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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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Tuning the electrolyte network structure to invoke quasi-solid state sulfur conversion and suppress lithium dendrite formation in Li–S batteries

Here, the lithium-sulfur battery is promising as an alternative to conventional lithium-ion technology due to the high energy density of both sulfur and lithium metal electrodes. Extended life time has been demonstrated, but two notable challenges still exist in battery applications: overcoming the undesired high electrolyte/sulfur ratio, and inhibiting Li dendrite growth and its parasitic reaction with the electrolyte. Here we demonstrate that by tuning the electrolyte structure, the challenges at both electrodes can be tackled simultaneously. The sulfur speciation pathway transforms from a dissolution-precipitation route to a quasi-solid-state conversion in the presence of lowered solvent activity and an extended electrolyte network structure as revealed by ab initio calculations, curtailing the need for high electrolyte volumes. With such an optimized structure, the Li plates dendrite-free and shows 20-fold reduction in parasitic reactions with Li, avoiding electrolyte consumption and greatly extending the life time of a low E/S (5 µl/mg -1 ) sulfur cell.

25 ENERGY STORAGE↗
DOE OSTI2022

Efficient conversion of low-concentration nitrate sources into ammonia on a Ru-dispersed Cu nanowire electrocatalyst

We report electrochemically converting nitrate ions, a widely distributed nitrogen source in industrial wastewater and polluted groundwater, into ammonia represents a sustainable route for both wastewater treatment and ammonia generation. However, it is currently hindered by low catalytic activities, especially under low nitrate concentrations. Here we report a high-performance Ru-dispersed Cu nanowire catalyst that delivers an industrial-relevant nitrate reduction current of 1 A cm –2 while maintaining a high NH 3 Faradaic efficiency of 93%. More importantly, this high nitrate-reduction catalytic activity enables over a 99% nitrate conversion into ammonia, from an industrial wastewater level of 2,000 ppm to a drinkable water level <50 ppm, while still maintaining an over 90% Faradaic efficiency. Coupling the nitrate reduction effluent stream with an air stripping process, we successfully obtained high purity solid NH 4 Cl and liquid NH 3 solution products, which suggests a practical approach to convert wastewater nitrate into valuable ammonia products. Density functional theory calculations reveal that the highly dispersed Ru atoms provide active nitrate reduction sites and the surrounding Cu sites can suppress the main side reaction, the hydrogen evolution reaction.

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

Semiconductor-based Multilayer Selective Solar Absorber for Unconcentrated Solar Thermal Energy Conversion

Solar thermal energy conversion has attracted substantial renewed interest due to its applications in industrial heating, air conditioning, and electricity generation. Achieving stagnation temperatures exceeding 200 °C, pertinent to these technologies, with unconcentrated sunlight requires spectrally selective absorbers with exceptionally low emissivity in the thermal wavelength range and high visible absorptivity for the solar spectrum. In this Communication, we then report a semiconductor-based multilayer selective absorber that exploits the sharp drop in optical absorption at the bandgap energy to achieve a measured absorptance of 76% at solar wavelengths and a low emittance of approximately 5% at thermal wavelengths. In field tests, we obtain a peak temperature of 225 °C, comparable to that achieved with state-of-the-art selective surfaces. Furthemore, with straightforward optimization to improve solar absorption, our work shows the potential for unconcentrated solar thermal systems to reach stagnation temperatures exceeding 300 °C, thereby eliminating the need for solar concentrators for mid-temperature solar applications such as supplying process heat

14 SOLAR ENERGY↗
DOE OSTI2017

X-ray spectroscopic study of amorphous and polycrystalline PbO films, α-PbO, and β-PbO for direct conversion imaging

We investigated the electronic structure of Lead Oxide (PbO) – one of the most promising photoconductor materials for direct conversion x-ray imaging detectors, using soft x-ray emission and absorption spectroscopy. Two structural configurations of thin PbO layers, namely the polycrystalline and the amorphous phase, were studied, and compared to the properties of powdered α-PbO and β-PbO samples. In addition, we performed calculations within the framework of density functional theory and found an excellent agreement between the calculated and the measured absorption and emission spectra, which indicates high accuracy of our structural models. Our work provides strong evidence that the electronic structure of PbO layers, specifically the width of the band gap and the presence of additional interband and intraband states in both conduction and valence band, depend on the deposition conditions. We tested several model structures using DFT simulations to understand what the origin of these states is. The presence of O vacancies is the most plausible explanation for these additional electronic states. Several other plausible models were ruled out including interstitial O, dislocated O and the presence of significant lattice stress in PbO.

42 ENGINEERING↗
DOE OSTI2022

Sustainable conversion of biomass to rationally designed lithium-ion battery graphite

The carbon net negative conversion of bio-char, the low value byproduct of pyrolysis bio-oil production from biomass, to high value, very high purity, highly crystalline flake graphite agglomerates with rationally designed shape and size tailored for lithium-ion battery energy storage material is reported. The process is highly efficient, 0.41 g/Wh; the energy content of its co-product of the process, bio-oil, exceeds that needed to power the process. It is shown that the shape of the starting material is retained during the transformation, allowing the ultimate morphology of the graphite agglomerates to be engineered from relatively malleable biomass. In contrast to commercial graphite production, the process can be performed at small scale with low equipment costs, enabling individual research laboratories to produce Li-ion grade graphite with customizable shape, size and porosity for Si/graphite composite and other graphite involved anodes. The mechanism of the graphitization of bio-char, a “non-graphitizable” carbon, is explored, suggesting the molten metal catalyst is absorbed into the pore structure, transported through and transforming the largely immobile biochar. Finally, the transformation of biomass to rationally designed graphite morphologies with Li-ion anode performance that closely mimic commercial shaped graphite is demonstrated.

09 BIOMASS FUELS↗
DOE OSTI2022

Critical Enzyme Reactions in Aromatic Catabolism for Microbial Lignin Conversion

The application of microbes to valorize aromatic compounds derived from the abundant plant biopolymer lignin is a rapidly developing area of research that may ultimately enable viable conversion of this recalcitrant and heterogeneous resource to valuable bio-based chemical products. Starting from the three canonical lignin building blocks, which differ in the extent of aromatic ring methoxylation, several common classes of enzymatic reaction occur in the upper pathways of aromatic catabolism to prepare aromatic compounds for assimilation into central carbon metabolism, including aromatic O-demethylation, hydroxylation and decarboxylation. These critical enzymatic steps can often be rate-limiting for efficient biological funnelling of aromatic compounds. Here we review the known enzymatic mechanisms for these reactions that are relevant for aerobic aromatic catabolism of lignin-related monomers, highlighting opportunities at the intersection of biochemistry, enzyme engineering and metabolic engineering for applications in the expanding field of microbial lignin valorization.

aromatic catabolism↗
DOE OSTI2022

Cation-doped ZnS catalysts for polysulfide conversion in lithium–sulfur batteries

Catalytic conversion of polysulfides is regarded as a crucial approach to enhancing kinetics and suppressing the shuttle effect in lithium-sulfur (Li-S) batteries. However, the activity prediction of Li-S catalysts remains elusive owing to the lack of mechanistic understanding of activity descriptors. Here, we report a volcano-shaped relationship between polysulfide adsorption ability and catalytic activity. In conjunction with theoretical analysis, we distinguish catalytic and anchoring effects to delineate the role of adsorption and emphasize the passivation of catalysts. These findings enable us to develop a composite catalyst, Co0.125Zn0.875S, which shows higher performance than simple binary compounds. Such a fundamental understanding of the intrinsic link between polysulfide adsorption and catalytic activity offers a rational viewpoint for designing Li-S catalysts and tuning their activities.

Shen, Zihan↗
DOE OSTI2025

Land conversion to energy crops for sustainable aviation fuel production reduces greenhouse gas emissions in the United States

Energy crops will be critical for scaling up production of Sustainable Aviation Fuel in the United States and reducing greenhouse gas emissions. Here we examine the economic incentives for the extent and type of land conversion needed to scale up fuel production from a mix of cellulosic feedstocks and quantify its greenhouse gas intensity. We show that even with the availability of marginal non-cropland, there will be incentives for converting cropland to produce energy crops as the price of sustainable aviation fuel increases. But contrary to expectations, we find that scaling up fuel production by converting more cropland and more non-cropland from existing uses to energy crops lowers its net greenhouse gas intensity, due to high soil carbon sequestration rate of energy crops, even after considering land use change emissions. The potential savings in emissions are larger than the foregone soil carbon accumulation benefits from keeping that land in current uses.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Reversible conversion of dominant polarity in ambipolar polymer/graphene oxide hybrids

The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. We conclude that this hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Designing overall stoichiometric conversions and intervening metabolic reactions

Existing computational tools for de novo metabolic pathway assembly, either based on mixed integer linear programming techniques or graph-search applications, generally only find linear pathways connecting the source to the target metabolite. The overall stoichiometry of conversion along with alternate co-reactant (or co-product) combinations is not part of the pathway design. Therefore, global carbon and energy efficiency is in essence fixed with no opportunities to identify more efficient routes for recycling carbon flux closer to the thermodynamic limit. Here, we introduce a two-stage computational procedure that both identifies the optimum overall stoichiometry (i.e., optStoic) and selects for (non-)native reactions (i.e., minRxn/minFlux) that maximize carbon, energy or price efficiency while satisfying thermodynamic feasibility requirements. Implementation for recent pathway design studies identified non-intuitive designs with improved efficiencies. Specifically, multiple alternatives for non-oxidative glycolysis are generated and non-intuitive ways of co-utilizing carbon dioxide with methanol are revealed for the production of C 2+ metabolites with higher carbon efficiency.

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

Electrohydrodynamic-assisted Assembly of Hierarchically Structured, 3D Crumpled Nanostructures for Efficient Solar Conversions

The tantalizing prospect of harnessing the unique properties of graphene crumpled nanostructures continues to fuel tremendous interest in energy storage and harvesting applications. However, the paper ball-like, hard texture, and closed-sphere morphology of current 3D graphitic nanostructure production not only constricts the conductive pathways but also limits the accessible surface area. Here, we report new insights into electrohydrodynamically-generated droplets as colloidal nanoreactors in that the stimuli-responsive nature of reduced graphene oxide can lead to the formation of crumpled nanostructures with a combination of open structures and doubly curved, saddle-shaped edges. In particular, the crumpled nanostructures dynamically adapt to non-spherical, polyhedral shapes under continuous deposition, ultimately assembling into foam-like microstructures with a highly accessible surface area and spatially interconnected transport pathways. The implementation of such crumpled nanostructures as three-dimensional rear contacts for solar conversion applications realize benefits of a high aspect ratio, electrically addressable and energetically favorable interfaces, and substantial enhancement of both short-circuit currents and fill-factors compared to those made of planar graphene counterparts. Further, the 3D crumpled nanostructures may shed lights onto the development of effective electrocatalytic electrodes due to their open structure that simultaneously allows for efficient water flow and hydrogen escape.

25 ENERGY STORAGE↗
DOE OSTI2014

Conversion of Biomass-Derived Small Oxygenates over HZSM-5 and its Deactivation Mechanism

HZSM-5 catalyst deactivation was studied using aqueous feed mixtures containing ethanol, ethanol+ acetic acid, ethanol+ethyl acetate, or ethanol+acetaldehyde in a fixed bed reactor at 360°C and 300psig. Compared to ethanol alone experiment, addition of other oxygenates reduced catalyst life in the order of: ethyl acetate<acetic acid<acetaldehyde. Based on the liquid product and the spent catalyst analyses from the individual ethanol, acetaldehyde, acetic acid, and ethyl acetate feed, the presence of acetaldehyde appears to produce high molecular weight aromatic compounds which deactivate the catalyst through a pore-blocking mechanism. Acetic acid deactivates the catalyst through an active site poisoning mechanism or strong adsorption of acetate intermediates on the active sites (hydroxyl groups). Ethanol deactivates the catalyst primarily through its pore-blocking mechanism, but the rate of ethanol deactivation is orders of magnitude slower than that of acetaldehyde. Ethyl acetate hydrolyzes to form acetic acid and ethanol which deactivate the catalyst through its respective mechanisms. In addition, each functional group of oxygenates requires different active sites/catalysts and different operating conditions due to competitive adsorptions on active sites for their conversion to the desired products. Therefore, it is necessary to pre-treat the mixture of oxygenates to produce a feed stream containing the same or similar functional group compounds before converting the feed stream to hydrocarbon compounds over HZSM-5 catalyst.

Ramasamy, Karthikeyan K.↗
DOE OSTI2015

Fluoride-free synthesis of a Sn-BEA catalyst by dry gel conversion

Sn containing molecular sieves with BEA topology (Sn-BEA) are active Lewis catalysts for a large variety of redox reactions. However, the synthesis of Sn-BEA often requires the use of toxic chemicals (e.g. hydrofluoric acid). In this study, we demonstrated that an active Sn-BEA catalyst can be directly synthesized in a non-fluoride medium via a dry gel conversion method with the aid of seed crystals. It was shown that seeding of zeolite BEA crystals can facilitate crystal growth and lead to BEA topology with framework Sn. Furthermore, it was found that ion-exchange with ammonium ions is indispensable to retain the crystal structure during calcination. The catalytic activity of the Sn-BEA catalyst was evaluated by the isomerization of glucose and reaction of pyruvaldehyde in the aqueous phase, and compared with the conventional hydrophobic Sn-BEA synthesized in a fluoride medium. The catalytic activity of the Sn-BEA synthesized in the absence of fluoride was found to be lower than that of the conventional Sn-BEA for catalyzing the isomerization of glucose in the aqueous phase, which could be attributed to its hydrophilic surface. For the reaction of pyruvaldehyde in the aqueous phase, the Sn-BEA synthesized in this study showed similar activity to the conventional hydrophobic Sn-BEA, indicating that the catalytic activity of Sn-BEA catalysts largely depends on the type of reactions. The current work provides the first example of direct preparation of a Sn-BEA catalyst in a caustic medium.

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

Zeolite-catalysed C–C bond forming reactions for biomass conversion to fuels and chemicals

Biomass conversion to fuels requires elimination of oxygenated functionalities along with formation of C–C bonds to help keeping the largest possible amount of carbon in the fuel range (e.g. C7–C15). Acidic zeolites are particularly effective in catalysing C–C bond forming reactions from molecules containing oxygenated functionalities such as carbonyl, carboxylic, and hydroxide groups, including acylation, ketonization, and alkylation. Finally, the nature of the active sites and possible reaction mechanisms for these reactions are discussed in this mini-review.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Role of precursor chemistry in the direct fluorination to form titanium based conversion anodes for lithium ion batteries

In this study, a new synthetic route for the formation of titanium oxydifluoride (TiOF 2 ) through the process of direct fluorination via a fluidized bed reactor system and the associated electrochemical properties of the powders formed from this approach are reported. The flexibility of this synthetic route was demonstrated using precursor powders of titanium dioxide (TiO 2 ) nanoparticles, as well as a reduced TiO x N y . An advantage of this synthetic method is the ability to directly control the extent of fluorination as a function of reaction temperature and time. The reversible capacity of TiOF 2 anodes was found to depend greatly upon the precursor employed. The TiOF 2 synthesized from TiO 2 and TiO x N y showed reversible capacities of 300 mAh g -1 and 440 mAh g -1 , respectively, over 100 cycles. The higher reversible capacity of the TiOF 2 powders derived from TiO x N y likely relate to the partial reduction of the Ti in the fluorinated electrode material, highlighting a route to optimize the properties of conversion electrode materials.

25 ENERGY STORAGE↗