Showing papers on "Ionic bonding published in 2020"

Giant thermopower of ionic gelatin near room temperature.

Abstract: Harvesting heat from the environment into electricity has the potential to power Internet-of-things (IoT) sensors, freeing them from cables or batteries and thus making them especially useful for wearable devices. We demonstrate a giant positive thermopower of 17.0 millivolts per degree Kelvin in a flexible, quasi-solid-state, ionic thermoelectric material using synergistic thermodiffusion and thermogalvanic effects. The ionic thermoelectric material is a gelatin matrix modulated with ion providers (KCl, NaCl, and KNO3) for thermodiffusion effect and a redox couple [Fe(CN)64–/Fe(CN)63–] for thermogalvanic effect. A proof-of-concept wearable device consisting of 25 unipolar elements generated more than 2 volts and a peak power of 5 microwatts using body heat. This ionic gelatin shows promise for environmental heat-to-electric energy conversion using ions as energy carriers.

Ultrathin Two-Dimensional Membranes Assembled by Ionic Covalent Organic Nanosheets with Reduced Apertures for Gas Separation

Abstract: Covalent organic frameworks (COFs) are a promising category of porous materials possessing extensive chemical tunability, high porosity, ordered arrangements at a molecular level, and considerable chemical stability. Despite these advantages, the application of COFs as membrane materials for gas separation is limited by their relatively large pore apertures (typically >0.5 nm), which exceed the sieving requirements for most gases whose kinetic diameters are less than 0.4 nm. Herein, we report the fabrication of ultrathin two-dimensional (2D) membranes through layer-by-layer (LbL) assembly of two kinds of ionic covalent organic nanosheets (iCONs) with different pore sizes and opposite charges. Because of the staggered packing of iCONs with strong electrostatic interactions, the resultant membranes exhibit features of reduced aperture size, optimized stacking pattern, and compact dense structure without sacrificing thickness control, which are suitable for molecular sieving gas separation. One of the hybrid membranes, TpEBr@TpPa-SO3Na with a thickness of 41 nm, shows a H2 permeance of 2566 gas permeation units (GPUs) and a H2/CO2 separation factor of 22.6 at 423 K, surpassing the recent Robeson upper bound along with long-term hydrothermal stability. This strategy provides not only a high-performance H2 separation membrane candidate but also an inspiration for pore engineering of COF or 2D porous polymer membranes.

Co-Construction of Sulfur Vacancies and Heterojunctions in Tungsten Disulfide to Induce Fast Electronic/Ionic Diffusion Kinetics for Sodium-Ion Batteries

Abstract: Engineering novel electrode materials with unique architectures has a significant impact on tuning the structural/electrochemical properties for boosting the performance of secondary battery systems. Herein, starting from well-organized WS2 nanorods, an ingenious design of a one-step method is proposed to prepare a bimetallic sulfide composite with a coaxial carbon coating layer, simply enabled by ZIF-8 introduction. Rich sulfur vacancies and WS2 /ZnS heterojunctions can be simultaneously developed, that significantly improve ionic and electronic diffusion kinetics. In addition, a homogeneous carbon protective layer around the surface of the composite guarantees an outstanding structural stability, a reversible capacity of 170.8 mAh g-1 after 5000 cycles at a high rate of 5 A g-1 . A great potential in practical application is also exhibited, where a full cell based on the WS2- x /ZnS@C anode and the P2-Na2/3 Ni1/3 Mn1/3 O2 cathode can maintain a reversible capacity of 89.4 mAh g-1 after 500 cycles at 1 A g-1 . Moreover, the underlying electrochemical Na storage mechanisms are illustrated in detail by theoretical calculations, electrochemical kinetic analysis, and operando X-ray diffraction characterization.

Interfacial Ferroelectricity by van-der-Waals Sliding

Abstract: Despite their ionic nature, many layered diatomic crystals avoid internal electric polarization by forming a centrosymmetric lattice at their optimal anti-parallel van-der-Waals stacking. Here, we report a stable ferroelectric order emerging at the interface between two naturally-grown flakes of hexagonal-boron-nitride, which are stacked together in a metastable non-centrosymmetric parallel orientation. We observe alternating domains of inverted normal polarization, caused by a lateral shift of one lattice site between the domains. Reversible polarization switching coupled to lateral sliding is achieved by scanning a biased tip above the surface. Our calculations trace the origin of the phenomenon to a subtle interplay between charge redistribution and ionic displacement, and our minimal cohesion model predicts further venues to explore the unique "slidetronics" switching.

Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

Abstract: A unified picture of different application areas for incipient metals is presented. This unconventional material class includes several main-group chalcogenides, such as GeTe, PbTe, Sb2 Te3 , Bi2 Se3 , AgSbTe2 and Ge2 Sb2 Te5 . These compounds and related materials show a unique portfolio of physical properties. A novel map is discussed, which helps to explain these properties and separates the different fundamental bonding mechanisms (e.g., ionic, metallic, and covalent). The map also provides evidence for an unconventional, new bonding mechanism, coined metavalent bonding (MVB). Incipient metals, employing this bonding mechanism, also show a special bond breaking mechanism. MVB differs considerably from resonant bonding encountered in benzene or graphite. The concept of MVB is employed to explain the unique properties of materials utilizing it. Then, the link is made from fundamental insights to application-relevant properties, crucial for the use of these materials as thermoelectrics, phase change materials, topological insulators or as active photonic components. The close relationship of the materials' properties and their application potential provides optimization schemes for different applications. Finally, evidence will be presented that for metavalently bonded materials interesting effects arise in reduced dimensions. In particular, the consequences for the crystallization kinetics of thin films and nanoparticles will be discussed in detail.

Ionoelastomer junctions between polymer networks of fixed anions and cations

Abstract: Soft ionic conductors have enabled stretchable and transparent devices, but liquids in such devices tend to leak and evaporate. In this study, we demonstrate diodes and transistors using liquid-free ionoelastomers, in which either anions or cations are fixed to an elastomer network and the other ionic species are mobile. The junction of the two ionoelastomers of opposite polarity yields an ionic double layer, which is capable of rectifying and switching ionic currents without electrochemical reactions. The entropically driven depletion of mobile ions creates a junction of tough adhesion, and the stretchability of the junction enables electromechanical transduction.

Classical and Emerging Characterization Techniques for Investigation of Ion Transport Mechanisms in Crystalline Fast Ionic Conductors.

Abstract: Ion transport in crystalline fast ionic conductors is a complex physical phenomenon. Certain ionic species (e.g., Ag+, Cu+, Li+, F–, O2–, H+) in a solid crystalline framework can move as fast as in...

Interface Engineering of Imidazolium Ionic Liquids toward Efficient and Stable CsPbBr3 Perovskite Solar Cells.

Abstract: The defect passivation of perovskite films is an efficacious way to further boost the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). In this work, ionic...

Distinguishing between chemical bonding and physical binding using electron localization function (ELF)

Abstract: To distinguish between chemical bonding and physical binding is usually simple. They differ, in the normal case, in both interaction strength (binding energy) and interaction length (structure). However, chemical bonding can be weak (e.g. in some metallic bonding) and physical binding can be strong (e.g. due to permanent electrostatic moments, hydrogen binding, etc) making differentiation non-trivial. But since these are shared-electron or unshared-electron interactions, respectively, it is in principle possible to distinguish the type of interaction by analyzing the electron density around the interaction point(s)/interface. After all, the former should be a contact while the latter should be a tunneling barrier. Here, we investigate within the framework of density functional theory typical molecules and crystals to show the behaviour of the electron localization function (ELF) in different shared-electron interactions, such as chemical (covalent) and metallic bonding and compare to unshared-electron interactions typical for physical binding, such as ionic, hydrogen and Keesom, dispersion (van der Waals) binding and attempt to categorise them only by the ELF and the electron population in the interaction region. It is found that the ELF method is not only useful for the characterization of covalent bonds but a lot of information can be extracted also for weaker types of binding. Furthermore, the charge integration over the interaction region(s) and tracing the ELF profile can reveal the strength of the bonding/binding ranging from the triple bonds to weak dispersion.

High oxide ion and proton conductivity in a disordered hexagonal perovskite

Abstract: Oxide ion and proton conductors, which exhibit high conductivity at intermediate temperature, are necessary to improve the performance of ceramic fuel cells. The crystal structure plays a pivotal role in defining the ionic conduction properties, and the discovery of new materials is a challenging research focus. Here, we show that the undoped hexagonal perovskite Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm−1), and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell that will combine the advantages of both oxide ion and proton-conducting electrolytes. Ba7Nb4MoO20 also showcases excellent chemical and electrical stability. Hexagonal perovskites form an important new family of materials for obtaining novel ionic conductors with potential applications in a range of energy-related technologies. Fast oxide ion and proton conductors at intermediate temperature are required to improve the performance of ceramic fuel cells. An undoped hexagonal perovskite Ba7Nb4MoO20 electrolyte with high proton and oxide ion conductivity (4.0 mS cm−1) at 510 °C is now reported.

Enhanced electrochemical performance of Ni-rich cathode materials with Li1.3Al0.3Ti1.7(PO4)3 coating

Abstract: In this work, a fast ionic conductor, Li1.3Al0.3Ti1.7(PO4)3 (LATP), has been successfully coated on a Ni-rich LiNi0.8Co0.1Mn0.1O2 surface by an improved sol–gel method with postannealing at 575 °C....

Dehydration-Triggered Ionic Channel Engineering in Potassium Niobate for Li/K-Ion Storage.

Abstract: Boosting charge transfer in materials is critical for applications involving charge carriers. Engineering ionic channels in electrode materials can create a skeleton to manipulate their ion and electron behaviors with favorable parameters to promote their capacity and stability. Here, tailoring of the atomic structure in layered potassium niobate (K4 Nb6 O17 ) nanosheets and facilitating their application in lithium and potassium storage by dehydration-triggered lattice rearrangement is reported. The spectroscopy results reveal that the interatomic distances of the NbO coordination in the engineered K4 Nb6 O17 are slightly elongated with increased degrees of disorder. Specifically, the engineered K4 Nb6 O17 shows enhanced electrical and ionic conductivity, which can be attributed to the enlarged interlamellar spacing and subtle distortions in the fine atomic arrangements. Moreover, subsequent experimental results and calculations demonstrate that the energy barrier for Li+ /K+ diffusion is significantly lower than that in pristine K4 Nb6 O17 . Interestingly, the diffusion coefficient of K+ is one order of magnitude higher than that of Li+ , and the engineered K4 Nb6 O17 presents superior electrochemical performance for K+ to Li+ . This work offers an ionic engineering strategy to enable fast and durable charge transfer in materials, holding great promise for providing guidance for the material design of related energy storage systems.

The Role of Grain Boundaries on Ionic Defect Migration in Metal Halide Perovskites

Abstract: Halide perovskites are emerging as revolutionary materials for optoelectronics. Their ionic nature and the presence of mobile ionic defects within the crystal structure have a dramatic influence on the operation of thin-film devices such as solar cells, light-emitting diodes, and transistors. Thin films are often polycrystalline and it is still under debate how grain boundaries affect the migration of ions and corresponding ionic defects. Laser excitation during photoluminescence (PL) microscopy experiments leads to formation and subsequent migration of ionic defects, which affects the dynamics of charge carrier recombination. From the microscopic observation of lateral PL distribution, the change in the distribution of ionic defects over time can be inferred. Resolving the PL dynamics in time and space of single crystals and thin films with different grain sizes thus, provides crucial information about the influence of grain boundaries on the ionic defect movement. In conjunction with experimental observations, atomistic simulations show that defects are trapped at the grain boundaries, thus inhibiting their diffusion. Hence, with this study, a comprehensive picture highlighting a fundamental property of the material is provided while also setting a theoretical framework in which the interaction between grain boundaries and ionic defect migration can be understood. (Less)

Emerging Ionic Soft Materials Based on Deep Eutectic Solvents.

Abstract: In the last 5 years, the use of deep eutectic solvents (DESs) have been opening new perspectives toward the creation of novel ionic soft materials as alternatives to expensive ionic liquids. This M...

Imidazolium‐Functionalized Ionic Hypercrosslinked Porous Polymers for Efficient Synthesis of Cyclic Carbonates from Simulated Flue Gas

Abstract: The rapid growth of CO2 emissions, especially from power plants, has led to the urgent need to directly capture and fix CO2 in the flue gas after simple purification rather than energy-intensive gas separation. Herein, imidazolium-functionalized ionic hypercrosslinked porous polymers (HCPs) bearing adjustable surface groups were straightforwardly synthesized through co-hypercrosslinking of benzylimidazole salts and crosslinker through Friedel-Crafts alkylation. Abundant microporosity and relatively high ionic moieties were obtainable in the ethyl-group-tethered ionic HCP, giving a remarkably selective CO2 capture performance with a CO2 uptake of 3.05 mmol g-1 and an ideal adsorbed solution theory (IAST) CO2 /N2 selectivity as high as 363 (273 K, 1 bar). This ionic polymer demonstrated high efficiency in the synthesis of cyclic carbonates from the coupling of various epoxides with the simulated flue gas (15 % CO2 and 85 % N2 ), giving high yields, large turnover numbers (up to 4800), and stable reusability under additive- and solvent-free conditions.

High and fast adsorption of Cd(II) and Pb(II) ions from aqueous solutions by a waste biomass based hydrogel.

Abstract: A waste biomass based hydrogel soybean residue-poly(acrylic acid) (SR–PAA) was prepared through a fast one-step reaction by UV radiation technology. SR–PAA was used to remove Cd(II) and Pb(II) ions from aqueous solutions. Effect of pH value, temperature, initial concentration, contact time, competitive ions in the solutions on metal ions adsorption and desorption/regeneration capacity of SR–PAA was discussed in detailed. It was found that the adsorption equilibrium was achieved within 20 min, and maximum adsorption for Cd(II) and Pb(II) ions were 1.43 and 2.04 mmol g−1, respectively. Besides, adsorption thermodynamic analysis indicates that the process of Cd(II) and Pb(II) ions adsorption was spontaneous, feasible and exothermic in nature. And experimental data fitted the pseudo-second-order and Freundlich isotherm model well. Moreover, XPS spectra analysis proves that the metal ions were adsorbed on SR–PAA due to the interaction of carboxyl, hydroxyl and amine with these ions as ionic bond, coordination bond and electrostatic interaction.

Chloride transport in conductive polymer films for an n-type thermoelectric platform

Abstract: Cl− transport in a conductive polymer (CP) film was demonstrated for n-type thermoelectric (TE) harvesting. CPs have been considered as an important group of p-type TE materials due to their high TE functionalities plus simple processing steps for a device. In particular, recently emerging p-type ionic CPs can be unique candidates due to their high Seebeck coefficients (S). However, n-type materials based on CPs suffer from very poor TE functionalities, and n-type ionic TE CP materials have not been realized so far. Here, we report the first example of n-type mixed ionic–electronic CP composite (NPC) films. The p-type TE properties of the PEDOT:PSS films was drastically converted into the n-type TE properties in the presence of CuCl2 through metal binding with polymers, thus resulting in the formation of Cl− channels. Fluorescence imaging using Cl− as an indicator and time-of-flight secondary ion mass spectrometry mapping confirmed that Cl− is transported in the film from the hot to the cold electrode. In addition, electron spin resonance spectroscopy indicated the major spin density transition from a polaron of PEDOT:PSS to the polymer-bound unpaired electron spin of Cu ions by increasing the CuCl2 content to prove the binding of metal ions with the PSS unit of the polymer chain. These mixed ionic–electronic NPC films recorded a surprisingly high negative S value of over −18.2 mV K−1 and a power factor of 1.7 mW m−1 K−2 at 80% RH with 40 wt% of CuCl2. Taking advantage of this high performance, the CP films were integrated with a p-type CP film as a flexible module-type TE harvester with 10 pairs of p–n legs on CNT electrodes. This TE harvester showed a thermovoltage of 1.55 V for a low temperature gradient of 4.5 K. This high anion transport in a TE CP hydrogel film might be a useful solution for environmentally benign and body-worn electronics.

Toward Rapid-Charging Sodium-Ion Batteries using Hybrid-Phase Molybdenum Sulfide Selenide-Based Anodes.

Abstract: To attain both high energy density and power density in sodium-ion (Na+ ) batteries, the reaction kinetics and structural stability of anodes should be improved by materials optimization. In this work, few-layered molybdenum sulfide selenide (MoSSe) consisting of a mixture of 1T and 2H phases is designed to provide high ionic/electrical conductivities, low Na+ diffusion barrier, and stable Na+ storage. Reduced graphene oxide (rGO) is used as a conductive matrix to form 3D electron transfer paths. The resulting MoSSe@rGO anode exhibits high capacity and rate performance in both organic and solid-state electrolytes. The ultrafast Na+ storage kinetics of the MoSSe@rGO anode is attributed to the surface-dominant reaction process and broad Na+ channels. In situ and ex situ measurements are conducted to reveal the Na+ storage process in MoSSe@rGO. It is found that the MoS and MoSe bonds effectively limit the dissolution of the active materials. The favorable Na+ storage kinetics of the MoSSe@rGO electrode are ascribed to its low adsorption energy of -1.997 eV and low diffusion barrier of 0.087 eV. These results reveal that anion doping of metal sulfides is a feasible strategy to develop sodium-ion batteries with high energy and power densities and long life-span.

Charge-Shift Bonding: A New and Unique Form of Bonding

Abstract: Charge-shift bonds (CSBs) constitute a new class of bonds different than covalent/polar-covalent and ionic bonds. Bonding in CSBs does not arise from either the covalent or the ionic structures of the bond, but rather from the resonance interaction between the structures. This Essay describes the reasons why the CSB family was overlooked by valence-bond pioneers and then demonstrates that the unique status of CSBs is not theory-dependent. Thus, valence bond (VB), molecular orbital (MO), and energy decomposition analysis (EDA), as well as a variety of electron density theories all show the distinction of CSBs vis-a-vis covalent and ionic bonds. Furthermore, the covalent-ionic resonance energy can be quantified from experiment, and hence has the same essential status as resonance energies of organic molecules, e.g., benzene. The Essay ends by arguing that CSBs are a distinct family of bonding, with a potential to bring about a Renaissance in the mental map of the chemical bond, and to contribute to productive chemical diversity.

Role of a high calcium ion content in extending the properties of alginate dual-crosslinked hydrogels

Abstract: Calcium ions (Ca2+) are extremely important for efficiently improving the mechanical properties of alginate dual-crosslinked hydrogels through the synergy of crack bridging of covalent crosslinking and hysteresis of ionic crosslinking, but it is hard to achieve a high content of Ca2+ (>5 wt%) in these hydrogels for the following reasons. The low solubility and poor dispersion of CaSO4 in the gelling solution lead to a low Ca2+ content (<0.1 wt%). The rapid formation of an alginate–Ca2+ “egg-box” structure during CaCl2 diffusion results in heterogeneous crosslinking, thus inhibiting further diffusion of Ca2+. Increasing the Ca2+ content, therefore, is a neglected strategy to extend the properties of hydrogels, for example, self-healing (dynamic ionic bonding of alginate–Ca2+), adhesion (dynamic ionic bonding of Ca2+ and carboxyl groups), anti-freezing (freezing point depression in the presence of Ca2+) and high conductivity (basic characteristics of Ca2+), particularly opening up a range of applications in low-temperature environments. Here we develop a highly Ca2+ crosslinked ald-alginate–gelatin imine-based (CaAG) hydrogel prepared by mixing a solution of ald-alginate and gelatin to form an ald-alginate–gelatin (AG) hydrogel, followed by immersing the AG hydrogel in CaCl2 solution with high solubility and good dispersion of Ca2+. Ald-alginate is covalently crosslinked in the network that retards the formation of alginate–Ca2+. By that, 7 wt% of Ca2+ (the highest Ca2+ content in alginate dual-crosslinked hydrogels as we know) of Ca2+ could be brought into hydrogels to extend their properties: (1) rapid self-healing (heals within 5 min), (2) strong and reversible adhesion to metal, skin, glass, and plastic, (3) anti-freezing (stretchable at −20 °C), and (4) high conductivity (1.5 S m−1). Furthermore, we show a concept skin strain sensor by using the CaAG hydrogel.

Ionic solids from common colloids

Abstract: From rock salt to nanoparticle superlattices, complex structure can emerge from simple building blocks that attract each other through Coulombic forces1–4. On the micrometre scale, however, colloids in water defy the intuitively simple idea of forming crystals from oppositely charged partners, instead forming non-equilibrium structures such as clusters and gels5–7. Although various systems have been engineered to grow binary crystals8–11, native surface charge in aqueous conditions has not been used to assemble crystalline materials. Here we form ionic colloidal crystals in water through an approach that we refer to as polymer-attenuated Coulombic self-assembly. The key to crystallization is the use of a neutral polymer to keep particles separated by well defined distances, allowing us to tune the attractive overlap of electrical double layers, directing particles to disperse, crystallize or become permanently fixed on demand. The nucleation and growth of macroscopic single crystals is demonstrated by using the Debye screening length to fine-tune assembly. Using a variety of colloidal particles and commercial polymers, ionic colloidal crystals isostructural to caesium chloride, sodium chloride, aluminium diboride and K4C60 are selected according to particle size ratios. Once fixed by simply diluting out solution salts, crystals are pulled out of the water for further manipulation, demonstrating an accurate translation from solution-phase assembly to dried solid structures. In contrast to other assembly approaches, in which particles must be carefully engineered to encode binding information12–18, polymer-attenuated Coulombic self-assembly enables conventional colloids to be used as model colloidal ions, primed for crystallization. Oppositely charged colloidal particles are assembled in water through an approach that allows electrostatic interactions to be precisely tuned to generate macroscopic single crystals.