Showing papers on "Ion published in 2019"

Double-slit photoelectron interference in strong-field ionization of the neon dimer.

Abstract: Wave-particle duality is an inherent peculiarity of the quantum world. The double-slit experiment has been frequently used for understanding different aspects of this fundamental concept. The occurrence of interference rests on the lack of which-way information and on the absence of decoherence mechanisms, which could scramble the wave fronts. Here, we report on the observation of two-center interference in the molecular-frame photoelectron momentum distribution upon ionization of the neon dimer by a strong laser field. Postselection of ions, which are measured in coincidence with electrons, allows choosing the symmetry of the residual ion, leading to observation of both, gerade and ungerade, types of interference.

A Eu3+-Eu2+ ion redox shuttle imparts operational durability to Pb-I perovskite solar cells.

Abstract: The components with soft nature in the metal halide perovskite absorber usually generate lead (Pb) 0 and iodine (I) 0 defects during device fabrication and operation. These defects serve as not only recombination centers to deteriorate device efficiency but also degradation initiators to hamper device lifetimes. We show that the europium ion pair Eu 3+ -Eu 2+ acts as the “redox shuttle” that selectively oxidized Pb 0 and reduced I 0 defects simultaneously in a cyclical transition. The resultant device achieves a power conversion efficiency (PCE) of 21.52% (certified 20.52%) with substantially improved long-term durability. The devices retained 92% and 89% of the peak PCE under 1-sun continuous illumination or heating at 85°C for 1500 hours and 91% of the original stable PCE after maximum power point tracking for 500 hours, respectively.

Trapped-ion quantum computing: Progress and challenges

Abstract: Trapped ions are among the most promising systems for practical quantum computing (QC). The basic requirements for universal QC have all been demonstrated with ions, and quantum algorithms using few-ion-qubit systems have been implemented. We review the state of the field, covering the basics of how trapped ions are used for QC and their strengths and limitations as qubits. In addition, we discuss what is being done, and what may be required, to increase the scale of trapped ion quantum computers while mitigating decoherence and control errors. Finally, we explore the outlook for trapped-ion QC. In particular, we discuss near-term applications, considerations impacting the design of future systems of trapped ions, and experiments and demonstrations that may further inform these considerations.

Ionic modulation and ionic coupling effects in MoS2 devices for neuromorphic computing.

Abstract: Coupled ionic-electronic effects present intriguing opportunities for device and circuit development. In particular, layered two-dimensional materials such as MoS2 offer highly anisotropic ionic transport properties, facilitating controlled ion migration and efficient ionic coupling among devices. Here, we report reversible modulation of MoS2 films that is consistent with local 2H-1T' phase transitions by controlling the migration of Li+ ions with an electric field, where an increase/decrease in the local Li+ ion concentration leads to the transition between the 2H (semiconductor) and 1T' (metal) phases. The resulting devices show excellent memristive behaviour and can be directly coupled with each other through local ionic exchange, naturally leading to synaptic competition and synaptic cooperation effects observed in biology. These results demonstrate the potential of direct modulation of two-dimensional materials through field-driven ionic processes, and can lead to future electronic and energy devices based on coupled ionic-electronic effects and biorealistic implementation of artificial neural networks.

Controllable ion transport by surface-charged graphene oxide membrane

Abstract: Ion transport is crucial for biological systems and membrane-based technology. Atomic-thick two-dimensional materials, especially graphene oxide (GO), have emerged as ideal building blocks for developing synthetic membranes for ion transport. However, the exclusion of small ions in a pressured filtration process remains a challenge for GO membranes. Here we report manipulation of membrane surface charge to control ion transport through GO membranes. The highly charged GO membrane surface repels high-valent co-ions owing to its high interaction energy barrier while concomitantly restraining permeation of electrostatically attracted low-valent counter-ions based on balancing overall solution charge. The deliberately regulated surface-charged GO membranes demonstrate remarkable enhancement of ion rejection with intrinsically high water permeance that exceeds the performance limits of state-of-the-art nanofiltration membranes. This facile and scalable surface charge control approach opens opportunities in selective ion transport for the fields of water transport, biomimetic ion channels and biosensors, ion batteries and energy conversions.

Construction of CoO/Co-Cu-S Hierarchical Tubular Heterostructures for Hybrid Supercapacitors.

Abstract: Hierarchical hollow structures for electrode materials of supercapacitors could enlarge the surface area, accelerate the transport of ions and electrons, and accommodate volume expansion during cycling. Besides, construction of heterostructures would enhance the internal electric fields to regulate the electronic structures. All these features of hierarchical hollow heterostructures are beneficial for promoting the electrochemical properties and stability of electrode materials for high-performance supercapacitors. Herein, CoO/Co-Cu-S hierarchical tubular heterostructures (HTHSs) composed of nanoneedles are prepared by an efficient multi-step approach. The optimized sample exhibits a high specific capacity of 320 mAh g-1 (2300 F g-1 ) at 2.0 A g-1 and outstanding cycling stability with 96.5 % of the initial capacity retained after 5000 cycles at 10 A g-1 . Moreover, an all-solid-state hybrid supercapacitor (HSC) constructed with the CoO/Co-Cu-S and actived carbon shows a stable and high energy density of 90.7 Wh kg-1 at a power density of 800 W kg-1 .

A facile composite material for enhanced cadmium(II) ion capturing from wastewater

Abstract: Cadmium (Cd(II)) ion is one of the most important toxic metals to remove from contaminated water for safe-guarding the public health. Elevated levels of Cd(II) ion in natural water may have a detrimental effect on both human health, environment and the eco-system. The functionalized materials have been investigated widely over the years for numerous uses to exert a considerable technological impact on future miniaturized, compact, cost effective, and efficient devices. From this point of view, the functional ligand based composite material was fabricated based on the direct anchoring methods for effective Cd(II) ion detection and removal from wastewater. The significant color was visualized upon addition of Cd(II) ion at optimum condition. The optimum pH was carefully evaluated, and pH 5.50 was selected based on the sensitivity, selectivity and color formation. The detection limit was 0.37 μg/L, which was lower than the permissible limit of Cd(II) ion in water. The variable experimental parameters such as solution pH, initial concentration, contact time and foreign ions were systematically evaluated both in monitoring and adsorption operations. The adsorption data were well fitted to the Langmuir adsorption model, and the maximum adsorption capacity was 186.36 mg/g. In the presence of competing ions, the Cd(II) detection and adsorption were not affected due to the specific binding affinity between the composite material and Cd(II) ions. The adsorb Cd(II) ion was desorbed from the composite material using 0.15 M HCl, and the material were simultaneously regenerated into the initial form for the next cycle use without loss the functionality.

Novel ligand functionalized composite material for efficient copper(II) capturing from wastewater sample

Abstract: Copper (Cu(II)) is a very toxic heavy metal that even at low concentration can affect living organisms. Therefore, designing effective materials with high selectivity and cost-efficiency is essential for the control capturing of toxic Cu(II) ions. This study was developed a ligand based composite material for simultaneous Cu(II) detection and removal from wastewater samples. The composite material was fabricated based on the ligand anchoring onto the mesoporous silica by direct coating approach. The application of Cu(II) detection and adsorption was measured at neutral pH region with exhibition of significant color visualization. The experiment conditions were optimized based on contact time, solution acidity, initial Cu(II) concentration and pH value and diverse metal salt concentrations. The results were revealed that the composite material was not affected with the existing foreign ions and the signal intensity was observed only toward the Cu(II) ion. The composite material was able to detected the low level Cu(II) ion as the detection limit was 0.25 μg/L and the adsorption of highest removal capacity was 171.33 mg/g. In addition, the diverse ions were not reduced the Cu(II) ion adsorption significantly, and the composite material has approximately no adsorption capacity for other ions at this pH. The elution of Cu(II) ions from the saturated composite material was desorbed successfully with 0.20 M HCl. The regenerated adsorbent that remained maintained the high selectivity to Cu(II) ions and exhibited almost the same sorption capacity as that of the original adsorbent. However, the sorption efficiency slightly decreased after ten cycles. Therefore, the proposed material offered a cost-effective material and may be considered a viable alternative for effectively toxic Cu(II) ion capturing from water samples without the need for sophisticated instrument.

Quantification of ion migration in CH3NH3PbI3 perovskite solar cells by transient capacitance measurements

Abstract: Ion migration in halide perovskite films leads to device degradation and impedes large scale commercial applications. We use transient ion-drift measurements to quantify activation energy, diffusion coefficient, and concentration of mobile ions in methylammonium lead triiodide (MAPbI3) perovskite solar cells, and find that their properties change close to the tetragonal-to-orthorhombic phase transition temperature. We identify three migrating ion species which we attribute to the migration of iodide (I−) and methylammonium (MA+). We find that the concentration of mobile MA+ ions is one order of magnitude higher than the one of mobile I− ions, and that the diffusion coefficient of mobile MA+ ions is three orders of magnitude lower than the one for mobile I− ions in our samples. This quantification of mobile ions in MAPbI3 will lead to a better understanding of ion migration and its role in operation and degradation of perovskite solar cells.

Tuning P2-Structured Cathode Material by Na-Site Mg Substitution for Na-Ion Batteries.

Abstract: Most P2-type layered oxides suffer from multiple voltage plateaus, due to Na+/vacancy-order superstructures caused by strong interplay between Na-Na electrostatic interactions and charge ordering in the transition metal layers. Here, Mg ions are successfully introduced into Na sites in addition to the conventional transition metal sites in P2-type Na0.7[Mn0.6Ni0.4]O2 as new cathode materials for sodium-ion batteries. Mg ions in the Na layer serve as "pillars" to stabilize the layered structure, especially for high-voltage charging, meanwhile Mg ions in the transition metal layer can destroy charge ordering. More importantly, Mg ion occupation in both sodium and transition metal layers will be able to create "Na-O-Mg" and "Mg-O-Mg" configurations in layered structures, resulting in ionic O 2p character, which allocates these O 2p states on top of those interacting with transition metals in the O-valence band, thus promoting reversible oxygen redox. This innovative design contributes smooth voltage profiles and high structural stability. Na0.7Mg0.05[Mn0.6Ni0.2Mg0.15]O2 exhibits superior electrochemical performance, especially good capacity retention at high current rate under a high cutoff voltage (4.2 V). A new P2 phase is formed after charge, rather than an O2 phase for the unsubstituted material. Besides, multiple intermediate phases are observed during high-rate charging. Na-ion transport kinetics are mainly affected by elemental-related redox couples and structural reorganization. These findings will open new opportunities for designing and optimizing layer-structured cathodes for sodium-ion batteries.

Higher energy and safer sodium ion batteries via an electrochemically made disordered Na3V2(PO4)2F3 material.

Abstract: The growing need to store an increasing amount of renewable energy in a sustainable way has rekindled interest for sodium-ion battery technology, owing to the natural abundance of sodium. Presently, sodium-ion batteries based on Na 3 V 2 (PO 4) 2 F 3 /C are the subject of intense research focused on improving the energy density by harnessing the third sodium, which has so far been reported to be electrochemically inaccessible. Here, we are able to trigger the activity of the third sodium electrochemically via the formation of a disordered Na x V 2 (PO 4) 2 F 3 phase of tetragonal symmetry (I4/mmm space group). This phase can reversibly uptake 3 sodium ions per formula unit over the 1 to 4.8 V voltage range, with the last one being re-inserted at 1.6 V vs Na + /Na 0. We track the sodium-driven structural/ charge compensation mechanism associated to the new phase and find that it remains disordered on cycling while its average vanadium oxidation state varies from 3 to 4.5. Full sodium-ion cells based on this phase as positive electrode and carbon as negative electrode show a 10-20% increase in the overall energy density.

A Metal-Organic Framework of Organic Vertices and Polyoxometalate Linkers as a Solid-State Electrolyte.

Abstract: A new three-dimensional metal-organic framework (MOF) was synthesized by linking ditopic amino functionalized polyoxometalate [N(C4H9)4]3[MnMo6O18{(OCH2)3CNH2}2] with 4-connected tetrahedral tetrakis(4-formylphenyl)methane building units through imine condensation. The structure of this MOF, termed MOF-688, was solved by single crystal X-ray diffraction and found to be triply interpenetrated diamond-based dia topology. Tetrabutylammonium cations fill the pores and balance the charge of the anionic framework. They can be exchanged with lithium ions to give high ionic conductivity (3.4 × 10-4 S cm-1 at 20 °C), a high lithium ion transference number (tLi+ = 0.87), and low interfacial resistance (353 Ω) against metallic lithium-properties that make it ideally suited as a solid-state electrolyte. Indeed, a prototype lithium metal battery constructed using MOF-688 as the solid electrolyte can be cycled at room temperature with a practical current density of ∼0.2 C.

How transport layer properties affect perovskite solar cell performance: insights from a coupled charge transport/ion migration model

Abstract: The effects of transport layers on perovskite solar cell performance, in particular anomalous hysteresis, are investigated. A model for coupled ion vacancy motion and charge transport is formulated and solved in a three-layer planar perovskite solar cell. Its results are used to demonstrate that the replacement of standard transport layer materials (spiro-OMeTAD and TiO2) by materials with lower permittivity and/or doping leads to a shift in the scan rates at which hysteresis is most pronounced to rates higher than those commonly used in experiment. These results provide a cogent explanation for why organic electron transport layers can yield seemingly “hysteresis-free” devices but which nevertheless exhibit hysteresis at low temperature. In these devices the decrease in ion vacancy mobility with temperature compensates for the increase in hysteresis rate with use of low permittivity/doping organic transport layers. Simulations are used to classify features of the current–voltage curves that distinguish between cells in which charge carrier recombination occurs predominantly at the transport layer interfaces and those where it occurs predominantly within the perovskite. These characteristics are supplemented by videos showing how the electric potential, electronic and ionic charge profiles evolve across a planar perovskite solar cell during a current–voltage scan. Design protocols to mitigate the possible effects of high ion vacancy distributions on cell degradation are discussed. Finally, features of the steady-state potential profile for a device held near the maximum power point are used to suggest ways in which interfacial recombination can be reduced, and performance enhanced, via tuning transport layer properties.

Molecular streaming and its voltage control in ångström-scale channels

Abstract: Over the past decade, the ability to reduce the dimensions of fluidic devices to the nanometre scale (by using nanotubes1-5 or nanopores6-11, for example) has led to the discovery of unexpected water- and ion-transport phenomena12-14. More recently, van der Waals assembly of two-dimensional materials15 has allowed the creation of artificial channels with angstrom-scale precision16. Such channels push fluid confinement to the molecular scale, wherein the limits of continuum transport equations17 are challenged. Water films on this scale can rearrange into one or two layers with strongly suppressed dielectric permittivity18,19 or form a room-temperature ice phase20. Ionic motion in such confined channels21 is affected by direct interactions between the channel walls and the hydration shells of the ions, and water transport becomes strongly dependent on the channel wall material22. We explore how water and ionic transport are coupled in such confinement. Here we report measurements of ionic fluid transport through molecular-sized slit-like channels. The transport, driven by pressure and by an applied electric field, reveals a transistor-like electrohydrodynamic effect. An applied bias of a fraction of a volt increases the measured pressure-driven ionic transport (characterized by streaming mobilities) by up to 20 times. This gating effect is observed in both graphite and hexagonal boron nitride channels but exhibits marked material-dependent differences. We use a modified continuum framework accounting for the material-dependent frictional interaction of water molecules, ions and the confining surfaces to explain the differences observed between channels made of graphene and hexagonal boron nitride. This highly nonlinear gating of fluid transport under molecular-scale confinement may offer new routes to control molecular and ion transport, and to explore electromechanical couplings that may have a role in recently discovered mechanosensitive ionic channels23.

g-C3N4 nanosheets enhanced solid polymer electrolytes with excellent electrochemical performance, mechanical properties, and thermal stability

Abstract: Solid polymer electrolytes (SPEs) are expected to improve the safety and performance of lithium ion batteries (LIB). However, the low ionic conductivity limit the further application of PEO based electrolytes. Herein, g-C3N4 nanosheets is proposed as a novel filler for PEO based electrolytes. The addition of g-C3N4 improves the electrical properties (ionic conductivity, lithium ion transference number and electrochemical window), mechanical properties and thermal stability of the composite electrolyte. The two-dimensional g-C3N4 forms an effective ion transport network in the composite electrolyte. In addition, the surface atoms of the g-C3N4 interact with groups in the lithium salt, promoting further dissociation of the lithium salt. Furthermore, the all solid state batteries assembled by the g-C3N4 composite electrolyte exhibited good cycle performance at 60 °C (remained at 155 mA h g−1 after 100 cycles). Owing to the simple synthesis and environmental friendliness, g-C3N4 nanosheets has a certain practical prospect as a filler for solid polymer electrolytes.

Artificial light-driven ion pump for photoelectric energy conversion

Abstract: Biological light-driven ion pumps move ions against a concentration gradient to create a membrane potential, thus converting sunlight energy directly into an osmotic potential. Here, we describe an artificial light-driven ion pump system in which a carbon nitride nanotube membrane can drive ions thermodynamically uphill against an up to 5000-fold concentration gradient by illumination. The separation of electrons and holes in the membrane under illumination results in a transmembrane potential which is thought to be the foundation for the pumping phenomenon. When used for harvesting solar energy, a sustained open circuit voltage of 550 mV and a current density of 2.4 μA/cm2 can reliably be generated, which can be further scaled up through series and parallel circuits of multiple membranes. The ion transport based photovoltaic system proposed here offers a roadmap for the development of devices by using simple, cheap, and stable polymeric carbon nitride. Biological light-driven ion pumps move ions against a concentration gradient to create a membrane potential, converting sunlight into an osmotic potential. Here, the authors make an artificial ion pump which drives ions thermodynamically uphill against a large concentration gradient upon illumination, which can be used for harvesting solar energy.

Binder-free hierarchical VS2 electrodes for high-performance aqueous Zn ion batteries towards commercial level mass loading

Abstract: Aqueous rechargeable zinc ion batteries with advantages of low cost and high level of safety have been considered as a promising candidate for large-scale energy storage. In this work, a freestanding, binder-free cathode comprising hierarchical VS2 in the 1T phase grown directly on a stainless steel mesh (VS2@SS) was developed for aqueous zinc ion batteries. The battery exhibited an excellent Zn ion storage capacity of 198 mA h g−1 and stable cycling performance (above 80% capacity retention over 2000 cycles at 2 A g−1). The detailed structural and chemical composition analyses revealed the phase evolution of VS2 and the reversible Zn ion insertion/extraction mechanism during the charge/discharge process. Notably, with an increased mass loading of VS2 over the commercial level (∼11 mg cm−2), a long-term cycling stability with 90% capacity retention after 600 cycles (only 0.017% loss per cycle) could be achieved, which suggests that the electrodes are promising for practical applications. Furthermore, flexible solid-state Zn ion batteries were demonstrated by using the VS2@SS electrodes, and reliable electrochemical performance could be observed even after 200 cycles.

Efficient molecular doping of polymeric semiconductors driven by anion exchange

Abstract: The efficiency with which polymeric semiconductors can be chemically doped—and the charge carrier densities that can thereby be achieved—is determined primarily by the electrochemical redox potential between the π-conjugated polymer and the dopant species1,2. Thus, matching the electron affinity of one with the ionization potential of the other can allow effective doping3,4. Here we describe a different process—which we term ‘anion exchange’—that might offer improved doping levels. This process is mediated by an ionic liquid solvent and can be pictured as the effective instantaneous exchange of a conventional small p-type dopant anion with a second anion provided by an ionic liquid. The introduction of optimized ionic salt (the ionic liquid solvent) into a conventional binary donor–acceptor system can overcome the redox potential limitations described by Marcus theory5, and allows an anion-exchange efficiency of nearly 100 per cent. As a result, doping levels of up to almost one charge per monomer unit can be achieved. This demonstration of increased doping levels, increased stability and excellent transport properties shows that anion-exchange doping, which can use an almost infinite selection of ionic salts, could be a powerful tool for the realization of advanced molecular electronics. The limitations of conventional chemical doping of polymeric semiconductors can be overcome by adding a second ionic species into the system, leading to enhanced doping, electrical conductivity and stability.

Lithiophilic montmorillonite serves as lithium ion reservoir to facilitate uniform lithium deposition.

Abstract: The growing demand for lithium batteries with higher energy densities requires new electrode chemistries. Lithium metal is a promising candidate as the anode material due to its high theoretical specific capacity, negative electrochemical potential and favorable density. However, during cycling, low and uneven lithium ion concentration on the surface of anode usually results in uncontrolled dendrite growth, especially at high current densities. Here we tackle this issue by using lithiophilic montmorillonite as an additive in the ether-based electrolyte to regulate the lithium ion concentration on the anode surface and thus facilitate the uniform lithium deposition. The lithiophilic montmorillonite demonstrates a pumping feature that improves the self-concentrating kinetics of the lithium ion and thus accelerates the lithium ion transfer at the deposition/electrolyte interface. The signal intensity of TFSI- shows negligible changes via in situ Raman tracking of the ion flux at the electrochemical interface, indicating homogeneous ion distribution, which can lead to a stable and uniform lithium deposition on the anode surface. Our study indicates that the interfacial engineering induced by the lithiophilic montmorillonite could be a promising strategy to optimize the lithium deposition for next-generation lithium metal batteries.

Astrophysical Detection of the Helium Hydride Ion HeH

Abstract: During the dawn of chemistry1,2, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential. With their higher ionization potentials, the helium ions He2+ and He+ were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe’s first molecular bond in the helium hydride ion HeH+ through radiative association with protons. As recombination progressed, the destruction of HeH+ created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH+ ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered3 as long ago as 1925, but only in the late 1970s was the possibility that HeH+ might exist in local astrophysical plasmas discussed4–7. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH+. Here we report observations, based on advances in terahertz spectroscopy8,9 and a high-altitude observatory10, of the rotational ground-state transition of HeH+ at a wavelength of 149.1 micrometres in the planetary nebula NGC 7027. This confirmation of the existence of HeH+ in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination. Studies of the planetary nebula NGC 7027, using an upgraded spectrometer onboard a high-altitude observatory, have identified the rotational ground-state transition of the helium hydride ion—the first molecule to form after the Big Bang and an essential precursor to molecular hydrogen.

Quantifying lithium concentration gradients in the graphite electrode of Li-ion cells using operando energy dispersive X-ray diffraction

Abstract: Safe, fast, and energy efficient cycling of lithium ion batteries is desired in many practical applications. However, modeling studies predict steep Li+ ion gradients in the electrodes during cycling at the higher currents. Such gradients introduce heterogeneities in the electrodes, which make it difficult to predict cell lifetimes as different portions of the cell age at different rates. There is a dearth of experimental methods to probe these concentration gradients across the depth of the electrode. Here we use spatially resolved energy dispersive X-ray diffraction to obtain a “movie” of lithiation and delithiation in different sections of the cell and quantify lithium gradients that develop in a porous graphite electrode during cycling at a 1C rate. Inhomogeneity in the total Li content, and in the individual ordered LixC6 phases formed during lithium insertion into (and extraction from) the graphite, has been observed in an operando fashion. The complex dynamics of lithium-staging in graphite with the distinct front propagation of phase changes have been characterized and new features of these dynamics are highlighted here. As large Li+ ion gradients contribute to cell polarization, our results suggest that Li plating conditions can be met near the graphite electrode surface, even when the cell is charged at a moderate (1C) rate.