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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Effect of Thermal Storage on the Emissions and Efficiency Performance of a Wood Pellet-Fired Residential Boiler

Wood pellet boilers for residential heating applications offer the promise of low emissions, high efficiency, and automatic operation. However, when operated in the field, these units operate often at very low loads causing them to cycle. In this study, the performance of a 25-kW modern pellet boiler under emulated field conditions and fixed nominal loads of 15% and 100% has been studied in a lab—with and without a buffer tank. A dilution tunnel approach was used for the measurement of particulate emissions, in accordance with U.S. certification testing requirements under EPA Methods 28 WHH and 28 WHH PTS. Results show that increasing the amount of thermal storage used decreases cycling rates leading to decreased emissions and increased efficiency. Without thermal storage, integrated efficiency over a 15% load test period was 57%, compared to 74% when thermal storage was used. Particulate emissions were 180 mg/MJ and 64 mg/MJ for the 15% load case without and with thermal storage, respectively.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2026

Efficient Low-Temperature Direct Lithium Extraction from Chloride Brines Enabled by High-Capacity Sorbent

The demand for lithium, a key component in rechargeable batteries for electric vehicles and renewable energy storage systems, has surged in recent years. Meeting this demand requires efficient extraction methods that are both environmentally friendly and economically viable. This study investigates the utilization of the high-capacity sorbent amorphous aluminum hydroxide for enabling efficient direct lithium extraction at low temperatures. Traditional extraction methods often involve acid-leaching and energy-intensive processes that are not only expensive but also environmentally taxing. In contrast, our approach leverages the exceptional sorption properties of amorphous aluminum hydroxide to facilitate lithium extraction directly from brine, achieving extraction efficiencies of 94.4% in case 1 and 96.2% in case 2 at low temperatures. Kinetic modeling using the Avrami–Erofe’ev framework reveals a nucleation-growth mechanism ( n = 0.71, k = 0.131 h –1 ), providing quantitative insights into the solid-state phase transformation process. This method significantly reduces energy consumption and minimizes the environmental footprint. Through systematic experimentation and optimization, we demonstrate the effectiveness and scalability of our approach, highlighting its potential to revolutionize lithium extraction processes. Our findings highlight the potential of high-capacity sorbents, particularly amorphous aluminum hydroxide toward sustainable lithium production, contributing to the advancement of clean-energy technologies.

anions↗
DOE OSTI2019

Efficient Ammonia Decomposition in a Catalytic Membrane Reactor To Enable Hydrogen Storage and Utilization

Liquid ammonia is a high density (17.7 wt. %) hydrogen carrier with a well-established production and distribution infrastructure. Efficient decomposition and purification are essential for its use as a hydrogen storage material. Here we demonstrate the production of high purity (> 99.7%) H 2 from NH 3 using a catalytic membrane reactor (CMR) in which a Ru catalyst is impregnated within a porous yttria-stabilized zirconia (YSZ) tube coated with a thin, 6 µm Pd film by electroless deposition. The intimate proximity of catalyst and membrane eliminates transport resistances that limit performance in the conventional packed bed membrane reactor (PBMR) configuration. The addition of a Cs promoter enabled complete NH 3 conversion at temperatures as low as 400°C, exceeding equilibrium constraints without the need for a sweep gas. A reactor model was developed that captured CMR performance with high fidelity. NH 3 decomposition was observed to follow first order kinetics due to efficient H 2 removal. Relative to a comparable PBMR, the Ru loading in the CMR was reduced an order of magnitude and the H 2 recovery increased 35%, enabling record volumetric productivity rates (> 30 mol m-3 s-1) that validate its promise for efficient, compact H 2 delivery from ammonia.

08 HYDROGEN↗
DOE OSTI2023

BiVO 4 –Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

BiVO 4 is an important photoanode material for water oxidation, but its photoelectrochemistry regarding the triiodide/iodide redox couple is not well understood. Here, we use a combination of open circuit potential measurements, photoelectrochemical scans, and liquid surface photovoltage spectroscopy (SPS) to confirm that BiVO 4 /triiodide/iodide electrolyte contacts produce up to 0.55 V photovoltage under 23 mW/cm –2 illumination from a 470 nm LED. Inspired by these results, we construct FTO/BiVO 4 /KI(I 2 ) aq /Pt sandwich photoelectrochemical cells from electrochemically grown 0.5 × 0.5 cm 2 BiVO 4 and Mo-doped BiVO 4 films. Under AM 1.5 illumination, the devices have up to 0.22% energy conversion efficiency, 0.32 V photovoltage, and 1.8 mA cm –2 photocurrent. Based on SPS, hole transfer to iodide is sufficiently fast to prevent the competing water oxidation reaction. Mo doping increases the incident photon-to-current efficiency to up to 55% (at 425 nm under front illumination) by improving the BiVO 4 conductivity, but this comes at the expense of a lower photovoltage resulting from recombination at the Mo defects and a detrimental Schottky junction at the interface with FTO. Additional photovoltage losses are caused by the offset between the BiVO 4 valence band edge and the triiodide/iodide electrochemical potential and by electron back transfer to iodide at the FTO back contact (shunting). Overall, this work provides the first example of a BiVO 4 –liquid photovoltaic cell and an analysis of its limitations. Finally, even though the larger band gaps of metal oxides constrain their solar energy conversion efficiency, their transparency to visible light and deep valence bands makes them suitable for tandem photovoltaic devices.

14 SOLAR ENERGY↗
DOE OSTI2025

Efficient Mn 2+ Doping in Non-Stoichiometric Cesium Lead Bromide Perovskite Quantum Dots

Doping magnetic transition metal ions (e.g., Mn 2+ ) into colloidal quantum dots endows novel optical and magnetic properties to the host materials. CsPbBr 3 quantum dots (QDs) are emerging light-emitting materials with high structural and chemical flexibility in the visible spectral regime. However, efficiently doping Mn 2+ ions in CsPbBr 3 QDs remains challenging, especially when size confinement and ensemble uniformity are needed for understanding the underexplored exciton-dopant exchange interaction. Here, we introduce a doping mechanism based on electrostatic surface Mn 2+ adsorption that enables efficient Mn 2+ incorporation in strongly confined CsPbBr 3 QDs. The resultant QDs are found to have a Cs-deficient stoichiometry compared to their undoped counterparts. A redox reaction-based purification method was developed to remove Mn 2+ cations that are tightly adsorbed on the surface to determine the concentration of lattice-incorporated Mn 2+ . Our synthesis enables a Mn 2+ doping/alloying concentration of up to ∼44% with a Mn 2+ photoluminescence efficiency exceeding 90%. This allows for the determination of the intrinsic exciton-to-dopant energy transfer rate.

Hidayatova, Lamia [Univ. of Oklahoma, Norman, OK (↗
DOE OSTI2017

Highly Efficient Photocatalytic Water Splitting over Edge-Modified Phosphorene Nanoribbons

Two-dimensional phosphorene with desirable optoelectronic properties (ideal band gap, high carrier mobility, and strong visible light absorption) is a promising metal-free photocatalyst for water splitting. However, the band edge positions of the valence band maximum (VBM) and conduction band maximum (CBM) of phosphorene are higher than the redox potentials in photocatalytic water splitting reactions. Here, phosphorene can only be used as the photocathode for hydrogen evolution reaction as a low-efficiency visible-light-driven photocatalyst for hydrogen production in solar water splitting cells. Here, we propose a new mechanism to improve the photocatalytic efficiency of phosphorene nanoribbons (PNRs) by modifying their edges for full reactions in photocatalytic water splitting. By employing first-principles density functional theory calculations, we find that pseudohalogen (CN and OCN) passivated PNRs not only show desired VBM and CBM band edge positions induced by edge electric dipole layer, but also possess intrinsic optoelectronic properties of phosphorene, for both water oxidation and hydrogen reduction in photocatalytic water splitting without using extra energy. Furthermore, our calculations also predict that the maximum energy conversion efficiency of heterojunction solar cells consisting of different edge-modified PNRs can be as high as 20% for photocatalytic water splitting.

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

Metal–Organic Framework Containing Planar Metal-Binding Sites: Efficiently and Cost-Effectively Enhancing the Kinetic Separation of C 2 H 2 /C 2 H 4

One of the emerging problems plaguing the chemical industry today is the efficient and cost-effective separation of C 2 hydrocarbons. In order to help address this problem, we report a new material, NbU-1, constructed by extremely cheap starting materials. The special structural characteristics of NbU-1 such as the planar, mixed-valence copper clusters and Lewis-basic adsorption channels enforce interactions with acetylene molecules that lead to the highest kinetic separation efficiency for C 2 H 2 /C 2 H 4 . Via DFT-D calculations, it is indicated that C 2 H 2 molecules are adsorbed onto the two adjacent Cu(I) centers, but not the usual single open metal sites of Cu centers. Here, the reported results not only provide information for a deep investigation into the separation mechanism but also offer an alternative strategy for preparing cost-effective materials that can perform highly efficient separations of light hydrocarbons.

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

Efficient Hydrogen Production from Methanol Using a Single-Site Pt 1 /CeO 2 Catalyst

Hydrogen is regarded as an attractive alternative energy carrier due to its high gravimetric energy density and only water production upon combustion. However, due to its low volumetric energy density, there are still some challenges in practical hydrogen storage and transportation. In the last decade, using chemical bonds of liquid organic molecules as hydrogen carriers to generate hydrogen in situ provided a feasible method to potentially solve this problem. Research efforts on liquid organic hydrogen carriers (LOHCs) seek practical carrier systems and advanced catalytic materials that have the potential to reduce costs, increase reaction rate, and provide a more efficient catalytic hydrogen genera-tion/storage process. In this work, we used methanol as a hydrogen carrier to release hydrogen in situ with the single-site Pt1/CeO 2 catalyst. Moreover, in this reaction, compared with traditional nanoparticle catalysts, the single site catalyst displays excellent hydrogen generation efficiency, 40 times higher than that of a 2.5 nm Pt/CeO 2 sample, and 800 times higher compared to a 7.0 nm Pt/CeO 2 sample. Our in-depth study highlights the benefits of single-site catalysts and paves the way for further rational design of highly efficient catalysts for sustainable energy storage applications.

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

Efficient Super-Resolution of Near-Surface Climate Modeling Using the Fourier Neural Operator

Downscaling methods are critical in efficiently generating high-resolution atmospheric data. However, state-of-the-art statistical or dynamical downscaling techniques either suffer from the high computational cost of running a physical model or require high-resolution data to develop a downscaling tool. Here, we demonstrate a recently proposed zero-shot super-resolution method, the Fourier neural operator (FNO), to efficiently perform downscaling without the need for high-resolution data. Because the FNO learns dynamics in Fourier space, FNO is a resolution-invariant emulator; it can be trained at a coarse resolution and produces emulation at any high resolution. We applied FNO to downscale a 4-km resolution Weather Research and Forecasting (WRF) Model simulation of near-surface heat-related variables over the Great Lakes region. The FNO is driven by the atmospheric forcings, and topographic features used in the WRF model at the same resolution. We incorporated a physics-constrained loss in FNO by using the Clausius-Clapeyron relation to better constrain the relations among the emulated states. Trained on merely 600 WRF snapshots at 4-km resolution, the FNO shows comparable performance with a widely used convolutional network, U-Net, achieving averaged modified Kling-Gupta Efficiency of 0.88 and 0.94 on the test dataset for temperature and pressure, respectively. We then employed the FNO to produce 1-km emulations to reproduce the fine climate features. Further, by taking the WRF simulation as ground truth, we show consistent performances at the two resolutions, suggesting the reliability of FNO in producing high-resolution dynamics. Our study demonstrates the potential of using FNO for zero-shot super-resolution in generating first-order estimation on atmospheric modeling.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Facile fabrication of large-grain CH 3 NH 3 PbI 3-x Br x films for high-efficiency solar cells via CH 3 NH 3 Br-selective Ostwald ripening

Organometallic halide perovskite solar cells (PSCs) have shown great promise as a low-cost, high-efficiency photovoltaic technology. Structural and electro-optical properties of the perovskite absorber layer are most critical to device operation characteristics. Here we present a facile fabrication of high-efficiency PSCs based on compact, large-grain, pinhole-free CH 3 NH 3 PbI 3-x Br x (MAPbI 3-x Br x ) thin films with high reproducibility. A simple methylammonium bromide (MABr) treatment via spin-coating with a proper MABr concentration converts MAPbI 3 thin films with different initial film qualities (for example, grain size and pinholes) to high-quality MAPbI 3-x Br x thin films following an Ostwald ripening process, which is strongly affected by MABr concentration and is ineffective when replacing MABr with methylammonium iodide. A higher MABr concentration enhances I-Br anion exchange reaction, yielding poorer device performance. Lastly, this MABr-selective Ostwald ripening process improves cell efficiency but also enhances device stability and thus represents a simple, promising strategy for further improving PSC performance with higher reproducibility and reliability.

14 SOLAR ENERGY↗
DOE OSTI2016

Donor polymer design enables efficient non-fullerene organic solar cells

To achieve efficient organic solar cells, the design of suitable donor–acceptor couples is crucially important. State-of-the-art donor polymers used in fullerene cells may not perform well when they are combined with non-fullerene acceptors, thus new donor polymers need to be developed. Here we report non-fullerene organic solar cells with efficiencies up to 10.9%, enabled by a novel donor polymer that exhibits strong temperature-dependent aggregation but with intentionally reduced polymer crystallinity due to the introduction of a less symmetric monomer unit. Our comparative study shows that an analogue polymer with a C2 symmetric monomer unit yields highly crystalline polymer films but less efficient non-fullerene cells. Based on a monomer with a mirror symmetry, our best donor polymer exhibits reduced crystallinity, yet such a polymer matches better with small molecular acceptors. This study provides important insights to the design of donor polymers for non-fullerene organic solar cells.

Science & Technology - Other Topics↗
DOE OSTI2016

Theory of highly efficient multiexciton generation in type-II nanorods

Multiexciton generation, by which more than a single electron–hole pair is generated on optical excitation, is a promising paradigm for pushing the efficiency of solar cells beyond the Shockley–Queisser limit of 31%. Utilizing this paradigm, however, requires the onset energy of multiexciton generation to be close to twice the band gap energy and the efficiency to increase rapidly above this onset. This challenge remains unattainable even using confined nanocrystals, nanorods or nanowires. Here, we show how both goals can be achieved in a nanorod heterostructure with type-II band offsets. Using pseudopotential atomistic calculation on a model type-II semiconductor heterostructure we predict the optimal conditions for controlling multiexciton generation efficiencies at twice the band gap energy. For a finite band offset, this requires a sharp interface along with a reduction of the exciton cooling and may enable a route for breaking the Shockley–Queisser limit.

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

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

Science & Technology - Other Topics↗
DOE OSTI2015

Flexible, highly efficient all-polymer solar cells

All-polymer solar cells have shown great potential as flexible and portable power generators. These devices should offer good mechanical endurance with high power-conversion efficiency for viability in commercial applications. In this work, we develop highly efficient and mechanically robust all-polymer solar cells that are based on the PBDTTTPD polymer donor and the P(NDI2HD-T) polymer acceptor. These systems exhibit high power-conversion efficiency of 6.64%. Also, the proposed all-polymer solar cells have even better performance than the control polymer-fullerene devices with phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor (6.12%). More importantly, our all-polymer solar cells exhibit dramatically enhanced strength and flexibility compared with polymer/PCBM devices, with 60- and 470-fold improvements in elongation at break and toughness, respectively. The superior mechanical properties of all-polymer solar cells afford greater tolerance to severe deformations than conventional polymer-fullerene solar cells, making them much better candidates for applications in flexible and portable devices.

14 SOLAR ENERGY↗
DOE OSTI2016

Concentrating solar thermoelectric generators with a peak efficiency of 7.4%

Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage, enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck effect, simplifying the system. The highest reported efficiency of STEGs so far is 5.2%. We report experimental measurements of STEGs with a peak efficiency of 9.6% at an optically concentrated normal solar irradiance of 211 kW m -2 , and a system efficiency of 7.4% after considering optical concentration losses. The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600 °C, and combining optical and thermal concentration. Our work suggests that concentrating STEGs have the potential to become a promising alternative solar energy technology.

14 SOLAR ENERGY↗
DOE OSTI2016

Monocrystalline CdTe solar cells with open-circuit voltage over 1 V and efficiency of 17%

The open-circuit voltages of mature single-junction photovoltaic devices are lower than the bandgap energy of the absorber, typically by a gap of 400 mV. For CdTe, which has a bandgap of 1.5 eV, the gap is larger; for polycrystalline samples, the open-circuit voltage of solar cells with the record efficiency is below 900 mV, whereas for monocrystalline samples it has only recently achieved values barely above 1 V. Here, we report a monocrystalline CdTe/MgCdTe double-heterostructure solar cell with open-circuit voltages of up to 1.096 V. The latticed-matched MgCdTe barrier layers provide excellent passivation to the CdTe absorber, resulting in a carrier lifetime of 3.6 μs. The solar cells are made of 1- to 1.5-μm-thick n-type CdTe absorbers, and passivated hole-selective p-type a-SiC y :H contacts. This design allows CdTe solar cells to be made thinner and more efficient. As a result, the best power conversion efficiency achieved in a device with this structure is 17.0%.

42 ENGINEERING↗
DOE OSTI2017

CRISPR-Cpf1 mediates efficient homology-directed repair and temperature-controlled genome editing

Cpf1 is a novel class of CRISPR-Cas DNA endonucleases, with a wide range of activity across different eukaryotic systems. Yet, the underlying determinants of this variability are poorly understood. Here, we demonstrate that LbCpf1, but not AsCpf1, ribonucleoprotein complexes allow efficient mutagenesis in zebrafish and Xenopus. We show that temperature modulates Cpf1 activity by controlling its ability to access genomic DNA. This effect is stronger on AsCpf1, explaining its lower efficiency in ectothermic organisms. We capitalize on this property to show that temporal control of the temperature allows post-translational modulation of Cpf1-mediated genome editing. Finally, we determine that LbCpf1 significantly increases homology-directed repair in zebrafish, improving current approaches for targeted DNA integration in the genome. Together, we provide a molecular understanding of Cpf1 activity in vivo and establish Cpf1 as an efficient and inducible genome engineering tool across ectothermic species.

59 BASIC BIOLOGICAL SCIENCES↗

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