Small Cluster Ions Research Articles

Design of non-fluorinated proton exchange membranes from Poly(Terphenyl fluorenyl isatin) with fluorene-linked sulfonate groups and microblock structures

Proton exchange membranes (PEMs) are essential components in energy storage and conversion devices, such as fuel cells and electrolyzers. In this study, we developed a series of non-fluorinated PEMs from poly (terphenyl fluorenyl isatin) with fluorene-pendent disulfonate groups. These polymers feature a microblock structure composed of hydrophobic blocks, hydrophilic blocks, and alternating blocks, arising from the differences in reactivity, concentration, and solubility between the hydrophobic p-terphenyl and hydrophilic disulfonated fluorene monomers. As a result, the sulfonic acid groups are unevenly distributed along the polymer chains, forming densely charged regions (IEC = 3.52 meq/g) with large ion clusters and lightly charged regions (IEC = 2.16 meq/g) with small ion clusters. This microstructure, combined with the degree of sulfonation, significantly influences the overall properties of the membranes, including robust mechanical strength (47.1–63.2 MPa), high thermal stability (up to 270 °C), low swelling ratio (18–25 % at 80 °C), and high proton conductivity (136–169 mS/cm in deionized water at 80 °C). The PFLSH60 membrane demonstrated comparable fuel cell performance to Nafion 212. Its hydrogen crossover current density was more than two times lower (0.86 mA/cm2 for PFLSH60 compared to 1.83 mA/cm2 for Nafion 212) under testing conditions of 80 °C and 100 % RH. This significantly reduced crossover improves fuel utilization in fuel cell stacks. This work offers valuable insights into the design of robust, high-performance PEMs by systematically analyzing the relationships between membrane structure, properties, and performance.

Master equation modeling of water dissociation in small ionic water clusters: Ag+(H2O) n , n = 4-6.

We model temperature-dependent blackbody infrared radiative dissociation (BIRD) rate coefficients of Ag+(H2O) n , n = 4-6, a system with loosely bound water molecules. We employ a master equation modeling (MEM) approach with consideration of absorption and emission of blackbody radiation, comparing single and multiple-well descriptions. The unimolecular dissociation rate coefficients are obtained using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory, employing two approaches to model the sum of states in the transition state, the rigid activated complex (RAC) and the phase space limit (PSL) approach. A genetic algorithm is used to find structures of low-lying isomers for the kinetic modeling. We show that the multiple-well MEM approach with PSL RRKM in the All Wells and Transition States Are Relevant (AWATAR) variant provides a reliable description of Ag+(H2O) n BIRD, in agreement with previously published experimental data. Higher-lying isomers contribute significantly to the overall dissociation rate coefficient, underlying the importance of the multiple-well ansatz in which all isomers are treated on the same footing.

Investigation of ion association kinetics in Na2SO4-H2O by excess Raman spectroscopy and 2D correlation Raman spectroscopy

The ion association of salts aqueous solutions have long captivated the attention of researchers within the field of physical chemistry. In this paper, we have performed a comprehensive analysis of ion interactions in sodium sulfate (Na2SO4) aqueous solutions using a combination of high-resolution techniques, including excess (ERS) and two-dimensional correlation (2DCRS) Raman spectroscopy in conjunction with molecular dynamics (MD) calculations. The Raman spectrum shows that two inflection points in the Raman shift of the O–H vibration are observed with the increase in Na2SO4 concentration. Simultaneously, a new peak of the SO42- vibration appears at first inflection point, representing the formation of ion association. Further analysis based on ERS and 2CRS reveals that these two inflection points correspond respectively to the formation of ion pairs (CIPs) and small ion clusters. Importantly, MD simulations confirm the above experimental results. Our study provides evidence for ion association and clustering in aqueous in salt ion aqueous solutions.

Hg-Hg bonding and its influence on the stability of (HgS)n clusters.

Pulsed laser ablation of a HgS(s) precursor shows the formation of small cluster ions, (HgS)n=2-4+, together with HgSn=1-8± and [(HgS)n + Sm]±. The computed structure, atomization energy, and HOMO-LUMO gap energy values of the lowest energy ring singlet show stable (HgS)n=2-8. However, the computed bond conductance of the Hg-Hg bond in (HgS)n shows a high value for (HgS)n=2-4 (ξ = 1.072-0.122), whereas it is low for (HgS)n=5-8 (ξ = 0.039-0.006) and decreases significantly as the ring expands, indicating that (HgS)n≥5 is unstable. It evidences that the weak chemical bonding between Hg2+-Hg2+ closed shell (5d10-5d10) electrons plays a significant role in the stability of ring (HgS)n=2-4. Thus, it validates the experimental observation of stable cluster ions up to (HgS)4+. In contrast, the low energy chain triplet (HgS)n=2-8 shows a progressive increase in stability and bond conductance with chain length, indicating sustained mercurophilic interactions in long chain clusters like its crystal structure. Furthermore, the lowest/low energy isomers of HgSn=1-8 have been computed for their energetics, HOMO-LUMO gaps, and electron affinity using DFT-B3LYP/PBE0 methods.

Molecular dynamics study with COMPASS II forcefield on nucleation and growth mechanism of sodium chloride in supercritical water

Supercritical water gasification (SCWG) is a promising technology for converting and utilizing high-salt organic waste, while salt deposition problems seriously hinder its industrial application. In this work, the formation and evolution of sodium chloride (NaCl) clusters in supercritical water (SCW) at the range of (0.1–0.3) g·cm−3 and (673–1073) K are investigated using molecular dynamics simulations. The findings demonstrate that the nucleation and growth process can be divided into three stages: ion pairs, small ionic clusters, and large clusters. Nucleation processes are completed within the initial 20 ps, with the nucleation rate of NaCl in SCW reaching magnitudes of 1036 m−3·s−1, exhibiting an increasing trend with temperature and density. Lower densities and higher temperatures facilitate NaCl nucleation, and clusters grown at lower densities exhibit a more compact structure.

Changes in the new particle formation and shrinkage events of the atmospheric ions during the COVID-19 lockdown

Impacts of environmental changes at Pune, India during the lockdown period imposed due to the Covid-19 pandemic, on the characteristics of the atmospheric ions and the new particle formation (i.e. the formation of molecular clusters and their subsequent growth to larger sizes) and shrinkage events have been investigated. The increase in the small and big cluster ion concentrations and the decrease in intermediate ion concentrations observed during the lockdown period have been associated with the decrease in the aerosols and precursor gases, respectively. During the NPF events, the nucleation mode particles of both polarities grow in size. However, during the unique shrinkage events observed here, particles increase in concentration but do not grow in size during the morning-to-noon period and shrink in the noon-to-evening period during the lockdown period. Simultaneously, the concentration of particles of >25 nm decrease i during the morning hours and increase during the afternoon hours .On the shrinkage event days, solar irradiance is higher and relative humidity is lower throughout the day than on the NPF/no-event days. Occurrence of shrinkage events has been proposed to be associated with the change in saturation vapour pressure of different chemical species with temperature/solar irradiance.

Infrared spectroscopy of ions and ionic clusters upon ionization of ethane in helium droplets.

Helium droplets are unique hosts for isolating diverse molecular ions for infrared spectroscopic experiments. Recently, it was found that electron impact ionization of ethylene clusters embedded in helium droplets produces diverse carbocations containing three and four carbon atoms, indicating effective ion-molecule reactions. In this work, similar experiments are reported but with the saturated hydrocarbon precursor of ethane. In distinction to ethylene, no characteristic bands of larger covalently bound carbocations were found, indicating inefficient ion-molecule reactions. Instead, the ionization in helium droplets leads to formation of weaker bound dimers, such as (C2H6)(C2H4)+, (C2H6)(C2H5)+, and (C2H6)(C2H6)+, as well as larger clusters containing several ethane molecules attached to C2H4 +, C2H5 +, and C2H6 + ionic cores. The spectra of larger clusters resemble those for neutral, neat ethane clusters. This work shows the utility of the helium droplets to study small ionic clusters at ultra-low temperatures.

Geometric Analysis of Shapes in Ion Mobility-Mass Spectrometry.

Experimental ion mobility-mass spectrometry (IM-MS) results are often correlated to three-dimensional structures based on theoretical chemistry calculations. The bottleneck of this approach is the need for accurate values, both experimentally and theoretically predicted. Here, we continue the development of the trend-based analyses to extract structural information from experimental IM-MS data sets. The experimental collision cross-sections (CCSs) of synthetic systems such as homopolymers and small ionic clusters are investigated in terms of CCS trends as a function of the number of repetitive units (e.g., degree of polymerization (DP) for homopolymers) and for each detected charge state. Then, we computed the projected areas of expanding but perfectly defined geometric objects using an in-house software called MoShade. The shapes were modeled using computer-aided design software where we considered only geometric factors: no atoms, mass, chemical potentials, or interactions were taken into consideration to make the method orthogonal to classical methods for 3D shape assessments using time-consuming computational chemistry. Our modeled shape evolutions favorably compared to experimentally obtained CCS trends, meaning that the apparent volume or envelope of homogeneously distributed mass effectively modeled the ion-drift gas interactions as sampled by IM-MS. The CCSs of convex shapes could be directly related to their surface area. More importantly, this relationship seems to hold even for moderately concave shapes, such as those obtained by geometry-optimized structures of ions from conventional computational chemistry methods. Theoretical sets of expanding beads-on-a-string shapes allowed extracting accurate bead and string dimensions for two homopolymers, without modeling any chemical interactions.

A simultaneous dual-polarity mass spectrometer with electron start for MeV-SIMS

The Capillary Heavy Ion MeV-SIMS Probe (CHIMP) at ETH Zürich has been redesigned with a second mass spectrometer and symmetric extraction to enable simultaneous analysis of positive and negative secondary ions. Secondary electrons are deflected within the negative spectrometer and detected independently. The fast secondary electron signal is used as a start signal for both Time-of-Flight mass spectrometers.The new setup enables the simultaneous acquisition and analysis of both secondary ion polarities emitted under identical conditions from the same sample location. This allows to study correlations between secondary ions of different polarities emitted from a single primary ion impact. Measurements with small primary Cn cluster ions show the influence of cluster size on the multiplicity of secondary ion emission. Furthermore, a cluster effect in the ratio between positive and negative ion yields of corresponding secondary ion species is identified, with the ratio approaching parity for larger cluster sizes n.

Material and Charge Transport of Large Organic Salt Clusters and Nanoparticles in Electrospray Ion Beam Deposition.

Electrospray ion beam deposition (ES-IBD) or ion soft landing has been demonstrated as a technique suitable for processing nonvolatile molecules in vacuum under perfectly controlled conditions, an approach also desirable for the deposition of nanoparticles. Here, we present results from several approaches to generate, characterize, and deposit nanoparticle ion beams in vacuum for deposition. We focus on cluster ion beams generated by ESI of organic salt solutions. Small cluster ions of the salts appear in the mass spectra as defined peaks. In addition, we find nanoparticle-sized aggregates, appearing as a low intensity background at high m/z-ratio, and show by IBD experiments that these clusters carry the major amount of material in the ion beam. This transition from clusters to nanoparticles, and their successful deposition, shows that ES-IBD can in principle handle ion beams of very heavy and highly charged nanoparticles. In related experiments, however, we found the deposition of nanoparticles from dispersions to be of low reproducibility, due to the lack of control by mass spectrometry.

Anhydrous proton conductivity of electrospun phosphoric acid-doped PVP-PVDF nanofibers and composite membranes containing MOF fillers.

A high-temperature proton exchange membrane was fabricated based on polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) blend polymer nanofibers. Using electrospinning method, abundant small ionic clusters can be formed and agglomerated on membrane surface, which would facilitate the proton conductivity. To further enhance the conductivity, phosphoric acid (PA) retention as well as mechanical strength, sulfamic acid (SA)-doped metal–organic framework MIL-101 was incorporated into PVP-PVDF blend nanofiber membranes. As a result, the anhydrous proton conductivity of the composite SA/MIL101@PVP-PVDF membrane reached 0.237 S cm−1 at 160 °C at a moderate acid doping level (ADL) of 12.7. The construction of long-range conducting network by electrospinning method combined with hot-pressing and the synergistic effect between PVP-PVDF, SA/MIL-101 and PA all contribute to the proton conducting behaviors of this composite membrane.

A comparison of ether- and alkyl-imidazolium-based ionic liquids diluted with CH3CN: A combined FTIR and DFT study

Ether-based functionalized ionic liquids (ILs) show great potential in electrochemical devices and energy applications, but their microscopic behaviour is seldom investigated. In this work, the microscopic structures of two imidazolium-based ILs (1-methoxyethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EOMIMFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI)) and their hydrogen bonding interactions with acetonitrile (CH3CN) at various concentrations are investigated by using attenuated total reflection infrared spectroscopy (ATR-FTIR), excess infrared spectroscopy and quantum chemical calculations. Additionally, the effects of introducing a functional group, i.e., an ether group, on the properties of the IL are explored. The main conclusions are as follows: (1) [EOMIM]+ can form an intra-molecular hydrogen bond with C2H or C5H, and the former is more stable. (2) The introduction of an ether group to the cation weakens the hydrogen bonding interactions between the cation and anion/CH3CN. (3) The introduction of an ether group to the cation changes the interaction sites between the ILs and CH3CN. In the EMIMFSI–CH3CN system, C2H is the main interaction site. In the EOMIMFSI–CH3CN system, the interaction site with CH3CN changes from C2H in the [EOMIM]+–CH3CN complex to C4H in the ion pair–CH3CN/ion cluster–CH3CN complex. (4) Some complexes such as ion clusters, small ion clusters and ion pairs in the two systems are identified by excess infrared spectroscopy and quantum chemical calculations.

Geometry and Stability of Small Gold Cluster Ions by Graph Theory and Hückel model

Structure and stability of the gold cluster ions of which skeleton are synthesized as a complex were analyzed using the Hückel method based on graph theory. Hückel Energy (HE) and Topological Resonance Energy (TRE) were determined for neutral, positive ion, and negative ion clusters, where all the isomers of the gold cluster up to octamer were considered. Since some graphically designed isomers include bonds that cannot be realized in three- dimensional space, the screening was carried out by a molecular force field calculation with LAMMPS (lammps.sandia.gov/.). Among the isomers thus obtained, both HE and TRE were most stable when the tetramer was Au4 2 + with a tetrahedral structure, and with the hexamer, Au6 2+ with two tetrahedrons sharing one side. The complexes with these structures have actually been synthesized. On the other hand, the synthesis example of the most stable cluster for octamer Au8 has not been reported.

Particle nucleation and growth in dusty plasmas: On the importance of charged-neutral interactions

Particle nucleation and growth in gases involves nucleation via growth of small molecular or ionic clusters, growth by vapor deposition on nanoparticle surfaces, and coagulation due to collisions between nanoparticles. Under typical conditions that apply in low-pressure nonthermal plasmas, all three of these phenomena are dominated by interactions between negatively charged bodies (anion clusters or nanoparticles) and neutral ones (molecules or nanoparticles), with collision rates enhanced by the dipole or image potential induced in the neutral collision partner. The current understanding of these phenomena is reviewed, with a focus on silane-containing plasmas in which silicon nanoparticles nucleate and grow.

Multivalent anions as universal latent electron donors.

Electrodes with low work functions are required to efficiently inject electrons into semiconductor devices. However, when the work function drops below about 4electronvolts, the electrode suffers oxidation in air, which prevents its fabrication in ambient conditions. Here we show that multivalent anions such as oxalate, carbonate and sulfite can act as powerful latent electron donors when dispersed as small ion clusters in a matrix, while retaining their ability to be processed in solution in ambient conditions. The anions in these clusters can even n-dope the semiconductor core of π-conjugated polyelectrolytes that have low electron affinities, through a ground-state doping mechanism that is further amplified by a hole-sensitized or photosensitized mechanism in the device. A theoretical analysis of donor levels of these anions reveals that they are favourably upshifted from ionic lattices by a decrease in the Coulomb stabilization of small ion clusters, and by irreversibility effects. We attain an ultralow effective work function of 2.4electronvolts with the polyfluorene core. We realize high-performance, solution-processed, white-light-emitting diodes and organic solar cells using polymer electron injection layerswith these universal anion donors, demonstrating a general approach to chemically designed and ambient-processed Ohmic electron contacts for semiconductor devices.

Specific Ion Effects on Hydrogen-Bond Rearrangements in the Halide-Dihydrate Complexes.

Small aqueous ionic clusters represent ideal systems to investigate the microscopic hydrogen-bonding structure and dynamics in ion hydration shells. In this context, halide-dihydrate complexes are the smallest systems where the interplay between halide-water and water-water interactions can be studied simultaneously. Here, quantum molecular dynamics simulations unravel specific ion effects on the temperature-dependent structural transition in X-(H2O)2 complexes (X = Cl, Br, and I), which is induced by the breaking of the water-water hydrogen bond. A systematic analysis of the hydrogen-bonding rearrangements at low temperature provides fundamental insights into the competition between halide-water and water-water interactions depending on the properties of the halide ion. While the halide-water hydrogen-bond strength decreases going from Cl-(H2O)2 to I-(H2O)2, the opposite trend in observed in the strength of the water-water hydrogen-bond, suggesting that nontrivial many-body effects may also be at play in the hydration shells of halide ions in solution, especially in frustrated systems (e.g., interfaces) where the water molecules can have dangling OH bonds.

Direct hydroxylation of benzene to phenol mediated by nanosized vanadium oxide cluster ions at room temperature.

Gas-phase vanadium oxide cluster cations and anions are prepared by laser ablation. The small cluster ions (<1000 amu) are mass-selected using a quadrupole mass filter and reacted with benzene in a linear ion trap reactor; large clusters (>1000 amu) with no mass selection are reacted with C6H6 in a fast flow reactor. Rich product variety is encountered in these reactions, and the reaction channels for small cationic and anionic systems are different. For large clusters, the reactivity patterns of (V2O5) n+ (n = 6-25) and (V2O5) n O- (n = 6-24) cluster series are very similar to each other, indicating that the charge state has little influence on the oxidation of benzene. In sharp contrast to the dramatic changes of reactivity of small clusters, a weakly size dependent reaction behavior of large (V2O5)6-25+ and (V2O5)6-24O- clusters is observed. Therefore, the charge state and the size are not the major factors influencing the reactivity of nanosized vanadium oxide cluster ions toward C6H6, which is not common in cluster science. In the reactions with benzene, the small and large reactive vanadium oxide cations show similar reactivity of hydroxyl radicals (OH•) toward C6H6 at higher and lower temperatures, respectively; different numbers of vibrational degrees of freedom and the released energy during the formation of adduct complexes can explain this intriguing correlation. The reactions investigated herein might be used as the models of how to realize the partial oxidation of benzene to phenol in a single step, and the observed mechanisms are helpful to understand the corresponding heterogeneous reactions, such as those over vanadium oxide aerosols and vanadium oxide catalysts.

Electrophoretic fabrication of proton exchange membranes in fuel cells

For the first time, the fabrication of proton exchange membranes in fuel cells via an electrophoretic deposition (EPD) method is demonstrated, taking extensively researched sulfonated poly(ether ether ketone) (SPEEK) membranes as a paradigm. The membranes are obtained via depositing SPEEK ionomers, dispersed in a mixed solvent consisting dimethylsulfoxide (DMSO) and water, onto the anodic electrode under different applied voltages ranging from 15 to 25 V. The electrodeposited membranes show a number of differences from cast SPEEK membranes, e.g. smaller ionic clusters, higher surface roughness, higher water uptake and higher dry density. Particularly, the SPEEK membrane electrodeposited at 25 V reaches a proton conductivity of 0.11 S cm−1 at 70 °C and 100% RH, remarkably surpassing its cast counterpart.

Ion Coulomb crystal in a polychromatic optical superlattice

We demonstrate that the earlier suggested new all-optical method of creating long-term small (containing two or three particles) ion clusters using the rectified optical forces (RFs) can be used to create cold trapped Coulomb crystals (consisting of several tens of resonant ions). The results of the supercomputer simulations of the dynamics of a mercury ion cloud in a polychromatic optical superlattice (induced by RFs) are presented and analysed. Such a cloud (including 49 ions) in the absence of the optical field expands rapidly (during the characteristic time of the order of ) as a result of the Coulomb explosion. It is shown that the polychromatic optical field can result in the ‘quenching’ of the Coulomb explosion and crystallisation of the ion cloud: creation of a quasi-2D array of ordered and strongly coupled cold ions (with the Coulomb coupling parameter and temperature ∼10−3 K). The mean destruction time of the studied metastable crystal is of the order of 10 s. Moreover, the central core of the ion cloud can retain its crystalline configuration for a much longer time.

Classification of the new particle formation events observed at a tropical site, Pune, India

A total number of 109 new particle formation events identified in the ion-mobility spectra measured with a Neutral Cluster and Air Ion Spectrometer in the mobility range of 3.16–0.00133 cm2 V−1s−1 (Diameter* range 0.36–47.1 nm) at a tropical site at Pune, (18.53 °N, 73.85 °E, 573 m amsl) India from March 08, 2010–December 31, 2012 are classified based on their shape characteristics under four categories. Most of these events occurred in the morning hours of the pre-monsoon season during the hottest months (April and May) of the year. The meteorological conditions and the changes in ion characteristics associated with some typical events are examined. Average ion-mobility spectrum for the event days shows a minimum in the negative big cluster ion (diameter, 0.85–1.6 nm) concentration and two maxima in the positive intermediate (diameter, 1.6–7.4 nm) and large ion (diameter, 7.4–47.1 nm) concentrations as compared to the average spectrum for all days. Analysis of 7-days airmass back trajectories shows that since the only source of big cluster ions is through the growth of small cluster ions (diameter, 0.36–0.85 nm) the growth of small to big cluster ions is faster when the airmass approaches our site from the land. Further, the concentrations of positive intermediate and light large (diameter, 7.4–22 nm) ions is more when the airmass approaches from the Arabian Sea.