Spatial Distribution Of Chemical Species Research Articles

Stacking pressure homogenizes the electrochemical lithiation reaction of silicon anode in solid-state batteries

Several tens of MPa stacking pressure is usually necessary to fully utilize the capacity of energy-dense silicon anode in solid-state batteries, presenting significant hurdles for real applications. It is thus critical to establish the link between the macroscopic stacking pressure and the microscopic electrochemical processes. In this work, we used titration gas chromatography to quantify the capacity-loss processes of silicon anodes under different stacking pressures. Furthermore, time-of-flight secondary ion mass spectrometry, electron microscopy, and phase-field modeling techniques were used to map the spatial distribution of chemical species (e.g., LixSi alloys), stress, and electrochemical overpotential upon (de)lithiation processes of the silicon anode. High stacking pressure was observed to significantly increase the extent that a Si anode can be lithiated because of the increased reaction homogeneity resulting from the strong electro-mechanical coupling, while its impact over lithium loss during the first cycle is rather limited. Our work provides a basis to unlock the full potential of Si-anode based solid-state batteries at near-ambient stacking pressure and calls for innovative strategies to minimize or compensate for the lithium loss at the first cycle.

Modelling the effect of 3D temperature and chemistry on the cross-correlation signal of transiting ultra-hot Jupiters: a study of five chemical species on WASP-76b

ABSTRACT Ultra-hot Jupiters are perfect targets for transmission spectroscopy. However, their atmospheres feature strong spatial variations in temperature, chemistry, dynamics, cloud coverage, and scale height. This makes transit observations at high spectral resolution challenging to interpret. In this work, we model the cross-correlation signal of five chemical species – Fe, CO, H2O, OH, and TiO – on WASP-76b, a benchmark ultra-hot Jupiter. We compute phase-dependent high-resolution transmission spectra of three-dimensional (3D) SPARC/MITgcm models. The spectra are obtained with gCMCRT, a 3D Monte-Carlo radiative-transfer code. We find that, on top of atmospheric dynamics, the phase-dependent Doppler shift of the absorption lines in the planetary rest frame is shaped by the combined effect of planetary rotation and the unique 3D spatial distribution of chemical species. For species probing the dayside (e.g. refractories or molecules like CO and OH), the two effects act in tandem, leading to increasing blueshifts with orbital phase. For species that are depleted on the dayside (e.g. H2O and TiO), the two effects act in an opposite manner, and could lead to increasing redshifts during the transit. This behaviour yields species-dependent offsets from a planet’s expected Kp value that can be much larger than planetary wind speeds. The offsets are usually negative for refractory species. We provide an analytical formula to estimate the size of a planet’s Kp offsets, which can serve as a prior for atmospheric retrievals. We conclude that observing the phase-resolved absorption signal of multiple species is key to constraining the 3D thermochemical structure and dynamics of ultra-hot Jupiters.

Coupled mesoscale–microscale modeling of air quality in a polluted city using WRF-LES-Chem

Abstract. To perform realistic high-resolution air quality modeling in a polluted urban area, the Weather Research and Forecasting (WRF) model is used with an embedded large-eddy simulation (LES) module and online chemistry. As an illustration, a numerical experiment is conducted in the megacity of Hong Kong, which is characterized by multi-type inhomogeneous pollution sources and complex topography. The results from the multi-resolution simulations at mesoscale and LES scales are evaluated by comparing them with ozone sounding profiles and surface observations. The comparisons show that both mesoscale and LES simulations reproduce the mean concentrations of the chemical species and their diurnal variations at the background stations well. However, the mesoscale simulations largely underestimate the NOx concentrations and overestimate O3 at the roadside stations due to the coarse representation of the traffic emissions. The LES simulations improve the agreement with the measurements near the road traffic, and the LES with the highest spatial resolution (33.3 m) provides the best results. The large-eddy simulations show more detailed structures in the spatial distributions of chemical species than the mesoscale simulations, highlighting the capability of LES to resolve high-resolution photochemical transformations in urban areas. Compared to the mesoscale model results, the LES simulations show similar evolutions in the profiles of the chemical species as a function of the boundary layer development over a diurnal cycle.

Fluorescence lifetime: Beating the IRF and interpulse window

Fluorescence lifetime imaging captures the spatial distribution of chemical species across cellular environments employing pulsed illumination confocal setups. However, quantitative interpretation of lifetime data continues to face critical challenges. For instance, fluorescent species with known in vitro excited-state lifetimes may split into multiple species with unique lifetimes when introduced into complex living environments. What is more, mixtures of species, which may be both endogenous and introduced into the sample, may exhibit 1) very similar lifetimes as well as 2) wide ranges of lifetimes including lifetimes shorter than the instrumental response function or whose duration may be long enough to be comparable to the interpulse window. By contrast, existing methods of analysis are optimized for well-separated and intermediate lifetimes. Here, we broaden the applicability of fluorescence lifetime analysis by simultaneously treating unknown mixtures of arbitrary lifetimes—outside the intermediate, Goldilocks, zone—for data drawn from a single confocal spot leveraging the tools of Bayesian nonparametrics (BNP). We benchmark our algorithm, termed BNP lifetime analysis, using a range of synthetic and experimental data. Moreover, we show that the BNP lifetime analysis method can distinguish and deduce lifetimes using photon counts as small as 500.

Molecular vibrational imaging at nanoscale.

The demand to visualize the spatial distribution of chemical species based on vibrational spectra is rapidly increasing. Driven by such a need, various Raman and infrared spectro-microscopies with a nanometric spatial resolution have been developed over the last two decades. Despite rapid progress, a large gap still exists between the general needs and what these techniques can achieve. This Perspective highlights the key challenges and recent breakthroughs of the two vibrational nano-imaging techniques, scattering-type scanning near-field optical microscopy and tip-enhanced Raman scattering.

(Invited) Diffusion Control of Metal Ions Close to Electrode in Ionic Liquid -Effect of Local Structure of Ionic Liquid-

Ionic liquids (ILs) have attracted keen attention due to its applicability to various kinds of electrochemical devices. However, we still lack enough knowledge of the interface structure and spatial distribution of chemical species during the electrochemical processes. In our previous study, we succeeded in the observation of the spatial distribution of Ag+ ions in ionic liquid solution close to the electrode under the applied potential using scanning electrochemical photoelectron spectroscopy (Scanning EC-PES) we originally developed. Interestingly, the diffusion layer where the concentration of metal ions is quite small (We named this region as “depletion layer”) was formed close to the electrode in a wide region. By a numerical simulation, we revealed that the metal ions diffused by the hopping-like mechanism, in which the apparent diffusion coefficient increased with increasing of the concentration of 'holes' (vacancies formed between IL molecules) acting as hopping sites.On the other hand, it can be anticipated that the local structure of ILs can be systematically controlled by changing of IL species (e.g. the alkyl chain length of imidazole cation, shape and size of anion), additive ions and/or temperature of solution. By using these techniques for controlling the local structure of ILs, we can strictly control the diffusion behavior of metal ions close to the electrode. In other words, we will be able to propose a new strategy for controlling the diffusion behavior of solutes in ionic liquid solutions close to the electrode. In this study, we investigated the factors for controlling the diffusion behavior of metal ion in IL electrolyte based on our proposing diffusion model, and revealed that the behavior of metal ions can be controlled by some factors.We investigated the additive effect using Li+ ion. In the case of the ~200 mM Ag+/BMI-TFSA((1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide) solution, the large depletion layer was formed close to the electrode, whereas the depletion layer was decreased when ~100 mM Li+ (as an electrochemically inactive additive) was added to the solution. This result indicates that the hopping-like diffusion was suppressed by the addition of the Li+ ion which efficiently occupied the holes (hopping sites) (Note that the depletion layer was formed by the fast hopping-like diffusion mechanism). On the other hand, when we added the excessive amount of additive (~500 mM Li+) to BMI-TFSA solution, a large depletion layer was formed again, indicating that the hopping diffusion was enhanced. This is due to that some Ag+ ions are drive out of the polar domain, and moved to the non-polar domain where the activation energy of hopping diffusion is relatively small. On the other hand, we carried out a similar experiment using HMI-TFSA instead of BMI-TFSA. We found that the hopping diffusion of Ag+ ion is enhanced compared with that in BMI-TFSA. This could also be explained by the local domain effect of ionic liquid. These results indicate that we can control the diffusion behavior of metal ions by adjusting the local structure of ionic liquid.

(Invited) Control of Diffusion Behavior of Metal Ions Close to Electrode By Using of Local Structure of Ionic Liquid Electrolyte

Ionic liquids (ILs) have attracted keen attention due to its applicability to various kinds of electrochemical devices. However, we still lack enough knowledge on the interface structure and spatial distribution of chemical species during the electrochemical processes. In our previous study, we succeeded in the observation of the spatial distribution of XPS spectra close to the electrode under the applied potential using scanning electrochemical photoelectron spectroscopy (Scanning EC-PES) we originally developed. Interestingly, the shape of the diffusion layer (The spatial distribution of the concentration of the metal ions) was largely different from the concave function usually supposed in the case of aqueous solution. By a numerical simulation, we revealed that the characteristic shape of the diffusion layer of IL electrolyte was formed due to the fact that the metal ions diffused by the fast hopping-like mechanism, in which the apparent diffusion coefficient increased with increasing of the concentration of 'holes' (vacancies formed between IL molecules) acting as hopping sites. Based on these results, we proposed the new diffusion model in which hopping diffusion and conventional diffusion (which follows Stokes-Einstein equation) coexist. The most prominent feature of our diffusion model is that the local structure of ionic liquid (hole density, arrangement of the holes and/or IL molecules) strongly affect the diffusion behavior of metal ions.On the other hand, it can be anticipated that the local structure of ILs can be systematically controlled by the IL species (e.g. the alkyl chain length of imidazole cation, shape and size of anion), additive ions and/or temperature of solution. By using of these techniques for controlling the local structure of ILs, we can strictly control the diffusion behavior of metal ions close to the electrode. In other words, we will be able to propose the new strategy for controlling the diffusion behavior of solutes in ionic liquid solutions close to the electrode. In this study, we investigated the factors for controlling the diffusion behavior of metal ion in IL electrolyte based on our proposing diffusion model, and revealed that the behavior of metal ions can be controlled by some factors mentioned above.

Insights into coarse particle optics based on field evidence of particle morphology, chemical composition and internal structure

Aerosol particles scatter and absorb solar radiation and affect the Earth's radiation budget. The aerosol particles are usually non-spherical in shape and inhomogeneous in chemical composition. For simplicity, these particles are approximated as homogeneous spheres/spheroids in radiative models and in retrieval algorithms of the ground and spaceborne observations. The lack of information on particle morphology (especially shape), chemical composition (that govern their spectral refractive indices) and most importantly internal structure (three dimensional spatial distribution of chemical species) lead to uncertainty in the numerical estimation of their optical and radiative properties. Here, we present a comprehensive assessment of the particles' volumetric composition. The particles were collected from Jaisalmer (arid environment) and Delhi (urban environment) of India and subjected to Focused Ion-Beam (FIB) coupled with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscope (EDS). Based on analysis of #2 particles from Jaisalmer, particles were observed to be composed of Fe, Ca, C, Al, Cu and Mg rich shell with Si and O rich core as opposed to those of Delhi particles (no #3) which were observed to be with Cu and S rich core and Hg, Ag, C, S and N rich shell. Based on the homogeneous sphere/spheroid assumption, conventional SEM-EDS and FIB-SEM-EDS results, different particle model shapes [single species homogeneous sphere (SP1) and spheroid (SPH1); multiple species homogeneously mixed sphere (SP2) and spheroid (SPH2); and core-shell (CS)] were considered for simulating their respective optical properties; SSA (Single Scattering Albedo) and g (Asymmetry parameter). The effect of internal structure on SSA was found to be prominent in particles having low value of the imaginary part of refractive index (k). While the same was observed to be low (nearly negligible) for the particle with the high value of k. The particles rich in copper are found to have high light absorbing property which causes positive radiative forcing.

(Invited) Control of Diffusion Behavior of Metal Ions at Ionic Liquid/Electrode Interface and Its Effect on Electrodeposits

Ionic liquids (ILs) have attracted keen attention due to its applicability to various kinds of electrochemical devices. However, we still lack enough knowledge on the interface structure and spatial distribution of chemical species during the electrochemical processes. In our previous study, we succeeded in the observation of the spatial distribution of XPS spectra close to the electrode under the applied potential using scanning electrochemical photoelectron spectroscopy (Scanning EC-PES) we originally developed. Interestingly, the shape of the diffusion layer (The spatial distribution of the concentration of the metal ions) was largely different from the concave function usually supposed in the case of aqueous solution. In the case of ionic liquid solution, the spatial distribution of concentration was convex and the depletion layer where the concentration of metal ions is quite small (We named this region as “depletion layer”) was formed close to the electrode in a wide region. By a numerical simulation, we revealed that the metal ions diffused by the hopping-like mechanism, in which the apparent diffusion coefficient increased with increasing of the concentration of 'holes' (vacancies formed between IL molecules) acting as hopping sites. In addition, we also revealed that the diffusion behavior (diffusion velocity) of metal ions can be controlled by controlling the concentration of the holes by using of the small amount of additive ions. These results indicate that we will be able to propose the new strategy for controlling the diffusion behavior of solutes in ionic liquid solutions close to the electrode. On the other hand, it is known that the diffusion behavior of metal ions affects the shape of the electrodeposits on the electrode. Therefore, the controlling of the diffusion behavior of metal ions close to the electrode enable us to control the shape of the electrodeposits. In this strudy, we investigated how we can control the diffuosion behavior of the metal ions based on the new diffusion model we previously proposed and we also investigated that how the diffusiton behavior of the metal ions in IL affects the shape of the electrodeposits on the surface. In the case of the ~200 mM Ag+/BMI-TFSA((1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide) solution, the large depletion layer was formed close to the electrode, whereas the depletion layer was decreased in the case that Li+ (as an electrochemically inactive additive) was added to the solution. This result indicates that the hopping-like diffusion was suppressed by the addition of the Li+ ion (Note that the depletion layer was formed by the fast hopping-like diffusion mechanism). On the other hand, the shape of the electrodeposit formed in the former solution is largely different from that formed in the latter solution. This is mainly due to the total diffusion velocity of Ag+ ion was largely decreased by the addition of Li+ ion. These result indicates that we can effectively control the shape of the electrodeposits by controlling the diffusion behavior of metal ions.

Predicting Precipitation Kinetics During the Annealing of Additive Manufactured Inconel 625 Components

The prediction of solidification microstructures associated with additive manufacture of metallic components is fundamental in the identification scanning strategies, process parameters and subsequent heat treatments for optimised component properties. Interactions between the powder particles and the laser heat source result in complex thermal fields in and around the metal melt pool, which will influence the spatial distribution of chemical species as well as solid-state precipitation reactions. This paper demonstrates that a multi-component, multi-phase precipitation model can successfully predict the observed precipitation kinetics in Inconel 625, capturing the anomalous precipitation behaviour exhibited in additively manufactured components. A computer coupling of phase diagrams and thermochemistry (CALPHAD)-based approach captures the impact of dendritic segregation of alloying elements upon precipitation behaviour. The model was successful in capturing the precipitation kinetics during annealing considering the Nb-rich and Nb-depleted regions that are formed during additive manufacturing.

2D/3D Microanalysis by Energy Dispersive X-ray Absorption Spectroscopy Tomography

X-ray spectroscopic techniques have proven to be particularly useful in elucidating the molecular and electronic structural information of chemically heterogeneous and complex micro- and nano-structured materials. However, spatially resolved chemical characterization at the micrometre scale remains a challenge. Here, we report the novel hyperspectral technique of micro Energy Dispersive X-ray Absorption Spectroscopy (μED-XAS) tomography which can resolve in both 2D and 3D the spatial distribution of chemical species through the reconstruction of XANES spectra. To document the capability of the technique in resolving chemical species, we first analyse a sample containing 2–30 μm grains of various ferrous- and ferric-iron containing minerals, including hypersthene, magnetite and hematite, distributed in a light matrix of a resin. We accurately obtain the XANES spectra at the Fe K-edge of these four standards, with spatial resolution of 3 μm. Subsequently, a sample of ~1.9 billion-year-old microfossil from the Gunflint Formation in Canada is investigated, and for the first time ever, we are able to locally identify the oxidation state of iron compounds encrusting the 5 to 10 μm microfossils. Our results highlight the potential for attaining new insights into Precambrian ecosystems and the composition of Earth’s earliest life forms.

The effect of the electric wind on the spatial distribution of chemical species in the positive corona discharge

The electrohydrodynamic air flow generated by a positive corona discharge, and its effect on the spatial distribution of chemical species within a wire-plate corona reactor, have been numerically simulated. The computational model is based on the solutions of the Navier–Stokes equation and the continuity equation of each chemical species generated by the electrical discharge. A simplified analytical expression of the electric force density, which only requires the current density as the input parameter, has been used in the Navier–Stokes equation to obtain the velocity field. For the solution of the continuity equations, a plasma chemistry model that includes the most important reactions between electrons, atoms and molecules in air has been used. Similar to the electric force, the electron density distribution has been approximated by using a semi-analytical expression appropriate for the electrode geometry. The results of the study show that the spatial distribution of chemical species can be very different, and depends on the interplay between the electrohydrodynamic flow, the chemical kinetics of the species and its characteristic lifetime.

(Invited) Behavior of Ionic Liquid and Solute Molecules at Electrode/Ionic Liquid Interface

Ionic liquids (ILs) have attracted keen attention due to its applicability to various kinds of electrochemical devices such as Li-ion battery, wet-type solar battery, etc. For most of such applications, the interface between ionic liquid and electrodes plays an important role in their performance. However, we still lack enough knowledge on the interface structure and spatial distribution of chemical species during the electrochemical processes. 1. Nanostructured electrode In an application of electrochemical devices, nanostructured electrodes have advantage on their large surface area leading to accumulation of large density energy at the interface. However, recent reports on IL/electrode interfaces revealed that quite strange structures can be formed and it is not clear how the interface forms and how it changes by forming an electric double layer (EDL). We investigated the interfacial capacitance of nanostructured Au electrodes with periodic 100 nm-sized dimples using electrochemical impedance spectroscopy (EIS). It was revealed that the capacitance of the nanostructured electrode was largely different from that of the flat electrode in the whole potential range. This result suggests that the thickness of the electric double layer formed in the nano-sized dimple is different from that formed on the flat surface. The dimple size dependence on the capacitance was also observed. 2. ILs confined in Nanopore It is known that ILs confined in small spaces exhibit characteristic properties which are different from those of bulk ILs. Therefore, it is an interesting subject to study how ILs and solutes behave in the nano-micro sized pore. We investigated the properties of IL(BMI-TFSA) and solute ions (Au3+, Ag+, Mg2+ etc.) confined in the porous silica whose diameter was 1.8 nm using XPS, IR and TEM. It was revealed that the molar ratio of all the ions existing in the pore is largely different from that in the bulk. Interestingly, the molar ratio of Au3+ to BMI+ (or TFSA-) was very large comparing with that of as prepared BMI-TFSA solution. The result of N-1s XPS spectra revealed that cation and anion of IL were organized in the nanopores. Such characteristic local structure in nanospace may affect the catalytic reaction in the pore. So, we tried to synthesize Au nanoparticles via a reductive reaction in an ionic liquid confined in a nanopore using an X-ray irradiation technique[1,2]. High density Au particles whose size was limited by the pore diameter were observed (Fig. 1 left). This result is very interesting and benefits not only for the formation of the high density carrier but also for the development of the porous electrode used for various kinds of electrochemical devices and/or techniques such as battery, electrochemical deposition, impurity removing devices and so on, because condensation of reactant ions in the nanopore leads to the effective electrochemical (or chemical) reaction. 3. Diffusion behavior of solute ions at IL/electrode interface It is known that most of ILs show extremely low vapor pressure, which enables us to apply various techniques that need vacuum conditions such as photoelectron spectroscopy. We recently developed the electrochemical photoelectron spectroscopy (EC-PES) to carry out in-situ XPS and UPS measurements under electrochemical condition using 3-electrodes type cell (Fig. 1 right). By observing the spatial distribution of concentration of contained ions close to the electrode (The mole fraction of solute and ionic liquid ions was plotted against the distance from the edge of the working electrode), we firstly succeeded in revealing the extraordinary diffusion behavior of solute ion (Ag+) in ionic liquid (BMI-TFSA). Under the applied potential of 0 V vs. Pt, the concentration of Ag+ ion was uniform. Under the applied potential of -1.2 V vs. Pt, a drastic change was observed: the concentration of Ag+ ion decreased at the edge of electrode, and gradually increased at larger distance from the electrode. This indicates that the diffusion layer was formed by the reductive reaction of Ag+ (Ag+ + e- => Ag) at the electrode. The thickness of the observed diffusion layer was 240 μm, which was much larger than the value usually supposed. By the numerical simulation, we revealed that the metal ions diffused by the hopping-like mechanism, in which the apparent diffusion coefficient increased with increasing of the concentration of ‘holes’ (vacancy formed between IL molecules) acting as hopping sites. [1] A. Imanishi, M. Tamura, S. Kuwabata, Chem. Commun. (2009)1775. [2] A. Imanishi, S. Gonsui, T. Tsuda, S. Kuwabata, K. Fukui, Phys. Chem. Chem. Phys., 13(2011)14823. Figure 1

(Invited) A Novel Diffusion Mechanism of Metal Ions at Ionic Liquid/Electrode Interface Studied By in-Situ Electrochemical XPS

Ionic liquids (ILs) have attracted keen attention due to its applicability to various kinds of electrochemical devices such as Li-ion battery, wet-type solar battery, etc. For most of such applications, the interface between ionic liquid and electrodes plays an important role in their performance. However, we still lack enough knowledge on the interface structure and spatial distribution of chemical species during the electrochemical processes. It is known that most of ILs show extremely low vapor pressure, which enables us to apply various techniques that need vacuum conditions such as photoelectron spectroscopy. We recently developed the electrochemical photoelectron spectroscopy (EC-PES) to carry out in-situ XPS and UPS measurements under electrochemical condition using 3-electrodes type cell (Fig. 1). In this study, we investigated the molecular behavior of ILs and its solute near the electrode under cathodic applied potential. BMI-TFSA (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide) and Ag-TFSA were mixed in a test tube, followed by stirring under ultrasonic irradiation to obtain 6.99 wt% Ag-TFSA/BMI-TFSA solution. The electrochemical cell was filled with thus prepared solution, and was left for over 6 h in a vacuum chamber to remove water. After that, the cell was transferred to an adjacent ultra high vacuum chamber of XPS. The electrode potential was controlled in a normal three-electrode system by a commercial potentiostat and potential programmer, with a Pt plate as the counter electrode (CE) and Pt wire as the reference electrode (RE). An Au plate, as the working electrode (WE), was placed on the IL surface (Au plane was set parallel to the liquid/air(or vacuum) interface). Spatial distribution of concentration and chemical states of each ions were investigated by spatial resolved XPS measurement. Al-Kα line (1486.6 eV) was used as an X-ray source. Fig. 2 shows the mole fraction of Ag+ ions plotted against the distance from the edge of the working electrode. Under the applied potential of 0 V vs. Pt, the concentration of Ag+ ion was uniform (not shown). Under the applied potential of -1.2 V vs. Pt, a drastic change was observed: the concentration of Ag+ ion decreased at the edge of electrode, and gradually increased at larger distance from the electrode. This indicates that the diffusion layer was formed by the reductive reaction of Ag+ (Ag+ + e- => Ag) at the electrode. The thickness of the observed diffusion layer was 240 µm, which was much larger than the value usually supposed. It was also found that the ratio of cation and anion was also affected by the applied potential. By the numerical simulation, it was revealed that this was due to a concentration-dependent diffusion coefficient, which is characteristic of the ionic liquid. We also revealed that the metal ions diffused by the hopping-like mechanism, in which the apparent diffusion coefficient increased with increasing of the concentration of ‘holes’ (vacancy formed between IL molecules) acting as hopping sites. The results on other kinds of metal ions and ILs will also be discussed. Figure 1

Hydrogeochemical modelling of corrosion effects and barite scaling in deep geothermal wells of the North German Basin using PHREEQC and PHAST

Highly mineralised formation water can cause compositional and structural alteration in well casing materials. Furthermore, precipitating minerals can lead to the clogging of wells and damage to pumping equipment. Hydrogeochemical modelling is a helpful tool for evaluating and predicting such natural hydrogeochemical and technically induced processes (e.g., scaling, corrosion, outgassing), during drilling and operation of a geothermal well. The software PHREEQC and its databases are used to model such processes at chemical equilibrium conditions. For a better understanding of the spatial distribution of chemical species and precipitating phases within an aquifer the software PHAST, which combines three-dimensional water flow and chemical equilibrium modelling is also applied.Formation waters from the North German Basin are taken as an example of the capabilities and limitations of such hydrogeochemical models. The groundwater in the deep aquifers in this area is dominated by Na+ and Cl− or by Na+, Ca2+ and Cl−. The amount of total dissolved solids ranges from 100gL−1 up to 400gL−1 and increases with depth and temperature. During the operation of geothermal wells in the North German Basin, various scalings (e.g., Ba and Sr sulphates, Fe sulphides and Pb hydroxides) are observed. Several model applications elucidating the hydrogeochemical behaviour of deep geothermal systems are presented. The first model is a simple example of iron corrosion at different environmental conditions, and is followed by modelling of the hydrogeochemical processes during the operation of one geothermal well in the North German Basin, at a depth of 4000m, a temperature of 150°C and with a Total Dissolved Solids (TDS) content of about 250gL−1. To evaluate the effects of barium sulphate scaling in a deep aquifer, induced by injected surface water containing Ca2+ and SO42−, a one- and a three-dimensional model scenario are presented. Furthermore, one scenario is calculated in which EDTA is added, to prevent the precipitation of barite by the formation of aqueous complexes.

Mitigating Voltage Fade in Cathode Materials By Improving Atomic Level Spatial Uniformity of Chemical Species

Lithium- and manganese-rich (LMR) layered-structure cathode materials deliver a much higher energy density than traditional cathode materials such as LiMn2O4 spinel and LiCoO2. However, significant challenges, including voltage fade and limited cycle life in LMR cathodes still remain to be overcome prior to their large-scale market penetration.Here, we report on the direct correlation between voltage fade and atomic level spatial distribution of chemical species among LMR cathode materials (Li[Li0.2Ni0.2M0.6]O2) prepared by several methods, including co-precipitation (CP), sol-gel (SG) and hydrothermal assisted (HA) methods. Quantitative chemical composition analysis was performed on these materials using large-area X-ray energy dispersive spectroscopy (XEDS) mapping. Meanwhile, we used aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS) to acquire detailed crystallographic data on Li[Li0.2Ni0.2Mn0.6]O2 cathode prepared by different methods. The atomic contrast in high-angle annular dark field (HAADF) STEM imaging identified the details of stacking and ordering in the particles while EELS chemical analysis revealed important chemistry information. We found that the materials prepared by the CP and SG methods exhibit a relatively high propensity for Ni segregation, leading to fast voltage fade and poor cycling stability. However, material prepared by the HA method exhibits very uniform Ni distribution and greatly reduced voltage fade. To the best of our knowledge, this is the first direct atomic-scale evidence to correlate atomic level cation uniformities with the electrochemical performance of cathode materials. More importantly, the voltage fade and energy degradation of LMR cathode materials can be significantly mitigated by improving the uniformity of chemical species in atomic level that are strongly affected by the preparation methods and synthesis conditions. These results also shine the light on the current debate regarding to the average/local structure of LMR cathode materials. LMR cathodes prepared by co-precipitation and sol-gel methods exhibit significant Ni segregation and dominated by LiMO2 R-3m phase, where the preferential segregation of Ni blocks lithium ion diffusion channels, weaken nickel-manganese interactions, lead to easy reduction of the manganese ions and fast voltage/capacity fade. In contrast, LMR cathodes prepared by the hydrothermal assisted method form a solid solution dominated by Li2MO3C2/m monoclinic symmetry with largely suppressed Ni segregation and are more stable against excessive lithium ion removal, enhance Ni-Mn interaction and stabilize crystal structure, leads to greatly reduced voltage fade and excellent cycling stability of LMR cathodes. Therefore, LMR cathodes with uniform distribution of chemical species (minimal Ni segregation) are very promising for use in high-energy Li-ion batteries for large-scale practical applications. The fundamental correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials found in this work also provides new perspective on the design and development of other functional materials with significantly enhanced stability. Acknowledgements This work is supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No. 18769, under the Batteries for Advanced Transportation Technologies program. The microscopic study described in this paper is supported by the Laboratory Directed Research and Development Program as part of the Chemical Imaging Initiative at Pacific Northwest National Laboratory (PNNL). The work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at PNNL. PNNL is operated by Battelle for the DOE under Contract DE-AC05-76RLO1830. The authors also would like to thank M. M. Thackeray for useful discussions.

Enhancement of the Spatial Resolution of the Chemical Imaging Sensor by a Hybrid Fiber-Optic Illumination

The chemical imaging sensor, which is based on the principle of the light-addressable potentiometric sensor (LAPS), is a powerful tool to visualize the spatial distribution of chemical species on the sensor surface. The spatial resolution of this sensor depends on the diffusion of photocarriers excited by a modulated light. In this study, a novel hybrid fiber-optic illumination was developed to enhance the spatial resolution. It consists of a modulated light probe to generate a photocurrent signal and a ring of constant light, which suppresses the lateral diffusion of minority carriers excited by the modulated light. It is demonstrated that the spatial resolution was improved from 92μm to 68μm.

Chemical Analysis Below the Diffraction Limit using Infrared-Coupled Atomic Force Microscopy (AFM-IR)

High resolution infrared spectroscopy is a popular technique for investigating biological structures. It is relatively simple to use, and in some cases considered to be a non-destructive technique. By combining atomic force microscopy and infrared spectroscopy (AFM-IR) into a single bench-top instrument, it is possible to resolve chemical differences on the scale of ca. 100 to 200 nm, which often reveals information that could not have been obtained with conventional infrared microspectroscopy. The AFM-IR technique is based on observing the rapid thermal expansion and contraction of material due to the absorption of nanoseconds-long IR radiation pulses, which is collectively known as the photothermal induced resonance (PTIR) phenomenon. This rapid movement is captured by an AFM cantilever equipped with a sharp tip that is in direct contact with the sample material. The resulting amplitude of the ringdown response is directly related to the absorption characteristics of the material across a given range of wavenumbers. Therefore, AFM-IR spectral band shapes are similar to the bulk IR measurement and the spectra are searchable against existing databases. By further modulating the pulse frequency of the infrared laser radiation to coincide with the contact resonance of the AFM cantilever, sensitivity is enhanced, enabling the detection of ∼ 20 nm-thick organic materials. In this presentation, we will examine several biological systems using this AFM-IR technique. Spectral changes in the IR spectra can be seen through the whole or cross-sections of proteinaceous materials. Functional group IR images acquired using the AFM-IR technique also reveal the spatial distribution of chemical species in the form of absorption characteristics can be achieved at below the diffraction limit.

Nanomotor mechanisms and motive force distributions from nanorotor trajectories

Nanomotors convert chemical energy into mechanical motion. For a given motor type, the underlying chemical reaction that enables motility is typically well known, but the detailed, quantitative mechanism by which this reaction breaks symmetry and converts chemical energy to mechanical motion is often less clear, since it is difficult experimentally to measure important parameters such as the spatial distribution of chemical species around the nanorotor during operation. Without this information on how motor geometry affects motor function, it is difficult to control and optimize nanomotor behavior. Here we demonstrate how one easily observable characteristic of nanomotor operation-the visible trajectory of a nanorotor-can provide quantitative information about the role of asymmetry in nanomotor operation, as well as insights into the spatial distribution of motive force along the surface of the nanomotor, the motive torques, and the effective diffusional motion.

Visualization of enzymatic reaction in a microfluidic channel using chemical imaging sensor

The chemical imaging sensor is a semiconductor-based chemical sensor which is capable of visualizing the spatial distribution of chemical species. In this study, we applied the chemical imaging sensor to a dye-free method of visualizing an enzymatic reaction in a microfluidic channel. Microgel beads loaded with enzyme molecules were trapped in the microchannel. The substrate of the enzyme was injected from the upstream, and then the product of enzymatic reaction was detected in the downstream as pH change. The spatiotemporal change of pH distribution caused by the enzymatic reaction was successfully visualized. The possibility of chemical imaging inside a microchannel also suggests potential application, for example, to chromatography.