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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Photocatalytic water splitting for large-scale solar-to-chemical energy conversion and storage

Sunlight-driven water splitting allows renewable hydrogen to be produced from abundant and environmentally benign water. Large-scale societal implementation of this green fuel production technology within energy generation systems is essential for the establishment of sustainable future societies. Among various technologies, photocatalytic water splitting using particulate semiconductors has attracted increasing attention as a method to produce large amounts of green fuels at low cost. The key to making this technology practical is the development of photocatalysts capable of splitting water with high solar-to-fuel energy conversion efficiency. Furthermore, advances that enable the deployment of water-splitting photocatalysts over large areas are necessary, as is the ability to recover hydrogen safely and efficiently from the produced oxyhydrogen gas. This lead article describes the key discoveries and recent research trends in photosynthesis using particulate semiconductors and photocatalyst sheets for overall water splitting, via one-step excitation and two-step excitation (Z-scheme reactions), as well as for direct conversion of carbon dioxide into renewable fuels using water as an electron donor. We describe the latest advances in solar water-splitting and carbon dioxide reduction systems and pathways to improve their future performance, together with challenges and solutions in their practical application and scalability, including the fixation of particulate photocatalysts, hydrogen recovery, safety design of reactor systems, and approaches to separately generate hydrogen and oxygen from water.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Understanding the Deactivation of Ag–ZrO 2 /SiO 2 Catalysts for the Single-step Conversion of Ethanol to Butenes

Ag–ZrO 2 /SBA-16 has recently been found to be efficient for catalyzing the single-step conversion of ethanol to butene (1- and 2-butene mixtures) in the presence of H 2 . The reaction proceeds via a cascading sequence of reactions over mixed metal and Lewis sites, with the catalyst composition tuned to selectively favor butene formation. However, the catalyst slowly deactivates when evaluated over long reaction times. Here, we evaluated the lifetime of the Ag–ZrO 2 /SBA-16 catalyst system for ethanol-to-butene conversion at 325 °C for up to 800 hours on stream. Several characterization techniques were used to elucidate the mechanism(s) by which catalyst deactivation occurs. Coke deposition, Ag particle sintering, and Ag 0 -to-Ag + oxidation state change were identified to be the major causes of catalyst deactivation. Coke deposits cover primarily Lewis acid sites which are responsible for aldol condensation, Meerwein-Ponndorf-Verley (MPV) reduction, and dehydration reactions. Ag particle sintering and Ag oxidation state change leads to a reduction in the number of metallic Ag sites responsible for the dehydrogenation/hydrogenation steps. The fresh catalyst likely experiences hydrothermal sintering in the early stage of reaction and permanently loses some active Lewis acid sites before reaching a new structural steady state. The deactivation of Lewis acid sites leads to a decrease in overall ethanol conversion, whereas the deactivation of the metallic Ag sites decreases the butene selectivity. For catalyst regeneration, oxidative calcination (at 500 °C) followed by reduction (at 325 °C) successfully removes all the coke species on the catalyst surface and restores the metallic Ag particles of the 4Ag–4ZrO 2 /SBA-16 catalysts.

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

Electrochemical Lignin Conversion

Lignin is the largest source of renewable aromatic compounds, making the recovery of aromatic compounds from this material a significant scientific goal. Recently, many studies have reported on lignin depolymerization and upgrading strategies. Electrochemical approaches are considered to be low cost, reagent free, and environmentally friendly, and can be carried out under mild reaction conditions. Here, different electrochemical lignin conversion strategies, including electrooxidation, electroreduction, hybrid electro-oxidation and reduction, and combinations of electrochemical and other processes (e.g., biological, solar) for lignin depolymerization and upgrading are discussed in detail. In addition to lignin conversion, electrochemical lignin fractionation from biomass and black liquor is also briefly discussed. Finally, the outlook and challenges for electrochemical lignin conversion are presented.

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

Integrated Capture and Conversion of CO 2 to Methane Using a Water-lean, Post-Combustion CO 2 Capture Solvent

Integrated Carbon Capture and Conversion of CO 2 into materials (IC3M) is an attractive solution to meet the global energy demand, reduce our dependence on fossil fuels and lower CO 2 emissions. In this work, using a water-lean post combustion capture solvent, (N-(2-ethoxyethyl)-3-morpholinopropan-1-amine) (2-EEMPA), >90% conversion of captured CO2 to hydrocarbons, mostly methane, is achieved in the presence of a heterogenous Ru catalysts under relatively mild reaction conditions (170 °C and <15 bar H 2 pressure). The catalytic performance was better in 2-EEMPA than aqueous 5M monoethanol amine (MEA). Operando NMR study showed in-situ formation of N-formamide intermediate, which underwent further hydrogenation to form methane and other higher hydrocarbons. The technoeconomic analyses (TEA) showed that the proposed integrated process can potentially improve the thermal efficiency by 5% and reduce the total capital investment and minimum synthetic natural gas (SNG) selling price by 32% and 12% respectively compared to conventional Sabatier process, highlighting the energetic and economic benefits of integrated capture and conversion. Methane derived from CO 2 and renewable H 2 source is an attractive fuel, and it has a great potential as a renewable hydrogen carrier as an environmentally responsible carbon capture and utilization approach.

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

Application of ultrathin TiO 2 layers in solar energy conversion devices

Abstract A vital pursuit in solar energy research is to achieve high efficiency and long‐term stability in energy conversion devices. Coating or sandwiching an ultrathin layer of TiO 2 onto active solar components has been demonstrated to be a remarkably effective and facile strategy to improve their stability. The TiO 2 film acts as a protection layer and enhances solar energy conversion efficiency by passivating surface recombination sites or facilitating electron transport. To date, numerous efforts have been devoted to applying ultrathin TiO 2 layers in various kinds of solar energy conversion devices. In this study, we review deposition techniques, characterization methods of the resulting ultrathin TiO 2 layer, as well as its applications in dye‐sensitized solar cells, organic–inorganic hybrid solar cells, and photoelectrochemical cells.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tailored Frequency Conversion in Nonlinear Subwavelength Grating Metaslabs

The use of metaslab waveguides consisting of subwavelength gratings (SWGs) is proposed as a highly flexible approach to obtain phase‐matched frequency conversion in nonlinear integrated devices. Control over the phase matching (PM) condition is achieved through modification of the linear modal propagation constants by the SWG. The method is experimentally demonstrated by fabrication of 0.4 mm‐long GaAs metaslabs designed for second harmonic generation of near‐infrared light. A controlled spectral shift of up to 100 nm in the PM condition, relative to a uniform slab is observed. Excellent agreement is found between the experimental results and finite‐difference eigenmode simulations, which predict a tunable frequency conversion bandwidth of ∼300 nm for the design parameters. The different regimes of PM control supported by the structure are discussed. This work highlights the potential of SWGs as building blocks for tailored frequency conversion in nonlinear integrated devices.

Form birefringence↗
DOE OSTI2017

Magneto‐Photoluminescence Based on Two‐Photon Excitation in Lanthanide‐Doped Up‐Conversion Crystal Particles

Experimental studies on magneto‐photoluminescence based on two‐photon excitation in up‐conversion Y 2 O 2 S:Er, Yb crystal particles are reported. It is found that the up‐conversion photoluminescence generated by two‐photon excitation exhibits magnetic field effects at room temperature, leading to a two‐photon excitation‐induced magneto‐photoluminescence, when the two‐photon excitation exceeds the critical intensity. By considering the spin selection rule in electronic transitions, it is proposed that spin‐antiparallel and spin‐parallel transition dipoles with spin mixing are accountable for the observed magneto‐photoluminescence. Specifically, the two‐photon excitation generates spin‐antiparallel electric dipoles between 4 S 3/2 – 4 I 15/2 in Er 3+ ions. The antiparallel spins are conserved by exchange interaction within dipoles. When the photoexcitation exceeds the critical intensity, the Coulomb screening can decrease the exchange interaction. Consequently, the spin–orbital coupling can partially convert the antiparallel dipoles into parallel dipoles, generating a spin mixing. Eventually, the populations between antiparallel and parallel dipoles reach an equilibrium established by the competition between exchange interaction and spin–orbital coupling. Applying a magnetic field can break the equilibrium by disturbing spin mixing through introducing spin precessions, changing the spin populations on antiparallel and parallel dipoles and leading to the magneto‐photoluminescence. Therefore, spin‐dependent transition dipoles present a convenient mechanism to realize magneto‐photoluminescence in multiphoton up‐conversion crystal particles.

Xu, Hengxing↗
DOE OSTI2018

Role of Bioreactors in Microbial Biomass and Energy Conversion

Bioenergy is the world’s largest contributor to the renewable and sustainable energy sector, and it plays a significant role in various energy industries. A large amount of research has contributed to the rapidly evolving field of bioenergy and one of the most important topics is the use of the bioreactor. Bioreactors play a critical role in the successful development of technologies for microbial biomass cultivation and energy conversion. In this chapter, after a brief introduction to bioreactors (basic concepts, configurations, functions, and influencing factors), the applications of the bioreactor in microbial biomass, microbial biofuel conversion, and microbial electrochemical systems are described. Importantly, the role and significance of the bioreactor in the bioenergy process are discussed to provide a better understanding of the use of bioreactors in managing microbial biomass and energy conversion.

Zhang, Liang↗
DOE OSTI2026

Resonant Landau-Zener conversion in multi-axion systems

Multiple axions may emerge in the low-energy effective theory of Nature. Generically, the potentials describing these axion fields are non-diagonal, leading to mass mixing between axion states which can be temperature-dependent due to QCD instanton effects. As the temperature of the Universe drops, level crossing can occur, causing resonant conversion between axion states. In this work, we present an analytic study of the cosmological evolution of multi-axion systems including adiabatic and non-adiabatic resonant conversion from one axion state into another during the misalignment process. We show how the Landau-Zener formalism accurately captures the non-adiabatic resonant conversion, permitting an analytic description of the relic abundances of each axion field for nearly any arbitrary two-state axion mass matrix. As an application, we study the mixing of a QCD axion with an axion-like-particle for specific potentials to identify the predictions for haloscope experiments. We conclude that the detection of an axion off the expected QCD mass-coupling line predicts other haloscope targets if it mixes with the QCD axion.

Axions and ALPs↗
DOE OSTI2025

An effective field theory for muon conversion and muon decay-in-orbit

Muon conversion is one of the best probes of charged lepton flavor violation. The experimental limit is soon expected to improve by four orders of magnitude, thus calling for precise predictions of the shape of the signal spectrum. Equally important are precise predictions for muon decay-in-orbit, the main background for muon conversion. While the calculation of electromagnetic corrections to the two processes above the nuclear scale does not involve significant challenges, it becomes substantially more complex below that scale due to multiple scales, bound-state effects and experimental setup. Here, we present a systematic framework that addresses these challenges by resorting to a series of effective field theories. Combining Heavy Quark Effective Theory (HQET), Non-Relativistic QED (NRQED), potential NRQED, Soft-Collinear Effective Theory I and II, and boosted HQET, we derive a factorization theorem and present the renormalization group equations. Our framework allows for the proper calculation of precise predictions for the rates of the two processes, with crucial implications for the upcoming muon conversion searches. We also provide the most accurate prediction of the signal shape for those searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Probing the photon polarization in B → K*γ with conversion

We re-examine the possibility to measure the photon polarization in B → K*γ decays, via decays in which the photon subsequently undergoes nuclear conversion to a lepton pair. We obtain compact expressions for the full decay-plus-conversion amplitude. With these results we show that interference between the B → (K* → Kπ)γ decay and the γN → ℓ + ℓ – N conversion permits both the ratio and relative weak phase between the left- and right-handed photon amplitudes to be probed by an angular observable, constructed from the final state dilepton, kaon and pion kinematic configuration. Exploiting this technique will be experimentally challenging. However, we present special kinematic cuts that enhance the statistical power of this technique by an O(1) factor. Furthermore, we verify this effect and extract pertinent angular kinematic distributions with dedicated numerical simulations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Enhanced Up-Conversion Emission in Al{sup 3+} Co-Doped ZnGa{sub 2}O{sub 4}:Yb{sup 3+},Tm{sup 3+} Powder Phosphors

Yb{sup 3+}-Tm{sup 3+} co-doped up-conversion powder phosphors using Zn(Al{sub x}Ga{sub 1-x}){sub 2}O{sub 4} (ZAGO) as the host materials were synthesized via solid-state reaction successfully. In addition, the morphology, structural characterization and up-conversion luminescent properties were all investigated by scanning electron microscope (SEM), x-ray diffraction (XRD) and fluorescence spectrophotometer (F-7000), respectively. Under the excitation of a 980 nm laser, all as-prepared powders can carry out blue emission at about 477 nm (corresponding to {sup 1}G{sub 4} → {sup 3}H{sub 6} transition of Tm{sup 3+} ions), and red emission at about 691 nm (attributed to {sup 3}F{sub 3} → {sup 3}H{sub 6} transition of Tm{sup 3+} ions). Also, the influence of doping Al{sup 3+} ions were investigated. In brief, the doping of Al{sup 3+} ions has no effect on the position of emission peak. Howbeit the up-conversion efficiency and intensity of ZAGO:Yb,Tm phosphors are stronger than ZGO:Yb,Tm and ZAO:Yb,Tm phosphors, while the crystallinity is the opposite. More particularly, all as-prepared powder phosphors emit strong luminescence, which is observable by the naked eye, demonstrating the potential applications in luminous paint, luminescent dye, etc.

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

Temperature Inhibition of Plasma-Driven Methane Conversion in DBD Systems

Low-temperature non-thermal plasmas produce highly reactive chemical environments made up of electrons, ions, radicals, and vibrationally excited molecules. These reactive species, when combined with catalysts, can help drive thermodynamically unfavorable chemical reactions at low temperatures and atmospheric pressure. The conversion of methane (CH 4 ) to produce other value-added chemicals is a good model system because of its applicability to a wide range of industries. To effectively create these plasma catalytic systems, a fundamental understanding of the plasma-phase chemistry alone is imperative. While there have been many studies on methane plasmas and how certain operating conditions (i.e., gas composition and power) affect the plasma, there is limited understanding on how changing bulk reaction temperature affects the plasma properties and ensuing plasma chemistry. Here, in this work, we use a dielectric barrier discharge to investigate the effects of temperature on the reaction chemistry and the plasma’s electrical properties in various methane-gas mixtures. Results show that increasing temperature leads to a reduction in methane conversion as well as changes to both the gas and dielectric material pre-breakdown, which manifests itself in temperature-dependent electrical properties of the plasma. Experiments at various temperatures and power show a positive correlation between key electrical plasma properties (average charge and lifetime per filament) and the measured methane conversion as a function of temperature.

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

Revisiting the conversion reaction voltage and the reversibility of the CuF2 electrode in Li-ion batteries

Deviation between thermodynamic and experimental voltages is one of the key issues in Li-ion conversion-type electrode materials; the factor that affects this phenomenon has not been understood well in spite of its importance. In this work, we combine first principles calculations and electrochemical experiments with characterization tools to probe the conversion reaction voltage of transition metal difluorides MF2 (M = Fe, Ni, and Cu). We find that the conversion reaction voltage is heavily dependent on the size of the metal nanoparticles generated. The surface energy of metal nanoparticles appears to penalize the reaction energy, which results in a lower voltage compared to the thermodynamic voltage of a bulk-phase reaction. Furthermore, we develop a reversible CuF2 electrode coated with NiO. Electron energy loss spectroscopy (EELS) elemental maps demonstrate that the lithiation process mostly occurs in the area of high NiO content. This suggests that NiO can be considered a suitable artificial solid electrolyte interphase that prevents direct contact between Cu nanoparticles and the electrolyte. Thus, it alleviates Cu dissolution into the electrolyte and improves the reversibility of CuF2.

Seo, Joon Kyo↗
DOE OSTI2017

Solar to fuels conversion technologies: a perspective

To meet increasing energy needs, while limiting greenhouse gas emissions over the coming decades, power capacity on a large scale will need to be provided from renewable sources, with solar expected to play a central role. While the focus to date has been on electricity generation via photovoltaic (PV) cells, electricity production currently accounts for only about one-third of total primary energy consumption. As a consequence, solar-to-fuel conversion will need to play an increasingly important role and, thereby, satisfy the need to replace high energy density fossil fuels with cleaner alternatives that remain easy to transport and store. The solar refinery concept, in which captured solar radiation provides energy in the form of heat, electricity or photons, used to convert the basic chemical feedstocks CO 2 and H 2 O into fuels, is reviewed as are the key conversion processes based on (1) combined PV and electrolysis, (2) photoelectrochemically driven electrolysis and (3) thermochemical processes, all focused on initially converting H 2 O and CO 2 to H 2 and CO. Recent advances, as well as remaining challenges, associated with solar-to-fuel conversion are discussed, as is the need for an intensive research and development effort to bring such processes to scale.

14 SOLAR ENERGY↗
DOE OSTI2024

Reinforcement induced microcracking during the conversion of polymer-derived ceramics

This study investigates the role of discontinuous reinforcement on the microcracking of a preceramic polymer matrix during polymer to ceramic conversion. The material system comprised a carbosilane-based, preceramic polymer reinforced with mullite particles. The preceramic resin slurry was formulated for photopolymerization on a digital light projection 3D printer. Micro X-ray computed tomography, using a synchrotron light source, monitored a printed composite part during pyrolysis. The conversion of the carbosilane matrix into Si(O)C generated microcracks in the matrix that radially extended from particles. The likelihood of microcrack formation positively correlated with particle size. The largest particles (>10 4 µm 3 volume or >60 µm side length) always abutted microcracks, while the matrix surrounding smaller particles (<5 µm) was free of microcracks. Numerical calculations showed the particles resist the shrinking matrix during its conversion. This created tensile stresses within the matrix. The driving force for microcrack growth was also analyzed with regard to the influence of matrix material parameters, particle form-factor and crack length. These results reveal the need to consider the form factor of discontinuous reinforcements, with regard to the material properties of the polymer-derived ceramic, in order to reduce or eliminate defects in the final part.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Acido-basicity of lanthana/alumina catalysts and their activity in ethanol conversion

Lanthana on alumina samples (0.2, 0.8 and 4.7 theoretical monolayers) were prepared by incipient wetness impregnation using γ-Al 2 O 3 as support. Characterization has been performed by BET, XRD, skeletal FT-IR, DR-UVvis, XPS, HR-TEM, IR spectra of the surface OH, adsorbed pyridine and CO 2 , and isopropanol TPD. Here ethanol conversion was investigated both in temperature-programmed surface reaction (TPSR) dynamic conditions as well as in steady-state flow reactor tests. Lanthanum addition stabilizes alumina with respect to sintering and loss of surface area and La- containing phases are observed only for the high-La loaded catalyst. La-alumina catalysts are less active in ethanol dehydration than alumina but more selective to diethyl ether at partial conversion. 5%La 2 O 3 /Al 2 O 3 is also equally or more selective than alumina to ethylene at high conversion, producing less carbonaceous material during reaction. Thus, this catalytic system might be a good candidate for (bio)ethylene production through (bio)ethanol dehydration.

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

Catalytic Conversion of Model Compounds of Plastic Pyrolysis Oil over ZSM-5

Mechanistic investigation of the catalytic conversion of model compounds for plastic pyrolysis oil (1-octene, octadiene, octane, and toluene) over ZSM-5 in a fixed-bed reactor was studied. 1-Octene breaks down into smaller olefins, which undergo further cracking, oligomerization, cyclization, and hydrogen transfer to eventually produce benzene, toluene, xylene (BTX), coke, and hydrogen. The effect of contact time on 1-octene conversion was further investigated and compared with thermodynamics analyses to elucidate the reaction network. Under the reaction conditions (500 oC, 1 atm), octadiene undergoes thermal coking, significantly contributing to reactor fouling. The products from octane cracking are similar to the products from 1-octene conversion whereas toluene undergoes disproportionation, dealkylation and coking. The analysis of spent catalyst showed long-chain hydrocarbons created by oligomerization reactions filled the pores and covered the surface of the catalyst. As a result, when mesoporous ZSM-5 is used instead of conventional, product selectivity is maintained for 70 hours in time-on-stream experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗