Free Water Molecules Research Articles

Hydroxyl-Binding Induced Hydrogen Bond Network Connectivity on Ru-based Catalysts for Efficient Alkaline Hydrogen Oxidation Electrocatalysis.

Understanding the role of adsorbed intermediates at the polarized catalyst-electrolyte interface on the structure of electrical double layer (EDL) is essential for developing highly efficient electrocatalysts. Here, we prepared a series of unconventional face-centered-cubic (fcc) phase Ru-based catalysts (i.e. fcc-Ru, fcc-RuCr, and fcc-RuCrW) by rational tuning the binding energetics of hydroxyl intermediate to engineer the electrochemical interface and boost the performance of alkaline hydrogen oxidation reaction (HOR). The introduction of oxyphilic metals Cr and W can regulate the orbital occupation of Ru, promote the adsorption of hydroxyl species, resulting in an anomalous behavior that HOR performance under alkaline media exceeds acidic media. Experimental results and theoretical calculations unravel that the modulated adsorption of hydroxyl species on the electrode surface are responsible for the reconstruction of interfacial water structure and dynamic evolution of free water molecules from nearest to the electrode surface to above the gap region in the EDL, thereby leading to significantly increased water connectivity and hydrogen bond network. Our work reveals a new understanding of the surface intermediates in controlling the dynamic process of interfacial water and hydrogen bonding network in HOR electrocatalysis, and will guide rational design of advanced electrocatalysts through electrochemical interfacial engineering.

Hydroxyl‐Binding Induced Hydrogen Bond Network Connectivity on Ru‐based Catalysts for Efficient Alkaline Hydrogen Oxidation Electrocatalysis

Understanding the role of adsorbed intermediates at the polarized catalyst‐electrolyte interface on the structure of electrical double layer (EDL) is essential for developing highly efficient electrocatalysts. Here, we prepared a series of unconventional face‐centered‐cubic (fcc) phase Ru‐based catalysts (i.e. fcc‐Ru, fcc‐RuCr, and fcc‐RuCrW) by rational tuning the binding energetics of hydroxyl intermediate to engineer the electrochemical interface and boost the performance of alkaline hydrogen oxidation reaction (HOR). The introduction of oxyphilic metals Cr and W can regulate the orbital occupation of Ru, promote the adsorption of hydroxyl species, resulting in an anomalous behavior that HOR performance under alkaline media exceeds acidic media. Experimental results and theoretical calculations unravel that the modulated adsorption of hydroxyl species on the electrode surface are responsible for the reconstruction of interfacial water structure and dynamic evolution of free water molecules from nearest to the electrode surface to above the gap region in the EDL, thereby leading to significantly increased water connectivity and hydrogen bond network. Our work reveals a new understanding of the surface intermediates in controlling the dynamic process of interfacial water and hydrogen bonding network in HOR electrocatalysis, and will guide rational design of advanced electrocatalysts through electrochemical interfacial engineering.

Computational Analysis of Sarin, Soman, and Their Water Mixtures in NU-1000: Interaction Mechanisms, Distribution Patterns, and Pairing Effects.

Due to their extraordinary structural stability under humid conditions, zirconium-based metal-organic frameworks (Zr-MOFs) have been widely investigated for the hydrolytic degradation of nerve agents. That said, mechanisms of hydrolysis in the solid state and the participation of environmental water are not well understood. This work utilizes computational techniques to evaluate the behavior of water and two organophosphorus nerve agents (sarin and soman) in NU-1000, a Zr-MOF with the characteristic attributes for hydrolytic efficiency under humid conditions. Density functional theory (DFT) calculations reveal that soman binds more favorably to NU-1000 active sites than sarin, resulting in different preferential locations of each nerve agent within the framework. The strength of nerve agent binding is also found to vary depending on the site environment, with more favorable binding of both nerve agents occurring in the c-pores of NU-1000 than in the mesopores. Molecular dynamics (MD) simulation results further illustrate that free water molecules in NU-1000 prioritize interactions with nerve agents. Given the variation in their affinity for active site interactions, the introduction of different nerve agents to the framework results in substantial differences in water distribution and behavior. The results give insight into potential variances in the functionality of NU-1000 toward the hydrolysis of each nerve agent. More importantly, they emphasize the significance of considering the role of environmental water in hydrolysis and the possibility of diverse reaction variables based on the type of nerve agent and the properties of the MOF.

Effects of SiO2 Particle Size in Soggy‐Sand Electrolyte on Electrochemical Performance of Zinc‐Ion Batteries

AbstractThe presence of free water molecules in the aqueous electrolyte leads to serious side reactions at the interface, easy dissolution of the cathode material, and uncontrolled growth of zinc dendrites in Zn‐ion batteries, which hinders their practical applications. Here, we propose a type of SiO2‐based soggy‐sand electrolyte (ZnSO4+MnSO4 electrolyte with SiO2, SiO2‐ZMSO4) and focus on the effect of the SiO2 nanoparticle size on the performance of soggy‐sand electrolyte. It is found that SiO2 with smaller nanoparticle size provides higher porosity, and the SiO2 network‐formed can effectively trap the free water in the electrolyte, which increases the ionic conductivity of electrolyte, widens working voltage window, and decreases the internal resistance of batteries. As a result, the Zn//MnO2 batteries with 20 nm SiO2‐based soggy‐sand electrolyte show stable cycling performance and rate capacities. The specific capacity of the battery can be maintained at 198.5 mAh g−1 after 1200 cycles at 1 A g−1 without capacity degradation. The specific capacity can be increased by 100 mAh g−1 even at a high rate of 5 A g−1. This study provides the rule of particle selection for the development of aqueous soggy‐sand electrolytes used in aqueous rechargeable batteries.

Mitigating anodic corrosion in aluminum–air batteries: Effects of alkali metal cation size on electrochemical performance

Anodic corrosion limits the performance of aluminum–air batteries (AABs) by reducing discharge capacity and hindering energy density. This study proposes a strategy to mitigate anodic corrosion by controlling electrolyte cations to decrease the activity of free water molecules in the anodic corrosion process. Alkali metal cations (Na+, K+, Rb+) are introduced into a 1mol dm−3 KOH solution to examine their solvation properties and effects on free water molecule activity. Results show that larger cations (Na+ < K+ < Rb+) enhance anode discharge capacity by promoting more stable discharge reactions. Raman spectroscopy reveals that as cation radius increases, free water molecule activity decreases due to increased hydration. X-ray photoelectron spectroscopy analysis shows that larger cations favor the formation of corrosion-resistant aluminum compounds like Al2O3 and Al(OH)3, due to their higher concentration in the electric double layer, inhibiting anodic corrosion. This study highlights the critical role of cation solvation in enhancing electrochemical performance and corrosion resistance of AAB anodes.

A Clay-Based Quasi-Solid-State electrolyte with high cation selective channels for High-Performance aqueous Zinc-Ion batteries

A clay-based quasi-solid-state electrolyte was prepared using dimethyl sulfoxide (DMSO) intercalated kaolinite as the raw material to suppress the adverse effects of free water molecules on aqueous zinc-ion batteries (AZIBs). Based on the inherent water absorption and retention properties of clay kaolinite, as well as the interlayer modification, this clay-based quasi-solid-state electrolyte not only achieved a low water content but also exhibited a strong water binding effect, which restricted the HER and side reactions involving water participation. Furthermore, the intercalation of DMSO increased the number of negative charges on the surface of kaolinite, resulting in the formation of a continuous spatial electrostatic field area around the kaolinite particles, which played a role in cation selectivity. The ionic transference number of the quasi-solid-state electrolyte reached 0.91. Additionally, the intercalation of DMSO broadened the interlayer ionic transport channels of kaolinite, further enhancing the transport efficiency of Zn2+ in the quasi-solid-state electrolyte, achieving uniform deposition of Zn2+ on the surface of the Zn anode, and suppressing dendrite growth to maintain a stable quasi-solid-state electrolyte/Zn anode interface. Zn||MnO2 battery assembled with this electrolyte demonstrated a discharge specific capacity of 301 mAh/g at a current density of 60 mA g−1. The Zn||MnO2 battery could be stably cycled for 1000 cycles at a current density of 150 mA g−1, and after 1000 cycles, the battery still maintained a discharge specific capacity of 248.2 mAh/g with a capacity retention rate of 84.8 %, showing excellent capacity performance and cycle stability. The Zn||MnO2 pouch battery could still provide stable power under heavy pressure, bending, and continuous tapping and had the potential for use in flexible batteries.

A 3D open-framework amino acid templated cerium phosphite-oxalate showing proton conductive property

Using L-histidine as template, a three-dimensional (3D) open-framework cerium phosphite-oxalate, Ce2(H2O)2(H2PO3)2(C2O4)3·C6H11N3O2·H2O (1), has been synthesized under hydrothermal condition. Interestingly, it is the first example of lanthanide phosphite-oxalate with amino acid as the template. Compound 1 shows 3D framework with 8-, 12- and 20-ring channels and has a mog Moganite topology. A large amount of free water molecules and histidine cations are located in the channels of 1, which are favorable to the efficient proton transfer. Correspondingly, compound 1 displays temperature and humidity dependent proton conductivity with the highest value of 3.67 × 10−4 S cm−1 at 75 °C and 98 % RH.

Triggering aqueous electrolyte molecular association via solvent eutectic strategy to enable zinc metal battery operation at −60℃

It is a great challenge to circumvent the performance deterioration of aqueous zinc metal batteries (AZMBs) at low temperatures, which root from solvent solidification of water. Herein, via triggering aqueous electrolyte molecular association by solvent eutectic strategy, an aqueous solvent eutectic electrolyte of DMF-H2O solvent (SE-electrolyte) is prepared for adapting to the application of zinc metal battery at low temperature. The SE-electrolyte reduces the content of free water molecules, lowers the freezing point of the electrolyte, thus avoiding side reactions and broadening the operating temperature range of zinc batteries to −60℃. At room temperature, Zn||PANI full battery can cycle stably more than 10,000 times at 2 A/g high discharge current, the capacity retention rate is about 50%, and the average Coulomb efficiency is 99.79%. Under the harsh conditions of −45℃ and −60℃, the Zn||PANI whole battery can be stably cycled more than 1000 cycles with the current density of 0.2 A/g, and the Coulomb efficiency is close to 100%. The excellent low temperature electrochemical performance of SE-electrolyte indicates a bright prospect for the use of aqua zinc batteries in low temperature, and is a key step for the comprehensive and extensive application of aqueous zinc metal batteries.

Trace alcohol ether electrolytes with dual-site hydrogen bonds and modulated solvation structures for ultralong-life zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are highly regarded for their affordability, stability, safety, and eco-friendliness. Nevertheless, their practical application is hindered by severe side reactions and the formation of zinc (Zn) dendrites on the Zn metal anode surface. In this study, we employ tetrahydrofuran alcohol (THFA), an efficient and cost-effective alcohol ether electrolyte, to mitigate these issues and achieve ultralong-life AZIBs. Theoretical calculations and experimental findings demonstrate that THFA acts as both a hydrogen bonding donor and acceptor, effectively anchoring H2O molecules through dual-site hydrogen bonding. This mechanism restricts the activity of free water molecules. Moreover, the two oxygen (O) atoms in THFA serve as dual solvation sites, enhancing the desolvation kinetics of [Zn(H2O)6]2+ and improving the deposition dynamics of Zn2+ ions. As a result, even trace amounts of THFA significantly suppress adverse reactions and the formation of Zn dendrites, enabling highly reversible Zn metal anodes for ultralong-life AZIBs. Specifically, a Zn-based symmetric cell containing 2 % THFA achieves an ultralong cycle life of 8,800 h at 0.5 mA cm−2/0.5 mAh cm−2, while a Zn//VO2 full cell containing 2 % THFA maintains a remarkable 80.03 % capacity retention rate at 5 A g−1 over 2,000 cycles. This study presents a practical strategy to develop dendrite-free, cost-effective, and highly efficient aqueous energy storage systems by leveraging alcohol ether compounds with dual-site hydrogen bonding capabilities.

Solving ZIB Challenges: The Dynamic Role of Water in Deep Eutectic Solvents Electrolyte

Zinc-Ion batteries (ZIBs) are considered one of the most promising technologies in the realm of post-lithium-ion batteries. Rechargeable chemistries with zinc anodes hold significant technological potential due to their high theoretical energy density, lower manufacturing costs, abundant raw materials, and inherent safety. ZIBs typically feature neutral or weakly acidic aqueous electrolytes and exhibit typical drawbacks of Zn anodes: hydrogen evolution, passivation, and shape changes.In aqueous electrolytes, two types of water molecules can be described: free water molecules and solvated water molecules that participate in Zn2+ solvation structure [Zn(H2O)6]2+. The free water easily reacts with metallic Zn at the electrode/electrolyte interface, leading to the aforementioned irreversibilities. Alternative electrolytes such as Deep Eutectic Solvents (DESs) can be used to modulate Zn solvation shell, preserving the green and safe characteristics of aqueous-based ones. DESs show relevant characteristics for battery applications, such as low vapor pressure, good thermal and chemical stability, non-flammability, easy moldability, wide electrochemical window, and structured interface. However, a main drawback for electrochemical applications is the high viscosity, low diffusivity, and sluggish kinetics.Water molecules can be added as a cosolvent to eutectic mixtures to increase the diffusion coefficient of electroactive species and reduce the electrolyte viscosity without destroying the eutectic nature by up to 40%. The hydration percentage of DES can modify the thickness of the electrolyte-electrode interface and the Zn2+ solvation structure. Thus, the tuning capability, on one hand, of the solution chemistry of Zn2+ containing electroactive species, and on the other hand, of the electrode–electrolyte interfacial structure and chemistry by the combined use of DES and water provides a flexible tool to control Zn plating and stripping processes.In this study, we investigate the electrochemistry of Zn in ethaline DES with different percentages of water (0%, 5%, 10%, 25%, 50%, 70%, respectively), transitioning from a water-in-salt structure to a salt-in-water one. Fundamental electrokinetic and electrocrystallization studies based on cyclic voltammetry and chronoamperometry at different cathodic substrates were complemented with galvanostatic cycling tests of Zn|Zn symmetric CR2032 coin cells, SEM imaging of electrodes, and in situ Surface Enhanced Raman spectroscopy (SERS).Moreover, the Zn solvation structure was investigated using spontaneous Raman spectroscopy . The employed methodology provided valuable insights into the Zn plating reaction. Water molecules are present in a "confined" state rather than a free one, directly interacting with choline cations and being trapped in the eutectic framework if the molar fraction is kept below 40%.When ZnSO4 is dissolved in anhydrous ethaline, the [ZnCl4]2− species is formed and stabilized by choline. The peculiarities of Zn2+ coordination were found to result in unusual voltammetric behavior, characterized by a cathodic peak in the cathodic branch of the anodic-going scan.Although tetrachlorozincate is the dominant species, it does not seem to be the complex from which Zn is deposited; indeed, [ZnCl4]2− has a very negative reduction potential. Mechanistic studies of Zn electrodeposition onto different cathodic materials have concluded that the metal is formed by the reduction of an intermediate Zn-containing species. The two organic components of the eutectic solvents can be dehydrogenated at a negative potential, forming RO-, which can replace one or more chloride ligands in [ZnCl4]2−.Hydrated DES exhibits faster kinetics, which, in turn, leads to a lower nucleation overpotential. This phenomenon has been explained with two different mechanisms occurring at the same time. Firstly, by increasing the hydration percentage in the eutectic framework, the coordination of Zn2+ changes, forming [ZnCl3(H2O)]-. The water molecule in the Zn2+ sheath has a lower energy barrier than chlorine in the step-by-step desolvation of Zn2+. Consequently, the [ZnCl3(H2O)]- complex exhibits a lower dissociation energy than [ZnCl4]2- present in anhydrous ethaline, resulting in a faster desolvation process that can reduce nucleation overpotentials.Secondly, water molecules hydrogen-bonded to DES components can be reduced at cathodic potential, forming H· radicals that can then participate in the decomposition of the organic component. This apparent side reaction can aid in the formation of RO- ligands that participate in the Zn-species undergoing reduction, thereby increasing the amount of reactants.This multi-technique approach, also applicable to the study of new electrolytes, leads to the optimization of DES hydration, reducing the presence of free water and addressing the main drawbacks associated with eutectic electrolytes. The nuanced understanding of the interplay between solvent composition, Zn solvation, and electrodeposition mechanisms paves the way for the development of more efficient and sustainable ZIB technologies. Figure 1

Supramolecular Metal-Organic Framework for the High Stability of Aqueous Rechargeable Zinc Batteries.

Aqueous rechargeable Zn batteries (AZBs) are considered to be promising next-generation battery systems. However, the growth of Zn dendrites and water-induced side reactions have hindered their practical application, especially with regard to long-term cyclability. To address these challenges, we introduce a supramolecular metal-organic framework (SMOF) coating layer using an α-cyclodextrin-based MOF (α-CD-MOF-K) and a polymeric binder. The plate-like α-CD-MOF-K particles, combined with the polymeric binder create dense and homogeneous Zn2+ ion conductive pore channels that can vertically transport Zn2+ ions through the cavity while restricting the contact of water molecules. Molecular dynamics (MD) simulation verifies that Zn2+ ions can reversibly migrate through the pores of α-CD-MOF-K by partial dehydration. The uniform Zn deposition/dissolution promotes a smooth solid-electrolyte interface layer on the Zn metal anode and effectively suppresses side reactions with free water molecules. The α-CD-MOF-K@Zn symmetric cell exhibits stable cycling and a small polarization voltage of 70 mV for 800 h at 5 mA cm-2, and the α-CD-MOF-K@Zn|α-MnO2 full cell shows only 0.12% capacity decay per cycle at a rate of 1 A g-1.

Functional group-specific reduction of Cr(VI) by low molecular weight organic acids in frozen solution: Kinetics, mechanism and DFT calculation

Low molecular weight organic acids (LMWOA) are commonly present in natural water and play a pivotal role in the reduction of Cr(VI). In frozen solutions, the efficiency of Cr(VI) reduction is significantly enhanced due to the freezing concentration effect. However, this facilitation is found to be contingent upon the functional groups of LMWOA in this study. To be specific, LMWOA and Cr(VI) can form five-membered ring complexes, which greatly enhance electron transfer efficiency through Ligand-to-Metal Charge Transfer (LMCT). DFT calculations indicate that oxygen-containing groups located on carbon atoms at α positions play a crucial role in forming these complexes, ultimately determining the kinetics of Cr(VI) reduction. Moreover, freezing not only increases proton concentrations but also reduces free water molecule content in the liquid-like layer (LLL), thereby affecting LMWOA species through regulation of protonation and hydrolysis, and subsequently impacting reaction mechanisms. The stoichiometric ratios between LMWOA and Cr(VI) exceed theoretical values due to complexation with Cr(III). The reduction of Cr(VI) by LMWOA in frozen solutions is inhibited by soil solution, while the degree of inhibition varies among different types of LMWOA.

Redox-active hydrogel electrolytes for carbon-based flexible supercapacitors over a wide temperature range

Hydrogel electrolytes are attractive for fabricating flexible supercapacitors (FSCs) due to their relatively high ionic conductivity, adjustable mechanical properties, and easy preparation processes. However, they still face challenges such as a narrow operational temperature range due to the presence of abundant free water molecules, and comparatively less favorable electrochemical properties compared to liquid electrolytes. In this study, a redox-active hydrogel electrolyte was synthesized, consisting of polyvinyl alcohol-H2SO4, TiO2 nanoparticles, carbon nanofibers and a mixture of redox-active species (FeBr3, Fe2(SO4)3 and KBr). The addition of thermally stable TiO2 and carbon nanofibers not only increased the thermal stability but also enhanced the ionic conductivity of the hydrogel. The Faradaic reactions of redox-active species during the charging/discharging processes contributed to improved electrochemical performance. Subsequently, binder-free carbon nanofiber@carbon cloth electrodes were prepared by directly growing carbon nanofibers on carbon cloth. By combining the electrodes with the redox-active hydrogel electrolyte, a redox electrolyte-enhanced FSC was assembled. It exhibited a capacitance of 182.8 mF cm−2 at 3.5 mA cm−2, an energy density of 8.3 Wh kg−1, and a capacitance retention of 84.3 % after 5000 charging/discharging cycles. The device was capable of operating under various temperature conditions (0–60 °C) and bending angles (0–180°). Overall, this work provides a novel but facile approach for fabricating FSCs with high electrochemical performance and versatile applications in different environments.

Hydrogel Based UV Photodetector Based on Polarization of Free Water Molecules

AbstractConductive hydrogels retain the intrinsic softness and elasticity that are hallmark features of traditional hydrogels, and they also assimilate the electrical properties of the embedded conductive materials. Conventional epitaxial growth techniques for heterojunctions require precise lattice matching between adjacent materials, significantly limiting technological advancements in photodetector innovation. The integration of conductive hydrogels with semiconductors to fabricate photodetectors presents a feasible solution that bypasses the traditional lattice matching constraints inherent in the epitaxial growth of heterojunction semiconductor photodetectors. Herein, device integration is enhanced by developing a transparent conductive hydrogel, positioned between graphene and gallium nitride, which effectively mitigates the fluidity issues of the polar liquid complicating device encapsulation. A comprehensive analysis of the photodetection characteristics of the graphene/conductive hydrogel/gallium nitride heterostructure is conducted, thereby establishing its structural framework. Flexible transparent devices are further prepared based on PEDOT/Alg (Ca2+) and demonstrate their potential application in 360° omnidirectional photodetection. This work introduces a novel approach for the enhanced integration of hydrogel‐based spectrally selective and flexible transparent photodetectors.

Soft confinement of water in aliphatic alcohols: MIR/NIR spectroscopic and DFT studies

Here, we present the first examination of the state of water under a soft confinement in eight aliphatic alcohols including cyclopentanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol, 2-octanol and 3-octanol. Due to relatively large size of the aliphatic part, water has limited solubility in all studied alcohols. Water content in saturated solutions was determined by Karl Fischer titration and correlated with the spectroscopic data. This way, we determined the molar absorptivity of the ν2+ν3 combination mode. The effect of addition of water and temperature variation was monitored by ATR-IR and NIR spectroscopy. Analysis of the experimental results was guided by DFT calculations, which provided the structures, harmonic MIR spectra and binding energies of selected alcohol-water complexes.Our studies demonstrated that the state of water in alcohols is related to its solubility, which depends on structure of solvent molecules. The solubility of water in 1-alcohols decreases on increasing of the chain length, but for long chain alcohols this effect is less evident. More apparent solubility reduction appears in going from the primary to secondary alcohols. The effective shielding of the OH group in the linear alcohols is achieved when on both sides of the OH group are ethyl or longer substituents, while the shielding by methyl groups is less efficient. Water is much better soluble in the cyclic alcohols as compared with the linear ones due to better accessibility of the OH group.The soft confinement of water in aliphatic alcohols allows for flexible structural arrangements and interactions. Even at low water content, we did not observe free molecules of water. At these conditions, the molecules of water are singly or doubly bonded to the OH groups from the alcohol. Increasing solubility of water reduces the number of the free OH groups and leads to formation of water clusters. Obtained results allow concluding that in alcohols with sizable aliphatic part the molecules of water are confined in the vicinity of the OH groups.

Chitosan/magnetic chitin nanowhisker polyelectrolyte membrane for direct methanol fuel cell applications: preparation, characterization, and performance analysis

ABSTRACT A hybrid chitosan-based nanocomposite was fabricated by chitin nanowhiskers coupled with silanized Fe3O4 nanoparticles as a polyelectrolyte membrane for direct methanol fuel cells (DMFCs). The morphological evaluations articulated that the magnetite nanoparticles were uniformly attached to the chitin nanowhiskers. After characterization of the synthesized nanowhiskers, they were incorporated into the chitosan, as a polycationic electrolyte, to investigate the performance of nanocomposite for DMFC applications. An external magnetic field was applied to the magnetic chitin nanowhiskers to induce alignment, and the effects of aligned nanowhiskers, as well as random ones, were also studied. The magnetic chitin nanowhiskers positively influenced the water uptake and proton conductivity due to the formation of hydrogen bonds between the surface functional groups of nanowhiskers and free water molecules. On the other hand, methanol permeation of the chitosan nanocomposites was reduced regarding the tortuous pathways and narrower transportation channels by the presence of nanowhiskers.

Ion-specific ice provides a facile approach for reducing ice friction

HypothesisIce friction plays a crucial role in both basic study and practical use. Various strategies for controlling ice friction have been developed. However, one unsolved puzzle regarding ice friction is the effect of ion–ice interplay on its tribological properties. Experiments and SimulationsHere, we conducted ice friction experiments and summarized the specific effects of hydrated ions on ice friction. By selecting cations and anions, the coefficient of ice friction can be reduced by more than 70 percent. Experimental spectra, low-field nuclear magnetic resonance (LF-NMR), density functional theory (DFT) calculations, and Molecular dynamics (MD) simulations demonstrated that the addition of ions could break the H-bonds in water. FindingsThe link between the charge density of ions and the coefficients of ice friction was revealed. A part of the ice structure was changed from an ice-like to a liquid-like interfacial water structure with the addition of ions. Lower charge density ions led to weaker ionic forces with the water molecules in the immobilized water layer, resulting in free water molecules increasing in the lubricating layer. This study provides guidance for preparing ice-making solutions with low friction coefficients and a fuller understanding of the interfacial water structure at low temperatures.

Modulation of Triton X-100 Aqueous Micelle Interface by Ionic Liquid: A Molecular Level Interaction Studied by Time-resolved Fluorescence Spectroscopy

Background: Self-assembly structure is an important area of research for understanding biological systems, owing to its resemblance to the membrane structure of the phospholipid bilayer. In a self-assembly medium, chemical reactions and chemical or physical processes are dramatically different than the bulk phase. Understanding this process in synthesizing self-assembly structures may allow us to explore various biological processes occurring in cell membranes. Objective: The study aimed to understand water dynamics in the TX-100 micellar interface via steady state and a time-resolved fluorescence spectroscopy study. The objective was also to determine the two different ionic liquids (ILs), namely 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF4]) and 1-decyl-3-methyl imidazolium tetrafluoroborate ([dmim][BF4]), inducing surfactant aggregation changes at the molecular level. Also, the focus was on determining the hydration and its dynamics at the palisade layer of TX-100 micelle in the presence of two different ionic liquids. Methods: Steady state and time-resolved fluorescence spectroscopy have been used to study TX-100 micellar systems. Employing time-resolved spectroscopy, two chemical dynamic processes, solvation dynamics and rotational relaxation dynamics, have been studied to investigate structural changes in TX100 by adding ILs. Solvation dynamics was studied by measuring the time-dependent Stokes shift of the fluorescent probe. From the Stokes shift, time-resolved emission spectra were constructed to quantify the solvation dynamics. Also, using the polarization properties of light, time-resolved anisotropy was constructed to explore the rotation relaxation of the probe molecule. Results: The absorption and emission spectra of C-153 in TX-100 were red-shifted in the presence of both the ILs. Also, the C-153 experienced faster solvation dynamics and rotational relaxation with the addition of both ILs. In our previous study, we observed a significantly increased rate of solvation dynamics with the addition of [bmim][BF4] (J. Phys. Chem. B, 115, 6957-6963) [38]. However, with the addition of the same amount of [dmim][BF4], the IL rate of solvation enhancement was more pronounced than with [bmim][BF4]. The faster solvation and rotational relaxation have been found to be associated with the penetration of more free water at the TX100 micellar stern layer, leading to increased fluidity of the micellar interface. Conclusion: Upon incorporating ILs in TX100 micelle, substantially faster solvation dynamics of water as well as rotational relaxation dynamics of C-153 have been observed. By decreasing surfactant aggregations, [bmim][BF4] ILs facilitated more water molecules approaching the TX-100 micellar phase. On the other hand, [dmim][BF4] ILs comprising mixed micelles induced even more free water molecules at the palisade layer, yielding faster solvation dynamics in comparison to pure TX-100 micelle or TX100 micelle + [bmim][BF4] ILs systems. Time-resolved anisotropy study has also supported the finding and strengthened the solvation dynamics observation.

Hybrid Molecular Sieve-Based Interfacial Layer with Physical Confinement and Desolvation Effect for Dendrite-free Zinc Metal Anodes.

The side reactions and dendrite growth at the interface of Zn anodes greatly limit their practical applications in Zn metal batteries. Herein, we propose a hybrid molecular sieve-based interfacial layer (denoted as Z7M3) with a hierarchical porous structure for Zn metal anodes, which contains 70 vol % microporous ZSM-5 molecular sieves and 30 vol % mesoporous MCM-41 molecular sieves. Through comprehensive molecular dynamics simulations, we demonstrate that the mesopores (∼2.5 nm) of MCM-41 can limit the disordered diffusion of free water molecules and increase the wettability of the interfacial layer toward aqueous electrolytes. In addition, the micropores (∼0.56 nm) of ZSM-5 can optimize the Zn2+ solvation structures by reducing the bonded water molecules, which simultaneously decrease the constraint force of solvated water molecules to Zn2+ ions, thus promoting the penetrability and diffusion kinetics of Zn2+ ions in Z7M3. The synergetic effects from the hybrid molecular sieves maintain a constant Zn2+ concentration on the surface of the Zn electrode during Zn deposition, contributing to dendrite-free Zn anodes. Consequently, Z7M3-coated Zn electrodes achieved excellent cycling stability in both half and full cells.

Dilute aqueous hybrid electrolyte endows a high-voltage window for supercapacitors

Developing aqueous electrolyte with wide electrochemical stability window (ESW) is one of the key technologies to boosting the energy density of aqueous electrochemical double-layer capacitors (EDLCs). However, expanding the ESW using super-concentrated electrolytes comes at the expense of cost, ionic conductivity and the mass density of the device. Herein, we selected a cost-effective and environmentally friendly molecular crowding agent, polyethylene glycol dimethyl ether (PEGDME-250), as the electrolyte additive designed to achieve high ESW at low salt concentrations. First, PEGDME can reduces the activity of water and increases the ESW of the electrolyte by forming hydrogen bonds with free water molecule. In addition, PEGDME does not have the interaction between terminal groups compared to conventional polyethylene glycols (PEG), which helps to reduce the viscosity and improve the ionic conductivity of the electrolyte. By adjusting the composition of the electrolyte, the optimal electrolyte with a high ESW of 2.96 V was achieved with the formula of 3 m NaClO4-25 % H2O-75 % PEGDME. The EDLCs assembled with this diluted aqueous electrolyte and YP-50 F electrodes presents a high operational voltage window of 2.4 V and outstanding cycle stability (>10000 cycles), and maintains excellent rate performance in a temperature range of −10–35 ℃.