Neutral Species Research Articles

Revisiting the Chemistry and Photophysics of 3‐(N‐Methylpyridinium‐4‐yl)Coumarins for Designing “Covalent‐Assembly” and “Molecular Disassembly” Fluorescent Probes**

AbstractThe constant need for high‐performance aniline‐ or phenol‐based fluorophores suitable for the construction of activity‐based fluorescent probes, led us to study both synthesis and photophysics of C3‐N‐methylpyridinium‐4‐yl substituted 7‐(dialkylamino)/7‐hydroxycoumarins. Indeed, in the field of photoactive organic molecules, the positively charged N‐alkylpyridinium‐4‐yl groups are often used as acceptor units to dramatically impact spectral features through promoting intramolecular charge transfer (ICT) processes. They are also known as effective water‐solubilizing and mitochondria targeting moieties. The poor fluorescence efficiency of cationic 7‐hydroxycoumarin derivatives in aqueous physiological conditions was highlighted and rationalized by the predominance of a neutral quinonoid form in such buffer medium. The ability of the excited singlet state (S1) of this neutral species to undergo intersystem crossing (ISC) to triplet state (T1) was partly supported by phosphorescence measurements of singlet oxygen. We also took advantage of green‐emissive properties of 7‐(diethylamino)‐3‐(N‐methylpyridinium‐4‐yl)coumarin to successfully design and validate a novel small‐molecule fluorescent probe for the detection of alkaline phosphatase (ALP), based on the “covalent‐assembly” principle. A practical use of ortho‐formylated 7‐hydroxy‐3‐(N‐methylpyridinium‐4‐yl)coumarin was next considered with the synthesis of a Fe(III)‐salen complex whose the potential as a “molecular disassembly” probe for fluorogenic sensing of pyrophosphate (PPi) anion was assessed.

Understanding the role of neutral species by means of high-order interaction in the rock-paper-scissors dynamics.

The existence of neutral species carries profound ecological implications that warrant further investigation. In this paper, we study the impact of neutral species on biodiversity in a spatial tritrophic system of cyclic competition, in which the neutral species are identified as the fourth species that may affect the competition process of the other three species under the rock-paper-scissors (RPS) rule. Extensive simulations showed that neutral species can promote coexistence in a high mobility regime within the system. When coexistence occurs, we found that the state can be maintained by two mechanisms: Species can either (i) adhere to traditional RPS rule or (ii) form patches to resist invasion. Our findings might aid in understanding the impact of neutral species on biodiversity in ecosystems.

Coupling multi-fluid dynamics equipped with Landau closures to the particle-in-cell method

The particle-in-cell (PIC) method is successfully used to study magnetized plasmas. However, this requires large computational costs and limits simulations to short physical run times and often to set-ups of less than three spatial dimensions. Traditionally, this is circumvented either via hybrid-PIC methods (adopting massless electrons) or via magneto-hydrodynamic-PIC methods (modelling the background plasma as a single charge-neutral magneto-hydrodynamical fluid). Because both methods preclude modelling important plasma-kinetic effects, we introduce a new fluid-PIC code that couples a fully explicit and charge-conserving multi-fluid solver to the PIC code SHARP through a current-coupling scheme and solve the full set of Maxwell's equations. This avoids simplifications typically adopted for Ohm's law and enables us to fully resolve the electron temporal and spatial scales while retaining the versatility of initializing any number of ion, electron or neutral species with arbitrary velocity distributions. The fluid solver includes closures emulating Landau damping so that we can account for this important kinetic process in our fluid species. Our fluid-PIC code is second-order accurate in space and time. The code is successfully validated against several test problems, including the stability and accuracy of shocks and the dispersion relation and damping rates of waves in unmagnetized and magnetized plasmas. It also matches growth rates and saturation levels of the gyro-scale and intermediate-scale instabilities driven by drifting charged particles in magnetized thermal background plasmas in comparison with linear theory and PIC simulations. This new fluid-SHARP code is specially designed for studying high-energy cosmic rays interacting with thermal plasmas over macroscopic time scales.

Necking Reduction at Low Temperature in Aspect Ratio Etching of SiO2 at CF4/H2/Ar Plasma.

This study investigated the effect of temperature on the aspect-ratio etching of SiO2 in CF4/H2/Ar plasma using patterned samples of a 200 nm trench in a low-temperature reactive-ion etching system. Lower temperatures resulted in higher etch rates and aspect ratios for SiO2. However, the plasma property was constant with the chuck temperature, indicated by the line intensity ratio from optical emission spectroscopy monitoring of the plasma. The variables obtained from the characterization of the etched profile for the 200 nm trench after etching were analyzed as a function of temperature. A reduction in the necking ratio affected the etch rate and aspect ratio of SiO2. The etching mechanism of the aspect ratio etching of SiO2 was discussed based on the results of the surface composition at necking via energy-dispersive X-ray spectroscopy with temperature. The results suggested that the neutral species reaching the etch front of SiO2 had a low sticking coefficient. The bowing ratio decreased with lowering temperature, indicating the presence of directional ions during etching. Therefore, a lower temperature for the aspect ratio etching of SiO2 could achieve a faster etch rate and a higher aspect ratio of SiO2 via the reduction of necking than higher temperatures.

Electrochemical and Spectroscopic Studies Performed for Indomethacin and 1-Naphthol Incorporated in 1-Butyl-3-methyl-imidazolium Bis(2-ethylhexyl) Sulfosuccinate Vesicles to Investigate Them as a Potentially pH-Sensitive Nanocarrier.

Characterization studies of 1-butyl-3-methyl-imidazolium bis(2-ethylhexyl) sulfosuccinate vesicles at different pH values have been carried out by using liquid surface tension, transmission electron microscopy, and dynamic light scattering. The results show that there are no vesicle changes in its size and negative Z potential at pH 3, 6, and 10. Furthermore, indomethacin and 1-naphthol, both pH-dependent, electroactive, and fluorescence probes, were used to further characterize the bilayer employing electrochemical and emission techniques. The partition of indomethacin and 1-naphthol between the water and bilayer pseudophases only occurs for the neutral species and does not happen for the anionic species because the highly negative Z bilayer potential prevents incorporation due to negative repulsion. For the neutral species, the partition constant values were evaluated by square wave voltammetry and emission spectroscopy. Finally, for the indomethacin incorporated into the vesicle bilayer at pH 3, the release profile was monitored over time at pH 6. It was found that a change in the pH values causes the complete release of indomethacin after 25 min, which led us to think that the vesicles presented in this work can be used as a pH-sensitive nanocarrier for neutral pH-sensitive drugs.

Small-molecule fluorogenic probes based on indole scaffold.

Indoles are the most versatile organic N-heterocyclic compounds widely present in bioactive natural products and used in different fields such as coordination chemistry, pharmacy, dyes, and medicine, as well as in the biology and polymer industries. More recently, the indole scaffold has been widely used in analytical chemistry for the design and development of small-molecule fluorescent chemosensors in the fields of molecular recognition and molecular imaging. The indole-based chemosensor derivatives contain heteroatoms like N-, O-, and S-, through which they interact with analytes (cations, anions, and neutral species), producing measurable analytical signals that can be used for the fluorimetric and colorimetric detection of different analytes in biological, agricultural and environmental samples. This review focuses on indole-based small-molecule fluorimetric and colorimetric chemosensors for detecting cations, anions, and neutral species in a comprehensive manner. Furthermore, the recognition mechanisms are discussed in detail, which could help researchers design and develop more powerful and efficient fluorescent chemosensors in the near future.

Two fluid dynamics in solar prominences

Aims. Solar prominences contain a significant number of neutral species. The dynamics of the ionised and neutral fluids composing the prominence plasma can be slightly different if the collisional coupling is not strong enough. The differential dynamics can be discerned by tracing line-of-sight velocities using observational techniques. Large-scale velocities can be quantified by measuring the global local and instantaneous displacement of spectral lines by the Doppler effect. Small-scale velocities leave their imprint on the width of spectral lines. In addition, these small-scale velocities can have a thermal (pure stochastic motion) nature or a non-thermal (small-scale unresolved instabilities, high-frequency waves, etc.) origin. For this work, we used one spectral line of ionised and two spectral lines of neutral elements to measure the resolved and unresolved velocities in a prominence with the aim to investigate the possible decoupling of the observed charged and neutral species. Methods. A faint prominence was observed with the German Vacuum Tower Telescope (VTT) on June 17, 2017. Time series consisting of repeated ten-position scans over the prominence were performed while simultaneously recording the intensity spectra of the Ca II IR 854.2 nm, Hα 656.28 nm, and He I D3 587.56 nm lines. The line-of-sight velocities and the Doppler width of the three spectral lines were determined at every spatial position and temporal moment. To make sure all spectral lines were sampling the same plasma volume, we applied selection criteria to identify locations with optically thin plasma. In addition, asymmetric or double-peaked profiles were also excluded for the analysis, since (even in an optically thin regime) they are indicative of the presence of strong velocity gradients or multiple components in the line of sight. Thus, only optically thin, symmetric, single-lobed profiles were retained for this study. As an additional reliability test of the selection criteria, we have also compared our results with optical thickness calculations. Results. After the application of all the selection criteria, only a region close to the prominence border met all requirements. The velocities of the three spectral lines turned out to be very similar over this region, with the ionised Ca II IR showing velocity excursions systematically larger compared to those of the neutral lines of Hα and He I at some moments. The latter was found to be much closer to each other. Most of the velocity differences were below 1 km s−1. The analysis of the Doppler widths indicated that the Ca II IR line shows an excess of unresolved motions. We cannot establish whether these velocities are related to a different temperature of the ions or to unresolved small-scale motions due to any non-thermal mechanism. Conclusions. The dynamics of the ionised and neutral plasma components in the observed prominence were very close to one another. The differences found may indicate that a localised decoupling between ions and neutrals may appear at particular spatial locations or instants of time. Indications of different unresolved motions between those species have also been obtained.

Ruthenium(II) complexes with phosphonate-substituted phenanthroline ligands as reusable photoredox catalysts.

Ru(II) complexes with polypyridyl ligands (2,2'-bipyridine = bpy, 1,10-phenanthroline = phen) play a central role in the development of photocatalytic organic reactions. In this work, we synthesized four mixed-ligand [Ru(phen)(bpy)2]2+-type complexes (Ru-Pcat-A) bearing two phosphonate substituents P(O)(OH)(OR) (R = H, Et) attached to the phen core at positions 3,8 (Ru-3,8PH and Ru-3,8PHEt) and 4,7 (Ru-4,7PH and Ru-4,7PHEt) of the heterocycle in high yields (87-99%) and characterized them using spectral methods. Single crystal X-ray diffraction was employed to determine the coordination mode of the ditopic phen ligand in Ru-4,7PH. This complex exists as the neutral species and forms a 1D hydrogen-bonded framework in the crystals. The light absorption characteristics were found to be similar for all complexes prepared in this work. However, the emission maxima in aqueous solutions were significantly affected by the substitution of the heterocycle, ranging from 629 nm for Ru-4,7PH to 661 nm for Ru-3,8PHEt. The emission quantum yields in Ar-saturated deionized water showed a strong dependence on the substitution pattern of the phen ligand, with maximal values reaching approximately 0.11 for Ru-4,7PHEt and Ru-4,7PH, which is twice as high as that of the classical [Ru(bpy)3]2+ complex (Ru-bpy). The photocatalytic performance of Ru-Pcat-A was investigated using visible light photoredox catalytic transformations of tertiary amines. With Ru-Pcat-A, we achieved the phosphonylation of N-aryl-1,2,3,4-tetrahydroisoquinolines (THIQs) and cyanation of THIQs and N,N-dimethylaniline in methanol, while a mixture of nitromethane/methanol (1 : 1 v/v) proved to be the optimal solvent for conducting the nitromethylation of THIQs. In the majority of the studied reactions, Ru-4,7PHEt exhibited greater efficiency compared to Ru-bpy, and it could be easily separated from the products using water extraction and reused in the next catalytic cycle. We successfully performed seven consecutive nitromethylation and phosphonylation of N-phenyl-1,2,3,4-tetrahydroisoquinoline using the recycled homogeneous photoredox catalyst.

Investigation of the effects on proton relaxation times upon encapsulation in a water-soluble synthetic receptor.

Sequestration of small molecule guests in the cavity of a water-soluble deep cavitand host has a variety of effects on their NMR properties. The effects of encapsulation on the longitudinal (T1) and transverse (T2) relaxation times of the protons in variably sized guest molecules are analyzed here, using inversion recovery and spin-echo experiments. Sequestration of neutral organic species from the bulk solvent reduces the overall proton relaxation times, but the magnitude of this effect on different protons in the same molecule has a variety of contributors, from the motion of the guest when bound, to the position of the protons in the cavity and the magnetic anisotropy induced by the aromatic walls of the host. These subtle effects can have large consequences on the environment experienced by the bound guest, and this sheds light on the nature of small molecules in enclosed environments.

Investigating the Influence of Free-Electron Pulses and Neutral Excited Species Formation on Discharge Development: By PD Quantum Optics Analysis and Plasma Simulation

Investigating the Influence of Free-Electron Pulses and Neutral Excited Species Formation on Discharge Development: By PD Quantum Optics Analysis and Plasma Simulation

Boron diamide derivatives containing N-N and N-P molecular fragments.

The cationic and neutral boron-diamide precursors are employed to target the inclusion of N2 and N-P molecular fragments. The species (HCN(Dipp))2BNH25, and (H2CN(Dipp))2BNH26 were prepared. While efforts to oxidize with [NO]+ gave mixtures of products, reactions with N2H4 gave the salts [(HCN(Dipp))2B(NHNH3)][O3SCF3] 7 [(H2CN(Dipp))2B(NHNH3)][O3SCF3] 8. Excess N2H4 gave the neutral species (HCN(Dipp))2B(NHNH2) 9 and (H2CN(Dipp))2B(NHNH2) 10, respectively. The species (H2CN(Dipp))2B(N3) 11 was prepared for comparative purposes. Turning to related NP species, compound 6 was converted to (HCN(Dipp))2B(NHPCl2) 12, while (HCN(Dipp))2BNK(SiMe3) 14 was used to give (HCN(Dipp))2BN(SiMe3)PCl215. Replacement of one of the chlorides gave (HCN(Dipp))2BN(SiMe3)PCl(OSO2CF3) 16 which converts to [(HCN(Dipp))2BNPCl]217. Similarly heating 15 afforded 17. The insights for the synthesis of further boron-N2 and boron-NP derivatives are discussed.

Measurement of the main neutral species densities and temperatures in iodine plasmas using optical absorption techniques

Iodine is a promising propellant for future plasma thrusters used in space propulsion. It is therefore important to understand the basic physics and chemistry of low-pressure iodine plasmas. In the present work, optical absorption methods are used to measure the densities of iodine molecules, I2, and iodine atoms, I, the translational temperature of the atoms and the dissociation fraction. The plasma is generated in a long quartz tube by a capacitively coupled RF discharge, and the pressure is varied between a few Pa and a few tens of Pa. The translational temperature of the atom vapour increases both with RF power and with pressure and reaches 1000 K at 50 W and 25 Pa. The molecules appear to be efficiently dissociated, with a dissociation fraction found above 65%, on average along the line-of-sight, at 120 W and 5 Pa. The population of the upper, 2P1/2∘ , fine-structure level of the atomic ground term is found to be negligible, which confirms the existence of a high quenching rate, due to collisions with molecules and/or atoms. These measurements can be helpful for chemistry models of iodine plasmas.

Surfaces of Atmospheric Droplet Models Probed with Synchrotron XPS on a Liquid Microjet.

ConspectusThe atmosphere is a key part of the earth system comprising myriad chemical species in all basic forms of matter. Ubiquitous nano- and microscopic aerosol particles and cloud droplets suspended in the air play crucial roles in earth's climate and the formation of air pollution. Surfaces are a prominent part of aerosols and droplets, due to the high surface area to bulk volume ratios, but very little is known about their specific properties. Many atmospheric compounds are surface-active, leading to enhanced surface concentrations in aqueous solutions. Their distribution between the surface and bulk may determine heterogeneous chemistry and many other properties of aerosol and cloud droplets, but has not been directly observed.We used X-ray photoelectron spectroscopy (XPS) to obtain direct molecular-level information on the surface composition and structure of aqueous solutions of surface-active organics as model systems for atmospheric aerosol and cloud droplets. XPS is a vacuum-based technique enabled for volatile aqueous organic samples by the application of a high-speed liquid microjet. In combination with brilliant synchrotron X-rays, the chemical specificity of XPS allows distinction between elements in different chemical states and positions within molecular structures. We used core-level C 1s and N 1s signals to identify the alkyl and hydrophilic groups of atmospheric carboxylic acids, alkyl-amines, and their conjugate acids and bases. From this, we infer changes in the orientation of surface-adsorbed species and quantify their relative abundances in the surface. XPS-derived surface enrichments of the organics follow trends expected from their surface activities and we observed a preferential orientation at the surface with the hydrophobic alkyl chains pointing increasingly outward from the solution at higher concentrations. This provides a first direct experimental observation of well-established concepts of surface adsorption and confirms the soundness of the method.We mapped relative abundances of conjugate acid-base pairs in the aqueous solution surfaces from the respective intensities of distinctive XPS signals. For each pair, the protonation equilibrium was significantly shifted toward the neutral form in the surface, compared to the bulk solution, across the full pH range. This represents an apparent shift of the pKa in the surface, which may be toward either higher or lower pH, depending on whether the acid or base form of the pair is the neutral species. The surface shifts are broadly consistent with the relative differences in surface enrichment of the individual acid and base conjugates in binary aqueous solutions, with additional contributions from nonideal interactions in the surface. In aqueous mixtures of surface-active carboxylate anions with ammonium salts at near-neutral pH, we found that the conjugate carboxylic acids were further strongly enhanced. This occurs as the coadsorption of weakly basic carboxylate anions and weakly acidic ammonium cations forms ion-pair surface layers with strongly enhanced local abundances, increasing the probability of net proton transfer according to Le Chatelier's principle. The effect is stronger when the evaporation of ammonia from the surface further contributes to irreversibly perturb the protonation equilibrium, leaving a surplus of carboxylic acid. These surface-specific effects may profoundly influence atmospheric chemistry mediated by aqueous aerosols and cloud droplets but are currently not taken into account in atmospheric models.

Electronic structure of 1,3‐diphenyl‐2‐azaallenyl radical cation

AbstractQuantum chemical simulations were conducted to elucidate the electronic structure of the 2‐azaallenyl radical cation, a key intermediate in several [3 + 2]‐cycloadditions initiated by the oxidation of 2H‐azirine. We propose one additional Lewis structure in resonance with the commonly accepted two Lewis structures for the model system of 1,3‐diphenyl‐2‐azaallenyl radical cation, drawn from comprehensive theoretical data including molecular shape, bond order analysis, partial atomic charges, and spin densities. In addition to the ground state chemistry, the chemical structure of excited state species can be also understood with these three Lewis structures. Theoretical data imply that a newly suggested one mainly accounts for the ground state structure, and the excited state structure is better represented by the previously reported ones. Our claim is further bolstered by the prediction of the excited state geometries of the dicationic and neutral species. This research presents the extended set of Lewis structures for a better understanding electronic structure of 2‐azaallenyl radical cation.

Investigating the Effect of Plasma Parameters on the Dielectric Constant of Sicoh Thin Films Grown by PECVD Using Dimethyldimethoxysilane

The demand for high-performance, low-power, and high-density semiconductor devices has led to the reduction in size of semiconductor chips, resulting in resistance-capacitance (RC) delay. To mitigate the RC delay, low dielectric constant (low-k) insulators have been developed, with the focus on developing new materials with lower dielectric constant. In this report, we present our investigation into the effect of electron density and temperature on the reduction of dielectric constant in SiCOH thin films, utilizing dimethyldimethoxysilane (DMDMS) as a variable with respect to pressure. Our results reveal that both electron density and temperature decline with increasing pressure due to localized electron kinetics and increased inelastic collisions between electrons and neutral species in the chamber, respectively. Our findings also show that the dielectric constant and refractive index of SiCOH thin films decrease at low electron density and temperature. Quadrupole mass spectroscopy reveals that CH3 radicals dissociate less at higher pressures, while Fourier transform infrared spectroscopy confirms an increase in Si-CH3 bonds in SiCOH thin films with increasing pressure. Our findings provide insights into the relationship between electron density and temperature and the dielectric constant of SiCOH thin films, which can contribute to the development of low-k insulators for high-performance semiconductor devices for applications such as big data, mobility, and the Internet of Things (IoT).

(Invited) Understanding Plasma-Assisted Atomic Layer Epitaxy of InN and Opportunities for Collaboration through the Office of Naval Research Global

The family of III-V nitride compound semiconductors has provided the foundation to a number of advanced electronic device technologies from light emitting diodes to radio frequency transistors to power switches. Of the family, binary indium nitride (InN) and ternaries/quaternaries containing InN have progressed at a slower pace due the material properties and related growth challenges. Having the weakest bonds in the family, the material has a lower melting point and more easily decomposes and phase separates (in ternaries and quaternaries). As such, a number of research efforts are looking for new growth approaches to overcome these challenges and realize the InN-based materials that will enable devices such has high speed switches and IR emitters and detectors.To this end, plasma-assisted atomic layer epitaxy (PA-ALE) of InN and InN-containing ternaries has been explored in recent years. Much like atomic layer deposition, ALE consists of a sequence of self-limiting surface half-reactions that promotes “layer-by-layer” growth of films. The cyclical growth process starts with exposure of the growth surface first to the group III precursor (trimethylindium, for example), then purging excess precursor and reaction byproducts leaving only the ad-/physi-/chemi-sorbed species on the surface. After this purge, these surfaces are then exposed to a collection of plasma species (ions, radicals, neutrals, etc.) which reacts with the “sorbed” layer. The growth cycle is finished with a purge of the surface reaction by-products and unreacted plasma species before repeating. The potential of the process is based on the premise that by providing energy from plasma species to the growth surface, one can lower the temperature of growth to improve the stability of the material. Further, the reactive neutral plasma species also play a role by lowering activation energies for chemical reactions compared to thermal ALD, without necessarily providing energy to the growth surface.A brief review of previous experimental demonstrations of epitaxial growth of InN and InN-containing ternaries will be presented showing the promise of the growth method to grow quality InN binary films and metastable ternaries containing InN not possible by conventional growth methods. For example, a metastable cubic phase of InN (NaCl) was realized as were ternary stoichiometries for both InAlN and InGaN that lie in the thermodynamic miscibility gap. Further, and in an effort to begin to understand this growth process and the role that plasma might play in growth mechanisms, synchrotron-based studies have been employed during growth of binary InN and digital InAlN and InGaN alloys. The results of these studies will be highlighted and key findings identified. Most recently, coherent x-ray scattering has been employed to provide additional insights including surface diffusion during each step of the cyclical growth process. The cumulative findings of these efforts will be presented, and future directions outlined.As the presenting author is now detailed as a Science Director for Power & Energy and Advanced Materials to the U.S. Office of Naval Research Global in London, the last portion of the talk will be dedicated to introducing ONRG and its mission to engage international researchers through research grants, travel grants and conference support. The hope is to increase awareness of collaborative opportunities to the global research community expected to be in attendance.

Understanding the Reaction Mechanism and Kinetics of Mediated Li-O2 Batteries Using Flow Set-Ups and Cyclic Voltammetry

Li-O2 batteries are very promising candidates for electromobility because of their very high theoretical energy density. Moreover, they are composed of abundant materials, as opposed to Li-ion batteries, which would make them a greener and cheaper alternative. The principal reaction in Li-O2 batteries is the formation of lithium peroxide during discharge via the oxygen reduction reaction (ORR), that is then oxidised during the charge by the oxygen evolution reaction (OER). One of the major challenges of Li-O2 batteries is related to the insulating nature of their discharge product, that significantly limits the capacity and hinders performance. A strategy to overcome this is by using redox mediators (RMs), which shuttle electrons from the electrode surface to the solution and thus facilitate a solution-based mechanism for the formation of large crystals. Understanding the reaction kinetics of these RMs can therefore aid in increasing the battery performance.Quinones, specifically 2,5-Di-tert-butyl-1,4-benzoquinone (DBBQ),is a commonly used discharge RM in this type of batteries. However, their reaction kinetics and how these vary with different electrolyte conditions are not yet well understood. DBBQ undergoes two single electron reductions, whose potentials and kinetics vary with salt concentrations and solvent having a direct effect on its ability to mediate the ORR.In this work, we have developed a Li-O2 flow cell to study the reaction mechanism and kinetics of DBBQ, and performed cyclic voltammetry (CV) studies to better understand how these vary with changing solvent and salt conditions. In the Li-O2 flow set-up the battery is positioned outside the nuclear magnetic resonance (NMR) magnet and plastic tubing then runs through the NMR and electron paramagnetic resonance (EPR) spectrometers. In this way, the reduction of the DBBQ can be monitored while the battery is cycling. In the proton NMR, the neutral DBBQ signals disappear on discharge as the singly reduced DBBQ semiquinone monoanion is a radical. The fast electron exchange between the neutral and radical species broaden out the NMR signals on discharge as the EPR signal grows. On charge, the neutral DBBQ signal reappears and the EPR signal disappears. The Li-O2 flow set-up is very sensitive to air and moisture exposure as the tubing is not perfectly impermeable to them. Therefore, having the CVs as a complementary method to study the reaction mechanisms and kinetics is very useful.We have developed a theoretical framework of Li-coupled electron transfer reactions that can predict the electrochemical kinetics in the presence of high and low donor number solvents and used to quantify thermodynamic and kinetic parameters. We define E0 app and k0 app as the apparent thermodynamic and kinetic parameters that describe the overall system and can be derived from the Nernst equation and Butler Volmer kinetics. These overall descriptors depend on the pathway the reaction takes (Figure 1). The different pathways in different solvents/salts are due to changes in the Li+ solvation strength as well as the competing ionic association of the counter anion.Experimentally, we have shown that in three different solvents, DME, tetraglyme and DMSO the behaviour of DBBQ can be explained by this theoretical framework. In DME, the DBBQ behaviour is most reminiscent of pathway 1 where the kinetics slow down with increasing Li+ concentration. In DMSO the kinetics present a maximum at Li+ concentrations around 1M. Simulations and fitting of the CV experiments in DMSO for the first reduction are in good agreement with pathways 2 and 3, while in tetraglyme it is harder to explain the trends as they do not fit into just one of the pathways.In conclusion we have studied the mechanism and kinetics of DBBQ as a RM for Li-O2 batteries with an in-situ flow set up and CVs and build a theoretical framework to understand how these vary in different electrolyte conditions. This method can be extended to study both the second reduction of DBBQ and other discharge and charge RMs for Li-O2 batteries. Figure 1

Electrolyte Mixtures and Organic Cathode Materials for Rechargeable Aluminum Batteries

Rechargeable aluminum (Al) metal batteries are an emerging energy storage technology ideal for use at a global scale: Al metal is energy dense, low cost, inherently safe, earth abundant, and highly recyclable. Despite such great promise, their technological progress has been hindered by the few electrolytes able to reversibly electrodeposit Al metal at room temperature, coupled with the limited number of positive electrode materials that are compatible with them. In this context, recent progress will be discussed in the development of electrolyte mixtures and organic cathode materials for rechargeable aluminum batteries. Chloroaluminate ionic liquid electrolytes and ionic liquid analogues prepared using mixtures of organic cations and/or neutral solvent species will be presented, which exhibit improved electrochemical properties for aluminum electrodeposition and in aluminum-graphite batteries, over temperatures ranging from ambient conditions down to -60 °C. Different organic structures will also be presented as organic cathode materials for aluminum batteries, where the effects of molecular structure on bulk energy storage properties will be discussed. Molecular-scale understanding of their ionic and electronic charge storage mechanisms will be elucidated through a combination of solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations. Lastly, by using different electrolytes in combination with an organic cathode, it will be shown that electrolyte speciation can affect the local environments of charge-compensating ions in cycled organic electrodes. Overall, the results and analyses are aimed at developing next-generation rechargeable aluminum metal batteries for diverse energy storage applications.

CFD modeling and simulation of benzyl alcohol oxidation coupled with hydrogen production in a continuous-flow photoelectrochemical reactor

Various conversion routes of biomass and its derivative compounds into high-value products has attracted attention from researchers recently. Among these, a solar-driven photoelectrochemical (PEC) oxidation approach of biomass alcohols to aldehydes is particularly of great interest for the potential applications because the reaction is selective and simultaneously accompanied with hydrogen production. Here, we propose a simulation of selective oxidation of benzyl alcohol into benzaldehyde coupled with hydrogen production in a 2-dimensional continuous-flow PEC reactor using COMSOL Multiphysics (5.6). In order to develop and fabricate a simple yet efficient reactor for a practical use, it is crucial to investigate the effects of operating and design parameters of the reactor on the reactions. Our studies demonstrated that the main contributions to product formation were the electrolyte flow velocity and the width of electrolyte channels. The optimized design parameter exhibited good photoelectrochemical performance with uniform potential distribution within the channels which served diffusion of neutral and charged species and electrochemical reaction. The maximum conversion of benzyl alcohol in this work was 48.25% with 100% selectivity of benzaldehyde. These findings are key for the design of the continuous-flow PEC reactor that can be applied to any series of biomass conversion reactions under mild conditions.

Theoretical modelling of the adsorption of neutral and charged sulphur-bearing species on to olivine nanoclusters

ABSTRACT Sulphur depletion in the interstellar medium (ISM) is a long-standing issue, as only 1 per cent of its cosmic abundance is detected in dense molecular clouds (MCs), while it does not appear to be depleted in other environments. In addition to gas phase species, MCs also contain interstellar dust grains, which are irregular, micron-sized, solid aggregates of carbonaceous materials, and/or silicates. Grains provide a surface where species can meet, accrete, and react. Although freeze-out of sulphur on to dust grains could explain its depletion, only OCS and, tentatively, SO2 were observed on their surfaces. Therefore, it is our aim to investigate the interaction between sulphur-containing species and the exposed mineral core of the grains at a stage prior to when sulphur depletion is observed. Here, the grain core is represented by olivine nanoclusters, one of the most abundant minerals in the ISM, with composition Mg4Si2O8 and Mg3FeSi2O8. We performed a series of quantum mechanical calculations to characterize the adsorption of nine S-bearing species, both neutral and charged, on to the nanoclusters. Our calculations reveal that the Fe–S interaction is preferred to Mg–S, causing sometimes the chemisorption of the adsorbate. These species are more strongly adsorbed on the bare dust grain silicate cores than on water ice mantles, and hence therefore likely sticking on the surface of grains forming part of the grain core. This demonstrates that the interaction of bare grains with sulphur species in cloud envelopes can determine the S-depletion observed in dense molecular clouds.