Harvesting ambient mechanical energy at the nanometer scale holds great promises for powering small electronics and achieving self-powered electronic devices. The self-powering capability allows ...electronic device packages to exclude bulky energy storage components and makes possible forgoing the inclusion of bulky battery components. Recent development of nanogenerators (NGs) has demonstrated a possible solution for the design of self-sufficient power source that directly draws energy from ambient mechanical resources. Piezoelectric nanowires (NWs) are the building blocks of NGs. In this review paper, theoretical calculations and experimental characterization methods for predicting or determining the piezoelectric potential output of NWs are reviewed first. Representative models of NGs are then discussed for harvesting mechanical energy from high-frequency acoustic waves and low-frequency vibrations/frictions. A numerical calculation is also presented to estimate the energy output from NW-based NGs. A potential practical application of NGs for harvesting energy from respiration is shown using piezoelectric polymer thin films. At the end, perspectives of the NG concept are discussed. The nanometer-scale piezoelectric and mechanical properties, the piezotronic effect, and large-scale manufacturing capability are suggested to be the essential aspects that would eventually lead the promising NG concept to a practical power source.
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► Calculation and characterization of piezopotential from deflected nanowires are reviewed. ► Representative designs of nanogenerators are discussed. ► A practical application of harvesting energy from respiration is highlighted. ► Perspectives, challenges, and opportunities of nanogenerator research are suggested.
Cellulose is the most abundant natural polymer on earth, providing a sustainable green resource that is renewable, degradable, biocompatible, and cost effective. Recently, nanocellulose‐based ...mesoporous structures, flexible thin films, fibers, and networks are increasingly developed and used in photovoltaic devices, energy storage systems, mechanical energy harvesters, and catalysts components, showing tremendous materials science value and application potential in many energy‐related fields. In this Review, the most recent advancements of processing, integration, and application of cellulose nanomaterials in the areas of solar energy harvesting, energy storage, and mechanical energy harvesting are reviewed. For solar energy harvesting, promising applications of cellulose‐based nanostructures for both solar cells and photoelectrochemical electrodes development are reviewed, and their morphology‐related merits are discussed. For energy storage, the discussion is primarily focused on the applications of cellulose‐based nanomaterials in lithium‐ion batteries, including electrodes (e.g., active materials, binders, and structural support), electrolytes, and separators. Applications of cellulose nanomaterials in supercapacitors are also reviewed briefly. For mechanical energy harvesting, the most recent technology evolution in cellulose‐based triboelectric nanogenerators is reviewed, from fundamental property tuning to practical implementations. At last, the future research potential and opportunities of cellulose nanomaterials as a new energy material are discussed.
The most recent advancements of processing, integration, and application of cellulose nanomaterials in the areas of solar energy harvesting, energy storage, and mechanical energy harvesting are reviewed, underlining cellulose nanomaterials as a new energy material with tremendous materials science value and application potential in many energy‐related fields.
Abstract
In recent years, ontology has been widely used to model world knowledge at the conceptual level. In recent years, machine translation has been widely used. This paper focuses on the ...evaluation of machine translation system. This paper reviews and compares the types and standards of machine translation, the content of system evaluation, and the main methods of system evaluation. The experimental results show that a high-quality machine translation system must fully integrate linguistic knowledge and language neutral world knowledge. This paper introduces an ontology based English Chinese machine translation model system, which organizes concepts into a hierarchical structure and establishes rich conceptual connections among concepts. The accuracy of machine translation is improved by mapping words in a language to concepts in ontology. The experimental results show that the accuracy of machine translation can be improved by 10.8%.
A self-powering nanosystem that harvests its operating energy from the environment is an attractive proposition for sensing, personal electronics and defence technologies. This is in principle ...feasible for nanodevices owing to their extremely low power consumption. Solar, thermal and mechanical (wind, friction, body movement) energies are common and may be scavenged from the environment, but the type of energy source to be chosen has to be decided on the basis of specific applications. Military sensing/surveillance node placement, for example, may involve difficult-to-reach locations, may need to be hidden, and may be in environments that are dusty, rainy, dark and/or in deep forest. In a moving vehicle or aeroplane, harvesting energy from a rotating tyre or wind blowing on the body is a possible choice to power wireless devices implanted in the surface of the vehicle. Nanowire nanogenerators built on hard substrates were demonstrated for harvesting local mechanical energy produced by high-frequency ultrasonic waves. To harvest the energy from vibration or disturbance originating from footsteps, heartbeats, ambient noise and air flow, it is important to explore innovative technologies that work at low frequencies (such as <10 Hz) and that are based on flexible soft materials. Here we present a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing the nanowires rooted on them with respect to each other, mechanical energy is converted into electricity owing to a coupled piezoelectric-semiconductor process. This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics.
Cellulose, the most abundant natural polymer, is renewable, biodegradable, and cost competitive. This paper reports the development of a high‐performance triboelectric nanogenerator (TENG) with both ...contacting materials made from cellulosic materials. Cellulose nanofibrils (CNFs) are used as the raw material, and chemical reaction approaches are employed to attach nitro groups and methyl groups to cellulose molecules to change the tribopolarities of CNF, which in turn significantly enhances the triboelectric output. Specifically, the nitro‐CNF possesses a negative surface charge density of 85.8 µC m−2, while the methyl‐CNF possesses a positive surface charge density of 62.5 µC m−2, reaching 71% and 52% of that for fluorinated ethylene propylene (FEP), respectively. The figure of merit of the nitro‐CNF and methyl‐CNF is quantified to be 0.504 and 0.267, respectively, comparable to or exceeding a number of common synthetic polymers, such as Kapton, polyvinylidene fluoride, and polyethylene. The TENG fabricated from nitro‐CNF paired with methyl‐CNF demonstrates an average voltage output of 8 V and current output of 9 µA, which approaches the same level obtained from TENG made from FEP. This work demonstrates a successful strategy of using environmentally friendly, abundant cellulosic materials for replacing the synthetic polymers in TENG development.
Cellulose nanofibrils (CNFs) are chemically functionalized with nitro groups and methyl groups to engineer their tribopolarities, which in turn significantly enhances the electrical output of the triboelectric nanogenerator. The figures of merit of the nitro‐CNF and methyl‐CNF are quantified to be 0.51 and 0.28, respectively, comparable to or exceeding a number of common synthetic triboelectric polymer materials.
As full-duplex wireless communication evolves into a practical technique, it will be built into communication nodes in many application scenarios. However, it is difficult to do so for legacy ...communication nodes. Thus, full-duplex communication nodes will coexist with half-duplex communication nodes in the same application environment. In this paper, a wireless local area network with a full-duplex access point (AP) and half-duplex clients is studied, and a media access control (MAC) protocol called asymmetrical duplex (A-Duplex) is developed to support efficient coexistence between half-duplex clients and the full-duplex AP. A-Duplex explores packet-alignment-based capture effect to establish dual links between the AP and two different clients. In this way, the capability of a full-duplex AP can be utilized by half-duplex clients, which leads to much improved network throughput. Moreover, to ensure fairness of the MAC protocol, a virtual deficit round-robin algorithm is proposed for the AP to select appropriate half-duplex clients for dual-link setup. A-Duplex does not require any change in the physical layer of half-duplex clients; only an update of MAC driver is necessary. Thus, it is well suited for coexistence between half-duplex clients and a full-duplex AP. Both analysis and simulations are conducted to evaluate performance of A-Duplex. Results show that it improves the throughput by 48% and 188% and reduces the average packet delay by 26% and 22%, as compared to the IEEE 802.11 Distributed Coordination Function with and without RTS/CTS, respectively. Moreover, the throughput remains steady as the number of clients grows. A-Duplex also maintains a high level of fairness.
Two‐dimensional (2D) materials have drawn tremendous attention in recent years. Being atomically thin, stacked with van der Waals force and free of surface chemical dangling bonds, 2D materials ...exhibit several distinct physical properties. To date, 2D materials include graphene, transition metal dichalcogenides (TMDS), black phosphorus, black P(1‐x)Asx, boron nitride (BN) and so forth. Owing to their various bandgaps, 2D materials have been utilized for photonics and optoelectronics. Photodetectors based on 2D materials with different structures and detection mechanisms have been established and present excellent performance. In this Review, localized field enhanced 2D material photodetectors (2DPDs) are introduced with sensitivity over the spectrum from ultraviolet, visible to infrared in the sight of the influence of device structure on photodetector performance instead of directly illustrating the detection mechanisms. Six types of localized fields are summarized. They are: ferroelectric field, photogating electric field, floating gate induced electrostatic field, interlayer built‐in field, localized optical field, and photo‐induced temperature gradient field, respectively. These localized fields are proved to effectively promote the detection ability of 2DPDs by suppressing background noise, enhancing optical absorption, improving electron‐hole separation efficiency, amplifying photoelectric gain and/or extending the detection range.
Localized fields are essential for two‐dimensional material photodetectors (2DPDs). They either suppress the dark current, promote the optical absorption, improve the electron‐hole seperation efficiency or extend the detection range. Fabricating different device structures can introduce various localized fields. The integration of multiple localized fields is promising for designing 2DPDs towards future practical applications.
Aqueous rechargeable zinc ion batteries (ARZIBs) is considered one of the most compelling candidates for grid-scale energy storage owing to their cost effectiveness, good safety, eco-friendliness, ...high output voltage, and high capacity. However, their practical applications are still largely limited by the undesirable cyclability and high-rate capability. Here, we report a discovery that using a small amount (2 vol%) of diethyl ether (Et2O) as the electrolyte additive could largely improve the performance of Zn–MnO2 batteries. The addition of Et2O yielded the first cycle coulombic efficiency of 95.6% at 50 mA/g, a high capacity of 115.9 mAh/g at 5 A/g and 97.7% retention of initial capacity after 4000 cycles, demonstrating an outstanding rate capability and cycling performance among the reported Mn-based zinc ions batteries in mild electrolyte. Ex-situ characterizations revealed that appropriate amount of Et2O molecules could effectively suppress the formation of Zn dendrites on Zn anode, which is the main mechanism for cyclability improvements.
Aqueous Zn–MnO2battery with 2 vol% diethyl ether (Et2O) electrolyte additive exhibited significantly improved cycling stability, especially at high rates. The improvement was attribute to the effective suppression of dendrite formation on Zn metal anodes. Display omitted
•Et2O as electrolyte additive successfully improves the coulombic efficiency of Zn–MnO2 battery.•A high capacity retention of 97.7% of the Zn–MnO2 with Et2O is achieved after 4000 cycles at 5 A/g.•The Zn–Zn symmetrical battery with Et2O electrolyte additive sustains for over 250 h at 0.2 mA/cm2.•The highly-polarized Et2O molecules preferably adsorb on Zn extrusions, suppressing dendrite formation.
We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide ...nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems.
Two dimensional lamellar membranes are attractive for anomalous water and ion transfer, but performance is hindered by swelling. Here, the authors stabilize a MXene membrane laminar architecture with ...fixed nanochannels, achieving highly selective acid recovery from iron-based wastewater.
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