrospinning process, followed by fast ramping rate calcination and subsequent chemical reduction in this work. The one-dimensional porous hollow structure effectively alleviates a large volume expansion during cycling as well as provides a short lithium-ion duffusion length. Furthermore, metallic nickel (Ni) nanoparticles converted from the NiO nanograins during the lithiation process reversibly decompose Li2O during delithiation process, which significantly improves the reversible capacity of the m-SNT anodes. In addition, Ag nanoparticles uniformly decorated on the m-SNT via a simple chemical reduction process significantly improve rate capability and also contribute to long-term cyclability. The m-SNT@Ag anodes exhibited excellent cycling stability without obvious capacity fading after 500 cycles with a high capacity of 826 mAh g–1 at a high current density of 1000 mA g–1. Furthermore, even at a very high current density of 5000 mA g–1, the charge-specific capacity remained as high as 721 mAh g–1, corresponding to 60% of its initial capacity at a current density of 100 mA g–1.
This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by ...electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.
Nanocrystalline SnO2 fibers are fabricated by electrospinning using Pd as a grain growth inhibitor and a catalyst for enhancing oxidation reactions. Pd‐loaded or unloaded (pristine) SnO2 fibers can be used as gas sensors capable of detecting trace concentrations as low as several parts per billion (ppb) of H2 and NO2, respectively.
Rapid charging capability is a requisite feature of lithium-ion batteries (LIBs). To overcome the capacity degradation from a steep Li-ion concentration gradient during the fast reaction, electrodes ...with tailored transport kinetics have been explored by managing the geometries. However, the traditional electrode fabrication process has great challenges in precisely controlling and implementing the desired pore networks and configuration of electrode materials. Herein, we demonstrate a density-graded composite electrode that arises from a three-dimensional current collector in which the porosity gradually decreases to 53.8% along the depth direction. The density-graded electrode effectively reduces energy loss at high charging rates by mitigating polarization. This electrode shows an outstanding capacity of 94.2 mAh g–1 at a fast current density of 59.7 C (20 A g–1), which is much higher than that of an electrode with a nearly constant density gradient (38.0 mAh g–1). Through these in-depth studies on the pore networks and their transport kinetics, we describe the design principle of rational electrode geometries for ultrafast charging LIBs.
Antiviral and antibacterial violacein embedded porous nanofiber that can sterilize itself is proposed as an effective solution to prevent aerosol and post-contact transmission of pathogens viruses ...for safer personal protective equipments.
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•Self-sterilizable nanofiber filter with naturally occurring violacein is developed.•Remarkable biocidal activities against infectious viruses and bacteria are achieved.•Viricidal efficacy for influenza and human coronavirus is studied by TCID50 analysis.•Porous nanofiber matrix immobile pathogens and prevents aerosol transmission.•Violacein endows nanofibers with UV shielding property to help protect skin.
Most respiratory masks are made of fabrics, which only capture the infectious virus carriers into the matrix. However, these contagious viruses stay active for a long duration (∼7 days) within the fabric matrix possibly inducing post-contact transmissions. Moreover, conventional masks are vulnerable to bacterial growth with prolonged exposure to exhaled breaths. Herein, we combined violacein, a naturally-occurring antimicrobial agent, with porous nanofiber membranes to develop a series of functional filters that autonomously sterilizes viruses and bacteria. The violacein-embedded membrane inactivates viruses within 4 h (99.532 % reduction for influenza and 99.999 % for human coronavirus) and bacteria within 2 h (75.5 % reduction). Besides, its nanofiber structure physically filters out the nanoscale (<0.8 μm) and micron-scale (0.8 μm − 3 μm) particulates, providing high filtration efficiencies (99.7 % and 100 % for PM 1.0 and PM 10, respectively) with long-term stability (for 25 days). In addition, violacein provides additional UV-resistant property, which protects the skin from sunlight. The violacein-embedded membrane not only proved the sterile efficacy of microbe extracted pigments for biomedical products but also provided insights to advance the personal protective equipment (PPE) to fight against contagious pathogens.
It is evident that the exhaustive use of fossil fuels for decades has significantly contributed to global warming and environmental pollution. To mitigate the harm on the environment, lithium–oxygen ...batteries (LOBs) with a high theoretical energy density (3458 Wh kg–1Li2O2) compared to that of Li-ion batteries (LIBs) have been considered as an attractive alternative to fossil fuels. For this purpose, porous carbon materials have been utilized as promising air cathodes owing to their low cost, lightness, easy fabrication process, and high performance. However, the challenge thus far lies in the uncontrollable formation of Li2CO3 at the interface between carbon and Li2O2, which is detrimental to the stable electrochemical performance of carbon-based cathodes in LOBs. In this work, we successfully protected the surface of the free-standing carbon nanofibers (CNFs) by coating it with a layer of iridium metal through direct sputtering (CNFs@Ir), which significantly improved the lifespan of LOBs. Moreover, the Ir would play a secondary role as an electrochemical catalyst. This all-in-one cathode was evaluated for the formation and decomposition of Li2O2 during (dis)charging processes. Compared with bare CNFs, the CNFs@Ir cathode showed two times longer lifespan with 0.2 VLi lower overpotentials for the oxygen evolution reaction. We quantitatively calculated the contents of CO3 2– in Li2CO3 formed on the different surfaces of the bare CNFs (63% reduced) and the protected CNFs@Ir (78% reduced) cathodes after charging. The protective effects and the reaction mechanism were elucidated by ex situ analyses, including scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy.
Ultra-stable pseudocapacitive electrodes for lithium-ion batteries (LIBs) are increasing in demand as highly sustainable energy storage system with excellent charge transport is important. The ...establishment of facile, controllable, and scalable synthesis of pseudocapacitive electrode materials is an attractive solution to realize such objectives. Here, we have successfully fabricated mesoporous orthorhombic Nb2O5 nanofibers (m-T-Nb2O5 NFs) by simple single-spinneret electrospinning followed by calcination at 600 °C. As-formed m-T-Nb2O5 NFs exhibit high surface area (23.7 m2 g−1) and a number of mesopores in the vacant sites where organic polymer was once decomposed. Such rationally designed m-T-Nb2O5-NFs allow facile Li ion and electron transport, with pseudocapacitive behavior. Arising from the high surface area coupled with mesopores in-between the Nb2O5 nanograins, it exhibits ultra-long cycle retention (a capacity of ∼160 mAh g−1 at 500 mA g−1 after 2000 cycles and ∼88 mAh g−1 at 3000 mA g−1 after 5000 cycles) and higher rate capability (∼70 mAh g−1 at 5000 mA g−1). Such cycle retention characteristics of m-T-Nb2O5-NFs are at least 100-fold slower capacity decay compared with previously reported one-dimensional (1D) Nb2O5 nanostructures and even superior or comparable to recently reported Nb2O5-graphene composite materials.
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•Mesoporous T-Nb2O5 nanofibers (m-T-Nb2O5 NFs) made by electrospinning & calcination.•m-T-Nb2O5 NFs showed high surface areas (23.7 m2 g−1) and many mesoporous sites.•The structural integrity of m-T-Nb2O5 NFs was maintained without agglomeration.•Pseudocapacitive characteristics of m-T-Nb2O5 NFs were further investigated.•m-T-Nb2O5 NFs demonstrated ultra-stable Li storage characteristics up to 5000 cycles.
Real-time temperature monitoring of individual blood packages capable of wireless data transmission to ensure the safety of blood samples and minimize wastes has become a critical issue in recent ...years. In this work, we propose flexible temperature sensors using silver nanowires (NWs) and a flexible colorless polyimide (CPI) film integrated with a wireless data transmission circuit. The unique design of the temperature sensors was achieved by patterning Ag NWs using a three-dimensional printed mold and embedding the patterned Ag NWs in the CPI film (p-Ag NWs/CPI), which resulted in a flexible temperature sensor with electrical, mechanical, and temperature stability for applications in blood temperature monitoring. Indeed, a reliable resistance change of the p-Ag NWs/CPI was observed in the temperature range of −20 to 20 °C with a robust bending stability of up to 5000 cycles at 5 mm bending radius. Real-time and wireless temperature monitoring using the p-Ag NWs/CPI was demonstrated with the packages of rat blood. The result revealed that the stable and consistent temperature monitoring of individual blood packages could be achieved in a blood box, which was mainly attributed to the conformal attachment of the p-Ag NWs/CPI to different packages in a blood container.
