Showing papers on "Ion published in 2015"

Rational material design for ultrafast rechargeable lithium-ion batteries

Abstract: Rechargeable lithium-ion batteries (LIBs) are important electrochemical energy storage devices for consumer electronics and emerging electrical/hybrid vehicles. However, one of the formidable challenges is to develop ultrafast charging LIBs with the rate capability at least one order of magnitude (>10 C) higher than that of the currently commercialized LIBs. This tutorial review presents the state-of-the-art developments in ultrafast charging LIBs by the rational design of materials. First of all, fundamental electrochemistry and related ionic/electronic conduction theories identify that the rate capability of LIBs is kinetically limited by the sluggish solid-state diffusion process in electrode materials. Then, several aspects of the intrinsic materials, materials engineering and processing, and electrode materials architecture design towards maximizing both ionic and electronic conductivity in the electrode with a short diffusion length are deliberated. Finally, the future trends and perspectives for the ultrafast rechargeable LIBs are discussed. Continuous rapid progress in this area is essential and urgent to endow LIBs with ultrafast charging capability to meet huge demands in the near future.

High‐Performance Sodium Ion Batteries Based on a 3D Anode from Nitrogen‐Doped Graphene Foams

Abstract: A 3D N-doped graphene foam with a 6.8 at% nitrogen content is prepared by annealing a freeze-dried graphene oxide foam in ammonia. It is used as an anode in sodium ion batteries to deliver a high initial reversible capacity of 852.6 mA h g(-1) at 1 C between 0.02 and 3 V with a long-term retention of 69.7% after 150 cycles.

Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

Abstract: . Elemental compositions of organic aerosol (OA) particles provide useful constraints on OA sources, chemical evolution, and effects. The Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is widely used to measure OA elemental composition. This study evaluates AMS measurements of atomic oxygen-to-carbon (O : C), hydrogen-to-carbon (H : C), and organic mass-to-organic carbon (OM : OC) ratios, and of carbon oxidation state ( OS C) for a vastly expanded laboratory data set of multifunctional oxidized OA standards. For the expanded standard data set, the method introduced by Aiken et al. (2008), which uses experimentally measured ion intensities at all ions to determine elemental ratios (referred to here as "Aiken-Explicit"), reproduces known O : C and H : C ratio values within 20% (average absolute value of relative errors) and 12%, respectively. The more commonly used method, which uses empirically estimated H2O+ and CO+ ion intensities to avoid gas phase air interferences at these ions (referred to here as "Aiken-Ambient"), reproduces O : C and H : C of multifunctional oxidized species within 28 and 14% of known values. The values from the latter method are systematically biased low, however, with larger biases observed for alcohols and simple diacids. A detailed examination of the H2O+, CO+, and CO2+ fragments in the high-resolution mass spectra of the standard compounds indicates that the Aiken-Ambient method underestimates the CO+ and especially H2O+ produced from many oxidized species. Combined AMS–vacuum ultraviolet (VUV) ionization measurements indicate that these ions are produced by dehydration and decarboxylation on the AMS vaporizer (usually operated at 600 °C). Thermal decomposition is observed to be efficient at vaporizer temperatures down to 200 °C. These results are used together to develop an "Improved-Ambient" elemental analysis method for AMS spectra measured in air. The Improved-Ambient method uses specific ion fragments as markers to correct for molecular functionality-dependent systematic biases and reproduces known O : C (H : C) ratios of individual oxidized standards within 28% (13%) of the known molecular values. The error in Improved-Ambient O : C (H : C) values is smaller for theoretical standard mixtures of the oxidized organic standards, which are more representative of the complex mix of species present in ambient OA. For ambient OA, the Improved-Ambient method produces O : C (H : C) values that are 27% (11%) larger than previously published Aiken-Ambient values; a corresponding increase of 9% is observed for OM : OC values. These results imply that ambient OA has a higher relative oxygen content than previously estimated. The OS C values calculated for ambient OA by the two methods agree well, however (average relative difference of 0.06 OS C units). This indicates that OS C is a more robust metric of oxidation than O : C, likely since OS C is not affected by hydration or dehydration, either in the atmosphere or during analysis.

Peanut shell hybrid sodium ion capacitor with extreme energy–power rivals lithium ion capacitors

Abstract: This is the first report of a hybrid sodium ion capacitor (NIC) with the active materials in both the anode and the cathode being derived entirely from a single precursor: peanut shells, which are a green and highly economical waste globally generated at over 6 million tons per year. The electrodes push the envelope of performance, delivering among the most promising sodiation capacity–rate capability–cycling retention combinations reported in the literature for each materials class. Hence the resultant NIC also offers a state-of-the-art cyclically stable combination of energy and power, not only in respect to previously but also as compared to Li ion capacitors (LICs). The ion adsorption cathode based on Peanut Shell Nanosheet Carbon (PSNC) displays a hierarchically porous architecture, a sheet-like morphology down to 15 nm in thickness, a surface area on par with graphene materials (up to 2396 m2 g−1) and high levels of oxygen doping (up to 13.51 wt%). Scanned from 1.5–4.2 V vs. Na/Na+ PSNC delivers a specific capacity of 161 mA h g−1 at 0.1 A g−1 and 73 mA h g−1 at 25.6 A g−1. A low surface area Peanut Shell Ordered Carbon (PSOC) is employed as an ion intercalation anode. PSOC delivers a total capacity of 315 mA h g−1 with a flat plateau of 181 mA h g−1 occurring below 0.1 V (tested at 0.1 A g−1), and is stable at 10 000 cycles (tested at 3.2 A g−1). The assembled NIC operates within a wide temperature range (0–65 °C), yielding at room temperature (by active mass) 201, 76 and 50 W h kg−1 at 285, 8500 and 16 500 W kg−1, respectively. At 1.5–3.5 V, the hybrid device achieved 72% capacity retention after 10 000 cycles tested at 6.4 A g−1, and 88% after 100 000 cycles at 51.2 A g−1.

3d single-ion magnets

Abstract: One of the determining factors in whether single-molecule magnets (SMMs) may be used as the smallest component of data storage, is the size of the barrier to reversal of the magnetisation, Ueff. This physical quantity depends on the magnitude of the magnetic anisotropy of a complex and the size of its spin ground state. In recent years, there has been a growing focus on maximising the anisotropy generated for a single 3d transition metal (TM) ion, by an appropriate ligand field, as a means of achieving higher barriers. Because the magnetic properties of these compounds arise from a single ion in a ligand field, they are often referred to as single-ion magnets (SIMs). Here, the synthetic chemist has a significant role to play, both in the design of ligands to enforce propitious splitting of the 3d orbitals and in the judicious choice of TM ion. Since the publication of the first 3d-based SIM, which was based on Fe(II), many other contributions have been made to this field, using different first row TM ions, and exploring varied coordination environments for the paramagnetic ions.

Hydrogen bonding in ionic liquids

Abstract: Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (ρBCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X–H σ* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak through to very strong H-bonds.

First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers

Abstract: Hysteresis in current–voltage curves has been an important issue for conversion efficiency evaluation and development of perovskite solar cells (PSCs). In this study, we explored the ion diffusion effects in tetragonal CH3NH3PbI3 (MAPbI3) and trigonal (NH2)2CHPbI3 (FAPbI3) by first-principles calculations. The calculated activation energies of the anionic and cationic vacancy migrations clearly show that I– anions in both MAPbI3 and FAPbI3 can easily diffuse with low barriers of ca. 0.45 eV, comparable to that observed in ion-conducting materials. More interestingly, typical MA+ cations and larger FA+ cations both have rather low barriers as well, indicating that the cation molecules can migrate in the perovskite sensitizers when a bias voltage is applied. These results can explain the ion displacement scenario recently proposed by experiments. With the dilute diffusion theory, we discuss that smaller vacancy concentrations (higher crystallinity) and replacement of MA+ with larger cation molecules will be...

In-operando high-speed tomography of lithium-ion batteries during thermal runaway

Abstract: Prevention and mitigation of thermal runaway presents one of the greatest challenges for the safe operation of lithium-ion batteries. Here, we demonstrate for the first time the application of high-speed synchrotron X-ray computed tomography and radiography, in conjunction with thermal imaging, to track the evolution of internal structural damage and thermal behaviour during initiation and propagation of thermal runaway in lithium-ion batteries. This diagnostic approach is applied to commercial lithium-ion batteries (LG 18650 NMC cells), yielding insights into key degradation modes including gas-induced delamination, electrode layer collapse and propagation of structural degradation. It is envisaged that the use of these techniques will lead to major improvements in the design of Li-ion batteries and their safety features.

Eu(III)-functionalized MIL-124 as fluorescent probe for highly selectively sensing ions and organic small molecules especially for Fe(III) and Fe(II).

Abstract: A layerlike MOF (MIL-124, orGa2(OH)4(C9O6H4)) has been prepared and chosen as a parent compound to encapsulate Eu3+ cations by one uncoordinated carbonyl group in its pores. The Eu3+-incorporated sample (Eu3+@MIL-124) is fully characterized, which shows excellent luminescence and good fluorescence stability in water or other organic solvents. Subsequently, we choose Eu3+@MIL-124 as sensitive probe for sensing metal ions, anions, and organic small molecules because of its robust framework. Studying of the luminescence properties reveals that the complex Eu3+@MIL-124 was developed as a highly selective and sensitive probe for detection of Fe3+ (detection limit, 0.28 μM) and Fe2+ ions through fluorescence quenching of Eu3+ and MOF over other metal ions. In connection to this, a probable sensing mechanism was also discussed in this paper. In addition, when Eu3+@MIL-124 was immersed in the different anions solutions and organic solvents, it also shows highly selective for Cr2O72–(detection limit, 0.15 μM)and a...

Dual nature of the excited state in organic–inorganic lead halide perovskites

Abstract: The rapid increase in efficiency of methylammonium lead halide perovskite solar cells necessitates further investigation into the nature of perovskite absorption features and optical properties. Films obtained from the deposition of solutions containing lead halides and the CH3NH3+ organic cation is known to yield the CH3NH3PbI3 perovskite structure upon annealing. In examining the precursor solution used in the processing of CH3NH3PbI3 solar cells, we find that Pb2+ readily forms plumbate complexes in the presence of excess iodide ions and exhibits characteristic absorption bands at 370 (PbI3−) and 425 nm (PbI42−). Through comparative spectral analysis of the absorption features of charge transfer complexes in the solution phase and the final solid-state perovskite films, we are able to fully classify the absorption features in the excited state of CH3NH3PbI3 across the transient absorption spectrum recorded following laser pulse excitation. In particular, we attribute the broad photoinduced absorption to a charge-transfer excited state, and show correlation between the photoinduced absorption and 480 nm bleach signals. These observations lead us to propose a band structure composed of two distinct transitions that is consistent with the various spectral features and kinetic behavior of the CH3NH3PbI3 excited state. Characterization of this unique dual excited state nature provides further insight into the optoelectronic behavior of hybrid lead halide perovskite films and thus aids in elucidating their exceptional photovoltaic properties.

A common single-site Pt(II)-O(OH)x- species stabilized by sodium on "active" and "inert" supports catalyzes the water-gas shift reaction.

Abstract: While it has long been known that different types of support oxides have different capabilities to anchor metals and thus tailor the catalytic behavior, it is not always clear whether the support is a mere carrier of the active metal site, itself not participating directly in the reaction pathway. We report that catalytically similar single-atom-centric Pt sites are formed by binding to sodium ions through −O ligands, the ensemble being equally effective on supports as diverse as TiO2, L-zeolites, and mesoporous silica MCM-41. Loading of 0.5 wt % Pt on all of these supports preserves the Pt in atomic dispersion as Pt(II), and the Pt–O(OH)x– species catalyzes the water-gas shift reaction from ∼120 to 400 °C. Since the effect of the support is “indirect,” these findings pave the way for the use of a variety of earth-abundant supports as carriers of atomically dispersed platinum for applications in catalytic fuel-gas processing.

Interpenetrated Gel Polymer Binder for High Performance Silicon Anodes in Lithium-Ion Batteries

Abstract: Silicon has attracted ever-increasing attention as a high-capacity anode material in Li-ion batteries owing to its extremely high theoretical capacity. However, practical application of silicon anodes is seriously hindered by its fast capacity fading as a result of huge volume changes during the charge/discharge process. Here, an interpenetrated gel polymer binder for high-performance silicon anodes is created through in-situ crosslinking of water-soluble poly(acrylic acid) (PAA) and polyvinyl alcohol (PVA) precursors. This gel polymer binder with deformable polymer network and strong adhesion on silicon particles can effectively accommodate the large volume change of silicon anodes upon lithiation/delithiation, leading to an excellent cycling stability and high Coulombic efficiency even at high current densities. Moreover, high areal capacity of ∼4.3 mAh/cm2 is achieved based on the silicon anode using the gel PAA–PVA polymer binder with a high mass loading. In view of simplicity in using the water soluble gel polymer binder, it is believed that this novel binder has a great potential to be used for high capacity silicon anodes in next generation Li-ion batteries, as well as for other electrode materials with large volume change during cycling.

Using lanthanide ions in molecular bioimaging

Abstract: Trivalent lanthanide ions offer remarkable opportunities in the design of bioimaging agents: this review presents an accessible discussion of their application in both optical and magnetic resonance imaging. Aspects of molecular design, control over key physical properties and biological compatibility are discussed in this context, together with developments and opportunities as responsive probes and in multimodal imaging.

Ion Mobility-Mass Spectrometry: Time-Dispersive Instrumentation

Abstract: The field of ion mobility-mass spectrometry (IM-MS) has grown with significant momentum in recent years in both fundamental advances and pioneering applications. A search of the terms “ion mobility” and “mass spectrometry” returns more than 2 000 papers, with over half of these being published in the past 4 years (Figure ​(Figure1,1, left). This increased interest has been motivated in large part by improved technologies which have enabled contemporary IM-MS to be amendable to a variety of samples in biology and medicine with high sensitivity, resolving power, and sample throughput. Figure 1 (Left) Histogram of the number of publications published per year in ion mobility and ion mobility-mass spectrometry. Note that the scale is truncated at 300 to highlight the number of publications specifically utilizing IM-MS. Further distinction is ... Highlights of the historical development of the field are presented in Figure ​Figure1,1, right. Ion mobility and mass spectrometry trace their foundations to the X-ray experiments of Thomson and Rutherford in the late 1800s,1 with Tyndall making significant improvements in the analytical capabilities of ion mobility around the 1930s.2,3 During this early era of discovery, a variety of ion mobility experimental parameters were explored, including differences in pressure,4,5 temperature,6,7 electric field,8 and the ion residence time (age) in the drift region.9 Hybrid IM-MS instruments of various configurations were developed by several groups in the 1960s to study gas-phase ion chemistry.10−12 Ion mobility measurements were used by Dole in the earliest development of electrospray ionization (ESI).13,14 Following commercialization,15 ion mobility instrumentation was used for structure-based characterization16 and differentiation of chemical isomers.17,18 In 1982, laser ionization was demonstrated with ion mobility as a means of generating simplified mobility spectra based on protonated species.19 The features which define modern IM-MS, namely, high resolution, high sensitivity, and broad sample compatibility, were developed in the 1990s and coincided with the rapid development of MS in response to the introduction of ESI and MALDI sample ionization.20−22 The last 2 decades saw significant improvements made in the coupling of IM to MS, notably the use of electrodynamic fields to confine, transfer, and focus ions across disparate pressure regions into high vacuum. An interesting observation to be made in this historical analysis is that many of the features we associate with contemporary ion mobility technology were key aspects of early ion mobility instrument design. Several noteworthy reviews of IM-MS have been published, which cover many aspects of the IM-MS technique and range of applications.23−28 A number of influential books covering various aspects of the ion mobility field are also available.29−34 Of particular relevance is Mason and McDaniel’s Transport Properties of Ions in Gases,35 which was recently republished by the American Society for Mass Spectrometry in their classic books series. Though last revised in 1988, this book is still widely considered the seminal treatment of the motion of ions in gases. The technologies and application areas which IM-MS now encompasses has expanded to such a breadth that new reviews covering IM-MS and related areas now appear every few years in the literature. A comprehensive and critical review of the field as a whole is no longer appropriate nor tractable, and as such it is the intent of this review to focus primarily on recent developments made with regard to temporally dispersive ion mobility techniques (drift tubes and traveling wave separators), with an emphasis on their use specifically in IM-MS instrumentation and methods. This focus is selected because of the recent commercial offerings in this regard that have become widely used in many research environments. The present review is not intended to be comprehensive of the ion mobility advances but rather focuses on time-dispersive IM-MS instrumentation over the past few years.

Structure of the high voltage phase of layered P2-Na2/3−z[Mn1/2Fe1/2]O2 and the positive effect of Ni substitution on its stability

Abstract: A combination of operando X-ray diffraction, pair distribution function (PDF) analysis coupled with electrochemical measurements and Mossbauer spectroscopy elucidates the nature of the phase transitions induced by insertion and extraction of sodium ions in P2-Na0.67[NiyMn0.5+yFe0.5−2y]O2 (y = 0, 0.10, 0.15). When phase transitions are avoided, the optimal cathode material – P2-Na0.67Fe0.2Mn0.65Ni0.15O2 – delivers 25% more energy than the unsubstituted material, sustaining high specific energy (350 Wh kg−1) at moderate rates and maintains 80% of the original energy density after 150 cycles – a significant improvement in performance vs. the unsubstituted analogue. The crystal structure of the high voltage phase is solved for the first time by X-ray PDF analysis of P2-Na0.67−zFe0.5Mn0.5O2 (where z ∼ 0.5), revealing that migration of the transition metals – particularly Fe3+ – into tetrahedral sites in the interlayer space occurs at high potential. This results in new short range order between two adjacent layers. Although the transition metal migration is reversible as proven by electrochemical performance, it induces a large disfavourable cell polarization. The deleterious high voltage transition is mitigated by substitution of Fe3+ by Mn4+/Ni2+, giving rise to better cycling performance. Moreover, as demonstrated by 57Fe Mossbauer spectroscopy, the much lower ratio of Fe4+O6 to Fe3+O6 observed systematically across the range of Ni content – compared to the values expected from a purely ionic model – suggests redox activity involves the O-2p orbitals owing to their overlap with the transition metal-3d orbitals.

Microporous and Mesoporous Materials

Abstract: Ion exchange of nanoporous (e.g., zeolite) membranes is of increasing importance in their applications as separation devices and catalytic reactors. Ion exchange processes in zeolite membranes are significantly limited by slow hydrated-ion transport rates and the low liquid-solid interfacial area available in com- parison to ion exchange of zeolites in powdered form, thereby leading to long membrane processing and regeneration times. Here, we consider ion exchange processes in zeolite membranes in more detail, and show the much higher efficacy of a vacuum-assisted liquid-vapor 'flow-through' method in compar- ison to both the conventional 'immersion/counter-diffusion' method as well as a liquid-liquid flow- through method. Na-MFI zeolite disk membranes, made by both in situ and seeded growth, were ion- exchanged with Ga 3+ ,Z n 2+ , and Pt 2+ ions in the temperature range of 23-70 C and exchange times of 5-24 h. The penetration of these ions into the zeolite membranes was investigated in detail by energy- dispersive X-ray (EDX) spectroscopy. Surprisingly, the quantity of exchanged ions in the membranes via the vacuum-assisted 'flow-through' technique is found to exceed that achieved by the other two methods by up to a factor of ten, with the liquid-liquid technique being the least efficient. Higher tem- peratures and longer ion exchange times increased the ion exchange efficiency in the vacuum-assisted method. Chemical analysis of the condensed permeate solution by inductively-coupled plasma (ICP) mass spectrometry revealed that both the original Na

Solving the Capacitive Paradox of 2D MXene using Electrochemical Quartz-Crystal Admittance and In Situ Electronic Conductance Measurements

Abstract: Fast ion adsorption processes in supercapacitors enable quick storage/delivery of significant amounts of energy, while ion intercalation in battery materials leads to even larger amounts of energy stored, but at substantially lower rates due to diffusional limitations. Intercalation of ions into the recently discovered 2D Ti3C2Tx (MXene) occurs with a very high rate and leads to high capacitance, posing a paradox. Herein, by characterizing the mechanical deformations of MXene electrode materials at various states-of-charge with a variety of cations (Li, Na, K, Cs, Mg, Ca, Ba, and three tetra­alkylammonium cations) during cycling by electrochemical quartz-crystal admittance (EQCA, quartz-crystal microbalance with dissipation monitoring) combined with in situ electronic conductance and electrochemical impedance, light is shone on this paradox. Based on this work, it appears that the capacitive paradox stems from cationic insertion, accompanied by significant deformation of the MXene particles, that occurs so rapidly so as to resemble 2D ion adsorption at solid-liquid interfaces. The latter is greatly facilitated by the presence of water molecules between the MXene sheets.

Two-Dimensional Transition Metal Dichalcogenide Monolayers as Promising Sodium Ion Battery Anodes

Abstract: A family of transition metal dichalcogenide (TMD) nanosheets has recently shown its potential as negative electrodes in lithium ion batteries (LIBs). Herein, Na ion adsorption and migration properties as well as the possibility of phase transition induced by the Na adsorption on TiS2, VS2, CrS2, CoTe2, NiTe2, ZrS2, NbS2, and MoS2 are predicted using first-principles calculations. In terms of average voltage and capacity, M = Ti, Zr, Nb, and Mo are found to be suitable as anodes for sodium ion batteries (SIBs) with voltages of 0.49–0.95 V and theoretical capacities of 260–339 mA h g–1. Among the latter four screened TMDs, in particular, TiS2 and NbS2 are expected to maintain the same configurational phase upon sodiation (favorable kinetics) with Na ion migration barriers of 0.22 and 0.07 eV, respectively, suggesting that these TMD compounds could be promising for high-power energy storage applications. It is shown that a proper treatment of phase transitions during sodiation, though often neglected in the ...

Design and construction of three dimensional graphene-based composites for lithium ion battery applications

Abstract: Three dimensional graphene-based composites (3DGCs) have attracted significant attention for lithium ion battery applications due to their unique structures and attractive properties. A large number of 3DGCs with novel structures and functions have been developed in the past few years. This review summarizes the current progress of 3DGCs, including their preparation and application in lithium ion batteries, especially from the viewpoint of structural and interfacial engineering, which have attracted more and more attention for the development of high performance electrode systems.

Influence of Covalency on the Mn4+ 2Eg→4A2g Emission Energy in Crystals

Abstract: + ( C C0 ) 2 (where (B, C (B0, C0) are the Racah parameters of the Mn 4+ ions in a crystal (free state), respectively) was recently introduced that allows for establishing a linear relationship between β1 and the energy of the 2Eg level. This makes it possible to understand the large variation in the energy of the 2 Eg → 4 A2g emission transition that is frequently encountered in the spectroscopy of the Mn 4+ ions in solids.

Negative hydrogen ion production mechanisms

Abstract: Negative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed.

Origins of hydration lubrication.

Abstract: Why is friction in healthy hips and knees so low? Hydration lubrication, according to which hydration shells surrounding charges act as lubricating elements in boundary layers (including those coating cartilage in joints), has been invoked to account for the extremely low sliding friction between surfaces in aqueous media, but not well understood. Here we report the direct determination of energy dissipation within such sheared hydration shells. By trapping hydrated ions in a 0.4–1 nm gap between atomically smooth charged surfaces as they slide past each other, we are able to separate the dissipation modes of the friction and, in particular, identify the viscous losses in the subnanometre hydration shells. Our results shed light on the origins of hydration lubrication, with potential implications both for aqueous boundary lubricants and for biolubrication. Subnanometre-thick hydration layers can greatly reduce the friction between two sliding objects, an effect termed hydration lubrication. Here, Ma et al.determine the frictional dissipation in such layers, which can account for the observed lubricating action of hydrated ions or zwitterions.

The coupling between stability and ion pair formation in magnesium electrolytes from first-principles quantum mechanics and classical molecular dynamics.

Abstract: In this work we uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potentials, e.g., at the metal anode. Through comprehensive calculations using both first-principles as well as well-benchmarked classical molecular dynamics over a matrix of electrolytes, covering solvents and salt anions with a broad range in chemistry, we elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. We find that Mg electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. Specifically, we observe that, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+ → Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susce...