Vibration energy harvesting typically involves a mechanical oscillatory mechanism to accumulate ambient kinetic energy, prior to the conversion to electrical energy through a transducer. The ...convention is to use a simple linear mass-spring-damper oscillator with its resonant frequency tuned towards that of the vibration source. In the past decade, there has been a rapid expansion in research of vibration energy harvesting into various nonlinear vibration principles such as Duffing nonlinearity, bistability, parametric oscillators, stochastic oscillators and other nonlinear mechanisms. The intended objectives for using nonlinearity include broadening of frequency bandwidth, enhancement of power amplitude and improvement in responsiveness to non-sinusoidal noisy excitations. However, nonlinear vibration energy harvesting also comes with its own challenges and some of the research pursuits have been less than fruitful. Previous reviews in the literature have either focussed on bandwidth enhancement strategies or converged on select few nonlinear mechanisms. This article reviews eight major types of nonlinear vibration energy harvesting reported over the past decade, covering underlying principles, advantages and disadvantages, and application-specific guidance for researchers and designers.
2D van der Waals (vdW) magnets, which present intrinsic ferromagnetic/antiferromagnetic ground states at finite temperatures down to atomic‐layer thicknesses, open a new horizon in materials science ...and enable the potential development of new spin‐related applications. The layered structure of vdW magnets facilitates their atomic‐layer cleavability and magnetic anisotropy, which counteracts spin fluctuations, thereby providing an ideal platform for theoretically and experimentally exploring magnetic phase transitions in the 2D limit. With reduced dimensions, the susceptibility of 2D magnets to a large variety of external stimuli also makes them more promising than their bulk counterpart in various device applications. Here, the current status of characterization and tuning of the magnetic properties of 2D vdW magnets, particularly the atomic‐layer thickness, is presented. Various state‐of‐the‐art optical and electrical techniques have been applied to reveal the magnetic states of 2D vdW magnets. Other emerging 2D vdW magnets and future perspectives on the stacking strategy are also given; it is believed that they will excite more intensive research and provide unprecedented opportunities in the field of spintronics.
2D van der Waals (vdW) magnets, which present intrinsic ferromagnetic/antiferromagnetic ground states down to atomiclayer thicknesses, open a new horizon in materials science. Recent state‐of‐the‐art characterization and tuning of the magnetic properties of 2D vdW magnets are outlined. Future perspectives and emerging 2D vdW magnets are also discussed, to provide unprecedented opportunities in the fields of spintronics.
Although only a few 2D materials have been predicted to possess ferroelectricity, 2D ferroelectrics are expected to play a dominant role in the upcoming nano era as important functional materials. ...The ferroelectric properties of 2D ferroelectrics are significantly different than those of traditional bulk ferroelectrics owing to their intrinsic size and surface effects. To date, 2D ferroelectrics have been reported to exhibit diverse properties ranging from bulk photovoltaic and piezoelectric/pyroelectric effects to the spontaneous valley and spin polarization. These properties are either dependent on ferroelectric polarization or coupled with it for easy electric control, thus making 2D ferroelectrics applicable to multifunctional nanodevices. At present, cumulative efforts are being made to explore 2D ferroelectrics in theories, experiments, and applications. Herein, such theories and methods are briefly introduced. Subsequently, intrinsic and extrinsic origins of 2D ferroelectricity are separately summarized. In addition, invented or laboratory‐validated 2D ferroelectric‐based applications are listed. Finally, the existing challenges and prospects of 2D ferroelectrics are discussed.
2D ferroelectrics are expected to play a dominant role in the upcoming nano era as important functional materials. Relevant theories, as well as intrinsic and extrinsic 2D ferroelectrics, are outlined. Further, the existing challenges and prospects of the exploration in 2D ferroelectrics are also discussed, which should provide unprecedented opportunities in the fields of electronics, spintronics, optoelectronics, and valleytronics.
Fe–N–C single-atom catalysts (SACs) exhibit high activity for oxygen reduction reaction (ORR). However, it remains controversial how the active center mediates catalysis, and the predicted potential ...deviates from experimental results, hindering development of ideal SACs. Here, using first-principles calculations, we present a microkinetic model for ORR on Fe–N–C SACs, disclosing a self-adjusting mechanism induced by its intrinsic intermediate. The modeling results show that the single-atom Fe site of the FeN4 center of Fe–N–C is covered with an intermediate OH* from 0.28 to 1.00 V. Remarkably, such OH* becomes part of the active moiety, Fe(OH)N4, and can optimize intermediate bindings on the Fe site, exhibiting a theoretical half-wave potential of ∼0.88 V. Partial current density analysis reveals the dominating associative path over the dissociative ones. In addition, ORR on Mn–N–C and Co–N–C SACs is unveiled. This work demonstrates the necessity of assessing the effect of intrinsic intermediates in single-atom catalysis and provides practical guidance for rational design of high-performance SACs.
Hornworts, liverworts and mosses are three early diverging clades of land plants, and together comprise the bryophytes. Here, we report the draft genome sequence of the hornwort Anthoceros angustus. ...Phylogenomic inferences confirm the monophyly of bryophytes, with hornworts sister to liverworts and mosses. The simple morphology of hornworts correlates with low genetic redundancy in plant body plan, while the basic transcriptional regulation toolkit for plant development has already been established in this early land plant lineage. Although the Anthoceros genome is small and characterized by minimal redundancy, expansions are observed in gene families related to RNA editing, UV protection and desiccation tolerance. The genome of A. angustus bears the signatures of horizontally transferred genes from bacteria and fungi, in particular of genes operating in stress-response and metabolic pathways. Our study provides insight into the unique features of hornworts and their molecular adaptations to live on land.
Despite wide applications of bimetallic electrocatalysis in oxygen evolution reaction (OER) owing to their superior performance, the origin of the improved performance remains elusive. The underlying ...mechanism was explored by designing and synthesizing a series of stable metal–organic frameworks (MOFs: NNU‐21–24) based on trinuclear metal carboxylate clusters and tridentate carboxylate ligands. Among the examined stable MOFs, NNU‐23 exhibits the best OER performance; particularly, compared with monometallic MOFs, all the bimetallic MOFs display improved OER activity. DFT calculations and experimental results demonstrate that introduction of the second metal atom can improve the activity of the original atom. The proposed model of bimetallic electrocatalysts affecting their OER performance can facilitate design of efficient bimetallic catalysts for energy storage and conversion, and investigation of the related catalytic mechanisms.
An iron atom in an Fe3 cluster is replaced by a second metal to form Fe2M clusters, which can serve as nodes to bridge with organic ligands and construct stable bimetallic MOFs. The introduction of the second metal atom can improve the activity of the original atom and thus improve the oxygen evolution reaction performance of electrocatalysts.
The conventional thermal transformation of metal–organic frameworks (MOFs) for electrocatalysis requires high temperature, an inert atmosphere, and long duration that result in severe aggregation of ...metal particles and non‐uniform porous structures. Herein, a precise and inexpensive laser‐induced annealing (LIA) strategy, which eliminates particle aggregation and rapidly generates uniform structures with a high exposure of active sites, is introduced to carbonize MOFs on conductive substrates under ambient conditions within a few minutes. By systematically considering 8 substrates and 12 MOFs, a series of LIA‐MOF/substrate devices with controllable sizes and good flexibility are successfully obtained. These LIA‐MOF/substrate devices can directly serve as working electrodes. Remarkably, LIA‐MIL‐101(Fe) on nickel foam exhibits an ultralow overpotential of 225 mV at a current density of 50 mA cm−2 and excellent stability over 50 h for facilitating the oxygen evolution reaction, outperforming most recently reported transition‐metal‐based electrocatalysts and commercial RuO2. Physical characterizations and theoretical calculations evidence that the high activity of LIA‐MIL‐101(Fe) arises from the favorable adsorption of intermediates at its Ni‐doped Fe3O4 overlayer that is formed during the laser treatment. Moreover, the LIA‐MOF/substrate devices are assembled for overall water splitting. The proposed LIA strategy demonstrates a cost‐effective route for manufacturing scalable energy storage and conversion devices.
A laser‐induced annealing (LIA) strategy is applied to synthesize a series of LIA‐metal–organic frameworks (MOFs) on conductive substrates under ambient conditions within a few minutes. The obtained LIA‐MOF/substrate devices with controllable sizes and good flexibility exhibit excellent performance for electrochemical water splitting due to the formation of an active Ni‐doped Fe3O4 overlayer during the laser treatment.
Investigations on the fatigue crack growth of commercial pure titanium are carried out with cruciform specimens under different biaxial load ratios (
= 0, 0.5, and 1) and crack inclination angles (
= ...90°, 60°, and 45°) in this paper. Based on the finite element results, the modified solution of stress intensity factors
and
for cruciform specimens containing mixed mode I-II crack is obtained by considering crack size, biaxial load ratio, and crack inclination angles. The experimental results show that the maximum tangential stress criterion is fit for the prediction of crack initiation angles for mixed model I-II crack under uniaxial or biaxial loading condition. When the biaxial load ratio increases, the crack propagation angle becomes smaller, and so does the fatigue crack growth rate of mode I crack or mixed mode I-II crack. Based on an equivalent stress intensity factor, a new valid stress intensity factor is proposed to better describe the biaxial fatigue crack growth behavior, which can demonstrate the contribution of mode I and mode II of stress intensity factor.
Atomically ordered intermetallic nanoparticles exhibit improved catalytic activity and durability relative to random alloy counterparts. However, conventional methods with time‐consuming and ...high‐temperature syntheses only have rudimentary capability in controlling the structure of intermetallic nanoparticles, hindering advances of intermetallic nanocatalysts. We report a template‐directed strategy for rapid synthesis of Pd‐based (PdM, M=Pb, Sn and Cd) ultrathin porous intermetallic nanosheets (UPINs) with tunable sizes. This strategy uses preformed seeds, which act as the template to control the deposition of foreign atoms and the subsequent interatomic diffusion. Using the oxygen reduction reaction (ORR) as a model reaction, the as‐synthesized Pd3Pb UPINs exhibit superior activity, durability, and methanol tolerance. The favored geometrical structure and interatomic interaction between Pd and Pb in Pd3Pb UPINs are concluded to account for the enhanced ORR performance.
This template‐directed synthetic strategy is a universal route for shape‐controlled synthesis of intermetallic nanocrystals and will provide new opportunities for intermetallic nanocatalysts.
Molybdenum disulfide (MoS2) has been widely studied as a potential earth‐abundant electrocatalyst for the hydrogen‐evolution reaction (HER). Defect engineering and heteroelemental doping are ...effective methods to enhance the catalytic activity in the HER, so exploring an efficient route to simultaneously achieve in‐plane vacancy engineering and elemental doping of MoS2 is necessary. In this study, Zinc, a low‐cost and moderately active metal, has been used to realize this strategy by generation of sulfur vacancies and zinc doping on MoS2 in one step. Density functional theory calculations reveal that the zinc atoms not only lower the formation energy of S vacancies, but also help to decrease ΔGH of S‐vacancy sites near the Zn atoms. At an optimal zinc‐reduced MoS2 (Zn@MoS2) example, the activated basal planes contribute to the HER activity with an overpotential of −194 mV at 10 mA cm−2 and a low Tafel slope of 78 mV/dec.
Zincing out loud: A method is proposed that uses zinc, a low‐cost and moderately active metal, to generate sulfur vacancies and realize zinc doping on MoS2 basal planes simultaneously.
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