Free Water Molecules Research Articles

Monitoring the Cation Coordination Sphere Using Hydrated Eutectic Electrolyte for Better Cyclic Stability and High Energy Density Zn-Ion Battery

Aqueous rechargeable Zn-ion batteries (ZiBs) are receiving increasing attention worldwide owing to their inherent safety and cost effectiveness. However, ZiBs are still struggling with rapid performance degradation caused by poor Zn anode reversibility and cathode dissolution into aqueous electrolytes. Inspired by the knowledge of industrial-scale Zn electroplating, a cyanide functional group containing a succinonitrile (SN) neutral ligand-based hydrated eutectic electrolyte was used to mitigate these issues. The ligand-oriented SN partially replaced free water molecules from the Zn2+ ion primary solvation sheath, resulting in delayed oxidation and a smaller Zn2+ ion desolvation energy barrier which promoted uniform Zn nucleation. Moreover, the MoO3@Mn3O4 cathode and Zn anode-based ZiB in an eutectic hydrated electrolyte with a 10:10 molar ratio of ZnCl2 and SN exhibited an ∼2.3 V working potential window which delivered a maximum of ∼476 mAh g–1 specific capacity and ∼232.2 Wh kg–1 energy density at a 0.2 A g–1 current density. The fabricated device exhibited ∼79.56% specific capacity retention after 5000 cycles at a 10 A g–1 current density. The coinsertion/extraction of H+ and Zn2+ ions and the Zn deposition/dissolution mechanism of the optimized hydrated eutectic electrolyte-based ZiBs are investigated by ex situ physicochemical and electrochemical studies. Overall, this work provides a new path on exploring green electrolytes and layered-structure materials for the development of high-performance ZiBs.

Water Confinement by a Zn2+-Conductive Aqueous/Inorganic Hybrid Electrolyte for High-Voltage Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have received extensive attention owing to the intrinsic safety and high specific energy. However, the practical performance of the ZIBs is impacted by the water-induced complicated interfacial reactions, including the corrosion/dendrites of a Zn anode and the dissolution/degradation of a cathode. Herein, we developed a type of inorganic Zn2+-interlayered montmorillonite-based aqueous/inorganic hybrid electrolyte (ZM-30% HE) that not only realizes low water content but also shows a strong water confinement effect, which leads to a significantly weakened water activity and water solvation effect. Therefore, the side reactions between the Zn anode and free water molecules are effectively suppressed and the diffusion/insertion of zinc ions into the cathode is substantially facilitated. At the Zn anode side, ZM-30% HE can stabilize the symmetric cell for 2000 h at 1 mA cm–2. Moreover, low water content enables the application of the intercalation-type Zn-ion cathode. Based on the ZM-30% HE and Mn4[Fe(CN)6]2.84·11.8H2O cathode, record-high voltage (1.70 V vs Zn2+/Zn) and voltage efficiency (92%) among the reported Zn metal cells with hybrid electrolytes and Zn2+-storage cathodes were achieved. Meanwhile, the dissolution/degradation problem of the cathode in the traditional liquid electrolyte was solved using the HE. The Zn/ZM-30% HE/Mn4[Fe(CN)6]2.84·11.8H2O full cell shows stable cycling up to 400 cycles even at a low current density of 100 mA g–1. The development of the hybrid electrolyte with unique water confinement effect provides a solution to boost the performance of the current ZIBs.

Light, Water, and Melatonin: The Synergistic Regulation of Phase Separation in Dementia.

The swift rise in acceptance of molecular principles defining phase separation by a broad array of scientific disciplines is shadowed by increasing discoveries linking phase separation to pathological aggregations associated with numerous neurodegenerative disorders, including Alzheimer's disease, that contribute to dementia. Phase separation is powered by multivalent macromolecular interactions. Importantly, the release of water molecules from protein hydration shells into bulk creates entropic gains that promote phase separation and the subsequent generation of insoluble cytotoxic aggregates that drive healthy brain cells into diseased states. Higher viscosity in interfacial waters and limited hydration in interiors of biomolecular condensates facilitate phase separation. Light, water, and melatonin constitute an ancient synergy that ensures adequate protein hydration to prevent aberrant phase separation. The 670 nm visible red wavelength found in sunlight and employed in photobiomodulation reduces interfacial and mitochondrial matrix viscosity to enhance ATP production via increasing ATP synthase motor efficiency. Melatonin is a potent antioxidant that lowers viscosity to increase ATP by scavenging excess reactive oxygen species and free radicals. Reduced viscosity by light and melatonin elevates the availability of free water molecules that allow melatonin to adopt favorable conformations that enhance intrinsic features, including binding interactions with adenosine that reinforces the adenosine moiety effect of ATP responsible for preventing water removal that causes hydrophobic collapse and aggregation in phase separation. Precise recalibration of interspecies melatonin dosages that account for differences in metabolic rates and bioavailability will ensure the efficacious reinstatement of the once-powerful ancient synergy between light, water, and melatonin in a modern world.

Tough Hydrogel Electrolytes for Anti-Freezing Zinc-Ion Batteries.

As the soaring demand for energy storage continues to grow, batteries that can cope with extreme conditions are highly desired. Yet, existing battery materials are limited by weak mechanical properties and freeze-vulnerability, prohibiting safe energy storage in devices that are exposed to low temperature and unusual mechanical impacts. Herein, a fabrication method harnessing the synergistic effect of co-nonsolvency and "salting-out" that can produce poly(vinyl alcohol) hydrogel electrolytes with unique open-cell porous structures, composed of strongly aggregated polymer chains, and containing disrupted hydrogen bonds among free water molecules, is introduced. The hydrogel electrolyte simultaneously combines high strength (tensile strength 15.6MPa), freeze-tolerance (<-77 °C), high mass transport (10× lower overpotential), and dendrite and parasitic reactions suppression for stable performance (30 000 cycles). The high generality of this method is further demonstrated with poly(N-isopropylacrylamide) and poly(N-tertbutylacrylamide-co-acrylamide) hydrogels. This work takes a further step toward flexible battery development for harsh environments.

Synthesis, Spectroscopic Characterization, and X-ray Structure of the Co-crystal Copper(II) Complex of the Dissymmetrical 1-(2 hydroxy-3-methoxybenzylidene)-5-(pyridin-2 ylmethylene) Carbnohydrazide Ligand

In the pentanuclear title complex, bis{<i>μ</i>₂-1-(2-oxido-3-methoxybenzylidene)-5-(pyridin-2-ylmethylene)carbonohydrazide}-1<i>κ</i>⁴<I>O</I>,<I>N</I>,<I>N</I>’,<I>N</I>’’:2<i>κ</i>²<I>O</I>,<I>N</I>;2<i>κ</i>²<I>O</I>,<I>N</I>:3<i>κ</i>⁴<I>O</I>,<I>N</I>,<I>N</I>’,<I>N</I>’’-1,2,3-tricopper(II) bis{[1-(2-oxido-3-methoxybenzylidene)-5-(pyridin-2-ylmethylene)carbonohydrazide]-<i>κ</i>⁴<I>O</I>,<I>N</I>,<I>N</I>’,<I>N</I>’’-copper(II)} tetraperchlorate tetrahydrate (1), two monocationic mononuclear units and one dianionic trinuclear unit co-exist. The Cu<SUP>II</SUP> centers in the mononuclear units as well as the two terminal Cu<SUP>II</SUP> centers in the trinuclear unit are located in the N₃O cavity of the ligand and are coordinated to a phenolate oxygen atom, to a pyridine nitrogen atom, to an imino nitrogen atom and to a hydrazinyl nitrogen atom. The third central Cu(II) atom in the trinuclear unit, which is hexacoordinated, is located in N₂O₄. The metal center is coordinated to two ligand molecule through one imino nitrogen atom one oxygen atom of a carbonyl moiety per ligand and two oxygen atom of water molecules. The tetracoordinated copper(II) ions are situated in distorted square planar environments, while the hexacoordinated copper(II) is located in octahedral geometry. In the mononuclear units, as well as in the trinuclear units, the methoxy oxygen atoms remain uncoordinated. Each atom of the uncoordinated perchlorate anions is disordered over two sets of sites in a 0.5 ratio. Four free water molecules are also present. In the crystal, the trinuclear cationic unit and the mononuclear cationic units are assembled into infinite layers. These layers are held together via electrostatic interactions, forming a three-dimensional structure.

Electrolyte Solvation Structure Design for High Voltage Zinc‐Based Hybrid Batteries

Zinc (Zn) metal anodes have enticed substantial curiosity for large‐scale energy storage owing to inherent safety, high specific and volumetric energy capacities of Zn metal anodes. However, the aqueous electrolyte traditionally employed in Zn batteries suffers severe decomposition due to the narrow voltage stability window. Herein, we introduce N‐methylformamide (NMF) as an organic solvent and modulate the solvation structure to obtain a stable organic/aqueous hybrid electrolyte for high‐voltage Zn batteries. NMF is not only extremely stable against Zn metal anodes but also reduces the free water molecule availability by creating numerous hydrogen bonds, thereby accommodating high‐voltage Zn‖LiMn2O4 batteries. The introduction of NMF prevented hydrogen evolution reaction and promoted the creation of an F‐rich solid electrolyte interphase, which in turn hampered dendrite growth on Zn anodes. The Zn‖LiMn2O4 full cells delivered a high average Coulombic efficiency of 99.7% over 400 cycles.

Quantifying Microalgae Growth by the Optical Detection of Glucose in the NIR Waveband.

Microalgae have become a popular area of research over the past few decades due to their enormous benefits to various sectors, such as pharmaceuticals, biofuels, and food and feed. Nevertheless, the benefits of microalgae cannot be fully exploited without the optimization of their upstream production. The growth of microalgae is commonly measured based on the optical density of the sample. However, the presence of debris in the culture and the optical absorption of the intercellular components affect the accuracy of this measurement. As a solution, this paper introduces the direct optical detection of glucose molecules at 940-960 nm to accurately measure the growth of microalgae. In addition, this paper also discusses the effects of the presence of glucose on the absorption of free water molecules in the culture. The potential of the optical detection of glucose as a complement to the commonly used optical density measurement at 680 nm is discussed in this paper. Lastly, a few recommendations for future works are presented to further verify the credibility of glucose detection for the accurate determination of microalgae's growth.

Hydrogen bonds of a water molecule in the second coordination sphere of amino acid metal complexes: Influence of amino acid coordination

The hydrogen bonds of free and coordinated amino acids with water molecule were studied by analyzing data in the crystal structures from the Cambridge Structural Database (CSD) and by quantum chemical calculations. The CSD data indicate bifurcated NH/O hydrogen bonds and O1/HO hydrogen bonds of coordinated oxygen. The O/HO hydrogen bonds of free zwitterions and non-coordinated carbonyl oxygen (O2/HO) in metal complexes form primarily linear, non-bifurcated hydrogen bonds. Calculated M06L-GD3/def2-TZVPP interaction energies for free zwitterions (glycine, cysteine, phenylalanine and, serine) and water molecule are in the range from −5.1 to −9.6 kcal/mol for NH/O and from −6.9 to −7.6 kcal/mol for O/HO interactions. Coordinated amino acids in neutral octahedral cobalt(III) complexes have NH/O interaction energies ca. -7.4 kcal/mol, independent of the amino acid. The singly and doubly charged complexes have stronger NH/O interactions; the strongest has energy of −16.9 kcal/mol. In the case of O1/HO hydrogen bond, the interaction energy decreases upon coordination; interactions are quite weak for neutral complexes (−2.2 to −2.6 kcal/mol). For O2/HO hydrogen bonds, all amino acids except serine show slightly stronger interaction in singly negative complexes (−6.3 to −8.0 kcal/mol), while interactions are weaker for neutral complexes (−2.8 to −4.4 kcal/mol), comparing to zwitterions.

Stable Zn–WO3 battery with a ZnCl2 water-in-salt electrolyte

Transition metal oxide, WO3, has shown great potential in zinc-ion rechargeable batteries as cathode material, yet the poor structural stability and low capacity significantly hindered its further application. Herein, a 30 m water-in-salt electrolyte (WiSE) was rationally designed to construct a stable Zn–WO3 battery. The relatively fewer free water molecules and lower desolvation barrier of [ZnCl4]2- ions in ZnCl2 WiSE not only resulted in a wide electrochemical stability window, low depth of discharge, high reduction potential but also contributed to the limited dissolution of WO3 and high electrochemical corrosion resistance. As a result, the assembled Zn–WO3 battery with 30 m ZnCl2 WiSE achieved a specific capacity of 94.8 mAh g−1 at 0.1 A g−1, energy density of 18.9 Wh kg−1 at a power density of 747.3 W kg−1 and capacitance retention of 94.8% after 1,000 cycles at a high rate of 1 A g−1. Furthermore, a flexible quasi-solid-state Zn–WO3 battery was fabricated using ZnCl2 WiSE without adding adhesives, demonstrating great potential for the next-generation energy storage application.

Achieving macroscale superlubricity with ultra-short running-in period by using polyethylene glycol-tannic acid complex green lubricant

Superlubricating materials can greatly reduce the energy consumed and economic losses by unnecessary friction. However, a long pre-running-in period is indispensable for achieving superlubricity; this leads to severe wear on the surface of friction pairs and has become one of the important factors in the wear of superlubricating materials. In this study, a polyethylene glycol-tannic acid complex green liquid lubricant (PEG10000-TA) was designed to achieve macroscale superlubricity with an ultrashort running-in period of 9 s under a contact pressure of up to 410 MPa, and the wear rate was only 1.19 × 10−8 mm3·N−1·m−1. This is the shortest running-in time required to achieve superlubricity in Si3N4/glass (SiO2). The results show that the strong hydrogen bonds between PEG and TA molecules can significantly reduce the time required for the tribochemical reaction, allowing the lubricating material to reach the state of superlubrication rapidly. Furthermore, the strong hydrogen bond can share a large load while fixing free water molecules in the contact zone to reduce shear interaction. These findings will help advance the use of liquid superlubricity technology in industrial and biomedical.

Recent progress in aqueous akali-metal-ion batteries at low temperatures

Aqueous alkali-metal-ion batteries are a popular frontier research area, expected to apply for large-scale energy storage due to their high safety, low cost, and environmental friendliness. Depending on diversified social development, batteries ought to function in various ambient, including polar regions and high-altitude locales. Delivering excellent electrochemical performance at low temperatures is crucial to develop aqueous alkali-metal-ion batteries. This review summarizes the representative research progress in the field of aqueous low-temperature alkali-metal-ion batteries in recent years, based on the subjects of electrolyte, electrode, and interface. Firstly, we discussed the challenges of aqueous alkali-metal-ion batteries operated at low temperatures and the corresponding failure mechanisms. At subzero temperatures, aqueous alkali-metal-ion batteries couldn't work or exhibit little capacity, arising from the frozen electrolytes, electrode materials with slow kinetics, and huge interface impedances, which seriously limits their wide application in low-temperature conditions. Then, combined with the latest research work, various strategies have been investigated to improve the electrochemical performance of batteries at low temperatures. To date, the strategies for reducing the freezing point of electrolytes have primarily focused on breaking H-bonds between free water molecules by increasing salt concentration, adding organic/inorganic additives, and using hydrogel as electrolytes. In terms of electrodes, the related studies have concentrated on regulating the structure and morphology of electrodes, introducing the dual ion battery mechanism, and using organic materials and Zn electrodes to alleviate the slow ion dynamics of electrodes. In addition, adding appropriate organic solvents that can generate protective layers with low interface impedance on the electrode surface in the electrolyte can also improve the low-temperature performance of aqueous alkali-metal-ion batteries. Finally, we evaluated multi-dimensionally all strategies, expected to provide a comprehensive reference and point out the direction for the further improvement and practical application of the aqueous alkali-metal-ion batteries at low temperatures.

Self-assembly and structures of nanoscale double emulsion droplets through coarse-grained molecular dynamics simulations.

Examples of self-assembled multiple emulsion droplets on the nanometre scale are very rare. In this work, we use coarse-grained (CG) molecular dynamics simulations to study the self-assembly of ternary mixtures consisting of water, n-heptane, and nonionic surfactant tetraethylene glycol monododecyl ether (C12E4). The water volume fractions studied are 1%, 3%, and 5%, respectively. Various nanoscale emulsions are obtained in a spontaneous process. When the water/surfactant volume ratio vm/s = 1.0/1.0, the obtained emulsion droplets are identified as oil-in-water-in-oil (O/W/O) double types, consisting of an oil core, an inner surfactant layer, a water layer, and an outer surfactant layer. The water molecules are distributed around the hydrophilic ends of the surfactants, while the hydrophobic ends of the surfactants wrap the oil cores and penetrate into the oil bulk. Hydrogen-bond interactions among water and the hydrophilic ends of the surfactants form cross-links that stabilize the double emulsion droplets. The sizes of all the oil cores inside the droplets are <6 nm in diameter, even with the highest water volume fraction of 5%. Both the concentration of free water molecules on the order of 10-6 mol/cm3 and the favourable energy change during emulsion formation indicate that the emulsion droplets are thermodynamically stable. In contrast, for vm/s = 1.0/5.5, no double emulsion but a simple water-in-oil emulsion was observed, with morphologies evolving from oblate to bicontinuous phases with an increase in the water volume fraction from 1% to 5%. Our coarse-grained molecular dynamics simulations provide valuable insight for the preparation of nanoscale double emulsions and the characterization of their structures.

Calculation of the Proportion of Free Water Molecules in Aqueous Solutions Using the Parameters of Their Dielectric Permittivity in the Terahertz Range, Based on the Onsager Theory

The question of the structure of aqueous solutions is one of the most fundamental and complex, while it is relevant to all natural science disciplines. An important parameter of the dynamically equilibrium structure of an aqueous solution is the number of free water molecules. To date, there are no reliable and fully justified methods for determining this parameter. Recently, the terahertz time-domain spectroscopy (THz-TDS) method has been developing. It makes it possible to record the spectra of the complex permittivity in the THz region, where an orientation relaxation band of free water molecules is detected for aqueous solutions. The purpose of this work is to establish the relationship of the parameters of THz dielectric permittivity with the number of free water molecules. For this purpose, the process of polarization of water in the THz region was theoretically considered using the formalism of electrodynamics of continuous media. The Onsager theory is taken as a basis and its development is carried out for the case of high-frequency fields. As a result, an analytical ratio was obtained for calculating the proportion of free water molecules in solutions. A comparison with other well-known, more simplified and poorly substantiated approaches is presented. Calculations of the fraction of free molecules for a number of aqueous solutions have been carried out. It can be argued that the first theoretically justified approach to calculating the population of free water molecules in a solution, which does not contain internal contradictions, is presented.

The effect of partial substitution of chloride by bromide in the 0-D hybrid material (C4H12N2)[CuCl4]·2H2O: Structural, vibrational, thermal, in silico and biological characterizations

A new organic-inorganic hybrid material with copper(II) as the transition metal, piperazine as the organic component and mixed bromide/chloride as halide ions, (C4H12N2)[CuBr4]0.42[CuCl4]0.58·2H2O (1), has been prepared and crystallographically investigated by single-crystal X-ray diffraction. Unlike the parent chloride or bromide-based materials which adopt the monoclinic system, this mixed halide hybrid material crystallizes in the space group Pnma of the orthorhombic system with the following parameters: a = 12.3496(6) Å, b = 16.3147(11) Å, c = 6.4415(3) Å, V = 1397.83(12) Å3 and Z = 4. Its 0-D crystal packing is built of isolated entities, a copper(II) ion surrounded by four chloride/bromide ions [CuBr4]2- and [CuCl4]2-, a diprotonated diamine (C4H12N2)2+ and free water molecules. Additionally, these entities are linked through different types of intermolecular hydrogen bonds N-H…Br, N-H…Cl, N-H…Ow, Ow-H…Br, Ow-H…Cl, and weak non-covalent interactions C-H…Br and C-H…Cl [Ow = water oxygen]. The thermal decomposition of the precursor proceeds through four stages leading to copper(II) oxide as a final product. The title compound possesses antimicrobial and anti-tumoral effects comparable to two previously described compounds, as assessed by in silico examinations. Compound 1 inhibited in a dose dependent manner, the proliferation of gram negative and positive bacteria and exhibited a microbial lipase inhibition from Candida rugosa.

Elucidation of inter/intra molecular H-bonding mediated charge transportation mechanism in water swelled, hydrophilic organic PVA-Co3O4 nanocomposite films

In this article, we have explored the water molecules mediated charge transportation kinetics in Polyvinyl alcohol (PVA)-Cobalt Oxide (Co3O4) flexible nanocomposite films that rely heavily on the comprehension of surface and interface chemistry. Understanding the chemical interactions at the aqueous hydrophilic PVA-Co3O4 interface is essential in recognising the H-bonding revolution for complex nanocomposite films. The amount of water intake with time evolution has been monitored by the contact angle and wettability measurements. The chemical interactions and the revolution of the weak dangling bonds have been studied by Fourier transform infrared spectroscopy (FTIR), Raman and photoluminance (PL) spectra of the water-swollen hydrophilic PVA-Co3O4 nanocomposite films. The dissociation of water molecules following the fragmentation of inter/intra-molecular dangling bonds is correlated with the water diffusion kinetics and saturation in the sorption capacity of water-swollen PVA-Co3O4 nanocomposite films. The trap-states development due to the interfacial charge accumulation, after absorption of water molecules, are favourable for the trap-assisted space charge limited current conduction (TA-SCLC) mechanism and increase current density ∼ 102 times as compared to the dehydrated nanocomposite films. Meticulous tuning of the strong interfacial interactions and the manifestations of fragmented H+ ions have been identified as the primary craftsman for enhancing the dielectric constant up to eight times in the presence of 30 μL deionized water. Due to the disintegration of the free water molecules at the measurement voltage, the ac conductivity (charge transport) changes from the Jonscher's power law type variation to the jump relaxation model (JRM). The origin and accumulation of H+ ions at the grain boundary interfaces have been analyzed with impedance spectroscopic (IS) studies. An electrical equivalent circuit model is proposed for the water-mediated charge transport mechanism in swelled, hydrophilic, organic nanocomposite films.

Synthesis of amyl ester grafted on carbon-nanopolymer composite as an inhibitor for cleaner shale drilling

Wellbore instability in oil and gas industry well drillings is a significant challenge that is linked to shale swelling when shale interacts with free water molecules in the water-based drilling fluid. Strategic design of environmentally benign, biodegradable, and effective shale hydration inhibitors is a prominent objective of contemporary exploration in well-drilling fluids as a replacement for the common KCl which is detrimental to aquatic lives. This work reports the synthesis and potential of novel green acrylic polymer-amyl ester activated carbon (-C) nanocomposite to hinder shale hydration in formations during drilling. Both less hydrophobic acrylic acid-acrylamide-activated carbon-amyl ester (AA-AAm-C-Amyl) and more hydrophobic acrylic acid-acrylamide-octadecene-activated carbon-amyl ester (AA-AAm-OD-C-Amyl) composites were synthesized, characterized, and tested with standard methods as a cleaner fluid additive for shale swelling inhibition, and their results compared with that of KCl. The polymer matrixes displayed remarkable thermal stability. Results also indicate that AA-AAm-C-Amyl and AA-AAm-OD-C-Amyl composites could stabilize wellbore effectively with 95.2% and 93.7% anti-swelling ratio, and shale recovery capacity of 97 and 95.2% respectively. The surface evaluation of the composite fluid-treated bentonite revealed that the mechanism of inhibition could be based on the collaborative action of nanopore plugging of carbon core and strong adsorption of the polymer component of the materials on clay surfaces via encapsulation and hydrogen bonding to form an impressive filter cake which could actively prevent water invasion into formation. Hence, AA-AAm-C-Amyl and AA-AAm-OD-C-Amyl composites could be a sustainable substitute for the conventional KCl as a shale inhibitor for well-drilling.

Flexible and biocompatible poly (vinyl alcohol)/multi-walled carbon nanotubes hydrogels with epsilon-near-zero properties

• Flexible PVA/MWCNTs hydrogels were fabricated by solution method, and cytotoxicity experiments proved that the process was environmentally friendly and hydrogels were biocompatible. • Epsilon-near-zero properties were realized at radio frequency from PVA/MWCNTs hydrogels, originated from the resonance of the induced electric dipole. • After the frequency achieving epsilon-near-zero, negative permittivity which was different from Drude model but related to interband transition, was observed. Epsilon-near-zero (ENZ) material has been a research hotspot in recent years due to unique physical properties such as inverse Doppler effect and negative refractive index, showing great potentials in the fields of flexible electronics, wearable devices, sensors, etc. The ENZ materials are mostly reported at visible, infrared and terahertz wavelengths, while the report about ENZ materials at radio frequency is rare. In this work, flexible and biocompatible poly (vinyl alcohol)/multi-walled carbon nanotubes (PVA/MWCNTs) hydrogels, which were successfully fabricated by an environmentally friendly method, were used as ENZ materials at radio frequency for the first time. Cytotoxicity experiments proved that the experimental process and products are green, environmentally friendly and biocompatible. The microstructure, crystalline structure, chemical composition and dielectric properties were investigated. Two different water states, which were free water molecules and bound water molecules, coexisted in these PVA/MWCNTs hydrogels and accounted for about 37.5 wt% and 15.9 wt% respectively by analyzing the thermogravimetric analysis curves. When the MWCNTs content reached 12 wt% and 15 wt%, the continuous conductive MWCNTs network was formed in the hydrogel, and ENZ phenomenon was observed at about 760 kHz and 580 kHz respectively, which was attributed to the interband transition. Considering the flexibility and non-toxicity of PVA/MWCNTs hydrogels, the ENZ properties of this structure at the radio frequency can be well used in wearable invisibility cloak, flexible electronics, skin sensors and other wearable devices.

Stabilizing the MXene by Ion Confinement Shielding in a Wide Temperature Range

Herein, the environmental stability of MXenes aqueous solution in a wide temperature range is successfully enhanced by a mechanism of ion‐confined shielding. Combined with experiments and molecular dynamics simulation, it is found that, in an aqueous solution, a confinement shielding layer formed by the electrostatic adsorption of the introduced hydronium ion onto the electronegative surface of nanosheets, which efficiently constrains free water molecules near the nanosheet surface through hydration, and prevents nanosheets from an attack of water molecules and dissolved oxygen through its steric hindrance effect. Moreover, the hydronium ions could induce the aggregation of nanosheets and further reduce the active surface area of exposed Ti3C2Tx. Under the aforementioned synergistic effect, the storage duration allowing Ti3C2Tx aqueous solution to keep stable is extended to 100 days at 25 °C and 30 days at 60 °C, respectively. In addition, hydronium ion has the advantages of low cost, environmentally friendly, and easy recovery. It also shows an excellent protection effect at low concentration, such as 2 mol L−1. The present study provides guidance for the prolongation of life of the MXenes device working under long‐term or high‐temperature aqueous conditions and the selection of electrolytes for supercapacitors.

Microgravimetric contributions of multivalent metal ions, water molecules and protons to the energy storage at the electrolyte/electrode interface of aqueous ion batteries

The aqueous battery employing multivalent metal ions as charge carriers is theoretically a high energy density electrochemical energy storage device due to the fact that it carries more charges. However, the storage mechanism of multivalent metal ions, especially Al3+ ions, in TiO2 materials has not been established.A new model associated with the contribution of multivalent metal ions, water molecules and protons in the charging/discharging process of the electrode is established in this work. The storage mechanism of aqueous Al3+ ion batteries is revealed from a new perspective by studying the relationship between the charge inside the TiO2 film and the mass at the interface. More importantly, a highlighted work is to reveal the changes in the amount of interfacial free water molecules and the hydration number of Al3+ ions due to the adsorption/desorption of hydrated ions during the charging/discharging process.The present work is of great significance for revealing the mechanism of multivalent cations on metal oxide surfaces in aqueous batteries, and meanwhile, the model established can also be extended to other fields such as supercapacitors, photovoltaics, and photocatalysis. The results obtained in this work may have an impact on the performance of energy storage batteries, especially the influence of the rearrangement of interface hydration ions and water molecules on the energy storage mechanism.

Graphene oxide suspension-based electrolyte promotes the cycling performance of aqueous sodium-ion batteries through the interaction between metal ions, free water molecules and functional groups

Prussian blue analogue (PBA)-based aqueous batteries are promising solutions for large-scale energy storage. However, PBA cathode materials are still facing erosion and dissolution originating from the strong polarity and high proton activity of water leading to the destruction of their frameworks and poor cycling performance. Herein, we developed a new route to protect Sodium Prussian blue analogue (PB–Na, Na0.65Fe[Fe(CN)6]0.91·□0.09·2.7H2O) by introducing graphene oxide (GO) into the aqueous electrolyte, which can in-situ form an ion selectivity membrane on the separator surface. GO can prevent the diffusion of transition metal ions of dissolved PB-Na penetrating the separator to the anode material by the coordination interaction between transition metal ions and the oxygen-containing functional groups (carboxyl, carbonyl, etc). Meanwhile, hydrophilic groups (hydroxyl, carboxyl, etc) of GO can absorb free water molecules by hydrogen bond and electrostatic interaction reducing the dissolution of PB-Na. Thus PB-Na cathode material-based sodium-ion batteries in the low-concentration aqueous electrolyte can still achieve a capacity of 65.5 mAh g−1 and a high capacity retention of 65.1% after 17000 cycles. This strategy can be considered a simple and effective method to protect active materials in the aqueous batteries.