Reliable Low-Current and Multilevel Memristive Electrochemical Neuromorphic Devices with Semi-Metal Sb Filament.

Memristors are used in artificial neural networks owing to their exceptional integration capabilities and scalability. However, traditional memristors are hampered by limited resistance states and randomness, which curtails their application. The migration of metal ions critically influences the number of conductance states and the linearity of weight updates. Semi-metal filaments can provide subquantum conductance changes to the memristors due to the smaller single-atom conductance, such as Sb (≈0.01 G0 = 7.69 × 10-7 S). Here, a memristor featuring an active electrode composed of semi-metal Sb is introduced for the first time. This memristor demonstrates precise conductance control, a large on/off ratio, consistent switching, and prolonged retention exceeding 105 s. Density functional theory (DFT) calculations and characterization methods reveal the formation of Sb filaments during a set process. The interaction between Sb and O within the dielectric layer facilitates the Sb filaments' ability to preserve their morphology in the absence of electric fields.

Metal Nanoclusters as a Superior Polysulfides Immobilizer toward Highly Stable Lithium-Sulfur Batteries.

Due to their high designability, unique geometric and electronic structures, and surface coordination chemistry, atomically precise metal nanoclusters are an emerging class of functional nanomaterials at the forefront of materials research. However, the current research on metal nanoclusters is mainly fundamental, and their practical applications are still uncharted. The surface binding properties and redox activity of Au24 Pt(PET)18 (PET: phenylethanethiolate, SCH2 CH2 Ph) nanoclusters are herein harnessed as an high-efficiency electrocatalyst for the anchoring and rapid conversion of lithium polysulfides in lithium-sulfur batteries (LSBs). Au24 Pt(PET)18 @G composites are prepared by using the large specific surface area, high porosity, and conductive network of graphene (G) for the construction of battery separator that can inhibit polysulfide shuttle and accelerate electrochemical kinetics. Resultantly, the LSB using a Au24 Pt(PET)18 @G-based separator presents a high reversible specific capacity of 1535.4 mA h g-1 for the first cycle at 0.2 A g-1 and a rate capability of 887 mA h g-1 at 5 A g-1 . After 1000 cycles at 5 A g-1 , the capacity is 558.5 mA h g-1 . This study is a significant step toward the application of metal nanoclusters as optimal electrocatalysts for LSBs and other sustainable energy storage systems.

A Mott-Schottky Heterojunction with Strong Chemisorption and Fast Conversion Effects for Room-Temperature Na-S Batteries.

The practical application of the room-temperature sodium-sulfur (RT Na-S) batteries is currently limited by low reversible capacity and serious capacity decay due to the sluggish reaction kinetics and shuttle effect. It is necessary to design a suitable sulfur host integrated with electrocatalysts to realize effective chemisorption and catalysis of sodium polysulfides (NaPSs). Herein, under the guidance of theoretical calculation, the Mott-Schottky heterojunction with a built-in electric field composed of iron (Fe) and iron disulfide (FeS2) components anchored on a porous carbon matrix (Fe/FeS2-PC) is designed and prepared. The enhanced chemisorption effect of Fe, the fast electrocatalytic effect of FeS2, and the fast transfer effect of the built-in electric field within the Fe/FeS2 heterojunction in the cathode of RT Na-S batteries work together to effectively improve the electrochemical performance. As a result, the Fe/FeS2-PC@S cathode exhibits high reversible capacity (815 mAh g-1 after 150 cycles at 0.2 A g-1) and excellent stability (516 mAh g-1 after 600 cycles at 5 A g-1, with only 0.07% decay per cycle). The design of the Fe/FeS2 heterojunction electrocatalyst provides a new strategy for the development of highly stable RT Na-S batteries.

An overview of COVID-19 aerosol box for preventing droplet and aerosol contaminations in healthcare providers performing airway intubation.

The COVID-19 is caused by the SARS-CoV-2, which is extremely infectious. Numerous virologist suggestions and guidelines advised using P2/N95 masks, gloves, goggles, face-shields, and frocks or gowns as routine specific protective tools during airway management to protect healthcare personnel from infection (PPE). However, numerous imitation research has indicated that conventional PPE cannot adequately protect healthcare personnel. Since then, numerous firms and healthcare professionals have created their personal reformed devices 'aerosol containment devices' (ACD). Their usage has expanded throughout the world without being properly evaluated for usefulness, efficacy, or safety. The practice of 'ACD' has been shown to make tracheal intubation (TI) more problematic in several simulated tests. Furthermore, the device should limit the transmission of droplets from a patient; however, it might put healthcare personnel at danger of being exposed to greater levels of viral aerosols. Consequently, the existing state of information suggests that 'ACD' deprived of a vacuum mechanism can simply protect healthcare personnel against viral transmission to a limited extent. We search various databases for the literature with keywords 'COVID-19,' 'aerosol box,' 'aerosol contaminations,' and 'droplet contaminations.' The current review focused on the aerosol box from various perspectives, including their mechanism, optimum time of use, the spread of aerosol control, current gaps, and future perspective for bridging those gaps.

Hybrid Aqueous/Nonaqueous Water-in-Bisalt Electrolyte Enables Safe Dual Ion Batteries.

Dual ion batteries (DIBs) have recently attracted ever-increasing attention owing to the potential advantages of low material cost and good environmental friendliness. However, the potential safety hazards, cost, and environmental concerns mainly resulted from the commonly used nonaqueous organic solvents severely hinder the practical application of DIBs. Herein, a hybrid aqueous/nonaqueous water-in-bisalt electrolyte with both broad electrochemical stability window and excellent safety performance is developed. The lithium-based DIB assembled using KS6 graphite and niobium pentoxide as the active materials in the cathode and anode exhibits good comprehensive performance including capacity, cycling stability, rate performance, and medium discharge voltage. Initial capacities of ≈47.6 and 29.6 mAh g-1 retention after 300 cycles can be delivered with a medium discharge voltage of around 2.2 V in the voltage window of 0-3.2 V at the current density of 200 mA g-1 . Good rate performance for the battery can be indicated by 29.7 mAh g-1 discharge capacity retention at 400 mA g-1 . It is noteworthy that the coulombic efficiency of the battery can reach as high as 93.9%, which is comparable to that of the corresponding DIBs using nonaqueous organic electrolytes.

Nb2 O5 /RGO Nanocomposite Modified Separators with Robust Polysulfide Traps and Catalytic Centers for Boosting Performance of Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) have shown great potential for application in high-density energy storage systems. However, the performance of LSBs is hindered by the shuttle effect and sluggish reaction kinetics of lithium polysulfides (LiPSs). Herein, heterostructual Nb2 O5 nanocrystals/reduced graphene oxide (Nb2 O5 /RGO) composites are introduced into LSBs through separator modification for boosting the electrochemical performance. The Nb2 O5 /RGO heterostructures are designed as chemical trappers and conversion accelerators of LiPSs. Originating from the strong chemical interactions between Nb2 O5 and LiPSs as well as the superior catalytic nature of Nb2 O5 , the Nb2 O5 /RGO nanocomposite possesses high trapping efficiency and efficient electrocatalytic activity to long-chain LiPSs. The effective regulation of LiPSs conversion enables the LSBs enhanced redox kinetics and suppressed shuttle effect. Moreover, the Nb2 O5 /RGO nanocomposite has abundant sulfophilic sites and defective interfaces, which are beneficial for the nucleation and growth of Li2 S, as evidenced by analysis of the cycled separators. As a result, LSBs with the Nb2 O5 /RGO-modified separators exhibit excellent rate capability (816 mAh g-1 at 3 A g-1 ) and cyclic performance (628 mAh g-1 after 500 cycles). Remarkably, high specific capacity and stable cycling performance are demonstrated even at an elevated temperature of 50 °C or with higher sulfur loadings.

Group IVA Element (Si, Ge, Sn)-Based Alloying/Dealloying Anodes as Negative Electrodes for Full-Cell Lithium-Ion Batteries.

To satisfy the increasing energy demands of portable electronics, electric vehicles, and miniaturized energy storage devices, improvements to lithium-ion batteries (LIBs) are required to provide higher energy/power densities and longer cycle lives. Group IVA element (Si, Ge, Sn)-based alloying/dealloying anodes are promising candidates for use as electrodes in next-generation LIBs owing to their extremely high gravimetric and volumetric capacities, low working voltages, and natural abundances. However, due to the violent volume changes that occur during lithium-ion insertion/extraction and the formation of an unstable solid electrolyte interface, the use of Group IVA element-based anodes in commercial LIBs is still a great challenge. Evaluating the electrochemical performance of an anode in a full-cell configuration is a key step in investigating the possible application of the active material in LIBs. In this regard, the recent progress and important approaches to overcoming and alleviating the drawbacks of Group IVA element-based anode materials are reviewed, such as the severe volume variations during cycling and the relatively brittle electrode/electrolyte interface in full-cell LIBs. Finally, perspectives and future challenges in achieving the practical application of Group IVA element-based anodes in high-energy and high-power-density LIB systems are proposed.

Vanadium Oxide Cathode Coinserted by Ni2+ and NH4+ for High-Performance Aqueous Zinc-Ion Batteries.

Vanadium-based oxides have garnered significant attention as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their high theoretical capacity and low cost. However, the limited reaction kinetics and poor long-term cycle stability hinder their widespread application. In this paper, we propose a novel approach by coinserting Ni2+ and NH4+ ions into V2O5·3H2O, i.e., NNVO. Structural characterization shows that the coinsertion of Ni2+ and NH4+ not only extends the interlayer spacing of V2O5·3H2O but also significantly promotes the transport kinetics of Zn2+ because of the synergistic "pillar" effect of Ni2+ and NH4+, as well as the increased oxygen vacancies that effectively lower the energy barrier for Zn2+ insertion. As a result, the AZIBs with an NNVO electrode exhibit a high capacity of 398.1 mAh g-1 (at 1.0 A g-1) and good cycle stability with 89.1% capacity retention even after 2000 cycles at 5.0 A g-1. At the same time, a highly competitive energy density of 262.9 Wh kg-1 is delivered at 382.9 W kg-1. Considering the simple scheme and the resultant high performance, this study may provide a positive attempt to develop high-performance AZIBs.

Notable Performance Enhancement of CsPbI2Br Solar Cells by a Dual-Function Strategy with CsPbBr3 Nanocrystals.

Herein, a dual-function strategy, in which CsPbI2Br is treated by CsPbBr3 nanocrystals (NCs) via addition and surface modification to construct the "electron bridge" and gradient heterojunction, respectively, to notably improve the performance of the CsPbI2Br solar cells, is proposed. The "electron bridge" formed by the CsPbBr3 NCs provides an extra transport channel for the photogenerated electrons in the CsPbI2Br layer, thus facilitating electron transport. Meanwhile, surface modification of CsPbI2Br by the CsPbBr3 NCs forms a gradient heterojunction between the CsPbI2Br layer and the P3HT layer, enhancing hole extraction accordingly. In addition, the CsPbBr3 NC treatment passivates the defects at the bulk and surface of the CsPbI2Br layers, thus suppressing carrier recombination. Thanks to these positive effects of the CsPbBr3 NCs, the demonstration device with a simple configuration of ITO/SnO2/CsPbI2Br/P3HT/Ag achieves a notable power conversion efficiency of 17.03%, which is among the highest efficiencies reported for CsPbI2Br-based solar cells.

A high linearity and multilevel polymer-based conductive-bridging memristor for artificial synapses.

Conductive-bridging memristors based on a metal ion redox mechanism have good application potential in future neuromorphic computing nanodevices owing to their high resistance switch ratio, fast operating speed, low power consumption and small size. Conductive-bridging memristor devices rely on the redox reaction of metal ions in the dielectric layer to form metal conductive filaments to control the conductance state. However, the migration of metal ions is uncontrollable by the applied bias, resulting in the random generation of conductive filaments, and the conductance state is difficult to accurately control. Herein, we report an organic polymer carboxylated chitosan-based memristor doped with a small amount of the conductive polymer PEDOT:PSS to improve the polymer ionic conductivity and regulate the redox of metal ions. The resulting device exhibits uniform conductive filaments during device operation, more than 100 and non-volatile conductance states with a ∼1 V range, and linear conductance regulation. Moreover, simulation using handwritten digital datasets shows that the recognition accuracy of the carboxylated chitosan-doped PEDOT:PSS memristor array can reach 93%. This work provides a path to facilitate the performance of metal ion-based memristors in artificial synapses.

A Biocompatible Supercapacitor Diode with Enhanced Rectification Capability toward Ion/Electron-Coupling Logic Operations.

The main challenge faced by the forthcoming human-computer interaction is that biological systems and electronic devices adopt two different information carriers, i.e., ions and electrons, respectively. To bridge the gap between these two systems, developing ion/electron-coupling devices for logic operation is a feasible and effective approach. Accordingly, herein a supercapacitor-based ionic diode (CAPode) that takes electrochemically amorphized molybdenum oxide as the working electrode is developed. Benefiting from its unique size and charge dual ion-sieving effects, the molybdenum oxide electrode exhibits a record-high rectification ratio of 136, which is over 10 times higher than those of reported systems. It also delivers an ultrahigh specific capacitance of 448 F g⁻1 and an excellent cycling stability of up to 20 000 cycles, greatly outperforming those of previous works. These excellent rectification capability and electrochemical performances allow the as-built CAPode to work well in AND and OR logic gates, validating great potential in ion/electron-coupling logic operations. More attractively, the superior biocompatibilities of molybdenum oxide and relevant constituent materials enable the constructed CAPode to be applied as bioelectronics without regard to biosafety, paving a new way toward forthcoming human-computer interaction.

Sheet-Like Stacking SnS2/rGO Heterostructures as Ultrastable Anodes for Lithium-Ion Batteries.

SnS2-based materials have attracted considerable attention in energy storage and conversion owing to their high lithium activity and theoretical capacity. However, the practical application is severely limited by the low coulombic efficiency and short cycle life due to irreversible side reactions, low conductivity, and serious pulverization in the discharge/charge process. In this study, sheet-like stacking SnS2/reduced graphene oxide (rGO) heterostructures were developed using a facile solvothermal method. It was found that the composites between SnS2 nanoplates and rGO nanosheets are closely coupled through van der Waals interactions, providing efficient electron/ion paths to ensure high electrical conductivity and sufficient buffer space to alleviate volume expansion. Therefore, the SnS2/rGO heterostructure anode can obtain a high capacity of 840 mA h g-1 after 120 cycles at a current density of 200 mA g-1 and maintain a capacity of 450 mA h g-1 after 1000 cycles at 1000 mA g-1. In situ X-ray diffraction tests showed that SnS2/rGO undergoes typical initial intercalation, conversion, and subsequent alloying reactions during the first discharge, and most of the reactions are dealloying/alloying in the subsequent cycles. The galvanostatic intermittent titration technique showed that the diffusion of lithium ions in the SnS2/rGO heterostructures is faster in the intercalation and conversion reactions than in the alloying reactions. These observations help to clarify the reaction mechanism and ion diffusion behavior in the SnS2 anode materials, thus providing valuable insights for improving the energy efficiency of lithium-ion batteries.

Ion-Selective Covalent Organic Framework Membranes as a Catalytic Polysulfide Trap to Arrest the Redox Shuttle Effect in Lithium-Sulfur Batteries.

In the wake of shaping the energy future through materials innovation, lithium-sulfur batteries (LSBs) are top-of-the-line energy storage system attributed to their high theoretical energy density and specific capacity inclusive of low material costs. Despite their strengths, LSBs suffer from the cross-over of soluble polysulfide redox species to the anode, entailing fast capacity fading and inferior cycling stability. Adding to the concern, the insulating character of polysulfides lends to sluggish reaction kinetics. To address these challenges, we construct optimized polysulfide blockers-cum-conversion catalysts by accommodating the battery separator with covalent organic framework@Graphene (COF@G) composites. We settle on a crystalline TAPP-ETTB COF in the interest of its nitrogen-enriched scaffold with a regular pore geometry, providing ample lithiophilic sites for strong chemisorption and catalytic effect to polysulfides. On another front, graphene enables high electron mobility, boosting the sulfur redox kinetics. Consequently, a lithium-sulfur battery with a TAPP-ETTB COF@G-based separator demonstrates a high reversible capacity of 1489.8 mA h g-1 at 0.2 A g-1 after the first cycle and good cyclic performance (920 mA h g-1 after 400 cycles) together with excellent rate performance (827.7 mA h g-1 at 2 A g-1). The scope and opportunities to harness the designability and synthetic structural control in crystalline organic materials is a promising domain at the interface of sustainable materials, energy storage, and Li-S chemistry.

Improved Comprehensive Photovoltaic Performance and Mechanisms by Additive Engineering of Ti3C2Tx MXene into CsPbI2Br.

CsPbI2Br is promising in the application of perovskite solar cells (PSCs) owing to its reasonable bandgap and good thermal stability. However, the reported power conversion efficiency (PCE) of the CsPbI2Br solar cells is still much lower than that of the organic-inorganic hybrid PSCs, mainly due to relatively poor CsPbI2Br crystal quality. Herein, additive engineering to the photoactive layer of CsPbI2Br using the Ti3C2Tx MXene nanosheets is reported. Thanks to the improved crystallinity/reduced defect density, together with the formation of the Schottky junction between the MXene nanosheets and CsPbI2Br, enhanced separation and transfer of the photogenerated electron-hole pairs can be achieved for optimal MXene addition. A simple device configuration of ITO/SnO2/Ti3C2Tx-added CsPbI2Br/P3HT/Ag can thus deliver a significantly boosted PCE of 15.10%, i.e., a ∼16.69% relative increment compared with that (12.94%) of the control device without adding MXene. In addition, the enhanced humidity resistance is achieved for the MXene-added CsPbI2Br layers.

Resistive Switching Memristor: On the Direct Observation of Physical Nature of Parameter Variability.

Ion-based memristive switching has attracted widespread attention from industries owing to its outstanding advantages in storage and neuromorphic computing. Major issues for achieving brain-inspired computation of highly functional memory in redox-based ion devices are relatively large variability in their operating parameters and limited cycling endurance. In some devices, volatile and nonvolatile operations often replace each other without changing operating conditions. To address these issues, it is important to observe directly what is happening in repeated operations. Herein, we use a planar device that enables direct capturing of microscopic behaviors in the nucleation and growth of metal whiskers under repeated switching to verify the microscopic origin of the large parameter variability. We report direct observations that reveal the physical origin for the large cycle-to-cycle and device-to-device variability in memristive switching, which was achieved using planar polymer atomic switches with a gap >1 µm. We find that the deposition location of metal atoms is closely related to the crystallinity of the ion transport layer (solid polymer electrolyte, SPE). The filament variability (shape, position, quantity, etc.) during different cycles and devices is indeed the main reason for the observed variability in the operating characteristics. The results shed unique light on the complexity of the operation of the ion device, that is, the evolution of the dielectric layer and metal filament must be considered.

High photosensitivity light-controlled planar ZnO artificial synapse for neuromorphic computing.

A light-controlled artificial synapse, which mimics the human brain has been considered to be one of the ideal candidates for the fundamental physical architecture of a neuromorphic computing system owing to the possible abilities of high bandwidth and low power calculation. However, the low photosensitivity of synapse devices can affect the accuracy of recognition and classification in neuromorphic computing tasks. In this work, a planar light-controlled artificial synapse having high photosensitivity (Ion/Ioff > 1000) with a high photocurrent and a low dark current is realized based on a ZnO thin film grown by radiofrequency sputtering. The synaptic functions of the human brain such as sensory memory, short-term memory, long-term memory, duration-time-dependent-plasticity, light-intensity-dependent-plasticity, learning-experience behavior, neural facilitation, and spike-timing-dependent plasticity are successfully emulated using persistent photoconductivity characteristic of a ZnO thin film. Furthermore, the high classification accuracy of 90%, 92%, and 86% after 40 epochs for file type datasets, small digits, and large digit is realized with a three-layer neural network based on backpropagation where the numerical weights in the network layer are mapped directly to the conductance states of the experimental synapse devices. Finally, characterization and analysis reveal that oxygen vacancy defects and chemisorbed oxygen on the surface of the ZnO film are the main factors that determine the performance of the device.

Improvement of the Optoelectrical Properties of a Transparent Conductive Polymer via the Introduction of ITO Nanoparticles and Its Application in Crystalline Silicon/Organic Heterojunction Solar Cells.

Compared with conventional transparent conductive indium tin oxide (ITO) films, poly(3,4-ethylenedioxythiophene):poly (styrenesulfonic acid) (PEDOT:PSS) as a conductive polymer material has been diffusely applied in organic optoelectronic devices. However, its optoelectrical properties need to be further improved. Therefore, a simple and universal approach with introducing ITO nanoparticles (NPs) was proposed to improve the optoelectrical properties of PEDOT:PSS thin films. The results show that the vertical conductivity (σDC⊥) and average transmittance (from 300 to 1200 nm) of PEDOT:PSS films were enhanced about 26.8 and 6.3%, respectively. Crystalline silicon (c-Si)/organic heterojunction solar cells (HSCs) with PEDOT:PSS/ITO NP hybrid films were fabricated and performances led to further improvement. The spatial distributions of relative electrical field intensity and the carrier generation rate of the HSCs under the standard AM 1.5 G condition were simulated, which were in good agreement with the experimental conclusions.

A highly stable and sensitive ethanol sensor based on Ru-decorated 1D WO3 nanowires.

Decorating materials with noble metal catalysts is an effective method for optimizing the sensing performance of sensors based on tungsten trioxide (WO3) nanowires. Ruthenium (Ru) exhibits excellent catalytic activity for oxygen adsorption/desorption and chemical reactions between gases and adsorbed oxygen. Herein, small Ru nanoparticles were uniformly distributed on the surface of one-dimensional WO3 nanowires. The nanowires were prepared by the electrospinning method through an ultraviolet (UV) irradiation process, and decoration with Ru did not change their morphology. A sensor based on 4% Ru nanowires (NWs) shows the highest response (∼120) to 100 ppm ethanol, which was increased around 47 times, and the lowest ethanol detection limit (221 ppb) at a lower temperature (200 °C) displays outstanding repeatability and stability even after 45 days or in higher-humidity conditions. Moreover, it also has faster response-recovery features. The improvement in the sensing performance was attributed to the stable morphology of the nanowires, the sensitization effect of Ru, the catalytic effect of RuO2 and the optimal atomic utilization efficiency. This work offers an effective and promising strategy for promoting the ethanol sensing performance of WO3.

Germanium anode with excellent lithium storage performance in a germanium/lithium-cobalt oxide lithium-ion battery.

Germanium is a highly promising anode material for lithium-ion batteries as a consequence of its large theoretical specific capacity, good electrical conductivity, and fast lithium ion diffusivity. In this work, Co3O4 nanowire array fabricated on nickel foam was designed as a nanostructured current collector for Ge anode. By limiting the voltage cutoff window in an appropriate range, the obtained Ge anode exhibits excellent lithium storage performance in half- and full-cells, which can be mainly attributed to the designed nanostructured current collector with good conductivity, enough buffering space for the volume change, and shortened ionic transport length. More importantly, the assembled Ge/LiCoO2 full-cell shows a high energy density of 475 Wh/kg and a high power density of 6587 W/kg. A high capacity of 1184 mA h g(-1) for Ge anode was maintained at a current density of 5000 mA g(-1) after 150 cycles.

Tunable white light emission by variation of composition and defects of electrospun Al2O3-SiO2 nanofibers.

Composite nanofibers consisting of Al2O3-SiO2 were prepared by electrospinning in combination with post-calcination in air. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to investigate the crystalline phase and microstructure of the composite nanofibers. Photoluminescence experiments indicated that the resulting white light emission can be tuned by the relative intensity of the individual spectral components, which are related to the individual defects such as: violet-blue emission from O defects, green emission from ≡Si(Al)-O-C∙=O, and red emission from intersystem radiative crossing. White light emission was realized at a Al/(Al-Si) ratio of 40 and 60 mol %. This research may offer a deeper understanding of the preparation of efficient and environmentally friendly, white luminescence materials.