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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Aqueous Cation-Amide Binding: Free Energies and IR Spectral Signatures by Ab Initio Molecular Dynamics

Understanding specific ion effects on proteins remains a considerable challenge. N-methylacetamide serves as a useful proxy for the protein backbone that can be well characterized both experimentally and theoretically. The spectroscopic signatures in the amide I band reflecting the strength of the interaction of alkali cations and alkali earth dications with the carbonyl group remain difficult to assign and controversial to interpret. Herein, we directly compute the IR shifts corresponding to the binding of either sodium or calcium to aqueous N-methylacetamide using ab initio molecular dynamics simulations. We show that the two cations interact with aqueous N-methylacetamide with different affinities and in different geometries. Since sodium exhibits a weak interaction with the carbonyl group, the resulting amide I band is similar to an unperturbed carbonyl group undergoing aqueous solvation. In contrast, the stronger calcium binding results in a clear IR shift with respect to N-methylacetamide in pure water. Support from the Czech Ministry of Education (grant LH12001) is gratefully acknowledged. EP thanks the International Max-Planck Research School for support and the Alternative Sponsored Fellowship program at Pacific Northwest National Laboratory (PNNL). PJ acknowledges the Praemium Academie award from the Academy of Sciences. Calculations of the free energy profiles were made possible through generous allocation of computer time from the North-German Supercomputing Alliance (HLRN). Calculations of vibrational spectra were performed in part using the computational resources in the National Energy Research Supercomputing Center (NERSC) at Lawrence Berkeley National Laboratory. This work was supported by National Science Foundation grant CHE-0431312. CJM is supported by the U.S. Department of Energy`s (DOE) Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. PNNL is operated for the Department of Energy by Battelle. MDB is grateful for the support of the Linus Pauling Distinguished Postdoctoral Fellowship Program at PNNL.

calcium↗
DOE OSTI2010

Modeling aerosol growth by aqueous chemistry in nonprecipitating stratiform cloud

A new microphysics module based on a two-dimensional (2D) joint size distribution function representing both interstitial and cloud particles is developed and applied to studying aerosol processing in non-precipitating stratocumulus clouds. The module is implemented in a three-dimensional dynamical framework of a large-eddy simulation (LES) model and in a trajectory ensemble model (TEM). Both models are used to study the modification of sulfate aerosol by the activation - aqueous chemistry - resuspension cycle in shallow marine stratocumulus clouds. The effect of particle mixing and different size-distribution representations on modeled aerosol processing are studied in a comparison of the LES and TEM simulations with the identical microphysics treatment exposes and a comparison of TEM simulations with a 2D fixed and moving bin microphysics. Particle mixing which is represented in LES and neglected in the TEM leads to the mean relative per particle dry mass change in the TEM simulations being about 30% lower than in analogous subsample of LES domain. Particles in the final LES spectrum are mixed in from different “parcels”, some of which have experienced longer in-cloud residence times than the TEM parcels, all of which originated in the subcloud layer, have. The mean relative per particle dry mass change differs by 14% between TEM simulations with fixed and moving bin microphysics. Finally, the TEM model with the moving bin microphysics is used to evaluate assumptions about liquid water mass partitioning among activated cloud condensation nuclei (CCN) of different dry sizes. These assumptions are used in large-scale models to map the bulk aqueous chemistry sulfate production, which is largely proportional to the liquid water mass, to the changes in aerosol size distribution. It is shown that the commonly used assumptions that the droplet mass is independent of CCN size or that the droplet mass is proportional to the CCN size to the third power do not perform well in the considered case. The explicitly predicted water partitioning indicates that the mean mass of droplets participating in the models aqueous chemistry calculations is proportional to the dry CCN size.

58 GEOSCIENCES↗
DOE OSTI2015

Aqueous proton transfer across single-layer graphene

Proton transfer across single-layer graphene proceeds with large computed energy barriers and is therefore thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while pyrylium-like ether terminations shut down proton exchange. Unfavourable energy barriers to helium and hydrogen transfer indicate the process is selective for aqueous protons.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A high-capacity and long-life aqueous rechargeable zinc battery using a metal oxide intercalation cathode

Although non-aqueous Li-ion batteries possess significantly higher energy density than their aqueous counterparts, the latter can be more feasible for grid-scale applications when cost, safety and cycle life are taken into consideration. Moreover, aqueous Zn-ion batteries have an energy storage advantage over alkali-based batteries as they can employ Zn metal as the negative electrode, dramatically increasing energy density. However, their development is plagued by a limited choice of positive electrodes, which often show poor rate capability and inadequate cycle life. We report a vanadium oxide bronze pillared by interlayer Zn 2+ ions and water (Zn 0.25 V 2 O 5 • n H 2 O), as the positive electrode for a Zn cell. A reversible Zn 2+ ion (de)intercalation storage process at fast rates, with more than one Zn 2+ per formula unit (a capacity up to 300 mAh g -1 ), is characterized. The Zn cell offers an energy density of ~450 Wh l -1 and exhibits a capacity retention of more than 80% over 1,000 cycles, with no dendrite formation at the Zn electrode.

25 ENERGY STORAGE↗
DOE OSTI2019

Electrochemically activated spinel manganese oxide for rechargeable aqueous aluminum battery

Aluminum is a naturally abundant, trivalent charge carrier with high theoretical specific capacity and volumetric energy density, rendering aluminum-ion batteries a technology of choice for future large-scale energy storage. Nonetheless, the frequent collapse of the host structure of the cathode materials and sluggish kinetics of aluminum ion diffusion have thus far hampered the realization of practical battery devices. Here, we synthesize Al x MnO 2 •nH 2 O by an in-situ electrochemical transformation reaction to be used as a cathode material for an aluminum-ion battery with a configuration of Al/Al(OTF) 3- H 2 O/Al x MnO 2 •nH 2 O. This cell is not only based on aqueous electrolyte chemistry but also delivers a high specific capacity of 467 mAh g -1 and a record high energy density of 481 Wh kg -1 . The high safety of aqueous electrolyte, facile cell assembly and the low cost of materials suggest that this aqueous aluminum-ion battery holds promise for large-scale energy applications.

25 ENERGY STORAGE↗
DOE OSTI2026

Nanoengineering of non-aqueous liquid electrolyte solutions for future lithium metal batteries

Research and development of non-aqueous electrolyte solutions are essential for practical advancement towards the production of high-energy lithium metal batteries (LMBs). An ideal LMB electrolyte solution should enable highly efficient, uniform and prolonged lithium metal plating and stripping, preserve the electrodes’ electro(chemo)mechanical properties and ensure compatibility with all cell components. However, despite extensive research efforts, scientists have yet to achieve an electrolyte design that meets these requirements simultaneously. Here, by examining the nanoengineering aspects of various non-aqueous electrolyte solution designs, we elucidate the understanding of the nanoscale physicochemical and electrochemical processes taking place in LMBs, which are mainly governed by the thermodynamic and kinetic properties of the electrolyte system. We also explore emerging research directions and propose an accelerated, iterative framework that integrates nanoengineering principles with machine learning, high-throughput computation and experimentation to facilitate the development of next-generation non-aqueous electrolyte solutions for practical LMBs.

Weintz, Dominik↗
DOE OSTI2019

Aqueous Li-ion battery enabled by halogen conversion–intercalation chemistry in graphite

The use of 'water-in-salt' electrolytes has considerably expanded the electrochemical window of aqueous lithium-ion batteries to 3 to 4 volts, making it possible to couple high-voltage cathodes with low-potential graphite anodes. However, the limited lithium intercalation capacities (less than 200 milliampere-hours per gram) of typical transition-metal-oxide cathodes preclude higher energy densities. Partial or exclusive anionic redox reactions may achieve higher capacity, but at the expense of reversibility. Here we report a halogen conversion-intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 milliampere-hours per gram (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li + . Experimental characterization and modelling attribute this high specific capacity to a densely packed stage-I graphite intercalation compound, C 3.5 [Br 0.5 Cl 0.5 ], which can form reversibly in water-in-bisalt electrolyte. By coupling this cathode with a passivated graphite anode, we create a 4-volt-class aqueous Li-ion full cell with an energy density of 460 watt-hours per kilogram of total composite electrode and about 100 per cent Coulombic efficiency. Here, this anion conversion-intercalation mechanism combines the high energy densities of the conversion reactions, the excellent reversibility of the intercalation mechanism and the improved safety of aqueous batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Optimal thermodynamic conditions to minimize kinetic by-products in aqueous materials synthesis

Abstract Phase diagrams offer substantial predictive power for materials synthesis by identifying the stability regions of target phases. However, thermodynamic phase diagrams do not offer explicit information regarding the kinetic competitiveness of undesired by-product phases. Here we propose a quantitative and computable thermodynamic metric to identify synthesis conditions under which the propensity to form kinetically competing by-products is minimized. We hypothesize that thermodynamic competition is minimized when the difference in free energy between a target phase and the minimal energy of all other competing phases is maximized. We validate this hypothesis for aqueous materials synthesis through two empirical approaches: first, by analysing 331 aqueous synthesis recipes text-mined from the literature; and second, by systematic experimental synthesis of LiIn(IO 3 ) 4 and LiFePO 4 across a wide range of aqueous electrochemical conditions. Our results show that even for synthesis conditions that are within the stability region of a thermodynamic Pourbaix diagram, phase-pure synthesis occurs only when thermodynamic competition with undesired phases is minimized.

Wang, Zheren (ORCID:0000000227429451)↗
DOE OSTI2013

On-demand generation of aqueous two-phase microdroplets with reversible phase transitions

Aqueous two-phase systems contained entirely within microdroplets enable a bottom-up approach to mimicking the dynamic microcompartmentation of biomaterial that naturally occurs within the cytoplasm of cells. Here, we demonstrate the on-demand generation of femtolitre aqueous two-phase droplets within a microfluidic oil channel. Gated pressure pulses were used to generate individual, stationary two-phase microdroplets with a well-defined time zero for carrying out controlled and sequential phase transformations over time. Reversible phase transitions between single-phase, two-phase, and core-shell microgel states were obtained via evaporation-induced dehydration and on-demand water rehydration. In contrast to other microfluidic aqueous two-phase droplets, which require continuous flows and high-frequency droplet formation, our system enables the controlled isolation and reversible transformation of a single microdroplet and is expected to be useful for future studies in dynamic microcompartmentation and affinity partitioning.

Boreyko, Jonathan B↗
DOE OSTI2015

Low-temperature aqueous-phase reforming of ethanol on bimetallic PdZn catalysts

Bimetallic PdZn catalysts supported on carbon black (CB) and carbon nanotubes (CNTs) were found to be selective for CO-free H-2 production from ethanol at low temperature (250 degrees C). On Pd, the H-2 yield was low (similar to 0.3 mol H-2/mol ethanol reacted) and the CH4/CO2 ratio was high (similar to 1.7). Addition of Zn to Pd formed the intermetallic PdZn beta phase (atomic ratio of Zn to Pd is 1) with increased H-2 yield (similar to 1.9 mol H-2/mol ethanol reacted) and CH4/CO2 ratio of <1. The higher H-2 yield and low CH4 formation was related to the improved dehydrogenation activity of the L1(0) PdZn beta phase. The TOF increased with particle size and the CNTs provided the most active and selective catalysts, which may be ascribed to pore-confinement effects. Furthermore, no significant changes in either the supports or the PdZn beta particles was found after aqueous-phase reforming (APR) indicating that the metal nanoparticles and the carbon support are hydrothermally stable in the aqueous phase at elevated temperatures and pressures (>200 degrees C, 65 bar). No CO was detected for all the catalysts performed in aqueous-phase reaction, indicating that both monometallic Pd and bimetallic PdZn catalysts have high water-gas shift activity during APR. However, the yield of H-2 is considerably lower than the theoretical value of 6 H-2 per mole ethanol which is due to the presence of oxygenated products and methane on the PdZn catalysts.

ALKANES↗
DOE OSTI2015

Sailing into uncharted waters: recent advances in the in situ monitoring of catalytic processes in aqueous environments

Catalysis in aqueous environments is attracting enormous interest. Many characterization methods are well established at gas-solid interfaces and a majority of the surface-science approaches were historically limited to model surfaces and vacuum conditions. However, practical scenarios with complex catalyst structures, elevated temperatures and pressures, as well as the presence of two or more condensed phases, can pose significant challenges to these techniques, particularly for catalysts at their dynamic working states. In such contexts, this review highlights the advances over the past five years in the in situ and real-time detection of catalytic processes and related phenomena in aqueous media, ideally under realistic conditions. We underline latest technical innovations, describe novel chemistries that are made accessible by recently developed toolboxes, and discuss future directions of in situ and time-resolved analytical approaches applicable to aqueous phase catalysis.

Heterogeneous catalysis, in situ, time-resolved, s↗
DOE OSTI2014

Structure and water exchange dynamics of hydrated oxo halo ions in aqueous solution using QMCF MD simulation, large angle X-ray scattering and EXAFS

Theoretical ab initio quantum mechanical charge field molecular dynamics (QMCF MD) has been applied in conjunction with experimental large angle X-ray scattering (LAXS) and EXAFS measurements to study structure and dynamics of the hydrated oxo chloro anions chlorite, ClO 2 – , chlorate, ClO 3 – , and perchlorate, ClO 4 – . In addition, the structures of the hydrated hypochlorite, ClO – , bromate, BrO 3 – , iodate, IO 3 – and metaperiodate, IO 4 – , ions have been determined in aqueous solution by means of LAXS. The structures of the bromate, metaperiodate, and orthoperiodate, H 2 IO 6 3– , ions have been determined by EXAFS as solid sodium salts and in aqueous solution as well. The results show clearly that the only form of periodate present in aqueous solution is metaperiodate. The Cl–O bond distances in the hydrated oxo chloro anions as determined by LAXS and obtained in the QMCF MD simulations are in excellent agreement, being 0.01–0.02 Å longer than in solid anhydrous salts due to hydration through hydrogen bonding to water molecules. The oxo halo anions, all with unit negative charge, have low charge density making them typical structure breakers, thus the hydrogen bonds formed to the hydrating water molecules are weaker and more short-lived than those between water molecules in pure water. The water exchange mechanism of the oxo chloro anions resembles those of the oxo sulfur anions with a direct exchange at the oxygen atoms for perchlorate and sulfate. Here, the water exchange rate for the perchlorate ion is significantly faster, τ 0.5 = 1.4 ps, compared to the hydrated sulfate ion and pure water, τ 0.5 = 2.6 and 1.7 ps, respectively. The angular radial distribution functions show that the chlorate and sulfite ions have a more complex water exchange mechanism. As the chlorite and chlorate ions are more weakly hydrated than the sulfite ion the spatial occupancy is less well-defined and it is not possible to follow any well-defined migration pattern as it is difficult to distinguish between hydrating water molecules and bulk water in the region close to the ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Optimizing supercapacitor electrode density: achieving the energy of organic electrolytes with the power of aqueous electrolytes

The value of electrode density is often overlooked in the pursuit of impressive supercapacitor metrics. Low-density electrodes deliver the best performance in terms of gravimetric energy and power densities when only the mass of the electrodes is considered. However, energy and power values with respect to the total system mass (electrode + electrolyte) or volume are more meaningful for practical application. Low-density electrodes are impractical due to both large mass contributions by the electrolyte and large system volumes. In this work, we use highly compressible graphene aerogel electrodes (up to 87.5% volumetric compression) to systematically characterize the effects of electrode density on energy and power metrics. The results reveal that electrode density is similar to electrode thickness in that both parameters have a squared effect on power. Accounting for the aqueous electrolyte's mass lowered the gravimetric energy and power by almost an order of magnitude for 0.144 g cm –3 dense carbon electrodes but only by a factor of 1.5 when the electrode density was increased to 1.15 g cm –3 through compression. The high-density electrodes achieve 8 W h kg –1 , 70 000 W kg –1 , and 144 F cm –3 in a symmetric electrode setup after factoring in the aqueous electrolyte's mass. Therefore, in the pursuit of high energy per mass, it can be just as effective to lower the system's mass with smaller electrolyte fractions as it is to use electrolytes with larger voltage ranges. High electrode densities allow aqueous electrolyte supercapacitors to attain energy densities per the system mass comparable to those of commercially-available organic electrolyte supercapacitors while maintaining 10–100× greater power.

25 ENERGY STORAGE↗
DOE OSTI2019

Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization

The structural changes underlying the deactivation of Sn-Beta zeolites under aqueous-phase reaction conditions at elevated temperatures (373 K) are investigated using spectroscopic characterization and site titration techniques together with turnover rates for glucose isomerization, a well-understood probe reaction for which changes in measured rates can be ascribed to specific changes in catalyst structure. In the case of hydrophobic, low-defect Sn-Beta zeolites (Sn-Beta-F), treatment in hot liquid water (373 K) for short times (<1 h) prior to reaction causes glucose–fructose isomerization turnover rates (per open Sn site, 373 K) to increase, while longer-term exposure (>3 h) to hot liquid water causes turnover rates to decrease and approach values characteristic of hydrophilic, defect-rich Sn-Beta zeolites (Sn-Beta-OH). However, turnover rates on hydrophilic Sn-Beta-OH zeolites are insensitive to the duration of hot liquid water exposure prior to reaction. Activation and deactivation phenomena on Sn-Beta-F zeolites occur concomitantly with the formation of silanol defects (by ~2–10×) with increasing durations (0–24 h) of hot water treatment, despite negligible differences in open and closed Sn site speciation as quantified ex situ by CD 3 CN IR spectra. Mechanistic interpretations of these phenomena suggest that silanol groups present at low densities serve as binding sites for water molecules and clusters, which confer enthalpic stability to kinetically-relevant hydride-shift transition states and increase turnover rates, while silanol groups present in higher densities stabilize extended hydrogen-bonded water networks, which entropically destabilize kinetically-relevant transition states and decrease turnover rates. Intraporous voids within hydrophobic Sn-Beta-F zeolites become increasingly hydrophilic as silanol groups are formed by hydrolysis of framework siloxane bridges with increasing durations of water treatment, thereby decreasing aqueous-phase glucose isomerization turnover rates (per open Sn site). These findings imply design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Site dependent reactivity of Pt single atoms on anatase TiO 2 (101) in an aqueous environment

The TiO 2 –Pt–water interface is of great relevance in photocatalysis where Pt is widely used as a co-catalyst for The TiO 2 –Pt–water interface is of great relevance in photocatalysis where Pt is widely used as a co-catalyst for enhancing hydrogen evolution in aqueous TiO 2 . Using ab initio molecular dynamics, we investigated this interface focusing on Pt single atoms supported on anatase TiO 2 (101) in a water environment. Based on recent experiments showing a broad distribution of Pt coordination sites in TiO 2 , we examined six distinct single-Pt supported species with different nominal Pt oxidation states, namely: Pt, PtOH, and PtO 2 species adsorbed on the stoichiometric surface; Pt adsorbed at a surface oxygen vacancy (O v ); and Pt substituting a surface Ti cation (PtTi), both without and with an accompanying O v (Pt Ti + O v ). As found for the pristine anatase surface, interfacial water remained intact in the presence of a nearly neutral Pt adatom within the time duration of our simulations (~15 ps). Similarly, no (or only temporary) water dissociation was observed at the Pt Ti + O v and PtO 2 interfaces, due to the formation of very stable planar Pt coordination structures that interact only weakly with water. In contrast, water dissociated with OH – (H + ) on the Pt atom when this substituted a surface Ti (oxygen) ion as well as on PtOH. Lastly, the significant proton affinity of Pt atoms at surface oxygen vacancies suggests that negatively charged Pt species are particularly efficient at catalyzing hydrogen evolution in aqueous TiO 2 .hydrogen evolution in aqueous TiO 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2019

Gamma radiolysis of hydrophilic diglycolamide ligands in concentrated aqueous nitrate solution

The radiation chemistry of a series of hydrophilic diglycolamides (DGAs: TEDGA, Me-TEDGA, Me 2 -TEDGA, and TPDGA) has been investigated under neutral pH, concentrated aqueous nitrate solution conditions. A combination of steady-state gamma and time-resolved pulsed electron irradiation experiments, supported by advanced analytical techniques and multi-scale modeling calculations, have demonstrated that: (i) the investigated hydrophilic DGAs undergo first-order decay with an average dose constant of (-3.18 ± 0.23) × 10 -6 Gy -1 ; (ii) their degradation product distributions are similar to those under pure water conditions, except for the appearance of NO x adducts; and (iii) radiolysis is driven by hydroxyl and nitrate radical oxidation chemistry moderated by secondary degradation product scavenging reactions. Overall, the radiolysis of hydrophilic DGAs in concentrated, aqueous nitrate solutions is significantly slower and less structurally sensitive than under pure water conditions, similar to their lipophilic analogs. Acid hydrolysis, not radiolysis, is expected to limit their useful lifetime. These findings are promising for the deployment of hydrophilic DGAs as actinide aqueous phase stripping and hold-back agents, due to the presence of high concentrations of nitrate in envisioned large-scale process conditions.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Failure of molecular dynamics to provide appropriate structures for quantum mechanical description of the aqueous chloride ion charge-transfer-to-solvent ultraviolet spectrum

The lowest band in the charge-transfer-to-solvent ultraviolet absorption spectrum of aqueous chloride ion is studied by experiment and computation. Interestingly, the experiments indicate that at concentrations up to at least 0.25 M, where calculations indicate ion pairing to be significant, there is no notable effect of ionic strength on the spectrum. The experimental spectra are fitted to aid comparison with computations. Classical molecular dynamic simulations are carried out on dilute aqueous Cl - , Na + , and NaCl, producing radial distribution functions in reasonable agreement with experiment and, for NaCl, clear evidence of ion pairing. Clusters are extracted from the simulations for quantum mechanical excited state calculations. Accurate ab initio coupled-cluster benchmark calculations on a small number of representative clusters are carried out and used to identify and validate an efficient protocol based on time-dependent density functional theory. The latter is used to carry out quantum mechanical calculations on thousands of clusters. The resulting computed spectrum is in excellent agreement with experiment for the peak position, with little influence from ion pairing, but is in qualitative disagreement on the width, being only about half as wide. It is concluded that simulation by classical molecular dynamics fails to provide an adequate variety of structures to explain the experimental CTTS spectrum of aqueous Cl - .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Reactive force fields for aqueous and interfacial magnesium carbonate formation

Here we develop Mg/C/O/H ReaxFF parameter sets for two environments: an aqueous force field for magnesium ions in solution and an interfacial force field for minerals and mineral–water interfaces. Since magnesium is highly ionic, we choose to fix the magnesium charge and model its interaction with C/O/H through Coulomb, Lennard-Jones, and Buckingham potentials. We parameterize the forcefields against several crystal structures, including brucite, magnesite, magnesia, magnesium hydride, and magnesium carbide, as well as Mg 2+ water binding energies for the aqueous forcefield. Then, we test the forcefield for other magnesium-containing crystals, solvent separated and contact ion-pairs and single-molecule/multilayer water adsorption energies on mineral surfaces. We also apply the forcefield to the forsterite–water and brucite–water interface that contains a bicarbonate ion. We observe that a long-range proton transfer mechanism deprotonates the bicarbonate ion to carbonate at the interface. Free energy calculations show that carbonate can attach to the magnesium surface with an energy barrier of about 0.22 eV, consistent with the free energy required for aqueous Mg–CO 3 ion pairing. Also, the diffusion constant of the hydroxide ions in the water layers formed on the forsterite surface are shown to be anisotropic and heterogeneous. These findings can help explain the experimentally observed fast nucleation and growth of magnesite at low temperature at the mineral–water–CO 2 interface in water-poor conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗