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Since its first discovery in 2017, evaporation-induced electricity has attracted extensive attention and shown significant advantages in green energy conversion. While the streaming potential-related electrokinetic effect has been intensively explored and widely recognized as the underlying mechanism, the role of coupling between water molecules and charge carriers in the material remains elusive. Here we show through carefully designed experiments that the streaming potential effect indeed plays a role but can only contribute about half to the total water-evaporation-induced voltage occurring within the partially-wetted region of the carbon black film where the solid-liquid-gas three-phase interface exists. It is also shown that water evaporation from carboxyl and amino-functionalized carbon black films produces opposite voltage signals. Detailed first-principles calculations unveil that the adsorption of water molecules can lead to reversed charge transfer in the carboxyl and amino-functionalized carbon substrates. Finally, an evaporation-driven charge transport mechanism is proposed for the induced electricity mediated by the coupling between water molecules and charge carriers in the material. The results reveal the important role of direct interaction between water molecules and materials, deepening our understanding of the mechanism for evaporation-induced hydrovoltaic effect beyond streaming potential.

Water evaporation is a ubiquitous natural process exploiting thermal energy from ambient environment. Hydrovoltaic technologies emerged in recent years offer one prospective route to generate electricity from water evaporation, which has long been overlooked. Herein, we developed a hybrid hydrovoltaic generator driven by natural water evaporation, integrating an “evaporation motor” with an evaporation-electricity device and a droplet-electricity device. A rotary motion of the “evaporation motor” relies on phase change of ethanol driven by water-evaporation induced temperature gradient. This motion enables the evaporation-electricity device to work under a beneficial water-film operation mode to produce output of ~4 V and ~0.2 µA, as well as propels the droplet-electricity device to convert mechanical energy into pulsed output of ~100 V and ~0.2 mA. As different types of hydrovoltaic devices require distinctive stimuli, it was challenging to make them work simultaneously, especially under one single driving force. We here for the first time empower two types of hydrovoltaic devices solely by omnipresent water evaporation. Therefore, this work presents a new pathway to exploiting water evaporation-associated ambient thermal energy and provides insights on developing hybrid hydrovoltaic generators.

Abstract Artificial biomaterials with dynamic mechano-responsive behaviors similar to those of biological tissues have been drawing great attention. In this study, we report a TiO2-based nanowire (TiO2NWs) scaffolds, which exhibit dynamic mechano-responsive behaviors varying with the number and amplitude of nano-deformation cycles. It is found that the elastic and adhesive forces in the TiO2NWs scaffolds can increase significantly after multiple cycles of nano-deformation. Further nanofriction experiments show the triboelectric effect of increasing elastic and adhesive forces during the nano-deformation cycles of TiO2NWs scaffolds. These properties allow the TiO2NW scaffolds to be designed and applied as intelligent artificial biomaterials to simulate biological tissues in the future.

Electrocatalysis plays a crucial role in the conversion and storage of renewable energy, offering significant potential for addressing the energy crisis and environmental concerns. High-entropy oxides (HEOs), a class of emerging functional materials, have gained increasing attention in electrocatalysis due to their stable crystal structure, exceptional geometric compatibility, unique electronic balance factors, and abundant active sites. In this comprehensive review, we present recent advancements in utilizing HEOs as catalysts for various energy-based electrocatalytic reactions. We begin with an overview of HEOs that includes definitions, fundamental properties, and theoretical investigations. Subsequently, we describe different synthetic methods for HEOs while highlighting two newly-developed techniques. Furthermore, we extensively discuss recent developments in HEO-based electrocatalysts with diverse crystal structures such as rock-salt-type, rutile-type, spinel-type, perovskite-type, and other specially-structured HEOs. Special emphasis is placed on designed strategies aimed at enhancing performance and exploring correlations between structure/ composition and electrocatalytic performance. Finally, we provide concluding remarks along with perspectives on future opportunities in this exciting field.

Regulation of human thermal radiation plays a vital role in personal heat management. Conventional textiles cannot satisfy the demands for dynamic heat dissipation because of their high emissivities. Recent studies on the regulation of textile emissivity through electricity, heat, sweat, and force have made significant progress in resolving this conundrum. However, this technology is still plagued by weak wearability, low stability, and limited dynamic regulation amplitude of heating/cooling. In this review, we first explain the heat transfer model of adjustable heat radiation smart textiles to comprehend the boundary conditions of heat management in this technology. The regulatory principles and recent developments related to electricity, heat, sweat, and force regulation are then systematically summarized. Finally, the difficulties encountered and future development directions are discussed. Therefore, it is necessary to rapidly promote the practical application of adjustable heat-radiating smart textiles.

ABSTRACTDeveloping high-performance nanostructured materials is key to deliver the potential of hydrovoltaic technology into practical applications. As single-component materials have approached its limit in generating hydrovoltaic electricity, the development of multi-component hydrovoltaic materials has been necessary in continuously boosting the electricity output. Here, we report a hydrovoltaic material by integrating reduced graphene oxides and polypyrrole nanoparticles (rGO/PPy), where the rGO contributes improved conductivity and large specific surface area while PPy nanoparticles enable enhanced interaction with water. The device fabricated with this material generates a short-circuit current of 6 μA as well as a maximum power density of over 1 μW/cm3 from natural evaporation of water. And the substantial ion–PPy interaction enables robust voltage generation from evaporation of various salt solutions. Moreover, an outstanding scaling ability is demonstrated by connecting 10 devices in series that generate a sustainable voltage of up to ~2.5 V, sufficing to power many commercial devices, e.g. LED bulb and LCD screen

Abstract Water, the source of life, contains immense energy and manifests in diverse forms. Hydrovoltaic technology enables the direct interaction between water and materials to generate electricity, a vital necessity for industry modernization. Due to the ubiquitous presence and easy availability of falling water, hydrovoltaic energy derived from water droplets has attracted considerable attention and shown great potential in raindrop energy harvesting. In this review, a comprehensive summary of the latest advancements in harvesting hydrovoltaic energy from water droplets is presented, with a focus on the configurations and underlying mechanisms of hydrovoltaic devices. Additionally, a brief discussion on the applications of droplet‐based hydrovoltaic devices is presented, along with future prospects for this energy‐harvesting technology.

Abstract Water constitutes the largest energy carrier on earth, absorbing more than 70% of the solar energy received by the earth's surface, yet its low exploitation has been a constant concern. The hydrovoltaic effect is an emerging technology that generates electricity through the direct interaction between nanomaterials and water of various forms (raindrops, waves, flows, moisture, and natural evaporation). Especially, the evaporation‐driven hydrovoltaic effect is a spontaneous and ubiquitous process that can directly convert thermal energy from the surrounding environment into electricity without the demand for additional mechanical work, which shows unique advantages compared with other hydrovoltaic effects. A variety of nanostructured materials have been steadily developed for evaporation‐driven hydrovoltaic devices (EHDs) in recent years. However, there has been a lack of a clear specification on the selection and design of materials for improving device performance. Herein, we first analyze the mechanisms of EHDs followed by a summarization of the recent advances in materials, including carbon materials, biomass‐based materials, metal oxides, composite materials, and others. We then discuss the strategies for improving the energy conversion efficiency and the output power in terms of structural design, surface modification, and interface treatment. Finally, we provide an outlook on the potential applications of electricity generation, sensors, and desalination technology, as well as the challenges and prospects for the development of this emerging technology in the future.

Generating electricity from air opens a promising way for green energy harvesting. Here, authors present a prototype driven by the integration of moisture adsorption with evaporation to generate continuous electricity for a long duration.

Abstract 2D materials (2DMs), due to spin‐valley locking degree of freedom, exhibit strongly bound exciton and chiral optical selection rules and become promising material candidates for optoelectronic and spin/valleytronic devices. Over the last decade, the manifesting of 2D materials by circularly polarized lights expedites tremendous fascinating phenomena, such as valley/exciton Hall effect, Moiré exciton, optical Stark effect, circular dichroism, circularly polarized photoluminescence, and spintronic property. In this review, recent advance in the interaction of circularly polarized light with 2D materials covering from graphene, black phosphorous, transition metal dichalcogenides, van der Waals heterostructures as well as small proportion of quasi‐2D perovskites and topological materials, is overviewed. The confronted challenges and theoretical and experimental opportunities are also discussed, attempting to accelerate the prosperity of chiral light‐2DMs interactions.

Abstract The buckling behavior of stiff/soft bilayer films has been extensively studied over the past three decades. However, strategies to characterize buckling structures on complex surfaces caused by bilayer film deformation, such as bending and spherical bilayers, are still lacking, preventing an accurate understanding of buckling behaviors in a broader context. Here, a frozen effect in a stiff/soft bilayer film is reported which provides a solution to the aforementioned problem. The buckling patterns in the stiff/soft bilayer film can be frozen by electron‐beam irradiation, which is attributed to the irradiation‐induced hardening transition of the soft film. After local freezing, the buckling patterns on a complex surface can be positioned on a plane by eliminating the compression across the bilayer and, hence, can be characterized by conventional means. This frozen characterization technique is similar to cryo‐electron microscopy and has vast potential applications in many fields.

Summary: In recent years, sustainable energy development has become a major theme of research. The combination of solar heating and daytime radiative cooling has the potential to build a competitive strategy to alleviate current environmental and energy problems. Several studies on the combination of daytime radiative cooling and solar heating have been reported to improve energy utilization efficiency. However, most integrations still have a low solar/mid-infrared spectrum regulation range, low heating/cooling performance, and poor stability. To promote this technology further for real-world applications, herein we summarize the latest progress, technical features, bottlenecks, and future opportunities for the current integration of daytime radiative cooling and solar heating through the switch mode (including electrical, thermal-responsive, and mechanical regulations) and collaborative mode.

Common photovoltaic effect is across the interface of heterojunctions. Here, the authors find that scanning a light beam can induce a persistent in-plane photoelectric voltage along silicon-water interfaces, due to the following movement of a charge packet in the vicinity of the silicon surface.

Controlled growth of heterostructures within 10 nm scale is crucial for potential applications of transition metal dichalcogenides. Here, the authors report strain-driven synthesis of ultra-long MoS2 nano-channels having several micrometers length and 2–30 nm width embedded within MoSe2 monolayer.

Regulating the motion of nanoscale objects on a solid surface is vital for a broad range of technologies such as nanotechnology, biotechnology, and mechanotechnology. In spite of impressive advances achieved in the field, there is still a lack of a robust mechanism which can operate under a wide range of situations and in a controllable manner. Here, we report a mechanism capable of controllably driving directed motion of any nanoobjects (e.g., nanoparticles, biomolecules, etc.) in both solid and liquid forms. We show via molecular dynamics simulations that a nanoobject would move preferentially away from the fluctuating region of an underlying substrate, a phenomenon termed fluctuotaxis--for which the driving force originates from the difference in atomic fluctuations of the substrate behind and ahead of the object. In particular, we find that the driving force can depend quadratically on both the amplitude and frequency of the substrate and can thus be tuned flexibly. The proposed driving mechanism provides a robust and controllable way for nanoscale mass delivery and has potential in various applications including nanomotors, molecular machines, etc. [ABSTRACT FROM AUTHOR]

First-principles calculation of Np[TM.sub.2] (Np = naphthalene, TM = V, Mn, Ti, Nb) sandwich nanowires has shown that the magnetic ordering in the Np[V.sub.2] nanowire can be adjusted by changing its charge state. The carrier-tunable magnetic ordering is unique to the Np[V.sub.2] nanowire and the bonding between the two nearest-neighbor metal atoms has played a major role in controlling the magnetic coupling of charge-neutral Np[TM.sub.2] nanowires.

The first-principles calculations were performed to mechanism underlying the topologically adsorbed fluorine atoms on boron nitride nanotubes which induce long-ranged ferromagnetic spin ordering along the tube to offer strong spin polarization around the Fermi level. The piezomagnetic function and behavior of F-BNNTs offer a new route to facilitate the design of tunable spin devices.

Semiempirical quantum mechanical molecular dynamics simulations and ab initio calculations were employed to examine the stability and electronic structures of the boron nitride nanotubes (BNNTs) with diameters below 4 [Angstrom]. The double-walled BNNT formed by the insertion of small BNNT into a larger one, with reduced the energy gap due to the coupled effect of wall buckling difference and interwall nearly free electron [NFE]-[pi]' hybridization could find potential application as desirable semiconductors.

The development of an single-walled carbon nanotube (SWNT) model is reported as the frame structure of a new kind of equivalent beam elements that could distinguish the in-plane [sigma]-[sigma] and out-of-plane [sigma]-[pi] bond angle bending rigidities of the corresponding C-C bonds. The model could be incorporated into any standard finite element software to study nanostructures beyond the computational capability of current atomistic approaches.

A novel electric field-enhanced chemical assembly approach for fabricating highly aligned single-walled carbon nanotube (SWNT) arrays on a solid surface with remarkably improved efficiency and packing density is reported. The molecular dynamics simulation results clarified the alignment of SWNTs with their long axes along the electric flux in solution, leading to the increase of packing density and efficiency through overcoming the steric hindrance of the 'giant' carbon nanotubes.

Introducing sp3 bonds in carbon nanotubes can significantly modify their electronic properties but need high pressure at room temperature. Here we show by molecular dynamics simulations that sp2 to sp3 bond transition can be realized through bending manipulation at the buckling location, resembling that of nanoindented carbon nanostructures but with more convenient operation technique. The capability of sp3 bond formation is sensitive to the thickness and diameter of the carbon nanotubes. This bending induced sp3 structures can serve as tunneling junction for electrons, thus bending manipulation could be a route to tailoring nanocircuits. [ABSTRACT FROM AUTHOR]

A study of the energetically favored chiral configurations of two adjoining tubes in multiwalled carbon nanotube (MWNT) is conducted by employing extensive calculations for the energy differences in different MWNT models. Results reveal that energetically optimum chiral configurations exist in MWNTs and the combination of zigzag to zigzag tubes is always energy favored irrespective of tube size.

Tunable electromagnetic properties of pristine two-dimensional boron phosphide (h-BP) nanosheet and its semihydrogenated structure were studied by density functional theory computations. In sharp contrast to previously reported tensile strain-induced red shift in two-dimensional semiconductors, the direct gap of h-BP undergoes blue shift under biaxial tensile strain. Once semihydrogenated, the h-BP not only transform from the nonmagnetic semiconductor into metal which is spin-resolved but also exhibits linear response between the magnetic moment and biaxial strain with a slope up to 0.005 iB/1%. These findings provide a simple and effective route to tune the electronic and magnetic properties of μ-BP nanostructures in a wide range and should inspire experimental enthusiasm. [ABSTRACT FROM AUTHOR]

We show by density functional theory calculations that asymmetric hetero-stacking of Bi2Te3/Sb2Te3 films can modulate the topological surface states. Due to the structure inversion asymmetry, an intrinsic Rashba-like splitting of the conical surface bands is aroused. While such splitting in homogeneous Bi2Te3-class topological insulators can be realized in films with more than three quintuple layers under external electric fields, the hetero-stacking breaks the limit of thickness for preserving the topological nature into the thinnest two quintuple layers. These results indicate that the hetero-stacking can serve as an efficient strategy for spin-resolved band engineering of topological insulators. [ABSTRACT FROM AUTHOR]

In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water. [ABSTRACT FROM AUTHOR]

We report molecular dynamics simulations of structural and mechanical properties of partially unzipped carbon nanotubes. Our results show that in the absence of edge passivation, partially unzipped carbon nanotubes are unstable with rising temperature depending on the geometry of cutting. When the length-to-width ratio of the graphene segment is not sufficiently large, the dangling bonds at the cutting front tend to reconnect to each other and form back to carbon nanotube structure; otherwise the structures roll up at the graphene end due to the competition of bending stiffness between longitudinal direction and transverse direction. When the graphene edges are hydrogen saturated, the self-healing behavior is suppressed. Tensile tests show that partially unzipped carbon nanotubes exhibit brittle fracture behavior, with a Young's modulus around 700 GPa, which is comparable to that of carbon nanotubes and graphene. [ABSTRACT FROM AUTHOR]

The interlayer energy between two circular graphene sheets of nanometer scale, which is curved into cylindrical shape with different curvature radius, is investigated by a molecular force field based on a registry-dependent interlayer interaction potential. It is found that there is a special interlayer stacking angle near which the interlayer energy is significantly lower. This interlayer energy-minimum stacking registry angle shifts away from the original Bernal (AB) stacking orientation when the curvature radius of curved graphene sheets is less than 20 nm, and increases with decreasing curvature radius beyond this point. The stability of interlayer energy-minimum stacking of the curved graphene sheets decreases with decreasing curvature radius. [ABSTRACT FROM AUTHOR]

The group velocities of longitudinal and flexural wave propagations in single- and multi-walled carbon nanotubes are studied in the frame of continuum mechanics. The dispersion relations between the group velocity and the wavenumber for flexural and longitudinal waves, described by a beam model and a cylindrical shell model, are established for both single- and multi-walled carbon nanotubes. The effect of microstructures in carbon nanotubes on the wave dispersion is revealed through the non-local elastic models of a beam and a cylindrical shell, including the second-order gradient of strain and a parameter of microstructure. It is shown that the microstructures in the carbon nanotubes play an important role in the dispersion of both longitudinal and flexural waves. In addition, the non-local elastic models predict that the cut-off wavenumber of the dispersion relation between the group velocity and the wavenumber is approximately 2×1010m−1 for the longitudinal and flexural wave propagations in both single- and multi-walled carbon nanotubes. This may explain why the direct molecular dynamics simulation cannot give a proper dispersion relation between the phase velocity and the wavenumber when the wavenumber approaches approximately 2×1010m−1, much lower than the cut-off wavenumber for the dispersion relation between the phase velocity and the wavenumber predicted by continuum mechanics. [ABSTRACT FROM AUTHOR]

Structures with notches have a tendency to develop critical crack growth because of the stress concentration. The strength of the structures with stress gradient usually shows strong three-dimensional (3D) effects even under in-plane loading. The commonly two-dimensional (2D) models for fracture assessments of bodies with notches and cracks may lead to inaccurate predictions when in-plane loading is applied to certain 3D geometries. In the paper, the recent researches on the 3D effects of stress concentrations at notches and 3D stress fields of cracks are summarized. A new concept of equivalent thickness of the point on the crack front line is proposed based on the detailed analyses of the 3D out-of-plane stress fields of cracks, and then new empirical formulae of the 3D out-of-plane stress constraint factor T z of I–II mixed-mode cracks are obtained by use of the equivalent thickness. Combining the T z with the in-plane constraint parameters T or Q, the 3D multi-parameter descriptions of the stress field in front of various types of cracks using K– T z, J– T z, K– T– T z and J– Q– T z combination can be formulated. [ABSTRACT FROM AUTHOR]