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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Scalable Frontal Oligomerization: Insights from Advanced Mass Analysis

Linear oligomers of dicyclopentadiene (DCPD) are reactive precursors for thermoplastic and thermoset materials. Unlike the foul-smelling parent monomer, oligomers composed of DCPD are odorless. With appropriate modification of the end-group or backbone chemistry, telechelic DCPD oligomers have potential utility as cross-linkers and as macromonomer precursors for block and graft copolymers. Most existing methods to produce oligo-DCPD, however, require solvent, are relatively slow, and necessitate air-free techniques. Here we show that frontal ring-opening metathesis oligomerization (FROMO) of neat DCPD and other norbornene derivatives rapidly generates hundreds of grams of material in minutes with catalyst loadings of 0.5 mM. This energy-efficient catalytic process utilizes the heat generated by the reaction to self-propagate oligomerization throughout the liquid monomer. FROMO employs a terminal olefin (e.g., styrene) in which a cross-metathesis reaction (i.e., chain transfer) competes with ring-opening metathesis (i.e., propagation). Kendrick mass analysis enables rapid identification and assignment of all the chain-end types present and quantifies the degree of branching resulting from the infrequent cyclopentene ring-opening reaction. This analytical technique also detects oligomer species derived from trace impurities in the monomer or chain-transfer agent that are otherwise difficult to observe with other characterization methods. Here, the obtained oligomers possess well-defined chain-ends and molecular weight distributions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

New Insights on the Structure of Electrochemically Deposited Lithium Metal and Its Solid Electrolyte Interphases via Cryogenic TEM

Lithium metal has been considered as the “holy grail” anode material for rechargeable batteries though the dendritic growth and low Coulombic efficiency (CE) have crippled its practical use for decades. Its high chemical reactivity and low stability make it difficult to explore the intrinsic chemical and physical properties of the electrochemically deposited lithium (EDLi) and its accompanied solid electrolyte interphase (SEI). To prevent the dendritic growth and enhance the electrochemical reversibility, it is crucial to understand the nano- and meso- structures of EDLi. However, Li metal is very sensitive to beam damage and has low contrast for commonly used characterization techniques such as electron microscopy. Inspired by biological imaging techniques, this work demonstrates the power of cryogenic (cryo)- electron microscopy to reveal the detailed structure of EDLi and the SEI composition at the nano scale while minimizing beam damage during imaging. Surprisingly, the results show that the nucleation dominated EDLi (five minutes at 0.5 mA cm-2) is amorphous while there is some crystalline LiF present in the SEI. The EDLi grown from various electrolytes with different additives exhibits distinctive surface properties. Consequently, these results highlight the importance of the SEI and its relationship with the CE. Our findings not only illustrate the capabilities of cryogenic microscopy for beam (thermal)-sensitive materials, but it yields crucial structural information of the EDLi evolution with and without electrolyte additives.

electrochemical deposition↗
DOE OSTI2019

Fundamental Insights into the Reactivity and Utilization of Open Metal Sites in Cu(I)-MFU-4 l

Metal organic frameworks (MOFs) having open metal sites have the potential to approach the activity of homogeneous organometallic complexes, thus combining the advantages of homogeneous and heterogeneous catalysis. We pre-sent a fundamental study of the effectiveness of incorporating open metal sites into MOFs. We have modeled the binding of a series of adsorbates in a Cu(I) substituted MOF, Cu(I)-MFU-4l using density functional theory, and compared the activity of the Cu(I) sites in Cu(I)-MFU-4l with two different Cu(I) scorpionate complexes. The computational results confirm the single-site nature of the Cu(I) active site. This is further supported by complementary experiments to measure the chemisorption uptake inside our synthesized samples in order to estimate the amount of active Cu sites present. We observed a level of chemisorption that is roughly half the theoretical maximum, which implies that only half of the Cu atoms incorporated into MFU-4l via metal-ion exchange are able to act as binding sites. We speculate that the inactive Cu atoms are coordinately saturated Cu(II) sites. Furthermore, our work suggests that the performance of Cu(I)-MFU-4l could be significantly increased by optimizing the metal exchange and activation processes.

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

Insights into the Cathode–Electrolyte Interphases of High-Energy-Density Cathodes in Lithium-Ion Batteries

Here we present a comprehensive study of cycled high-Ni (LiNi 1–x M x O 2 , M = metals), Li-rich (Li 1+x Mn y M 1–x–y O 2 ), and high-voltage spinel (LiMn 1.5 Ni 0.5 O 4 ) electrodes with time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy in conjunction with electrochemical techniques to better understand their evolving cathode–electrolyte interphase structure during cycling. TOF-SIMS provides fragment-specific information regarding the surface film content for each of the electrodes. High-Ni cathodes show thick surface films initially containing Li 2 CO 3 , later developing oxidized organic carbonates throughout cycling. Li-rich electrode surface films develop strong characteristics during their first activation cycles, where released O 2 oxidizes organic carbonates to form polymeric carbons and decomposes LiPF 6 . High-voltage spinel electrodes operate outside the standard electrolyte stability window, generating reactive oxidized electrolyte species that further decompose LiPF 6 . The distribution and concentration of these different chemical fragments measured by TOF-SIMS are finally summarized by color-coded high-resolution images of cycled high-Ni, Li-rich, and high-voltage spinel electrodes.

25 ENERGY STORAGE↗
DOE OSTI2020

Computational and Experimental Mechanistic Insights into the Ethanol-to-Butanol Upgrading Reaction over MgO

The mechanism of ethanol upgrading to higher products is still under debate, especially regarding intermediate species and hydrogenation and dehydrogenation steps. In this work, we conducted a combined theoretical and experimental approach to contribute to this discussion. For such, detailed electronic structure density functional theory calculations (aiming at probing density of states, infrared spectra, geometric parameters, charge densities, and reaction energetics) and diffuse reflectance infrared Fourier transform spectroscopy experiments were carried out revealing the relevance of an appropriate combination of reactive surface sites to support the formation of several intermediates that are formed in the C-C coupling over MgO. The roles of Mg and O sites were also studied under an electronic perspective and different geometrical arrangements. We found that a kink configuration was the most adequate for ethanol to 1-butanol upgrading. Our calculations also gave us arguments to propose distinct reaction routes, whose mutual predominance would depend upon reaction temperature. At temperatures up to 573 K, the so-called β-route, which goes through scission of a Cβ-H bond and formation of an oxametallacycle-like intermediate, would dominate the coupling, whereas at higher temperatures, up to 673 K, a more usual Guerbet mechanism, via an aldol coupling step and then consecutive hydrogenations, would be expected. Here, the theoretical conclusions were followed by a careful experimental strategy using sequential experimental planning techniques in order to estimate accurate parameters with the lowest possible experimental load. Information from these different sources were coupled to develop a mathematical model for the rate of the ethanol upgrading reaction, using a Langmuir-Hinshelwood-Hougen-Watson approach. The developed and statistically validated model adequately described the experimental data at 673 K and 1.1 bar total pressure for ethanol partial pressures in the range from 0 to 20 kPa.

09 BIOMASS FUELS↗
DOE OSTI2021

Mechanistic Insights into CO 2 Electroreduction on Ni 2 P: Understanding Its Selectivity toward Multicarbon Products

Recently, nickel phosphides (Ni x P y ) have been reported to enable selective electrochemical formation of multicarbon products (C 3 and C 4 ) via the CO 2 reduction reaction (CO 2 RR); nevertheless, their activities remain low. In order to understand the roots of their high selectivity and low activity and to direct the design of more active Ni x P y -based CO 2 RR catalysts, we investigate the CO 2 RR mechanism on Ni 2 P using density functional theory (DFT) calculations. Iin this work, we reveal that the reaction proceeds through the formate pathway, followed by formaldehyde (H 2 CO*) formation and self-condensation. Moreover, we demonstrate that surface hydride transfer steps, along with surface-mediated C–C coupling, are essential in order to avoid C 1 product formation and boost selectivity toward multicarbon products. In addition, we find that the thermal surface hydride transfer from the surface to the physisorbed CO 2 is one of the key rate-limiting steps, and since it is not electroactive, it cannot be accelerated by applying an overpotential. Finally, our results also show that the hydrogen affinity of the surface and the dynamic surface reconstruction via H adsorption facilitate selective CO 2 reduction and C–C coupling on Ni 2 P. These findings provide an impetus for exploring materials design space to identify the physical principles that govern the thermodynamics of rate-limiting thermal steps in electrocatalytic processes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanistic Insights into the Hydrogenolysis of Levoglucosanol over Bifunctional Platinum Silica–Alumina Catalysts

In this paper, we report on the hydrogenolysis of the biorenewable intermediate levoglucosanol (Lgol) over bifunctional platinum catalysts supported on silica–alumina in tetrahydrofuran solvent. 13 C radiolabeling is used to confirm the ring rearrangement forming tetrahydrofurandimethanol. The reaction rate and product selectivity are comparable between 1.1 and 5.3 wt % Pt loadings, indicating that, at these metal loadings, the rate-limiting step is acid catalyzed. The measured zero-order dependence in hydrogen indicates that a non-rate-determining hydrogenation step follows an acid-catalyzed irreversible rate-determining step. The measured first-order dependence in Lgol indicates that the acid sites are not highly covered by Lgol. A physical mixture of Pt/SiO 2 and SiAl catalysts displayed product selectivity similar to that of the Pt/SiAl catalyst, indicating that nanoscale proximity of metal and acid sites is not required to carry out Lgol hydrogenolysis selectively. As the Pt loading in Pt/SiAl catalysts is decreased, or when the bare SiAl support is separated from a Pt/SiO 2 catalyst in a dual-layer configuration, the selectivity toward identified products decreases. These results suggest that degradation reactions are avoided when the reactive intermediates formed over acid sites are rapidly hydrogenated over metal sites. First-principles simulations are performed to investigate the energetics of the proposed reaction pathway. A detailed reaction mechanism for Lgol hydrogenolysis is proposed on the basis of a combination of the experimental and computational results. Our findings provide a fundamental understanding of the catalytic conversion of levoglucosanol over bifunctional metal–acid catalysts, facilitating rationally designed processes to produce renewable chemicals from biomass-derived levoglucosenone.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Interfacial Reactivity and Speciation Emerging from Na-Montmorillonite Interactions with Water and Formic Acid at 200 °C: Insights from Reactive Molecular Dynamics Simulations, Infrared Spectroscopy, and X-ray Scattering Measurements

Reactive organic fluid - mineral interactions at elevated temperatures contribute to the evolution of planetary matter. One of the less studied but important transformations in this regard involves the reactions of formic acid with naturally occurring clays such as sodium montmorillonite. To advance a mechanistic understanding of these interactions, we use ReaxFF reactive molecular dynamics simulations in conjunction with infrared (IR) spectroscopy and X-ray scattering experiments to investigate the speciation behavior of water-formic acid mixtures on sodium montmorillonite interfaces at 473 K and 1 atm. Using a newly developed reactive forcefield, we show that the experimental IR spectra of unreacted and reacted mixture can be accurately reproduced by ReaxFF/MD. We further benchmark the simulation predictions of sodium carbonate and bicarbonate formation in the clay interlayers using Small and Wide-Angle X-ray Scattering measurements. Subsequently, leveraging the benchmarked forcefield, we interrogate the pathway of speciation reactions with emphasis on carbonate, formate, and hydroxide groups elucidating the energetics, transition states, intermediates, and preferred products. Further, we also delineate the differences in reactivities and catalytic effects of clay edges, facets, and interlayers owing to their local chemical environments, which have far reaching consequences in their speciation behavior. The experimental and simulation approaches described in this study and the transferable forcefields can be applied translationally to advance the science of clay-fluid interactions for several applications including subsurface fluid storage and recovery and clay-pollutant dynamics.

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

Simultaneous Insight into Dissolution and Aggregation of Metal Sulfide Nanoparticles through Single-Particle Inductively Coupled Plasma Mass Spectrometry

Nanoparticles (NPs) and their colloidal aggregates are ubiquitous and play important roles in the transport and release of metals. Knowledge of their dissolution rates and aggregation behavior in solution are crucial for better prediction of their fate in biogeochemical cycling, ecotoxicity, and environmental remediation. There are however significant technical challenges to accurately obtain such information as a result of the heterogeneity and highly dynamic transformation exhibited by NPs, particularly at relatively low particle concentrations in aqueous systems. Here, we quantitatively examine the simultaneous dissolution and aggregation behavior of metal sulfide NPs using single-particle inductively coupled plasma mass spectrometry (spICP–MS). We focus on nickel sulfide (NiS), with additional data presented for copper sulfide (CuS) and cobalt sulfide (CoS). The kinetics of metal release (dissolution and disaggregation) of NiS was fastest under strongly oxidizing conditions (from 0.04 to >3 min –1 with H 2 O 2 ) and were slower under near-neutral (HEPES buffer/H 2 O) and acidic (1 mM HNO 3 ) conditions (≤0.006 min –1 ). Metal release kinetics in HNO 3 was not faster than in H 2 O or HEPES, suggesting that the solution pH has an influence over both the dissolution kinetics of individual particles and the NP aggregation states, which in combination affect metal release rates over time. Between different metal sulfides, the measured metal release rates were largely consistent with predictions based on the crystallinity, solubility products, and specific surface areas of the NPs, following an order of CoS > NiS > CuS. Here, the spICP–MS approach described here can be easily applied to the characterization of metal release and aggregation of other NPs at low concentrations (~10 5 particles/mL) typically found in natural environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗