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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Study of the Hydrogen Pretreatment of Gallium and Platinum Promoted ZSM-5 for the Ethane Dehydroaromatization Reaction

Here, the performances of gallium and platinum promoted ZSM-5 catalysts, fresh and reduced, were studied for the dehydroaromatization of ethane to aromatics. Fresh and reduced 2% Ga/ZSM-5, 1.5% Ga–0.5% Pt/ZSM-5, and 0.5% Pt/ZSM-5 were tested in a fixed-bed reactor system at 615 °C for 2 h time on stream. It was observed that the hydrogen reduction of the fresh Pt-containing catalysts led to an increase in catalytic conversion. The addition of platinum to the gallium catalyst resulted in an increase in the reducibility of the Ga species on the surface of the zeolite. The GaPt catalysts exhibited an increase in ethane conversion and the stability of aromatic production selectivity over the Ga and Pt catalysts. The as-prepared fresh catalysts were characterized by ICP and BET methods. The fresh and reduced catalysts were further analyzed by XRD, H 2 -TPR, XPS, pyridine DRIFTS, TGA, and TEM.

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

Simple but tricky: Investigations of terephthalic acid purity obtained from mixed PET waste

In this study, we report for the first time, the basic depolymerization of mixed waste-polyethylene terephthalate (PET) by hydrolysis and subsequent terephthalic acid monomer recovery at high purity using benign reaction conditions. Several conditions were tested for depolymerization such as PET chips size, concentration of aqueous sodium hydroxide (20 or 30%), organic co-solvent (ethylene glycol or ethanol), temperature at which the reaction was run and duration of the heating. More importantly, several batches of PET were utilized as starting materials including a commercial PET, chopped PET obtained from clean bottles whose caps and labels were removed and the purity of the product from each condition was evaluated via nuclear magnetic resonance (1HNMR and 13CNMR), differential scanning calorimetry (DSC) and powder Xray diffraction (XRD). Unsurprisingly, the conversion of PET is dependent on the particle size varying from 100% conversion for fine powder to 73% conversion for (300 µm, mesh 6 – 20 or mesh 14-20). Ethanol appears to be more efficient as a co-solvent than ethylene glycol, with higher PET depolymerization conversions (94% versus 75-80%), shorter reaction times (2h versus 6h) and lower temperatures (80 °C versus 110 °C). The terephthalic acid (TPA) recovered appeared to have only subtle differences among the batches, most notably a pink color when the reaction was run in ethanol/base. The DSC of the compounds produced in ethylene glycol water appear to display a melting point (280-288 °C) while the samples prepared in ethanol as well as a commercial sample did not. Overall, the purity of the various TPA batches is comparable, and similar to commercial TPA, demonstrating the utility of the method to depolymerize realistic waste streams. The method is simple, demonstrated on multigram scale (15-30g) and allows for the complete removal of waste other than PET unaffected by alkaline conditions.

Cosimbescu, Lelia↗
DOE OSTI2021

Graphitized Biocarbon Derived from Hydrothermally Liquefied Low-Ash Corn Stover

Graphitized biocarbon can be utilized for energy storage applications such as supercapacitors. The scientific community have geared their attention to obtain such value-added product from abundantly available and low-cost biomass feedstock agricultural residues such as corn stover. Lignocellulosic components embedded within the cell wall of biomass substrates can provide a fine template for enhanced ion storage, transport, and rate capabilities, desirable for electrochemical storage. Presented is the utilization of homogenized low ash content corn stover milled and sieved to desired specifications, which underwent hydrothermal liquefaction in the presence of Ni-based catalytic salts at 275 o C. The hydrochar obtained by solid residue extracted from the reaction slurry was washed to acid neutral and subjected to catalytic activation using ZnCl 2 , followed by thermal annealing at 400 o C for morphological and pore size enhancement of the resulting biochar. Carbonization was performed on acid neutralized hydrochar at 850 °C to further enhance pore structures and increase graphitization for improved conductivity. Catalytic materials exhibited a specific capacitance of 316 F g -1 and held a 100% retention beyond 10,000 cycles. BET, Raman, XRD, cyclic voltammetry, chronopotentiometry, and EIS are discussed herein.

Biomass↗
DOE OSTI2026

Sustainable H 2 -Rich Syngas Production via Microwave-Assisted vs Conventional Catalysis of Pinewood

Catalytic gasification of biomass is a promising method for producing hydrogen-rich syngas, which is a valuable resource for cleanenergy applications. In this study, microwave-assisted biomass gasification was compared with conventional thermally driven biomass gasification using pinewood as the biomass without the use of external gasifying agents (such as air, steam, and CO 2 ), under non-catalytic and catalytic conditions. The catalysts consisted of either an iron or a nickel catalyst, and the pinewood used as biomass contained 42% oxygen. This comparative analysis explores the differences in reaction chemistry, product yields, and the role of key reactions such as the water gas shift (WGS) reaction, Boudouard reaction, etc. The gas-phase and liquid-phase products were analyzed using online gas chromatography, and the fresh and spent catalysts were analyzed using X-ray diffraction (XRD) techniques. It was found that microwave-assisted gasification offers advantages in terms of enhanced reaction efficiency, catalyst stability, and hydrogen yield. For the microwave-assisted reaction, the gas yield reached 87%, the char yield was 12.1%, and the tar yield was less than 1% (0.793%) at 550 °C. In contrast, thermal-assisted gasification using the same catalyst produced a gas yield of 85.796%, char yield of 11.438%, and higher tar yield of 2.8% at 900 °C. The higher microwave-assisted performance was attributed to faster heating and better control over reaction conditions, higher reaction rates, and more favorable conditions for hydrogen production.

biomass↗
DOE OSTI2026

Cobalt-Doped Tungsten Oxide Nanoparticles for Electrochemical Sensing and Detection of a Penicillin Antibiotic: Amoxicillin

A sensitive electrochemical sensor for the determination of antibacterial amoxicillin (AMXL) in pharmaceutical dosage and environmental samples was developed, since its residues were found in water, food, and biological samples to pose adverse health risks such as immune–allergic reactions and antimicrobial resistance. WO 3 -based sensors are reported to provide higher sensitivity, selectivity, and stability during the electrochemical reaction. Considering this, Co-doped WO 3 nanostructures were synthesized by the hydrothermal method yielding a mixture of nanoparticle and nanorod structures and applied to the assay of AMXL. Extensive characterizations were carried out by SEM, XRD, TEM, and XPS analysis that confirm the monoclinic crystal structure with a uniform Co distribution in the WO 3 lattice. The optimum doping amount of Co in the lattice is found to be 1.80 at %. The electrochemical performance of the Co-WO 3 /carbon paste electrode (CPE) was evaluated for the determination of AMXL under optimum conditions using cyclic voltammetry, electrochemical impedance spectroscopy, and square wave voltammetry. The Co-WO 3 /CPE showed two linear detection ranges at 0.01–0.1 μM with the linear regression I pa = 3.73 [AMXL] + 0.77 with R 2 = 0.96 and at 0.1 to 30.0 μM with the linear regression I pa = 3.76 [AMXL] + 0.69 with R 2 = 0.95. The limit of detection was 9.1 nM (SNR = 3), and the limit of quantification was 30.6 nM (SNR = 10). The sensitivities for lower and higher concentration ranges were 63.22 and 63.73 μA μM –1 cm –2 , respectively. Furthermore, Co-WO 3 /CPE showed high selectivity and anti-interference capabilities. In conclusion, the sensing and disposable Co-WO 3 /CPE sensor showed a great potential for AMXL analysis in spiked soil, water, and Amoxil tablet samples with desirable percentage recovery.

Shanbhag, Mahesh M. [KLE Technological University,↗
DOE OSTI2020

Size Dependence of Lattice Parameter and Electronic Structure in CeO2 Nanoparticles

Intrinsic properties of a compound (e.g. electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. However, the literature on this size-dependence and on the involved mechanisms is quite elusive and scarce. Here, we explore the size-dependence of both crystal and electronic properties of CeO2 nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. XRD, XPS and HERFD-XANES demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of CeIV ions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to FTIR and TGA measurements. In addition, the size-dependence of the eg level in the Ce LIII XANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.

Lanthanide, CeO2, HEFRD-XANES, Electronic structur↗
DOE OSTI2021

Crystallization and Phase Transformations of Aluminum (Oxy)hydroxide Polymorphs in Caustic Aqueous Solution

Gibbsite, bayerite, and boehmite are important aluminum (oxy)hydroxide minerals in nature and have been widely deployed in various industrial applications. They are also major components in caustic nuclear wastes stored at various U.S. locations. Knowledge of their crystallization and phase transformation processes contributes to understanding their occurrence and could help optimize waste treatment processes. While it has been reported that partial conversion of bayerite and gibbsite to boehmite occurs in basic solutions at elevated temperatures, systematic studies of factors affecting the phase transformation as well as the underlying reaction mechanisms are non-existent, particularly in highly alkaline solutions. We explored the effects of sodium hydroxide concentrations (0.1~3 M), reaction temperature (60~100 ?) and aluminum concentrations (0.1~1 M) on the crystallization and transformation of these aluminum (oxy)hydroxides. Detailed structural and morphological characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectrometry revealed that these processes depend largely on the reaction temperature and the Al/OH- ratio. When 1 = Al/OH- = 2.5, the reactions favor formation of high crystallinity precipitates, whereas at Al/OH- ratio ? 2.5 precipitation ceases unless the Al concentration is higher than 1 M. We identified pseudoboehmite, bayerite and gibbsite as intermediate phases to bayerite, gibbsite and boehmite, respectively, all of which transform via dissolution-reprecipitation. Gibbsite transforms to boehmite in both acidic and weak caustic environments at temperatures above 80 oC. However, a ‘bar-shaped’ gibbsite morphology dominates in highly caustic environments (3 M NaOH). The findings enable a robust basis for selection of various solid phases by tuning the reaction conditions.

aluminum (oxy)hydroxide polymorphs, crystallizatio↗
DOE OSTI2021

Hyperstoichiometric Uranium Dioxides: Rapid Synthesis and Irradiation-Induced Structural Changes

Uranium dioxide (UO 2 ), the primary fuel for commercial nuclear reactors, incorporates excess oxygen forming a series of hyperstoichiometric oxides. Thin layers of these oxides, such as UO 2.12 , form readily on the fuel surface and influence its properties, performance, and potentially geologic disposal. This work reports a rapid and straightforward combustion process in uranyl nitrate–glycine–water solutions to prepare UO 2.12 nanomaterials and thin films. We also report on the investigation of the structural changes induced in the material by irradiation. Despite the simple processing aspects, the combustion synthesis of UO 2.12 has a sophisticated chemical mechanism involving several exothermic steps. Raman spectroscopy and single-crystal X-ray diffraction (XRD) measurements reveal the formation of a complex compound containing the uranyl moiety, glycine, H 2 O, and NO 3 – groups in reactive solutions and dried combustion precursors. Combustion diagnostic methods, gas-phase mass spectroscopy, differential scanning calorimetry (DSC), and extracted activation energies from DSC measurements show that the rate-limiting step of the process is the reaction of ammonia with nitrogen oxides formed from the decomposition of glycine and uranyl nitrate, respectively. However, the exothermic decomposition of the complex compound determines the maximum temperature of the process. In situ transmission electron microscopy (TEM) imaging and electron diffraction measurements show that the decomposition of the complex compound directly produces UO 2 . The incorporation of oxygen at the cooling stage of the combustion process is responsible for the formation of UO 2.12 . Spin coating of the solutions and brief annealing at 670 K allow the deposition of uniform films of UO 2.12 with thicknesses up to 300 nm on an aluminum substrate. Irradiation of films with Ar 2+ ions (1.7 MeV energy, a fluence of up to 1 × 10 17 ions/cm 2 ) shows unusual defect-simulated grain growth and enhanced chemical mixing of UO 2.12 with the substrate due to the high uranium ion diffusion in films. As a result, the method described in this work allows the preparation of actinide oxide targets for fundamental nuclear science research and studies associated with stockpile stewardship.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Magnetism Studies of Bis(acyl)phosphide-Supported Eu 3+ and Eu 2+ Complexes

A series of bis(acyl)phosphide-supported Eu complexes were synthesized (bis(acyl)phosphide = BAP). Here, in this study, BAP ligands proved to be excellent ligands for the synthesis of both Eu 3+ and Eu 2+ molecular complexes. Sodium bis(mesitoyl)phosphide (Na( mes BAP)) and sodium bis(2,4,6-triisopropylbenzoyl)phosphide (Na( tripp BAP)) were employed as ligand precursors for the synthesis of the Eu 3+ complexes Eu(bis(mesitoyl)phosphide) 3 (thf) 2 (Eu( mes BAP) 3 (thf) 2 ) and Eu(bis(2,4,6-triisopropylbenzoyl)phosphide) 3 (Eu( tripp BAP) 3 ), as well as the Eu 2+ complex, Eu(bis(2,4,6-triisopropylbenzoyl)phosphide) 2 (dme) 2 (Eu( tripp BAP) 2 (dme) 2 ) (thf = tetrahydrofuran, dme = 1,2-dimethoxyethane). All complexes were characterized using a combination of UV–vis–NIR–IR and NMR spectroscopies, and single-crystal X-ray diffraction (SC-XRD). The magnetic properties of these three monomeric Eu complexes were investigated by variable-temperature magnetic susceptibility. The magnetic data are typical for these ions, with Eu( tripp BAP) 2 (dme) 2 displaying Curie-type behavior. Both Eu( tripp BAP) 3 and Eu( mes BAP) 3 (thf) 2 possess similar 7 F 0 - 7 F 1 spin–orbit energy gaps and a similar zero-field splitting of the 7 F 1 state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Synthesis and Characterization of Homo- and Heteroleptic Neptunium(IV) Heteroarylalkenolate Complexes

Heteroleptic An IV (An = U, Np) chlorido-ketoenaminate complexes of the type [AnCl 2 (TFB-tBuA) 2 (THF)] (An-1 type: U-1, Np-1; TFB-tBuA = 4-(tertbutylamino)- 1,1,1-trifluorobut-3-en-2-one) and the homoleptic Np IV heteroarylalkenolate complexes [Np(PyTFP) 4 ] (Np-2, PyTFP = 1-(pyridin-2-yl)-3,3,3-trifluoroprop- 1-en-2-ol) and [Np(DMOTFP) 4 ] (Np-3, DMOTFP = 1-(4,5-dimethyloxazol- 2-yl)-3,3,3-trifluoroprop-1-en-2-ol) were synthesized and characterized (SC-XRD, NMR, Vis-NIR, MS). While their solid-state structures compare well to those of their uranium analogues, the behavior in solution showed significant differences. The binding motif of the DMOTFP ligand in complex Np-3 can change to form two different complex isomers, as seen by paramagnetic chemical shifts in NMR experiments. Furthermore, the flexibility and the influence of the steric effects at the N-side of the ligands are discussed and compared with its uranium counterpart.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Spectroscopic and Theoretical Studies of Ruthenium Complexes with a Noninnocent N 2 S 2 Ligand in Different Redox States

Herein we report an electronic structure investigation of neutral and oxidized Ru complexes containing a redox noninnocent N 2 S 2 ligand derived from o-phenylenediamide (L1). UV–vis spectroelectrochemistry (SEC) studies were conducted on the square pyramidal complex [Ru I I(L1)(PPh 3 )] (1) and the six-coordinate complexes [Ru I I(μ-BH 3 )(L1)(PPh 3 )] (2) – which has BH 3 bound in a metal–ligand cooperative (MLC) fashion across Ru and L1 – and [Ru II (L1)(PPh 3 )(MeCN)] (3). The SEC results yielded spectra assigned to singly and doubly oxidized 1 and 3, revealing electronic structure changes as a function of oxidation state and in response to the presence and absence of bound MeCN. By contrast, the SEC results of 2 showed that it rapidly loses MLC-bound BH 3 upon oxidation. The SEC results for 1 and 3 were compared to single-crystal XRD data and UV–vis, EPR, and P K-edge, S K-edge, and Ru L 3 -edge X-ray absorption spectroscopy (XAS) data collected on isolated samples of chemically oxidized 3. The data revealed that the first two oxidations are primarily localized on the ligand, which was supported by DFT and TDDFT calculations. DFT calculations for the doubly oxidized species revealed a singlet ground state with a singlet–triplet gap of 8.9 kcal/mol. CASPT2 calculations corroborated the DFT calculations and further revealed that the singlet ground state is multiconfigurational with 21% radical character. Collectively, the results establish redox formalisms and the underlying electronic structure of Ru complexes containing a noninnocent tetradentate ligand in different oxidation states.

electronic structure↗
DOE OSTI2025

Structural and Spectroscopic Characterization of Plutonium and Other Tetravalent Metals Complexed to a Keggin Ion

Here, we report the isolation of the first plutonium(IV) complex with a Keggin ion chelator: Cs 20 [Pu(PW 11 O 39 ) 2 ] 2 ·13H 2 O. Single crystal XRD and solid-state UV–vis absorbance analysis demonstrate the stabilization of Pu 4+ by the Keggin ligand. The unit cell contains two [Pu(PW 11 O 39 ) 2 ] 10– complexes (Pu(PW 11 ) 2 ) bridged by Cs + . Raman and 31 P NMR spectra of Pu(PW 11 ) 2 are consistent with the analogous Zr 4+ , Hf 4+ , Ce 4+ , and Th 4+ complexes. The Pu–O bond distances at the two Pu sites are 2.35(3) and 2.34(3) Å, matching the value extrapolated from the bonding trend built with the other 8-coordinated tetravalent cations. However, the long-range arrangement of the Pu(PW 11 ) 2 complexes within the lattice is unique in the series of M IV (PW 11 ) 2 compounds: pairs of Pu(PW 11 ) 2 are organized perpendicular to each other. Based on solution-state UV–visible absorbance, small-angle X-ray scattering (SAXS), and 31 P NMR, the tetravalent cations quantitatively form the 1:2 species in solution ([Pu(PW 11 O 39 ) 2 ] 10– (aq) ) and no 1:1 species ([Pu(PW 11 O 39 )(H 2 O) x ] 3– (aq) ). Finally, a linear correlation exists between the metal–oxygen distances in the M IV (PW 11 ) 2 compounds and the corresponding metal dioxides, allowing for extrapolation for Pa 4+ , Am 4+ , and Bk 4+ . The results indicate that our microscale POM approach represents a viable pathway to probe properties of rare actinide ions in discrete molecules, beyond the traditional oxide extended solids.

and nuclear chemistry↗
DOE OSTI2020

Hollow Au Nanosphere-Cu 2 O Core–Shell Nanostructures with Controllable Core Surface Morphology

Design of metal-semiconductor interfaces and heterostructures is of strong interest for various catalytic applications including photocatalysis. Here, a series of hollow Au nanosphere (HGN)-Cu 2 O core-shell nanostructures with varying core surface rugosities are synthesized and investigated for possible photocatalytic applications. HGN surface rugosity is tuned by pH modification during galvanic exchange, and carboxyl groups are utilized as coordination sites to deposit uniform Cu 2 O shells onto the gold surfaces. Final core-shell structures are verified by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). Information regarding chemical state and electronic band structure is acquired by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Ultrafast transient absorption (TA) reveals that charge separation in bumpy HGN (bHGN)-Cu 2 O may effectively provide longer-lived photoexcited carriers, offering great potential for utilization in advanced photocatalytic processes.

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

Radiation-Induced Changes in Single Crystal Calcite and Dolomite: Mineral Analogues of Light Water Reactor, Nuclear Power Plant Concrete Aggregates

Two analogues of aggregates (calcite and dolomite) found in nuclear power plant (NPP) concrete have been neutron irradiated to fluences up to 2 × 10 20 n/cm 2 at 52 °C and 4 × 10 19 n/cm 2 at 95 °C (E > 0.1 MeV). X-ray diffraction studies showed that these aging conditions affected crystallography of both calcite and dolomite, with both showing a growth in their unit cells compared to that of the unirradiated samples. Only dolomite samples showed a continuous increase of its lattice parameters with the increase in irradiation. In calcites, the lattice growth with irradiation dissipated after a fluence of 5 × 10 18 n/cm 2 . Radiation-induced disordering of the crystal structure was observed in both materials, while a healing effect of irradiation temperature was mainly observed in calcites. Dislocation densities calculated by using XRD data also supported these observations. Insights made into the unit cells of both minerals by using Fourier synthesis showed that the Mg sites are more prone to the neutron irradiation than the Ca sites, resulting in larger radiation effects and higher disruption in the crystal structure of dolomite than that of calcite. Furthermore, other than the polycrystalline characteristics observed by using TEM, these minerals did not show complete amorphization or significant structural decomposition at the studied irradiation fluences.

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

Vapor-Phase Intercalation of Cesium into Black Phosphorous

Cesium vapors were charged into black phosphorous (BP) flakes at varied times and at a temperature gradient of 150 °C. The X-ray diffraction (XRD) measurements of these samples suggest a reduction in the strength of van der Waal interactions between BP layers leading to the loss of coherence of out-of-plane peaks. At the same time, the three main Raman modes of BP (A g 1 , B 2 g , and A g 2 ) steadily redshifted as exposure times were increased, with modes B 2 g and A g 2 shifting faster than A g 1 . After initial rapid downshifts of active BP phonon modes, this intercalation strategy showed its limits following prolonged exposure times. Saturation of BP flakes by Cs vapors ensued and the kinetics was fitted with an exponential decay function. Furthermore, the thermoelectric power (TEP) of cesiated BP exhibited an inversion in sign from positive to negative around 400 K, lending credence to the transformation of as-prepared BP which is a p-type semiconductor to an n-type equivalent due to Cs atom intercalation driven shifting of the Fermi level toward the conduction band of BP and the donation of electrons from Cs. Furthermore, density functional theory (DFT) calculations were used to delve deeper into understanding Cs intercalation on the structural evolution of BP.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A Study of How LaFeO 3 and CaTiO 3 Supports Affect the Oxidation, Hydrogenation, and Methane Steam Reforming Activity of Pt and Ni Catalysts

The structure and catalytic properties of Pt and Ni supported on thin films of LaFeO 3 and CaTiO 3 , prepared by Atomic Layer Deposition (ALD), were investigated. X-Ray diffraction (XRD) and scanning transmission electron microscopy (STEM) show that reduction at 1073 K causes Pt-Fe intermetallic compound formation for Pt/LaFeO 3 . For Pt/CaTiO 3 , 1073-K reduction induces local decomposition of the CaTiO 3 with migration of Ti to the Pt. Reduced Pt/LaFeO 3 and Pt/CaTiO 3 exhibited CO-oxidation activity similar to that for Pt supported on MgAl 2 O 4 but were much less active for propane oxidation and hydrogenation of 1-hexene and toluene. In contrast, Ni/CaTiO 3 behaved similarly to a conventional supported Ni catalyst for the methane-steam-reforming (MSR) and 1-hexene hydrogenation. There was also no evidence for local decomposition of the perovskite in the vicinity of the Ni particles. Furthermore, the results obtained in this study demonstrate that metal-perovskite interactions that affect reactivity are specific to each component.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Investigating the Role of Silver Oxidation State on the Thermodynamic Interactions between Xenon and Silver-Functionalized Zeolites

The molecular level understanding of the strong adsorption of Xe to silver-modified zeolites remains elusive. Here, we probe the effect of silver oxidation state on the thermodynamics of Xe sorption in silver-functionalized zeolites by measuring the enthalpies of adsorption after various treatments using inverse gas chromatography (IGC). The enthalpy of adsorption was measured for silver-functionalized chabazites (AgCHA) before and after hydrogen reduction and subsequent reoxidation. The sorption enthalpy (ΔH) for AgCHA was 35.2 kJ/mol, which decreased to 25.8 kJ/mol with hydrogen reduction. After reoxidation (O 2 -AgCHA), 95% of the binding strength was restored. Hydrogen reduction of the base chabazite (CHA) did not influence Xe adsorption. Henry’s law constant for Xe adsorption increased in the order AgCHA > O 2 -AgCHA > H 2 -AgCHA > CHA. A decrease in enthalpy and Henry’s constant with silver reduction and increase with reoxidation suggest that ionic silver is playing a role in Xe binding. The effect of reduction and reoxidation on the zeolite microstructure was analyzed using surface area analysis, powder X-ray diffraction (p-XRD), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), and X-ray photoelectron spectroscopy (XPS). Finally, these results lay the groundwork for better material design of strong noble gas adsorbents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Degradation in Ni-Rich LiNi 1– x – y Mn x Co y O 2 /Graphite Batteries: Impact of Charge Voltage and Ni Content

Ni-rich LiNi 1– x–y Mn x CoyO 2 (NMC) materials are attractive as cathodes for Li-ion batteries due to their high energy density and low Co content. However, these materials may display poor electrochemical reversibility relating to structural and interfacial instabilities. The influence of Ni content and level of delithiation during charge on degradation mechanisms and relevance to electrochemical cycling behavior are probed for LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathode materials in a full cell configuration under two upper voltage limits (4.1 and 4.3 V). The combined use of dQ/dV analysis of electrochemical voltage profiles, operando XRD, and postcycling scanning electron microscopy (SEM) measurements indicates that a major contributor to capacity fade is the large anisotropic volume change from an H2 $\leftrightarrows$ H3 phase transition and associated mechanical degradation particularly for NMC811. Notably, transition metal dissolution and deposition on the negative electrode are found to correlate with the structural changes occurring in the cathode under high voltage charge. X-ray photoelectron spectroscopy (XPS) analyses of the cycled cathodes reveal a more organic-rich cathode–electrolyte interphase (CEI) when cycling to 4.3 V with lower relative amounts of LiF. Surface reconstruction is not a significant factor under these cycling conditions as determined by soft X-ray absorption spectroscopy (sXAS) analysis. The results emphasize the opportunity to match the electrochemical test parameters with the specific NMC active material to mitigate degradation and extend cycle life.

36 MATERIALS SCIENCE↗