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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Controlling ZIF-67 crystals formation through various cobalt sources in aqueous solution

Zeolitic imidazolate frameworks ZIF-67 were prepared under hydrothermal (120 °C) and non-hydrothermal (room temperature) from various cobalt sources and 2-methylimidazolate (Hmim) in aqueous solution within 30 min. The particle size and morphology were found to be related to the reactivity of the cobalt salt, Hmim/Co{sup 2+} molar ratios and experimental condition. Using Co(NO{sub 3}){sub 2} as cobalt source, small-sized ZIF-67 crystals with agglomeration were formed. For CoCl{sub 2}, small-sized rhombic dodecahedron were obtained. While large-sized crystals of rhombic dodecahedron structure were obtained from CoSO{sub 4} and Co(OAc){sub 2}. Under hydrothermal condition, the size of ZIF-67 crystals tended to be more uniform and the morphology were more regular comparing to non-hydrothermal condition. This study provides a simple way to control the size and morphology of ZIF-67 crystals prepared in aqueous solution. - Graphical abstract: Zeolitic imidazolate frameworks ZIF-67 were prepared under hydrothermal (120 °C) and non-hydrothermal (room temperature) from four different cobalt sources (Co(NO{sub 3}){sub 2}, CoCl{sub 2}, CoSO{sub 4} and Co(OAc){sub 2}) in aqueous solution within 30 min. The particle size and morphology were found to be related to the reactivity of the cobalt salt, Hmim/Co{sup 2+} molar ratios and experimental condition. - Highlights: • The particle size and morphology were determined by the reactivity of cobalt salt. • ZIF-67 could be prepared from CoSO{sub 4} and Co(OAc){sub 2} at Hmim/Co{sup 2+} molar ratio of 10. • Uniform and regular particles were obtained under hydrothermal condition.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A series of Zn/Cd coordination polymers constructed from 1,4-naphthalenedicarboxylate and N-donor ligands: Syntheses, structures and luminescence sensing of Cr{sup 3+} in aqueous solutions

A novel series of Zn/Cd coordination polymers based on H{sub 3}L, namely, [Zn{sub 2}(HL){sub 2}(bipy){sub 2}(H{sub 2}O){sub 6}]{sub n} (1), [Zn(HL)(phen)]{sub n} (2), [Cd{sub 3}L{sub 2}(bbi){sub 3}]{sub n} (3), [Zn{sub 3}L{sub 2}(bbi){sub 3}]{sub n} (4) [(H{sub 3}L =4-[(1-carboxynaphthalen-2-yl)oxy]phthalic acid, bipy =4,4′-bipyridine, phen =1,10-phenanthroline, bbi =1,1′-(1,4-butanediyl)bis(imidazole] have been successfully synthesized by solvothermal reaction. Compound 1 possesses two diverse 1D chains constructed by different bipy coligands, which were further connected to form a 3D supramolecular architecture by hydrogen bonding interactions. Compound 2 possesses a complicated 1D chain based on secondary building unit (SBU) with binuclear Zn cluster. Compounds 3 and 4 exhibit similar 2D→3D framework, which can be rationalized as (3,4,4)-connected 3D net with a Schläfli symbol of (6{sup 3}.8.10{sup 2}){sub 2}(6{sup 3}){sub 2}(6{sup 4}.8.10). In particular, compound 3 exhibited a high sensitivity for Cr{sup 3+} in aqueous solutions, which suggest that compound 3 is a promising luminescent probe for selectively sensing Cr{sup 3+}. - Graphical abstract: A series of novel Zn/Cd coordination polymers have been successfully synthesized by solvothermal reaction. The unique 3D Cd{sup 2+} polymer containing bbi as second ligand demonstrates high sensitivity for detection of toxic Cr{sup 3+} in aqueous solutions. Display Omitted - Highlights: • π-conjugated semirigid tricarboxylate ligands with naphthalene rings(H{sub 3}L) were rationally designed. • Four Zn/Cd coordination polymers based on H{sub 3}L have been successfully synthesized by solvothermal reaction. • Compound 3 is a promising luminescent probe for selectively sensing Cr{sup 3+} with high sensitivity in aqueous solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Fabrication of core-shell Fe{sub 3}O{sub 4}@MIL-100(Fe) magnetic microspheres for the removal of Cr(VI) in aqueous solution

Facile regeneration of an adsorbent is very important for commercial feasibility. One typical highly porous metal-organic framework (MOF) materials based on MIL-100(Fe) and magnetic iron oxide particles (denoted as MMCs) with diameter about of 350 nm were successfully synthesized. The growth of MIL-100(Fe) shell on the surface of Fe{sub 3}O{sub 4} was utilized precursor as crystal seed via in-situ step hydrothermal reaction. It is a simple way to obtain well organized core-shell MOF composites, compared to the step-by-step method. MMCs were firstly used to uptake of Cr(VI) anions in aqueous solution. Adsorption experiments were carried out in batch sorption mode investigating with the factors of contact time (0–1000 min), pH (from 2 to 12), dose of adsorbent (4–25 mg), and initial Cr(VI) concentration (range from 10 to 100 ppm). - Graphical abstract: One typical highly porous metal-organic framework (MOF) materials based on MIL-100(Fe) and magnetic iron oxide particles (denoted as MMCs) were successfully synthesized. Utilizing Fe{sub 3}O{sub 4} precursor as crystal seed to grow MIL-100(Fe) shell by in-situ step hydrothermal reaction. It is a simple way to obtain core-shell MOF composites. MMCs could effectively uptake of Cr(VI) anions in aqueous solution. - Highlights: • Fe{sub 3}O{sub 4}@MIL-100(Fe) composites with core-shell structure were successfully prepared through a simple method. • The influence factors on Cr(VI) adsorption by Fe{sub 3}O{sub 4}@MIL-100(Fe) were investigated. • Cr(VI) can efficiently adsorbed by Fe{sub 3}O{sub 4}@MIL-100(Fe) composites from aqueous solution.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Adsorption mechanism of alkyl polyglucoside (APG) on calcite nanoparticles in aqueous medium at varying pH

In this study, adsorption mechanism of alkyl polyglucoside (APG) on calcium carbonate (CaCO{sub 3}) nanoparticles (CCNPs) in aqueous medium at varying pH was identified. An initial adsorption of APG on CCNP surface seemed to be occurred due to the van der Waals force. An initial surface charge influenced determination of a major driving force, which resulted in hydrogen bonds (pH 7) and the hydrophobic interaction (pH 10) as a main sources of adsorption of APG on the CCNP surface. Even if the initial surface charge of CCNPs had little effect on a quantitative adsorption of APG on CCNPs, eventually, it influence on the definitive adsorption structure between APG and CCNPs and improvement of dispersion stability of CCNPs in water. In conclusion, it was revealed that 0.39% APG aqueous solution was most appropriate to improve the dispersion stability of CCNPs, which is postulated to be used effectively in food and pharmaceutical fields. - Graphical abstract: An initial adsorption of APG on CCNP surface seemed to be occurred due to the van der Waals force. An initial surface charge influenced determination of a major driving force, which resulted in hydrogen bonds (pH 7) and the hydrophobic interaction (pH 10) as a main sources of adsorption of APG on the CCNP surface. The difference in adsorption structure caused difference in improvement of dispersion stability of CCNPs in an aqueous medium. - Highlights: • The initial adsorption of APG on CCNPs occurs by a weak hydrophobic interaction. • At pH 7, the positively charged surface of CCNPs causes hydrogen bonds with APG. • At pH 7, the interfacial hydrogen bonds cause low stability of CCNPs in DI water. • At pH 10, zero charge of CCNPs causes a strong hydrophobic interaction with APG. • At pH 10, the hydrophobic interaction cause high stability of CCNPs in DI water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Fabrication of platinum nanoparticles in aqueous solution and solid phase using amphiphilic PB-b-PEO copolymer nanoreactors

Graphical abstract: TEM image of Pt nanoparticles produced by reducing by NaBH{sub 4} within PB-b-PEO micelles in aqueous media (scale bar 1 nm). - Highlights: • Pt nanoparticles were synthesized within amphiphilic diblock copolymer micelles. • The effects of reducing agents and precursor dose on Pt np size were investigated. • The effect on fabrication of Pt np by reducing in aqueous and solid phases was compared. • The size of nanoparticles was about 1.4 nm for all doses and reducing agents types. - Abstract: Fabrication of Pt nanoparticles using an amphiphilic copolymer template in aqueous solution was achieved via polybutadiene-block-polyethyleneoxide copolymer micelles, which acted as nanoreactors. In addition, Pt nanoparticles were synthesized using hydrogen gas as the reducing agent in solid state for the first time to compare against solution synthesis. The influences of loaded precursor salt amount to micelles and the type of reducing agent on the size of nanoparticles were investigated through transmission electron microscopy. It was found that increasing the ratio of precursor salt to copolymer and using different type of reducing agent, even in solid phase reduction, did not affect the nanoparticle size. The average size of Pt nanoparticles was estimated to be 1.4 ± 0.1 nm. The reason for getting same sized nanoparticles was discussed in the light of nucleation, growth process, stabilization and diffusion of nanoparticles within micelles.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Aqueous solution synthesis and photoluminescence properties of two-dimensional dendritic PbWO{sub 4} nanostructures

Graphical abstract: PbWO{sub 4} two-dimensional dendritic nanostructures (2DDNs) were prepared at room temperature through a facile aqueous solution route using only Pb(NO{sub 3}){sub 2} and Na{sub 2}WO{sub 4} as reaction reagents and distilled water as solvent. - Highlights: • Two-dimensional dendritic PbWO4 nanostructures were prepared through a facile aqueous solution route at room temperature. • A “two-step” growth mechanism was proposed for the formation of two-dimensional dendritic PbWO4 nanostructures. • The two-dimensional dendritic PbWO4 nanostructures exhibit good photoluminescence properties. - Abstract: PbWO{sub 4} two-dimensional dendritic nanostructures (2DDNs) were prepared at room temperature through a facile aqueous solution route. X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray energy dispersive spectrometer were used to characterize the obtained samples. The PbWO{sub 4} 2DDN was in one plane, with a nearly circular shape and sizes of ∼10 μm. The PbWO{sub 4} 2DDNs were composed of curved nanowires around 200 nm in diameters, which were connected together to form a network nanostructure. The effects of reaction conditions including the concentration of react reagents, the reaction temperature, and the reaction time were systematically investigated and a possible formation mechanism for the formation of 2DDNs was proposed. The optical properties, such as UV–vis spectra and photoluminescence spectra of PbWO{sub 4}, were studied. The advantages of this synthetic route include the first synthesis of PbWO{sub 4} 2DDNs, simple synthetic procedure, room reaction temperature, and high reproducibility of the process.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Silica coating of luminescent quantum dots prepared in aqueous media for cellular labeling

Graphical abstract: A facile route based on modified Stöber method was used for the synthesis of silica coated QDs (QD@SiO{sub 2}) starting from aqueously prepared CdTe/CdS QDs. The resultant QD@SiO{sub 2} exhibited a significant increase in emission efficiency compared with that of the initial QDs, along with a small size (∼5 nm in diameter), great stability and low cytotoxicity, which makes it a good candidate as robust biomarker. - Highlights: • We present a facile modified Stöber method to prepare highly luminescent QD@SiO{sub 2}. • The PL efficiency of QDs increases significantly after silica coating. • QD@SiO{sub 2} exhibits small size (∼5 nm) and great dispersibility in aqueous solution. • QD@SiO{sub 2} presents extraordinary photo and colloidal stability. • The silica shell eliminates QD cytotoxicity, providing the access of bioconjugation. - Abstract: Silica coating is an effective approach for rendering luminescent quantum dots (QDs) with water dispersibility and biocompatibility. However, it is still challenging to prepare silica-coated QDs (QD@SiO{sub 2}) with high emission efficiency, small size and great stability in favor for bioapplication. Herein, we reported a modified Stöber method for silica coating of aqueously-prepared CdTe/CdS QDs. With the coexistence of Cd{sup 2+} and thioglycolic acid (TGA), a thin silica shell was formed around QDs by the hydrolysis of tetraethyl orthosilicate (TEOS). The resultant QD@SiO{sub 2} with a small size (∼5 nm in diameter) exhibits significantly higher emission efficiencies than that of the initial QDs. Also, QD@SiO{sub 2} has extraordinary photo and colloidal stability (pH range of 5–13, 4.0 M NaCl solution). Protected by the silica shell, the cytotoxicity of QDs could be reduced. Moreover, the QD@SiO{sub 2} conjugated with folic acid (FA) presents high specific binding toward receptor-positive HeLa cells over receptor-negative A549 cells.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Aggregation of heteropolyanions in aqueous solutions exhibiting short-range attractions and long-range repulsions

Charged colloids and proteins in aqueous solutions interact via short-range attractions and long-range repulsions (SALR) and exhibit complex structural phases. These include homogeneously dispersed monomers, percolated monomers, clusters, and percolated clusters. We report the structural architectures of simple charged systems in the form of spherical, Keggin-type heteropolyanions (HPAs) by small-angle X-ray scattering (SAXS) and molecular dynamics (MD) simulations. Structure factors obtained from the SAXS measurements show that the HPAs interact via SALR. Concentration and temperature dependences of the structure factors for HPAs with –3e (e is the charge of an electron) charge are consistent with a mixture of nonassociated monomers and associated randomly percolated monomers, whereas those for HPAs with –4e and –5e charges exhibit only nonassociated monomers in aqueous solutions. Our experiments show that the increase in magnitude of the charge of the HPAs increases their repulsive interactions and inhibits their aggregation in aqueous solutions. MD simulations were done to reveal the atomistic scale origins of SALR between HPAs. As a result, the short-range attractions result from water or proton-mediated hydrogen bonds between neighboring HPAs, whereas the long-range repulsions are due to the distributions of ions surrounding the HPAs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ions scavengers and hydrophobicity localized in solvent clusters. In this work we show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer and a hydrophobic anode-electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH - -reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reductions; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries.

25 ENERGY STORAGE↗
DOE OSTI2026

Epitaxial Electrodeposition of Fe with Controlled In-Plane Variants for a Reversible Metal Anode in an Aqueous Electrolyte

The development of reversible metal anodes is a key challenge for advancing aqueous battery technologies, particularly for scalable and safe stationary energy storage applications. Here, in this study, we demonstrate a strategy to realize epitaxial electrodeposition of iron (Fe) on single-crystal copper (Cu) substrates in aqueous electrolytes. We compare the electrodeposition behavior of Fe on polycrystalline and single-crystalline Cu substrates, revealing that the latter enables highly uniform, dense, and crystallographically aligned Fe growth. Comprehensive electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analysis confirms the formation of Fe with specific out-of-plane and in-plane orientations, including well-defined rotational variants. Our findings highlight that epitaxial electrodeposition of Fe can suppress dendritic growth and significantly enhance Coulombic efficiency during plating/stripping cycles. This approach bridges fundamental crystallography with practical electrochemical performance, providing a pathway toward high-efficiency aqueous batteries utilizing Earth-abundant materials.

aqueous battery↗
DOE OSTI2021

pH-Mediated Colorimetric and Luminescent Sensing of Aqueous Nitrate Anions by a Platinum(II) Luminophore@Mesoporous Silica Composite

Increased levels of nitrate (NO 3 – ) in the environment can be detrimental to human health. Herein, we report a robust, cost-effective, and scalable, hybrid material-based colorimetric/luminescent sensor technology for rapid, selective, sensitive, and interference-free in situ NO 3 – detection. These hybrid materials are based on a square-planar platinum(II) salt [Pt(tpy)Cl]PF6 (tpy = 2,2';6',2''-terpyridine) supported on mesoporous silica. The platinum salt undergoes a vivid change in color and luminescence upon exposure to aqueous NO 3 – anions at pH ≤ 0 caused by substitution of the PF6– anions by aqueous NO 3 – . This change in photophysics of the platinum salt is induced by a rearrangement of its crystal lattice that leads to an extended Pt···Pt···Pt interaction, along with a concomitant change in its electronic structure. Furthermore, incorporating the material into mesoporous silica enhances the surface area and increases the detection sensitivity. A NO 3 – detection limit of 0.05 mM (3.1 ppm) is achieved, which is sufficiently lower than the ambient water quality limit of 0.16 mM (10 ppm) set by the United States Environmental Protection Agency. The colorimetric/luminescence of the hybrid material is highly selective to aqueous NO 3 – anions in the presence of other interfering anions, suggesting that this material is a promising candidate for the rapid NO 3 – detection and quantification in practical samples without separation, concentration, or other pretreatment steps.

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

Hydrophobic Molecule Monolayer Brush-Tethered Zinc Anodes for Aqueous Zinc Batteries

Aqueous zinc batteries are of great interest as a rechargeable energy storage system, particularly owing to the low cost and high safety of aqueous electrolytes, as well as the high capacity of zinc anodes. Unfortunately, the wide commercialization of aqueous zinc batteries is impeded by the irreversible water reduction and irregular zinc evolution issues on the anode side. Hereby, a hydrophobic and ultrathin polystyrene molecule brush layer is tethered onto the surface of zinc metal anodes to tackle the above limitations. Here, experimental investigations reveal that the waterproof artificial layer can sustain fast interfacial ionic transportation, minimize hydrogen evolution, and smoothen Zn deposition, thus conferring enhanced electrochemical performance to the as-protected Zn anode in both symmetric Zn//Zn cells and Zn//LiV 3 O 8 full cells.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Amphiphile-Induced Phase Transition of Liquid Crystals at Aqueous Interfaces

We report that monolayer assemblies of amphiphiles at planar interfaces between thermotropic liquid crystals (LCs) and an aqueous phase can give rise to configurational transitions of the underlying LCs. A common assumption has been that a reconfiguration of the LC phase is caused by an interdigitation of the hydrophobic tails of amphiphiles with the molecules of the LC at the interface. A different mechanism is discovered here, whereby reorientation of the LC systems is shown to occur through lowering of the orientation-dependent surface energy of the LC due to formation of a thin isotropic layer at the aqueous interface. Using a combination of atomistic molecular dynamics simulations and experiments, we demonstrate that a monolayer of specific amphiphiles at an aqueous interface can cause a local nematic-to-isotropic phase transition of the LC by disturbing the antiparallel configuration of the LC molecules. Lastly, these results provide new insights into the interfacial, molecular-level organization of LCs that can be exploited for rational design of biological sensors and responsive systems.

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

Electrolyte Effect on the Electrochemical Performance of Mild Aqueous Zinc-Electrolytic Manganese Dioxide Batteries

Recently, mild aqueous rechargeable Zn-MnO 2 batteries have attracted increasing interest for energy storage due to the appealing attributes of low cost of Zn and Mn resource and high safety and environmental benignity. Despite extensive types of MnO 2 have been proposed for cathodes, the different reported performance, complex synthesis methods and lacking a thorough understanding of reactions in MnO 2 cathodes greatly hinder their practical applications for long life energy storage. Here we demonstrate the low cost and commercially available electrolytic manganese dioxide (EMD) as a promising and reversible cathode for mild aqueous rechargeable Zn-MnO 2 batteries through a rational manipulation of redox reactions in EMD cathode. In optimal Zn(TFSI)2-based electrolyte, the EMD cathode exhibits a mixed diffusion controlled conversation relation between EMD and H + and diffusion-free pseudocapacitance-like reactions without phase change. This mechanism enables EMD cathode with excellent cycling stability over 5000 cycles with a capacity retention of 94%. This study provides new opportunity to develop mild aqueous Zn-MnO 2 batteries with low cost and high-performance cathode materials by a rational control of the reaction mechanisms.

25 ENERGY STORAGE↗
DOE OSTI2024

Shallow Rate-Redox Potential Scaling in Aqueous Molecular Oxygen Reduction Electrocatalysis Across a Family of Iron Macrocycles

Rate-overpotential scaling relationships have been employed widely to understand trends in oxygen reduction reaction (ORR) electrocatalysis by dissolved metal macrocycles in organic electrolytes. Similar scaling relationships remain unknown for surface-adsorbed ORR electrocatalysts in the acidic aqueous environments germane to proton-exchange membrane (PEM) fuel cells. Herein, we examine ORR catalysis in aqueous perchloric acid media for a structurally diverse array of iron macrocycle complexes adsorbed on Vulcan carbon black. The macrocycles encompass Fe– N 4 , Fe–N 2 N' 2 and Fe–N x C 4-x motifs bearing pyrrolic, pyridinic, and N-heterocyclic carbene (NHC) moieties in the primary ligation sphere, giving rise to a 670 mV range in Fe(III/II) redox potentials, E Fe(III/II) . Experimental Tafel data in the micropolarization regime were extrapolated to the E Fe(III/II) to furnish estimated per-site-normalized current density (j per-site ) values that span ~4.6 orders of magnitude across the family of compounds. Despite the structural diversity of this family of compounds, extrapolated j per-site values correlate with the Fe(III/II) redox potentials in a roughly log-linear fashion with a shallow scaling factor of approximately 145 mV/decade. Further, these findings highlight that negative shifts in E Fe(III/II) lead to diminishing returns in catalytic rate promotion and suggest that changes to the primary ligating environment in a macrocycle are insufficient to break fundamental rate-potential scaling relationships in aqueous ORR catalysis. Together these studies motivate the further development of higher-potential iron complexes that employ motifs beyond the equatorial ligation plane to enhance ORR catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Towards Understanding of Cracking during Drying of Thick Aqueous-Processed LiNi 0.8 Mn 0.1 Co 0.1 O 2 Cathodes

Replacing N-methyl-2-pyrrolidone (NMP) with water for processing of lithium-ion battery (LIB) electrodes has both cost and environmental benefits, which include reduced drying time, lower dryer capital cost, elimination of NMP recovery capital equipment, and no release of volatile organic compounds (VOCs) into the environment. However, aqueous-processed thick cathodes (≳4 mAh/cm 2 ) typically exhibit detrimental cracking during drying that is not observed for the NMP-based counterpart. The reasons for cracking of these water-based thick electrodes are still not well understood due to the complex nature of the colloidal dispersions used in the LIB electrode processing steps. In this work, the contributions of various factors responsible for cracking are discussed. We show that eliminating hydrogen evolution due to corrosion of the aluminum current collector eliminated the majority of the cracks regardless of the coating thickness, identifying the gas evolution as the primary reason for electrode cracking. Some secondary cracks and pinhole-type defects remained after addressing the aluminum current collector corrosion, which are thought to be caused by an inferior binding network formed by carbon black and binder in aqueous-processed cathodes compared to those processed with NMP. The thick aqueous processed cathodes are not able to sufficiently withstand the drying stresses without crack formation. We demonstrate reduction of these secondary defects by either improving the binding network or by reducing the drying stress. The former was achieved by replacing carbon black with vapor grown graphite tubes (VGGTs) that caused a more efficient utilization of the emulsion binder. Here, the latter was achieved by adding a small amount of IPA as a co-solvent that has been shown to reduce capillary stresses.

25 ENERGY STORAGE↗
DOE OSTI2011

Effect of Aqueous Fe(II) on Arsenate Sorption on Goethite and Hematite

Biogeochemical iron cycling often generates systems where aqueous Fe(II) and solid Fe(III) oxides coexist. Reactions between these species result in iron oxide surface and phase transformations, iron isotope fractionation, and redox transformations of many contaminant species. Fe(II)-induced recrystallization of goethite and hematite has recently been shown to cause the repartitioning of Ni(II) at the mineral-water interface, with adsorbed Ni incorporating into the iron oxide structure and preincorporated Ni released back into aqueous solution. However, the effect of Fe(II) on the fate and speciation of redox inactive species incompatible with iron oxide structures is unclear. Arsenate sorption to hematite and goethite in the presence of aqueous Fe(II) was studied to determine whether Fe(II) causes substantial changes in the sorption mechanisms of such incompatible species. Sorption isotherms reveal that Fe(II) minimally alters macroscopic arsenate sorption behavior except at circumneutral pH in the presence of elevated concentrations (10{sup -3} M) of Fe(II) and at high arsenate loadings, where a clear signature of precipitation is observed. Powder X-ray diffraction demonstrates that the ferrous arsenate mineral symplesite precipitates under such conditions. Extended X-ray absorption fine structure spectroscopy shows that outside this precipitation regime arsenate surface complexation mechanisms are unaffected by Fe(II). In addition, arsenate was found to suppress Fe(II) sorption through competitive adsorption processes before the onset of symplesite precipitation. This study demonstrates that the sorption of species incompatible with iron oxide structure is not substantially affected by Fe(II) but that such species may potentially interfere with Fe(II)-iron oxide reactions via competitive adsorption.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

Does Nitric Acid Dissociate at the Aqueous Solution Surface?

Nitric acid is a prevalent component of atmospheric aerosols, and the extent of nitric acid dissociation at aqueous interfaces is relevant to its role in heterogeneous atmospheric chemistry. Several experimental and theoretical studies have suggested that the extent of dissociation of nitric acid near aqueous interfaces is less than in bulk solution. Here, dissociation of HNO3 at the surface of aqueous nitric acid is quantified using X-ray photoelectron spectroscopy of the nitrogen local electronic structure. The relative amounts of undissociated HNO3(aq) and dissociated NO3-(aq) are identified by the distinguishable N1s core-level photoelectron spectra of the two species, and we determine the degree of dissociation, αint, in the interface (the first ~3 layers of solution) as a function of HNO3 concentration. Our measurements show that dissociation is decreased by approximately 20% near the solution interface compared with bulk, and furthermore that dissociation occurs even in the top-most solution layer. The experimental results are supported by first-principles MD simulations, which show that hydrogen-bonds between HNO3 and water molecules at the solution surface stabilize the molecular form at low concentration, in analogy to the stabilization of molecular HNO3 that occurs in bulk solution at high concentration. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

54 ENVIRONMENTAL SCIENCES↗