Search

Water is crucial for various physicochemical processes at the liquid-solid interfaces. In particular, the interfacial water, mediating the electric field and solvation effect along with the solid, corporately determine the electrochemical properties. Understanding the interaction between solid properties and the interface water holds significant importance in interfacial dynamics. However, the impact of alterations in the charged state of solid surfaces induced by contact electrification on interfacial water remains unknown. Here, the evolution of atomic-level resolution maps of hydration layers are reported on charged surfaces using 3D atomic force microscopy (3D-AFM). These findings demonstrate that electrostatic interactions can reinforce, distort, or collapse the characteristic structure of hydration layers. More importantly, these interactions exhibit interlayer differences and sample specificity in hydration layer structures of different substrates. In addition, similar oscillations of the hydration layer are observed at the electrochemical interface under different voltage biases. This suggests that contact-electrification has the potential to serve as a novel method for manipulating and regulating chemical reactions at the interface., (© 2024 Wiley‐VCH GmbH.)

Wettability significantly influences various surface interactions and applications at the liquid-solid interface. However, the understanding is complicated by the intricate charge exchange occurring through contact electrification (CE) during this process. The understanding of the influence of triboelectric charge on wettability remains challenging, especially due to the complexities involved in concurrently measuring contact angles and interfacial electrical signals. Here, the relationship is investigated between surface charge density and change of contact angle of dielectric films after contact with water droplets. It is observed that the charge exchange when water spared lead to a spontaneous wetting phenomenon, which is termed as the contact electrification induced wetting (CEW). Notably, these results demonstrate a linear dependence between the change of contact angle (CA) of the materials and the density of surface charge on the solid surface. Continuous CEW tests show that not only the static CA but also the dynamics of wetting are influenced by the accumulation charges at the interface. The mechanism behind CEW involves the redistribution of surface charges on a solid surface and polar water molecules within liquid. This interaction results in a decrease in interface energy, leading to a reduction in the CA. Ab initio calculations suggest that the reduction in interface energy may stem from the enhanced surface charge on the substrate, which strengthens the hydrogen bond interaction between water and the substrate. These findings have the potential to advance the understanding of CE and wetting phenomena, with applications in energy harvesting, catalysis, and droplet manipulation at liquid-solid interfaces., (© 2024 Wiley‐VCH GmbH.)

Polyhalogenated carbazoles (PHCZs), an emerging persistent halogenated organic pollutant, have been detected in the environment. However, our understanding of PHCZs in the ocean remains limited. In this study, 47 seawater samples (covering 50 - 4000 m) and sediment samples (49 surface and 3 cores) were collected to investigate the occurrence and spatial distribution patterns of carbazole and its halogenated derivants (CZDs) in the Western Pacific Ocean. In seawater, the detection frequencies of CZ (97.87%) and 3-CCZ (57.45%) were relatively high. In addition, the average concentration of ΣPHCZs in the upper water (< 150 m, 0.23 ± 0.21 ng/L) was significantly lower than that in the deep ocean (1000 - 4000 m, 0.65 ± 0.56 ng/L, P < 0.05), which may indicate the vertical transport of PHCZs in the marine environment. The concentration of ΣCZDs in surface sediment ranges from 0.46 to 6.48 ng/g (mean 1.54 ng/g), among which CZ and 36-CCZ were the predominant components. Results from sediment cores demonstrate a noteworthy negative correlation between the concentration of CZDs and depth, indicating the ongoing natural degradation process occurring in sediment cores over a long period. This study offers distinctive insights into the occurrence, composition, and vertical features of CZDs in oceanic environments., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Tailoring materials with prescribed properties and regular structures is a critical and challenging research topic. Early transition metals were found to form supermagic M 8 C 12 metallocarbohedrenes (Met-Cars); however, stable metal carbides are not limited to this common stoichiometry. Utilizing self-developed deep-ultraviolet laser ionization mass spectrometry, here, we report a strategy to generate new titanium carbides by reacting pure Ti n clusters with acetylene. Interestingly, two products corresponding to Ti 17 C 2 and Ti 19 C 10 exhibit superior abundances in addition to the Ti 8 C 12 Met-Cars. Using global-minimum search, the structures of Ti 17 C 2 and Ti 19 C 10 are determined to be an ellipsoidal D 4d and a rod-shaped D 5h geometry, respectively, both with carbon-capped Ti 4 C moieties and superatomic features. We illustrate the electronic structures and bonding nature in these carbon-doped superatoms concerning their enhanced stability and local aromaticity, shedding light on a new class of metal-carbide nanomaterials with atomic precision.

Bulk cobalt does not react with water at room temperature, but cobalt nanometals could yield corrosion at ambient conditions. Insights into the cobalt cluster reactions with water and oxygen enable us to better understand the interface reactivity of such nanometals. Here we report a comprehensive study on the gas-phase reactions of Co n ±/0 clusters with water and oxygen. All these Co n ±/0 clusters were found to react with oxygen, but only anionic cobalt clusters give rise to water dissociation whereas the cationic and neutral ones are limited to water adsorption. We elucidate the influences of charge states, bonding modes and dehydrogenation mechanism of water on typical cobalt clusters. It is unveiled that the additional electron of anionic Co n - clusters is not beneficial to H 2 O adsorption, but allows for thermodynamics- and kinetics-favourable H atom transfer and dehydrogenation reactions. Apart from the charge effect, size effect and spin effect play a subtle role in the reaction process. The synergy of multiple metal sites in Co n - clusters reduces the energy barrier of the rate-limiting step enabling hydrogen release. This finding of water dissociation on cobalt clusters put forward new connotations on the activity series of metals, providing new insights into the corrosion mechanism of cobalt nanometals., (© 2024. The Author(s).)

Chemical analysis of ions and small organic molecules in liquid samples is crucial for applications in chemistry, biology, environmental sciences, and health monitoring. Mainstream electrochemical and chromatographic techniques often suffer from complex and lengthy sample preparation and testing procedures and require either bulky or expensive instrumentation. Here, we combine triboelectrification and charge transfer on the surface of electrical insulators to demonstrate the concept of triboelectric spectroscopy (TES) for chemical analysis. As a drop of the liquid sample slides along an insulating reclined plane, the local triboelectrification of the surface is recorded, and the charge pattern along the sample trajectory is used to build a fingerprinting of the charge transfer spectroscopy. Chemical information extracted from the charge transfer pattern enables a new nondestructive and ultrafast (<1 s) tool for chemical analysis. TES profiles are unique, and through an automated identification, it is possible to match against standard and hence detect over 30 types of common salts, acids, bases and organic molecules. The qualitative and quantitative accuracies of the TES methodology is close to 93%, and the detection limit is as low as ppb levels. Instruments for TES chemical analysis are portable and can be further miniaturized, opening a path to in situ and rapid chemical detection relying on inexpensive, portable low-tech instrumentation.

Iodomethane and bromomethane (CH 3 I/CH 3 Br) are common chemicals, but their chemistry on nanometals is not fully understood. Here, we analyze the reactivity of Rh n + ( n = 3-30) clusters with halomethanes and unveil the spin effect and concentration dependence in the C-H and C-X bond activation. It is found that the reactions under halomethane-rich conditions differ from those under metal-rich conditions. Both CH 3 I and CH 3 Br undergo similar dehydrogenation on the Rh n + clusters in the presence of small quantity reactants; however, different reactions are observed in the presence of sufficient CH 3 I/CH 3 Br, showing dominant Rh(CH 3 Br) x + ( x = 1-4) products but a series of Rh n C x H y I z + species ( x = 1-4, y = 1-12, and z = 1-5) pertaining to H 2 , HI, or CH 4 removal. Density functional theory calculations reveal that the dehydrogenation and demethanation of CH 3 Br are relatively less exothermic and will be deactivated by sufficient gas collisions if helium cooling takes away energy immediately; instead, the successive adsorption of CH 3 Br gives rise to a series of Rh(CH 3 Br) x + species with accidental C-Br bond dissociation.

Ferromagnets constructed from nanometals of atomic precision are important for innovative advances in information storage, energy conversion, and spintronic microdevices. Considerable success has been achieved in designing molecular magnets, which, however, are challenging in preparation and may suffer from drawbacks on the incompatibility of high stability and strong ferromagnetism. Utilizing a state-of-the-art self-developed mass spectrometer and a homemade laser vaporization source, we have achieved a highly efficient preparation of pure iron clusters, and here, we report the finding of a strongly ferromagnetic metal-carbon cluster, Fe 12 C 12 - , simply by reacting the Fe n - clusters with acetylene in proper conditions. The unique stability of this ferromagnetic Fe 12 C 12 - cluster is rooted in a plumb-bob structure pertaining to Jahn-Teller distortion. We classify Fe 12 C 12 - as a new member of metallo-carbohedrenes and elucidate its structural stability mechanism as well as its soft-landing deposition and magnetization measurements, providing promise for the exploration of potential applications.

Probing atomic clusters with magic numbers is of supreme importance but challenging in cluster science. Pronounced stability of a metal cluster often arises from coincident geometric and electronic shell closures. However, transition metal clusters do not simply abide by this constraint. Here, we report the finding of a magic-number cluster Rh 19 - with prominent inertness in the sufficient gas-collision reactions. Photoelectron spectroscopy experiments and global-minimum structure search have determined the geometry of Rh 19 - to be a regular O h ‑[Rh@Rh 12 @Rh 6 ] - with unusual high-spin electronic configuration. The distinct stability of such a strongly magnetic cluster Rh 19 - consisting of a nonmagnetic element is fully unveiled on the basis of its unique bonding nature and superatomic states. The 1-nanometer-sized O h -Rh 19 - cluster corresponds to a fragment of the face-centered cubic lattice of bulk rhodium but with altered magnetism and electronic property. This cluster features exceptional electron-spin state isomers confirmed in photoelectron spectra and suggests potential applications in atomically precise manufacturing involving spintronics and quantum computing.

Contact electrification (CE) in water has attracted much attention, owing to its potential impacts on the chemical reactions, such as the recent discovery of spontaneous generation of hydrogen peroxide (H 2 O 2 ) in water microdroplets. However, current studies focus on the CE of bulk water, the measurement of CE between micrometer-size water droplets is a challenge and its mechanism still remains ambiguous. Here, a method for quantifying the amount of charge carried by the water microdroplets produced by ultrasonic atomization is proposed. In the method, the motions of water microdroplets in a uniform electric field are observed and the electrostatic forces on the microdroplets are calculated based on the moving speed of the microdroplets. It is revealed that the charge transfer between water microdroplets is size-dependent. The large microdroplets tend to be positively charged while the small microdroplets tend to receive negative charges, implying that the negative charges transfer from large microdroplets to the small microdroplets during ultrasonic atomization. Further, a theoretical model for microdroplets charging is proposed, in which the curvature-induced surface potential/energy difference is suggested to be responsible for the charge transfer between microdroplets. The findings show that the electric field strength between two microdroplets with opposite charges during separation is strong enough to convert OH ‒ to OH*, providing evidence for the CE-induced spontaneous generation of H 2 O 2 in water microdroplets.

Regulating the ranking of polymer in triboelectric series over a wide range is of great help for material's selection of triboelectric nanogenerators (TENGs). Herein, fluorinated poly(phthalazinone ether)s (FPPEs) with tunable molecular structure and aggregate structure are synthesized by co-polycondensation, while the large positive ranking shift in the triboelectric series can be achieved by introducing phthalazinone moieties with strong electron donating capability. FPPE-5, which includes abundant phthalazinone moieties, is more positive than all of the previously reported triboelectric polymers. Hence, the regulating range of FPPEs in this work updates a new record in triboelectric series, which is wider than that of previous works. A peculiar crystallization behavior, capable of trapping and storing more electrons, has been observed in FPPE-2 with 25% phthalazinone moieties. Correspondingly, FPPE-2 is more negative than FPPE-1 without a phthalazinone moiety, which is an unexpected shift against the common changing tendency in triboelectric series. With FPPEs films as the probing material, a tactile TENG sensor is applied to enable material identification via electrical signal polarity. Hence, this study demonstrates a strategy to regulate the series of triboelectric polymers by copolymerization using monomers with distinct electrification capabilities, where both the monomer ratio and the peculiar nonlinear behavior can control triboelectric performance., (© 2023 Wiley-VCH GmbH.)

Contact between water droplets with hydrophobic surfaces is a common phenomenon at functional interfaces, and it has been extensively studied. However, quantifying the charge transfer between the liquid-solid interfacial contacting, especially for the charge density distribution throughout the movement of liquid droplet on a dielectric surface, remains to be investigated. Here, we developed a pixeled droplet triboelectric nanogenerator (pixeled droplet-TENG) array with high-density electrode array as a probe for measuring the charge transfer at a liquid-solid interface when a water drop moves on the hydrophobic surface. To intuitively observe the charge transfer between the liquid-solid interface, we "imaged" the transferred charges along movement trajectory of a water droplet as it slides along a tilted solid surface at a spatial resolution of 0.4 mm and time sensitivity of 0.02 s. Our study shows that the transferred charges are not uniformly distributed along the path, which is possibly due to the two-step model of electron transfer and ion adsorbed on the solid surface, and thus the formation of an electric double layer will inevitably shield the net surface on the solid surface. Our study presents a probe technology with potential applications in surface chemistry, physics, material science, and cell biology.

Tribovoltaic direct-current (DC) nanogenerator made of dynamic semiconductor heterojunction is emerging as a promising mechanical energy harvesting technology. However, fundamental understanding of the mechano-electronic carrier excitation and transport at dynamic semiconductor interfaces remains to be investigated. Here, we demonstrated for the first time, that tribovoltaic DC effect can be tuned with metal - insulator transition (MIT). In a representative MIT material (vanadium dioxide, VO 2 ), we found that the short-circuit current ( I SC ) can be enhanced by >20 times when the material is transformed from insulating to metallic state upon static or dynamic heating, while the open-circuit voltage ( V OC ) turns out to be unaffected. Such phenomenon may be understood by the Hubbard model for Mott insulator: orders' magnitude increase in conductivity is induced when the nearest hopping changes dramatically and overcomes the Coulomb repulsion, while the Coulomb repulsion giving rise to the quasi-particle excitation energy remains relatively stable.

Electron transfer has been proven the dominant charge carrier during contact electrification at the liquid-solid interface. However, the effect of electron spin in contact electrification remains to be investigated. This study examines the charge transfer between different liquids and ferrimagnetic solids in a magnetic field, focusing on the contribution of O 2 molecules to the liquid-solid contact electrification. The findings reveal that magnetic fields promote electron transfer at the O 2 -containing liquid-solid interfaces. Moreover, magnetic field-induced electron transfer increases at higher O 2 concentrations in the liquids and decreases at elevated temperatures. The results indicate spin-selected electron transfer at liquid-solid interface. External magnetic fields can modulate the spin conversion of the radical pairs at the O 2 -containing liquid and ferrimagnetic solid interfaces due to the Zeeman interaction, promoting electron transfer. A spin-selected electron transfer model for liquid-solid contact electrification is further proposed based on the radical pair mechanism, in which the HO 2 molecules and the free unpaired electrons from the ferrimagnetic solids are considered radical pairs. The spin conversion of the [HO 2 • •e - ] pairs is affected by magnetic fields, rendering the electron transfer magnetic field-sensitive., (© 2022. The Author(s).)

A stretchable triboelectric nanogenerator (TENG) can be a promising solution for the power supply of various flexible electronics. However, the detailed electrification mechanism of elastic triboelectric materials still needs to be clarified. In this work, we found crystallization behavior induced by strain and low temperature can lead to a shift in a triboelectric series for commonly used triboelectric elastomers and even reverse the triboelectric polarity. This effect is attributed to the notable rearrangement of surface electron cloud density happening along with the crystallization process of the molecular chain. This effect is significant with natural rubber, and silicone rubber can experience this effect at low temperature, which also leads to a shift in a triboelectric series, and an applied strain at low temperature can further enhance this shift. This study demonstrated that the electrification polarity of triboelectric materials should be re-evaluated under different strains and different temperatures, which provides a mechanism distinct from the general understanding of elastic triboelectric materials.

The role of the electrostatic environment in chemical reactions has long been an important research field, but most studies have focused on the influence of external electric fields on chemical processes, while the effect from the intrinsic electrostatic charges on the solution itself has been ignored. How an electrostatic field generated by contact electrification affects the solvent environment in a chemical reaction and then the chemical reactivity is still ambiguous. Here, based on the inspiration of the droplet triboelectric nanogenerator, electrostatic interactions between a statically charged luminol droplet and the surrounding directional electrostatic field were analyzed, and we demonstrate a relationship between the sign of the luminol sample (negatively or positively charged) and its effect on the reaction reactivity. Our results show that the increased reaction activity and the enhanced chemiluminescence (CL) only occurred when the luminol droplet yields positive charges, while a negatively charged luminol, on the contrary, tends to inhibit the CL, which brings direct evidence of the charge carriers of triboelectricity being electrons at the liquid-solid interface. This work provides a strategy for electrostatically regulating CL by simply statically charging a reaction solution with a dielectric solid and also carries a cautionary message on what to consider when preparing a sample for a chemical reaction.

Interfaces between a liquid and a solid (L-S) are the most important surface science in chemistry, catalysis, energy, and even biology. Formation of an electric double layer (EDL) at the L-S interface has been attributed due to the adsorption of a layer of ions at the solid surface, which causes the ions in the liquid to redistribute. Although the existence of a layer of charges on a solid surface is always assumed, the origin of the charges is not extensively explored. Recent studies of contact electrification (CE) between a liquid and a solid suggest that electron transfer plays a dominant role at the initial stage for forming the charge layer at the L-S interface. Here, we review the recent works about electron transfer in liquid-solid CE, including scenerios such as liquid-insulator, liquid-semiconductor, and liquid-metal. Formation of the EDL is revisited considering the existence of electron transfer at the L-S interface. Furthermore, the triboelectric nanogenerator (TENG) technique based on the liquid-solid CE is introduced, which can be used not only for harvesting mechanical energy from a liquid but also as a probe for probing the charge transfer at liquid-solid interfaces.

Contact electrification (CE) is a common physical phenomenon, and its mechanisms for solid-solid and liquid-solid cases have been widely discussed. However, the studies about liquid-liquid CE are hindered by the lack of proper techniques. Here, a contactless method is proposed for quantifying the charges on a liquid droplet based on the combination of electric field and acoustic field. The liquid droplet is suspended in an acoustic field, and an electric field force is created on the droplet to balance the acoustic trap force. The amount of charges on the droplet is thus calculated based on the equilibrium of forces. Further, the liquid-solid and liquid-liquid CE are both studied by using the method, and the latter is focused. The behavior of negatively precharged liquid droplet in the liquid-liquid CE is found to be different from that of the positively precharged one. The results show that the silicone oil droplet prefers to receive negative charges from a negatively charged aqueous droplet rather than positive charges from a positively charged aqueous droplet, which provides a strong evidence about the dominant role played by electron transfer in the liquid-liquid CE., (© 2021 Wiley-VCH GmbH.)

The phenomenon of triboelectricity involves the flow of charged species across an interface, but conclusively establishing the nature of the charge transfer has proven extremely difficult, especially for the liquid-solid cases. Herein, we developed a self-powered droplet triboelectric nanogenerator (droplet-TENG) with spatially arranged electrodes as a probe for measuring the charge transfer process between liquid and solid interfaces. The information on the electric signal on spatially arranged electrodes shows that the charge transfer between droplets and the solid is an accumulation process during the dropping and that the electron is the dominant charge-transfer species. Such a droplet-TENG showed a high sensitivity to the ratio of solvents in the mixed organic solution, and we postulated this is due to the possibility of generation of a hydrogen bond, affecting the electric signal on the spatially arranged electrodes. This work demonstrated a chemical sensing application based on the self-powered droplet triboelectric nanogenerator.

Temperature effects on the contact electrification (CE) is of great interest. Here, different kinds of substoichiometric oxide films, such as TiO 2- x , Al 2 O 3- x , Ta 2 O 5- x , and Cr 2 O 3- x , are deposited and annealed at different temperatures, and the CE between the films and a Pt-coated tip is performed by using Kelvin probe force microscopy (KPFM). An intriguing finding is that the polarity on the TiO 2- x surface changes from negative to positive with the increase of the sample annealing temperature in air atmosphere. Such a result is attributed to the fact that annealing under an oxidative atmosphere repairs oxygen vacancies and helps upgrade the low valency of Ti 3+ to a stable high valency of Ti 4+ . On the contrary, after annealing occurs in an Ar/H 2 atmosphere, the polarity on the TiO 2- x surface reverses from positive to negative. This is mainly due to the increase of oxygen vacancies after annealing in reducing atmosphere. Through the KPFM results of Al 2 O 3- x , Ta 2 O 5- x , and Cr 2 O 3- x films, the effect of oxygen vacancies is further confirmed, that is, the decrease of oxygen vacancies eases the films at capturing positive charges. Based on this, TiO 2- x -based identical material triboelectric nanogenerators (IM-TENGs) are designed and prepared for the first time to control the current direction. Moreover, a surface state model for explaining the CE mechanism between the metal and annealed dielectric is proposed. This study is conducive to the development of the IM-TENGs which regulate the current direction or voltage output accurately in the future and also provides a further understanding of the dominant mechanism of electron transfer in the CE.

Liquid-solid triboelectric nanogenerator (L-S TENG) is one of the major techniques to collect energy from tiny liquids, while the saturated charge density at the L-S interface is the key element to decide its performance. Here, we found that the saturated charge density of L-S contact electrification (CE) can be further increased under the illumination of an ultraviolet (UV) light. The fluorine-containing polymers and SiO 2 are chosen as the electrification materials and with and without UV illumination on the L-S TENG. A series of experiments have been done to rule out the possible influences of anion generation, chemical change of solid surface, ionization of water, and so on. Therefore, we proposed that electrons belonging to water molecules can be excited to high energy states under UV illumination, which then transfer to solid surface and captured by the solid surface. Finally, a photoexcited electron transfer model is proposed to explain the enhancement of CE under the UV illumination. This work not only helps to further understand CE at L-S interface, but also offers an approach to further enhance the performance of L-S TENG, which can promote the TENG applications in the field of microfluidic systems, liquid energy harvesting, and droplet sensory.

It has been demonstrated that substantial electric power can be produced by a liquid-based triboelectric nanogenerator (TENG). However, the mechanisms regarding the electrification between a liquid and a solid surface remain to be extensively investigated. Here, the working mechanism of a droplet-TENG was proposed based on the study of its dynamic saturation process. Moreover, the charge-transfer mechanism at the liquid-solid interface was verified as the hybrid effects of electron transfer and ion adsorption by a simple but valid method. Thus, we proposed a model for the charge distribution at the liquid-solid interface, named Wang's hybrid layer, which involves the electron transfer, the ionization reaction, and the van der Waals force. Our work not only proves that TENG is a probe for investigating charge transfer at interface of all phases, such as solid-solid and liquid-solid, but also may have great significance to water energy harvesting and may revolutionize the traditional understanding of the liquid-solid interface used in many fields such as electrochemistry, catalysis, colloidal science, and even cell biology.

The high-performance filter capacitor is a hot research topic in the field of filter circuits for flexible and wearable devices, whereas traditional aluminum electrolytic capacitors still experience widespread problems in terms of large error factors and poor stability. To avoid these disadvantages, in this work, we have developed a liquid dual-layer supercapacitor (SC). When it is employed as the filter capacitor in a filter circuit, any waveform signal can be transformed into a linear signal. The maximum fluctuation of the output signal is less than 16 mV; the SC also demonstrates excellent filtering stability in a frequency range of 1 ∼ 100 000 Hz, as well as an amplitude window of 0 ∼ 10 V. In this framework, our filter SC demonstrates unparalleled processing properties, and can greatly improve the stability and extend the lifetime of the entire electronic circuit. The fact that the requirements of high-end electronic products can be fulfilled due to the contribution of this filter SC are particularly significant.

Wurtzite-structured CdS material is widely used in information sensing and energy harvesting. Based on the piezoelectric property of CdS, we present a flexible piezoelectric nanogenerator (PENG) with three-dimensional-structured CdS nanowall arrays. Under index finger oscillations at a slow rate, the maximal open-circuit voltage and short-circuit current are 1.2 V and 6 nA respectively. Meanwhile, the working mechanism of this PENG was successfully studied with piezoelectric potential distribution and energy band theory respectively. All of the results show that an increase in the bending degree and bending frequency will affect the output of the PENG, suggesting that it can be used as a flexible sensor. In addition, the fabricated PENG can be used as a self-powered pressure sensor relying on the linear relationship between the output voltage and the vertical pressure. This work may provide a new approach to fabricating piezoelectric nanogenerators based on three-dimensional materials as an energy harvester, which may also facilitate the development of flexible and wearable electric sensing technology.

Contact electrification (CE) at interfaces is sensitive to the functional groups on the solid surface, but its mechanism is poorly understood, especially for the liquid-solid cases. A core controversy is the identity of the charge carriers (electrons or/and ions) in the CE between liquids and solids. Here, the CE between SiO 2 surfaces with different functional groups and different liquids, including DI water and organic solutions, is systematically studied, and the contribution of electron transfer is distinguished from that of ion transfer according to the charge decay behavior at surfaces at specific temperature, because electron release follows the thermionic emission theory. It is revealed that electron transfer plays an important role in the CE between liquids and functional group modified SiO 2 . Moreover, the electron transfer between the DI water and the SiO 2 is found highly related to the electron affinity of the functional groups on the SiO 2 surfaces, while the electron transfer between organic solutions and the SiO 2 is independent of the functional groups, due to the limited ability of organic solutions to donate or gain electrons. An energy band model for the electron transfer between liquids and solids is further proposed, in which the effects of functional groups are considered. The discoveries in this work support the "two-step" model about the formation of an electric double-layer (Wang model), in which the electron transfer occurs first when the liquids contact the solids for the very first time.

Polymers are commonly used to fabricate triboelectric nanogenerators (TENGs). Here, several polymer films with similar main chains but different functional groups on the side chain are employed to clarify the contributions of each functional group to contact electrification (CE). The results show that the electron-withdrawing (EW) ability and density of these functional groups on the main chain can determine both the polarity and density of CE-induced surface charges. Similar results are obtained for CE in both the polymer-polymer and polymer-liquid modes. A theoretical mechanism involving electron cloud overlap is proposed to explain all of these results. More importantly, the unsaturated groups on poly(tetrafluoroethylene) molecular chain are proved to have a much stronger EW ability than the saturated groups. The density of these unsaturated groups can be increased using a sputtering technique, suggesting that this is a facile and effective method of enhancing the performance of TENGs. These results clarify the correlation between the molecular structure and macroscopic electrification behavior of polymers., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Here we present the complete mitochondrial genome of Tetraclita squamosa squamosa , which is 15,191 bp in length with 67.20% AT content. It contains 13 protein-coding genes, 2 ribosomal-RNA genes and 22 transfer-RNA genes. All PCGs except nad4l in T. squamosa squamosa start with ATN, and terminated with a complete stop codon, except nad3. Phylogenetic analysis based on mitochondrial PCGs shows that T. squamosa squamosa is clustered with T. serrata into a branch (BP = 100). Our result is consistent with previous reports that genus Tetraclita and family Tetraclitidae are not monophyletic. This study contributes to further phylogenetic analysis within Cirripedia., (© 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Contact electrification (CE or triboelectrification) is a common phenomenon, which can occur for almost all types of materials. In previous studies, the CE between insulators and metals has been widely discussed, while CE involving semiconductors is only recently. Here, a tribo-current is generated by sliding an N-type diamond coated tip on a P-type or N-type Si wafers. The density of surface states of the Si wafer is changed by introducing different densities of doping. It is found that the tribo-current between two sliding semiconductors increases with increasing density of surface states of the semiconductor and the sliding load. The results suggest that the tribo-current is induced by the tribovoltaic effect, in which the electron-hole pairs at the sliding interface are excited by the energy release during friction, which may be due to the transition of electrons between the surface states during contact, or bond formation across the sliding interface. The electron-hole pairs at the sliding interface are subsequently separated by the built-in electric field at the PN or NN heterojunctions, which results in a tribo-current, in analogy to that which occurs in the photovoltaic effect., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new marine tardigrade, Moebjergarctus clarionclippertonensis sp. nov., is described based on specimens collected from a manganese nodule area in the Clarion-Clipperton Fracture Zone of the abyssal North-eastern Pacific. The new species is a member of the bathyal/abyssal subfamily Euclavarctinae Renaud-Mornant, 1983. Within the Euclavarctinae, the genus Moebjergarctus Bussau, 1992, with only one described species, M. manganis Bussau, 1992, is characterised by simple claws, club-shaped and anteriorly bent primary clavae, well-developed spherical secondary clavae and cephalic cirri separated into three parts: short cirrophore, long and annulated scapus, and a short flagellum. Moebjergarctus clarionclippertonensis sp. nov. can be distinguished from M. manganis by the morphology of cephalic cirri which have scapi annulated only in the proximal part and by the presence of a caudodorsal bulge covered by a crescent-shaped cuticular thickening.

Contact electrification (CE) has been known for more than 2600 years but the nature of charge carriers and their transfer mechanisms still remain poorly understood, especially for the cases of liquid-solid CE. Here, we study the CE between liquids and solids and investigate the decay of CE charges on the solid surfaces after liquid-solid CE at different thermal conditions. The contribution of electron transfer is distinguished from that of ion transfer on the charged surfaces by using the theory of electron thermionic emission. Our study shows that there are both electron transfer and ion transfer in the liquid-solid CE. We reveal that solutes in the solution, pH value of the solution and the hydrophilicity of the solid affect the ratio of electron transfers to ion transfers. Further, we propose a two-step model of electron or/and ion transfer and demonstrate the formation of electric double-layer in liquid-solid CE.

As a well-known phenomenon, contact electrification (CE) has been studied for decades. Although recent studies have proven that CE between two solids is primarily due to electron transfer, the mechanism for CE between liquid and solid remains controversial. The CE process between different liquids and polytetrafluoroethylene (PTFE) film is systematically studied to clarify the electrification mechanism of the solid-liquid interface. The CE between deionized water and PTFE can produce a surface charges density in the scale of 1 nC cm -2 , which is ten times higher than the calculation based on the pure ion-transfer model. Hence, electron transfer is likely the dominating effect for this liquid-solid electrification process. Meanwhile, as ion concentration increases, the ion adsorption on the PTFE hinders electron transfer and results in the suppression of the transferred charge amount. Furthermore, there is an obvious charge transfer between oil and PTFE, which further confirms the presence of electron transfer between liquid and solid, simply because there are no ions in oil droplets. It is demonstrated that electron transfer plays the dominant role during CE between liquids and solids, which directly impacts the traditional understanding of the formation of an electric double layer (EDL) at a liquid-solid interface in physical chemistry., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Here we present the complete mitochondrial genome of Megabalanus tintinnabulum . The genome is 15,107 bp in length with a 67.35% AT content. It contains 13 protein-coding genes (PCGs), 2 rRNAs genes, and 22 tRNAs. Both rRNAs are encoded on the light strand, as in the other crustacean and barnacle mitochondrial genomes. Besides five tRNAs are encoded on the light strand (nad1, trnV, trnL1, trnC, trnQ, and trnK). Only one PCG is encoded on the light strand (nad1), whereas the other 12 PCGs are located on the heavy strand, which is consistent with M . ajax . Phylogenetic analysis based on mitochondrial PCGs shows that M . tintinnabulum is clustered with M . ajax into a branch (BP = 100), and the group with M . volcano with high support. This study contributes to further phylogenetic analysis within Cirripedia., Competing Interests: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article., (© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Contact electrification (CE) (or triboelectrification) is a well-known phenomenon, and the identity of the charge carriers and their transfer mechanism have been discussed for decades. Recently, the species of transferred charges in the CE between a metal and a ceramic was revealed as electron transfer and its subsequent release is dominated by the thermionic emission process. Here, the release of CE-induced electrostatic charges on a dielectric surface under photon excitation is studied by varying the light intensity and wavelength, but under no significant raise in temperature. The results suggest that there exists a threshold photon energy for releasing the triboelectric charges from the surface, which is 4.1 eV (light wavelength at 300 nm) for SiO 2 and 3.4 eV (light wavelength at 360 nm) for PVC; photons with energy smaller than this cannot effectively excite the surface electrostatic charges. This process is attributed to the photoelectron emission of the charges trapped in the surface states of the dielectric material. Further, a photoelectron emission model is proposed to describe light-induced charge decay on a dielectric surface. The findings provide an additional strong evidence about the electron transfer process in the CE between metals and dielectrics as well as polymers., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The phenomenon of contact electrification (CE) has been known for thousands of years, but the nature of the charge carriers and their transfer mechanisms are still under debate. Here, the CE and triboelectric charging process are studied for a metal-dielectric case at different thermal conditions by using atomic force microscopy and Kelvin probe force microscopy. The charge transfer process at the nanoscale is found to follow the modified thermionic-emission model. In particular, the focus here is on the effect of a temperature difference between two contacting materials on the CE. It is revealed that hotter solids tend to receive positive triboelectric charges, while cooler solids tend to be negatively charged, which suggests that the temperature-difference-induced charge transfer can be attributed to the thermionic-emission effect, in which the electrons are thermally excited and transfer from a hotter surface to a cooler one. Further, a thermionic-emission band-structure model is proposed to describe the electron transfer between two solids at different temperatures. The findings also suggest that CE can occur between two identical materials owing to the existence of a local temperature difference arising from the nanoscale rubbing of surfaces with different curvatures/roughness., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Triboelectric nanogenerators (TENGs) have been widely applied for energy harvesting and self-powered sensing, whereas smart deformable materials can be combined with the TENG to acquire a more intelligent and self-adaptive system. Here, based on the vapor-driven actuation material of a perfluorosulfonic acid ionomer (PFSA), we propose a type of humidity-responsive TENG. The integrated TENG array can automatically bend to the desired angles in response to different humidity conditions, and thus, it can effectively collect energy from both wind and rain drops, where the power density can reach 1.6 W m -2 at a wind speed of 25 m s -1 and 230 mW m -2 under rainy conditions. Meanwhile, this TENG array can fully lay down in dry weather, using the reflective surface to reflect sunlight and heat radiation. The vapor absorption process of the PSFA film can also result in the charge accumulation process. Accordingly, relying on the strong absorption capability of PFSA, a TENG-based vapor sensor with high sensitivity has been developed for monitoring chemical vapor leakage and humidity change. This work opens up a promising approach for the application of the humidity-responsive materials in the field of energy harvesting and self-powered sensors. It can also promote the development of TENG toward a more intelligent direction.

Piezoelectric organic-inorganic lead halide perovskites have recently attracted much attention in the field of optoelectronic devices. However, their piezoelectric properties as a possible way to modulate device performances have rarely been reported. Here, we study experimentally a photodetector based on CH 3 NH 3 PbI 3 (MAPbI 3 ) single crystals, whose performance is effectively modulated via an emerging effect-the piezo-phototronic effect, which is to use the piezoelectric polarization charges to tune the optoelectronic processes at the interface. A piezoelectric coefficient of 10.81 pm/V of the CH 3 NH 3 PbI 3 single crystal is obtained. Under 680 nm laser illumination with a power density of 3.641 mW/cm 2 and at an external bias of 2 V, compared to the case without straining, the light current of the photodetector is enhanced by ∼120% when a 43.48 kPa compressive pressure is applied. The response speed of the photocurrent is 3 and 2 times faster than the cases without applying pressure for the light-on and light-off states, respectively. This work proves that the performance of the photodetector based on MAPbI 3 single crystals can be effectively enhanced by the piezo-phototronic effect, providing a good method for optimizing the performance of future perovskite-based optoelectronic devices.