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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Chemical Grafting of Highly Dispersed VO x /CeO 2 for Increased Catalytic Activity in Methanol Oxidative Dehydrogenation

Vanadia supported on well-defned ceria nanocubes are synthesized at various loadings using a liquid-phase chemical grafting technique and are compared to those prepared using traditional incipient wetness impregnation. Raman and IR characterization reveal that, as vanadia loading is increased to near monolayer coverage, vanadia deposited using grafting shows greatly enhanced dispersion (i.e., improved VO x monomer/dimer distribution). Methanol is used as a probe molecule to explore the redox behavior of the catalysts. IR and temperature programmed desorption of methanol show increased CO 2 formation occurs on the bare ceria support and increasing the dispersion of vanadia promotes dehydrogenation to formaldehyde due to the inhibited oxygen vacancy formation on VO x /CeO 2 . Hydrogen temperature programmed reduction demonstrates that the catalyst reducibility and formation of surface oxygen vacancy are directly related to the degree of vanadia oligomerization. In conclusion, the samples prepared using grafting exhibit superior catalytic performance for methanol oxidative dehydrogenation to formaldehyde compared to the impregnated samples, due to the presence of highly dispersed VO x species (i.e., monomers and dimers).

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

Rate Controlling in Low-Temperature Standard NH 3 -SCR: Implications from Operando EPR Spectroscopy and Reaction Kinetics

Here, a series of seven Cu/SSZ-13 catalysts with Si/Al = 6.7 are used to elucidate key rate-controlling factors during low-temperature standard ammonia-selective catalytic reduction (NH 3 -SCR), via a combination of SCR kinetics and operando electron paramagnetic resonance (EPR) spectroscopy. Strong Cu-loading-dependent kinetics, with Cu atomic efficiency increasing nearly by an order of magnitude, is found when per chabazite cage occupancy for Cu ion increases from ~0.04 to ~0.3. This is due mainly to the release of intercage Cu transfer constraints that facilitates the redox chemistry, as evidenced from detailed Arrhenius analysis. Operando EPR spectroscopy studies reveal strong connectivity between Cu-ion dynamics and SCR kinetics, based on which it is concluded that under low-temperature steady-state SCR, kinetically most relevant Cu species are those with the highest intercage mobility. Transient binuclear Cu species are mechanistically relevant species, but their splitting and cohabitation are indispensable for low-temperature kinetics.

catalytic reactions↗
DOE OSTI2025

Effect of cell compression on the performance and the structure of proton exchange membrane water electrolyzer (PEMWE) assembly

Here, in the field of water electrolysis, the proton exchange membrane water electrolyzer (PEMWE) is currently the most advanced technology for producing hydrogen without emitting CO 2 . Although PEMWE plants are already in operation, further research is needed to improve cell efficiency and reduce the use of rare materials, such as iridium oxide catalysts for the oxygen evolution reaction (OER). One of the main causes of performance loss in PEMWE is the relatively low electric conductivity of the porous transport layer (PTL) and of the anode catalyst layer, which results in ohmic losses and low catalyst utilization during high current density operation. The objective of this study is to investigate how optimization of the PTL and electrode interface can increase the cell performance. To this end, we tested different cell assemblies using fibrous and sintered PTLs, decreasing membrane thickness, reducing iridium loading, and inserting a microporous layer to increase contact surface area. Electrochemical characterization of each cell configuration was systematically performed at various compression levels as the pressure is a crucial parameter influencing the electrode/PTL contact area. In parallel, X-ray microcomputed tomography (micro-CT) was employed to investigate the effects of cell hydration and compression on the structure of PEMWE components. This study combining electrochemistry and micro-CT imaging presents how optimizing the electrode/PTL contact surface area, minimizes ohmic losses, and enables PEMWE operation with low iridium loading at high current densities.

Catalyst - PTL interface↗
DOE OSTI2024

Underpotential Deposition of 3D Transition Metals: Versatile Electrosynthesis of Single-Atom Catalysts on Oxidized Carbon Supports

Use of single-atom catalysts (SACs) has become a popular strategy for tuning activity and selectivity toward specific pathways. However, conventional SAC synthesis methods require high temperatures and pressures, complicated procedures, and expensive equipment. Recently, underpotential deposition (UPD) has been investigated as a promising alternative, yielding high-loading SAC electrodes under ambient conditions and within minutes. Yet only few studies have employed UPD to synthesize SACs, and all have been limited to UPD of Cu. In this work, a flexible UPD approach for synthesis of mono- and bi-metallic Cu, Fe, Co, and Ni SACs directly on oxidized, commercially available carbon electrodes is reported. The UPD mechanism is investigated using in situ X-ray absorption spectroscopy and, finally, the catalytic performance of a UPD-synthesized Co SAC is assessed for electrochemical nitrate reduction to ammonia. In conclusion, the findings expand upon the usefulness and versatility of UPD for SAC synthesis, with hopes of enabling future research toward realization of fast, reliable, and fully electrified SAC synthesis processes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

AST Development in M2FCT (ASTWG and iDWG) Update to 21CTP [Slides]

Accelerated Stress Tests (ASTs) are required to evaluate fuel cell component durability in a reasonable time. Current DOE and FCTT ASTs are light duty focused with 5000 – 8000 hour durability requirements. Heavy duty ASTs need to reflect the 25000+ hour durability requirement. Interim solution is to extend the duration of the current light duty ASTs: Catalyst AST has been extended from 30,000 cycles to 90,000 cycles (From 50 hours to 150 hours). We need to understand Heavy duty stressors and tailor ASTs for heavy duty applications: Longer lifetimes; Higher efficiencies – Higher loadings - Potentially higher operating temperatures and voltages; Heat rejection during low speed hill climbs – Higher operating temperature; Longer Idling times – Higher operating voltages and drier operation; Take into account different hybridization strategies (Vary size of battery).

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

4D Imaging of ZnO-Coated Nanoporous Al 2 O 3 Aerogels by Chemically Sensitive Ptychographic Tomography: Implications for Designer Catalysts

The 3D chemical structure (4D spectromicroscopy) of nanoporous Al 2 O 3 aerogels coated with ZnO by atomic layer deposition (ALD) was studied by multienergy scanning transmission X-ray microscopy. These materials are representative of a class of designer catalysts in which the nanoporous support is prepared separately from the active catalyst material, which is subsequently introduced by ALD, thereby allowing independent optimization of the morphology, chemistry, and spatial distribution of the support and catalyst. The samples studied were prepared by Ga ion and Xe plasma focused ion beam (FIB) milling as well as drop casting from water suspension. Zn L and Al K edge spectra of six samples with three different ZnO loadings were measured to investigate how loading and different sample preparation methods affect the 3D distribution of the ZnO and Al 2 O 3 . Scanning transmission X-ray microscopy (STXM) and ptychographic imaging at two energies each at the Zn L 3 and Al K edge were measured. The ptychography data were analyzed by using the SHARP reconstruction code to generate quantitative 2D chemical maps of the Al 2 O 3 and the ZnO. The STXM and ptychography maps were then measured at a sequence of tilt angles, covering up to 160° of rotation. The 3D structure of the ZnO and Al 2 O 3 was derived from the tilt series data by tomographic reconstruction using a compressed sensing algorithm. A twodimensional spatial resolution (half-period) of 6 nm, measured by Fourier ring correlation, and a 3D spatial resolution (half-period) of 9 nm, measured by Fourier shell correlation, were achieved when using the COSMIC beamline at the Advanced Light Source (ALS). The results show that for all of the ZnO loadings studied there is nonuniform coverage of the ZnO on the Al 2 O 3 aerogel framework. In addition, we found that both FIB methods create sample artifacts, although the distortion was less with Xe plasma than Ga ion FIB.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Practical low-temperature gasoline combustion for very high efficiency off-road, medium- and heavy-duty engines

Low-temperature gasoline combustion (LTGC) with additive-mixing fuel injection (AMFI) is a new combustion strategy that has been demonstrated to deliver 9%–25% better brake thermal efficiency than similar-sized market-leading diesel engines over the operating map. Moreover, the LTGC-AMFI engine shows near-zero smoke, and NOx emissions are 4–100 times lower than those of a diesel, sufficiently low that no aftertreatment, or only passive NOx aftertreatment, would be sufficient (diesel exhaust fluid is not required). LTGC-AMFI combustion is based on kinetically controlled compression ignition of a dilute charge with a variable amount of low-to-moderate fuel stratification. Fast combustion control is provided by adding minute amounts of an ignition-enhancing additive into the fuel each engine cycle to control its reactivity. This strategy was used to operate a medium-duty (MD) LTGC-AMFI engine at loads from idle to 16.3 bar BMEP and speeds from 600 to 2400 rpm with regular E10 gasoline, which covers nearly the entire operating map of a typical MD engine. Turbine-out temperatures were sufficient for an oxidation catalyst to control hydrocarbon and CO emissions. Autonomie simulations over the GEM ARB Transient and the GEM 55 mph Cruise driving cycles for class-6 trucks using this technology showed fuel economies of 8.1 and 11.4 mpg-gasoline-equivalent, respectively, corresponding to 18.6% and 13.4% improvements over a similar-size diesel engine. Engine-out NOx emissions were 0.024 and 0.01 g/bhp-h, respectively, well below current U.S. emission standards. These results show that switching from diesel to LTGC-AMFI engines would greatly reduce greenhouse gas (GHG) emissions for off-road, MD and HD applications, which will continue to rely on combustion engines because electrification is not practical in the foreseeable future. Finally, with their reduced fuel consumption, the lower cost of gasoline compared to diesel fuel, and much lower aftertreatment costs, LTGC-AMFI engines also offer a significantly lower total cost of ownership.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Tailoring electrode microstructure via ink content to enable improved rated power performance for platinum cobalt/high surface area carbon based polymer electrolyte fuel cells

Improvements in polymer electrolyte fuel cell (PEFC) electrode performance have primarily focused on catalyst and ionomer developments, marginalizing the importance of catalyst ink formulation. In this study, the effect of ink formulation is examined across a series of cathodes comprised of PtCo supported on high surface area carbon (PtCo/ HSC ) and Nafion ionomer using an array of in situ electrochemical and ex situ characterization techniques. In contrast to prior work on Pt/Vu systems, ink water content had little effect on the electrochemically determined ionomer coverage for the PtCo/HSC electrocatalyst examined here. Characterization using nano-scale resolution X-ray computed tomography (nano-CT) demonstrated that water-rich ink formulations lead to a reduction in aggregate size (ionomer + PtCo/HSC), improving local O 2 transport. This understanding, combined with the use of a commercially-available electrocatalyst was used to produced state-of-the-art membrane electrode assemblies with Pt loadings of 0.03/0.08 mg Pt /cm 2 on the anode and cathode respectively, having; i) > 1 A/mg Pt (0.9 V iR-free , 150 kPa, 80 °C, 100% RH, H 2 /O 2 ), ii) 320 mA/cm 2 at 0.8 V, 150 kPa, 80 ° C, 100% RH, H 2 /Air), and iii) > 1 W/cm 2 elec at rated power (0.67 V, 250 kPa, 94 °C, 65% RH, H 2 /Air) or < 0.11 g Pt /kW rated .

25 ENERGY STORAGE↗
NASA NTRS2010

Packing Optimization of an Intentionally Stratified Sorbent Bed Containing Dissimilar Media Types

The Fire Cartridge is a packed bed air filter with two different and separate layers of media designed to provide respiratory protection from combustion products after a fire event on the International Space Station (ISS). The first layer of media is a carbon monoxide catalyst made from gold nanoparticles dispersed on iron oxide. The second layer of media is universal carbon, commonly used in commercial respirator filters. Each layer must be optimally packed to effectively remove contaminants from the air. Optimal packing is achieved by vibratory agitations. However, if post-packing movement of the media within the cartridge occurs, mixing of the bed layers, air voids, and channeling could cause preferential air flow and allow contaminants to pass. Several iterations of prototype fire cartridges were developed to reduce post-packing movement of the media within each layer (settling), and to prevent mixing of the two media types. Both types of movement of the media contribute to decreased fire cartridge performance. Each iteration of the fire cartridge design was tested to demonstrate mechanical loads required to cause detrimental movement within the bed, and resulting level of functionality of the media beds after movement was detected. In order to optimally pack each layer, vertical, horizontal, and orbital agitations were tested and a final packed bulk density was calculated for each method. Packed bulk density must be calculated for each lot of catalyst to accommodate variations in particle size, shape, and density. In addition, a physical divider sheet between each type of media was added within the fire cartridge design to further inhibit intermixing of the bed layers.

Kidd, Jessica↗
DOE OSTI2023

Boosting Hydrogen Evolution in Neutral Medium by Accelerating Water Dissociation with Ru Clusters Loaded on Mo 2 CTx MXene

Abstract Electrocatalytic hydrogen evolution reaction (HER) in mild neutral medium is a compelling goal for environmentally sustainable energy conversion, but its development is greatly limited by slow kinetics. Platinum group noble metals exhibit ultra‐high HER activities, but their scarcity and performance instability restrict wide application. Herein, taking advantage of excellent catalyst carrier properties of 2D‐layered transition metal carbides (MXenes), highly dispersed of Ru clusters anchored on Mo 2 CT x MXene are demonstrated as a superior HER electrocatalyst, which is prepared by a facile in situ reduction strategy. The as‐prepared Ru/Mo 2 CT x catalyst exhibits a very low overpotential of 73 mV to achieve a current density of −10 mA cm −2 and Tafel slope of 57 mV dec −1 in neutral medium, surpassing performance of most previously reported MXene‐based catalysts. In addition, Ru/Mo 2 CT x catalyst also presents superior stability compared to commercial Pt/C. Experimental results and theoretical calculations indicate that the interaction between Ru clusters modulates the electronic structure of active sites and promotes H 2 O dissociation and hydrogen desorption.

Wu, Yanze↗
DOE OSTI2020

End of Green Sahara amplified mid- to late Holocene megadroughts in mainland Southeast Asia

Between 5 and 4 thousand years ago, crippling megadroughts led to the disruption of ancient civilizations across parts of Africa and Asia, yet the extent of these climate extremes in mainland Southeast Asia (MSEA) has never been defined. This is despite archeological evidence showing a shift in human settlement patterns across the region during this period. We report evidence from stalagmite climate records indicating a major decrease of monsoon rainfall in MSEA during the mid- to late Holocene, coincident with African monsoon failure during the end of the Green Sahara. Through a set of modeling experiments, we show that reduced vegetation and increased dust loads during the Green Sahara termination shifted the Walker circulation eastward and cooled the Indian Ocean, causing a reduction in monsoon rainfall in MSEA. Our results indicate that vegetation-dust climate feedbacks from Sahara drying may have been the catalyst for societal shifts in MSEA via ocean-atmospheric teleconnections.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Understanding the Origin of Highly Selective CO 2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Abstract Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO 2 electroreduction (CO 2 R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO 2 reduction (CO 2 R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO 2 R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.

Koshy, David M.↗
DOE OSTI2021

Density functional theory studies of transition metal carbides and nitrides as electrocatalysts

Transition metal carbides and nitrides are interesting non-precious materials that have been shown to replace or reduce the loading of precious metals for catalyzing several important electrochemical reactions. The purpose of this review is to summarize density functional theory (DFT) studies, describe reaction pathways, identify activity and selectivity descriptors, and present a future outlook in designing carbide and nitride catalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), nitrogen reduction reaction (N 2 RR), CO 2 reduction reaction (CO 2 RR) and alcohol oxidation reactions. Furthermore, this topic is of high interest to scientific communities working in the field of electrocatalysis and this review should provide theoretical guidance for the rational design of improved carbide and nitride electrocatalysts.

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

Energy Performance Validation of a Gaseous Air Cleaning Technology for Commercial Buildings

The U.S. Department of Energy (DOE) Building Technologies Office Commercial Building Integration group conducts evaluations of new energy efficiency technologies as part of the High Impact Technology Catalyst program. The subject of this field validation project is an air cleaning technology that removes gaseous contaminants from indoor air to reduce outdoor air ventilation requirements. Reducing the volume of outdoor air required reduces heating, ventilating, and air conditioning (HVAC) loads and can provide significant energy savings for some buildings in certain climates. The technology, called the HLR (HVAC Load Reduction), was developed by enVerid. The technology uses a solid regenerable sorbent material that was developed by DOE's National Energy Technology Laboratory and licensed to the vendor for this application. The sorbent material was originally developed to adsorb carbon dioxide (CO2); the vendor continued to develop the sorbent and the overall system so that it can also remove volatile organic compounds (including aldehydes), carbon monoxide, ozone, and particulate matter 2.5 micrometers in diameter or smaller (PM2.5) from the air. This material has low regeneration temperature requirements, and its sorption properties are unaffected by humidity levels, both of which are beneficial for building applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Low-Cost Intermediate-Temperature Fuel-Flexible Protonic-Ceramic Fuel Cell and Stack

Large, centralized power plants are currently the most efficient way to convert fuels such as natural gas to electricity. Fuel cells, however, could become highly efficient generators across a range of sizes from tens of watts to megawatts. In particular, fuel cells with an electrical efficiency of 50% could displace small generators of 25 kilowatts (kW) or less in applications such as remote power, telecommunications, and residential cogeneration. Current 25 kW natural gas generators employing internal combustion engines are typically only 25-30% efficient and expensive to maintain. Furthermore, fuel cells could provide valuable services to the grid, such as the ability to ramp power up or down in response to load conditions. While there are different types of fuel cells, each with their strengths and weaknesses, fuel cells generally are very expensive. For example, lower temperature fuel cells can be started up quickly, but require highly pure hydrogen fuel and expensive catalysts. High-temperature fuel cells can operate on a range of fuels, but they have costly system components and can degrade rapidly.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2005

Investigation of Ruthenium Dissolution in Advanced Membrane Electrode Assemblies for Direct Methanol Based Fuel Cell Stacks

Dissolution of ruthenium was observed in the 80-cell stack. Duration testing was performed in single cell MEAs to determine the pathway of cell degradation. EDAX analysis on each of the single cell MEAs has shown that the Johnson Matthey commercial catalyst is stable in DMFC operation for 250 hours, no ruthenium dissolution was observed. Changes in the hydrophobicity of the cathode backing papers was minimum. Electrode polarization analysis revealed that the MEA performance loss is attributed to changes in the cathode catalyst layer. Ruthenium migration does not seem to occur during cell operation but can occur when methanol is absent from the anode compartment, the cathode compartment has access to air, and the cells in the stack are electrically connected to a load (Shunt Currents). The open-to-air cathode stack design allowed for: a) The MEAs to have continual access to oxygen; and b) The stack to sustain shunt currents. Ruthenium dissolution in a DMFC stack can be prevented by: a) Developing an internally manifolded stacks that seal reactant compartments when not in operation; b) Bringing the cell voltages to zero quickly when not in operation; and c) Limiting the total number of cells to 25 in an effort to limit shunt currents.

alternative power sources↗