Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “enhanced stability”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Untangling causality in midlatitude aerosol–cloud adjustments

Aerosol–cloud interactions represent the leading uncertainty in our ability to infer climate sensitivity from the observational record. The forcing from changes in cloud albedo driven by increases in cloud droplet number (Nd) (the first indirect effect) is confidently negative and has narrowed its probable range in the last decade, but the sign and strength of forcing associated with changes in cloud macrophysics in response to aerosol (aerosol–cloud adjustments) remain uncertain. This uncertainty reflects our inability to accurately quantify variability not associated with a causal link flowing from the cloud microphysical state to the cloud macrophysical state. Once variability associated with meteorology has been removed, covariance between the liquid water path (LWP) averaged across cloudy and clear regions (here characterizing the macrophysical state) and Nd (characterizing the microphysical) is the sum of two causal pathways linking Nd to LWP: Nd altering LWP (adjustments) and precipitation scavenging aerosol and thus depleting Nd. Only the former term is relevant to constraining adjustments, but disentangling these terms in observations is challenging. We hypothesize that the diversity of constraints on aerosol–cloud adjustments in the literature may be partly due to not explicitly characterizing covariance flowing from cloud to aerosol and aerosol to cloud. Here, we restrict our analysis to the regime of extratropical clouds outside of low-pressure centers associated with cyclonic activity. Observations from MAC-LWP (Multisensor Advanced Climatology of Liquid Water Path) and MODIS are compared to simulations in the Met Office Unified Model (UM) GA7.1 (the atmosphere model of HadGEM3-GC3.1 and UKESM1). The meteorological predictors of LWP are found to be similar between the model and observations. There is also agreement with previous literature on cloud-controlling factors finding that increasing stability, moisture, and sensible heat flux enhance LWP, while increasing subsidence and sea surface temperature decrease it. A simulation where cloud microphysics are insensitive to changes in Nd is used to characterize covariance between Nd and LWP that is induced by factors other than aerosol–cloud adjustments. By removing variability associated with meteorology and scavenging, we infer the sensitivity of LWP to changes in Nd. Application of this technique to UM GA7.1 simulations reproduces the true model adjustment strength. Observational constraints developed using simulated covariability not induced by adjustments and observed covariability between Nd and LWP predict a 25 %–30 % overestimate by the UM GA7.1 in LWP change and a 30 %–35 % overestimate in associated radiative forcing.

Daniel T. McCoy↗
NASA NTRSDate not supplied

Optimization of Aerogels for High Temperature Applications

Aerogels can be used in spaceflight applications as thermal insulators due to their low density, low thermal conductivity, and tortuous path for solid conduction. However, the aerogel formulation must be optimized to increase the thermal stability of the aerogels as drastic densification and decrease in surface area is often exhibited after high-temperature exposure. Current research investigates yttria-stabilized zirconia (YSZ) aerogels, which have low thermal conductivity and are expected to be used between 600°C and 1000°C. We anticipate that new sol-gel chemistries and processing will yield YSZ aerogels that display retained mesoporous structure, increased surface area, and minimized shrinkage upon exposure to higher temperatures in the projected use range. This work investigates the cationic surfactant, cetrimonium bromide (CTAB), as a templating agent to prevent the collapse of the aerogel pore structure upon gelation and drying. It was determined that adding one-half times the critical micelle concentration (CMC) of CTAB increased the surface area and pore volume of the aerogels, as compared to aerogels without CTAB or with twice the CMC of CTAB, following high-temperature exposure. By optimizing CTAB, the thermal stability of YSZ aerogels can be enhanced to make these materials more efficient when used as thermal management systems.

Rebecca C Walker↗
NASA NTRSDate not supplied

Optimizing Surfactant Templating of Yttria-stabilized Zirconia Aerogels for High-temperature Applications: Effect of Anionic & Nonionic Surfactant

Aerogels are useful thermal insulators due to low density, low thermal conductivity, and a tortuous path for solid conduction. However, the formulation must be optimized to increase thermal stability as drastic densification and surface area decrease is often exhibited after high-temperature exposure. Current research investigates yttria-stabilized zirconia (YSZ) aerogels for expected use between 600°C and 1000°C. We anticipate that new sol-gel chemistries will yield YSZ aerogels with retained mesoporous structure, increased surface area, and minimized shrinkage upon high-temperature exposure. This work investigates the anionic surfactant, sodium dodecyl sulfate (SDS), and the nonionic surfactant, Pluronic® P-123, as templating agents to prevent the collapse of the aerogel pore structure upon gelation and drying. To determine the effect of surfactant, characterization techniques such as nitrogen physisorption, x-ray diffraction, and scanning electron microscopy are used. By optimizing surfactant concentration, the thermal stability of YSZ aerogels can be enhanced, producing more efficient thermal insulators.

Rebecca C. Walker↗
NASA NTRS2026

Microstructural Evolution and Mechanical Properties of LP-DED NASA HR-1 – A Hydrogen Resistant AM Superalloy for Space Propulsion Applications

The National Aeronautics and Space Administration (NASA) has actively pursued metal additive manufacturing (AM) technologies for spaceflight applications since the late 2000s. AM offers transformative advantages in cost, schedule, part consolidation, and design flexibility. Among the various AM techniques, laser powder directed energy deposition (LP-DED) is particularly well suited for fabricating complex geometries with fine feature resolution. In propulsion systems that utilize high-pressure gaseous hydrogen—such as liquid hydrogen rocket engines—hydrogen environment embrittlement (HEE) presents a serious threat to material performance 1,2 . Mechanical property degradation under these conditions can compromise component reliability, especially under cyclic loading. To address this challenge, NASA developed NASA HR-1 (Hydrogen Resistant-1) as a solution for liquid rocket engine components operating in hydrogen-rich environments, using the LP-DED technique 3-9 . A key component in a liquid rocket engine is the exhaust nozzle, which is typically regeneratively cooled (regen) due to the high heat flux. NASA HR-1 was specifically developed for regen nozzle applications using hydrogen as a propellant, providing resistance to HEE, a critical issue for many materials. The AM version of NASA HR-1 was also formulated to achieve high ultimate tensile strength, along with high yield strength and ductility in this environment 5,6 . Low-cycle fatigue (LCF) is another important consideration in nozzle design, as components are expected to endure multiple starts and missions. Additionally, the LP-DED version of the alloy exhibits improved thermal conductivity compared to its wrought counterpart, which benefits nozzle cooling. Overall, NASA HR-1 offers an excellent balance of high strength, HEE resistance, LCF performance, thermal conductivity, and ductility to meet the demanding requirements of channel-cooled nozzles and other components used with hydrogen and other propellants. The LP-DED–processed NASA HR-1 requires several post-processing heat treatment steps to achieve the material properties desirable for its intended application 6 . These steps include stress relief, homogenization, solution annealing, and aging for precipitation hardening. The stress relief treatment mitigates residual stresses accumulated during the LP-DED process and minimizes the potential for distortion. Homogenization, a common step for AM materials, reduces elemental segregation and promotes recrystallization to develop a more equiaxed grain structure. The subsequent solution annealing treatment heats the part to a solid solution temperature to dissolve the undesirable η-phase that forms during cooling from homogenization, followed by rapid cooling to retain an η-phase–free microstructure. Finally, aging promotes precipitation of the strengthening γ′ phase in the alloy. The integration of compositional design and optimized thermal processing enables high-quality LP-DED NASA HR-1 components with excellent microstructural and mechanical stability. Improved chemical and microstructure homogeneity enhances ductility and fatigue resistance—both critical for safe and reliable operation in high-pressure hydrogen environments. NASA has successfully fabricated and hot-fire tested multiple subscale and full-scale channel wall nozzles using LP-DED NASA HR-1 5,6, 9-14 . These efforts included process refinements to support thin-wall construction and various channel geometries. Throughout development, several key observations emerged. After homogenization, the as-built columnar grain structure transforms into a fully equiaxed microstructure. However, subsequent treatments—such as solution annealing and aging—result in changes that are more difficult to track. The grain structure remains largely unchanged, and the γ′ precipitates, typically 5–10 nm in diameter, are beyond the resolution of scanning electron microscopy (SEM). While transmission electron microscopy (TEM) can resolve these fine precipitates, TEM sample preparation is time-consuming and difficult for LP-DED material. As an alternative, differential scanning calorimetry (DSC) offers a useful, qualitative approach to monitor precipitate evolution throughout different stages of heat treatment. The overall goal is to improve the understanding of how heat treatment affects the microstructure and mechanical performance of LP-DED NASA HR-1. This paper presents heat treatment design considerations, microstructural characterization, mechanical testing – including tensile and LCF testing in both air and hydrogen environments.

Superalloy↗
DOE OSTI2021

Li-substituted layered spinel cathode materials for sodium ion batteries

Systems, methods, and compositions are disclosed for a Li-substituted layered-tunneled O3/spinel Na(NixFeyMnz)O2 cathode material, Na0.87Li0.25Ni0.4Fe0.2Mn0.4O2+∂ (LS-NFM) for enhanced sodium ion storage and cycling stability. The LS-NFM electrode is prepared by adjusting the stoichiometric ratio of the Na ion over the sum of Li and transition metal ions below 1. The Rietveld refinement of XRD data indicates that the cathode is composed of 94% layered and 6% spinel components. When cycled at a high current density of 100 mA g−1, LS-NFM cathode exhibited a first-cycle Coulombic efficiency of 88% and reversible discharge capacity of 107 mAh g−1 after 50 cycles with the capacity retention of 95%.

Xiong, Hui↗
DOE OSTI2025

Improving durability and performance of solid oxide electrolyzers by controlling surface composition on oxygen electrodes

Solid oxide electrolysis cell (SOEC) is a promising technology for high-efficiency energy conversion, enabling the production of hydrogen, syngas, synthetic fuels, and various commodity chemicals. Unlike traditional thermochemical processes, SOECs operate at elevated temperatures (600-850°C), benefiting from favorable thermodynamics and reaction kinetics. This makes them highly energy efficient compared to alkaline or polymer electrolyte membrane (PEM) electrolysis technologies. However, despite these advantages, SOECs face significant challenges related to performance degradation over time. A primary issue is the degradation of the oxygen electrode due to strontium (Sr) segregation and impurity poisoning from chromium (Cr) and sulfur (S). This is because the pathway to deposition of Cr and S include the reaction of Cr and S with the segregated SrO at the surface. Sr segregation leads to the formation of insulating compounds such as SrCrO4 and SrSO4, which block active sites, reduce oxygen exchange rates, and compromise the electrode's electrochemical stability. The degradation mechanisms involve complex interactions between the electrode material's surface chemistry, microstructure, and the operating environment. Sr segregation is particularly problematic because it facilitates the deposition of Cr and S impurities, exacerbating performance losses. Addressing these issues is critical to enhancing the durability and economic viability of SOEC technology. The primary goal of this project is to improve the durability and performance of SOECs by controlling the surface composition of the oxygen electrode. This is achieved by suppressing Sr segregation, thereby mitigating impurity poisoning pathways. The project aims to enhance the oxygen exchange rate, improve cell stability, and extend the operational lifespan of SOECs without necessitating major changes to electrode chemistry or stack components.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

On Stability and Electrochemical Performance of 316 Stainless Steel in Wastewater: Implications for Resource Recovery

Electrochemical nutrient recovery systems rely on stable electrode materials capable of operating in chemically complex wastewater environments. We investigated corrosion resistance and interfacial electrochemical behavior of 316 stainless steel (SS316) in a synthetic wastewater matrix representative of centrate streams, a key knowledge gap in electrochemical phosphorus recovery. A comprehensive suite of electrochemical techniques (chronoamperometry, cyclic voltammetry, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS)) and surface characterization methods (scanning electron microscopy, X-ray diffraction) were employed. Results revealed that wastewater containing typical ionic constituents (such as PO 4 3- , NH 4 + , and divalent cations) exhibited enhanced cathodic activity and the formation of a more stable, protective surface film on SS316 that mitigated chloride-induced corrosion. In contrast, SS316 in the NaCl solution showed significant susceptibility to passive layer breakdown and localized corrosion. Time-resolved EIS further confirmed improved interfacial stability and restricted charge transfer in WW over time, in stark contrast to the progressive passive layer degradation in NaCl. Surface analyses corroborated these findings, showing limited surface attack in WW compared to distinct localized corrosion features in NaCl. These findings indicate that competing ionic species in WW effectively mitigate chloride aggressiveness, enhance SS316 stability, and demonstrate improved electrode longevity and reliability for sustainable wastewater-based electrochemical phosphorus recovery applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Region-Based Stability Analysis of Resilient Distribution Systems with Hybrid Grid-Forming and Grid-Following Inverters

In this paper, distribution system stability considering mixed grid-forming (GFM) and grid-following (GFL) inverters is discussed. A holistic small-signal model of the distribution feeder accommodating both GFM and GFL inverters is derived. In contrast to conventional point-by-point stability analysis, a region-based stability assessment approach is proposed and implemented to evaluate small-signal system stability with both GFM and GFL controls. Furthermore, to enhance the computational efficiency, an Artificial Intelligence (AI) assisted Kernel Ridge Regression (KRR) approach is developed to obtain the stability region boundary. Therefore, with the derived stability region, the impact of critical parameters on system stability is intuitively shown, and more importantly, the relationship between the maximum penetration level and the corresponding feasible range of the selected control parameters can be quantified. The proposed approach has been validated using MATLAB/Simulink.

grid-following↗
NASA NTRS2015

Advancing the State-of-the-Practice for Liquid Rocket Engine Injector Design

Current shortcomings in both the overall injector design process and its underlying combustion stability assessment methodology are rooted in the use of empirically based or low fidelity representations of complex physical phenomena and geometry details that have first order effects on performance, thermal environments and combustion stability. The result is a design and analysis capability that is often inadequate to reliably arrive at a suitable injector design in an efficient manner. Specifically, combustion instability has been particularly difficult to predict and mitigate. Large hydrocarbon-fueled booster engines have been especially problematic in this regard. Where combustion instability has been a problem, costly and time-consuming redesign efforts have often been an unfortunate consequence. This paper presents an overview of a recently completed effort at NASA Marshall Space Flight Center to advance the state-of-the-practice for liquid rocket engine injector design. Multiple perturbations of a gas-centered swirl coaxial (GCSC) element that burned gaseous oxygen and RP-1 were designed, assessed for combustion stability, and tested. Three designs, one stable, one marginally unstable and one unstable, were used to demonstrate both an enhanced overall injector design process and an improved combustion stability assessment process. High-fidelity results from state-of-the-art computational fluid dynamics CFD simulations were used to substantially augment and improve the injector design methodology. The CFD results were used to inform and guide the overall injector design process. They were also used to upgrade selected empirical or low-dimensional quantities in the ROCket Combustor Interactive Design (ROCCID) stability assessment tool. Hot fire single element injector testing was used to verify both the overall injector designs and the stability assessments. Testing was conducted at the Air Force Research Laboratory and at Purdue University. Companion papers provide details of the overall injector design process, full- and sub-scale testing, ROCCID-based stability assessments and the CFD simulations.

Tucker, P. K.↗
DOE OSTI2020

Systems with greater perenniality and crop diversity enhance soil biological health

Abstract Soil health has received heightened interest because of its association with long‐term agricultural sustainability and ecological benefits, including soil carbon (C) accumulation. We examined the effects of crop diversity and perenniality on soil biological health and assessed impacts on mineralization and C stabilization processes across 10 systems including four no‐till annual row crops, two monoculture perennials, and four polyculture perennials. Crop diversity increased soil biological health in both annual and perennial systems. Rotated annuals with a cover crop increased permanganate oxidizable C (POXC) and soil organic matter relative to continuous corn ( Zea mays L.). Perennial polycultures also had 88% and 23% greater mineralizable C relative to the annual and monoculture perennial systems, respectively. All polyculture perennials had significantly greater POXC relative to switchgrass ( Panicum virgatum L.) and annual systems, with the exception of restored prairie. Of the systems assessed in this study, incorporating perennial polycultures into rotations is the most effective way to increase soil biological health and enhance C stabilization.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Hierarchical nickel valence gradient stabilizes high-nickel content layered cathode materials

High-nickel content cathode materials offer high energy density. However, the structural and surface instability may cause poor capacity retention and thermal stability of them. To circumvent this problem, nickel concentration-gradient materials have been developed to enhance high-nickel content cathode materials’ thermal and cycling stability. Even though promising, the fundamental mechanism of the nickel concentration gradient’s stabilization effect remains elusive because it is inseparable from nickel’s valence gradient effect. To isolate nickel’s valence gradient effect and understand its fundamental stabilization mechanism, we design and synthesize a LiNi 0.8 Mn 0.1 Co 0.1 O 2 material that is compositionally uniform and has a hierarchical valence gradient. The nickel valence gradient material shows superior cycling and thermal stability than the conventional one. The result suggests creating an oxidation state gradient that hides the more capacitive but less stable Ni 3+ away from the secondary particle surfaces is a viable principle towards the optimization of high-nickel content cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

An epoxy-reinforced ceramic sheet as a durable solid electrolyte for solid state Na-ion batteries

In a conventional Na-ion battery system using liquid electrolyte, there are critical safety issues due to the instability of the liquid electrolyte. Na 3 Zr 2 Si 2 PO 12 (NASICON) solid electrolyte is a material that is sufficient to replace a liquid electrolyte as it has high ionic conductivity and thermal and electrochemical stability. However, as there is a large interfacial resistance in the NASICON solid electrolyte powder, even when used in combination with a polymer electrolyte, the advantageous effects of ceramics are not easily exhibited. In this study, we propose a top-down method of combining a polymer with a ceramic in which an ion transport channel is previously formed. In this method, a NASICON solid electrolyte is partially sintered to form ion transport channels. Then the NASICON solid electrolyte pores are filled with an epoxy polymer to increase the strength of the epoxy-NASICON composite electrolyte. This method demonstrates the possibility of our composite electrolyte being used as a thin and strong film. As a result of our methods, the ionic conductivity and thermal and electrochemical stability of NASICON were maintained, while the physical strength was enhanced by approximately 2 times. In addition, a capacity of 120 mA h g -1 and stability of 20 cycles were confirmed in a half cell with a Na 3 V 2 (PO 4 ) 3 cathode and Na metal. This method proposes a new direction for research regarding composite electrolytes created using an oxide-based solid electrolyte.

25 ENERGY STORAGE↗
DOE OSTI2024

Ultrafast Annealing Improves SNR and Long-Term Stability of a Highly Multiplexed Line-by-Line FBG Array Inscribed by Femtosecond Laser in a Coreless Fiber for Extreme-Temperature Applications

This study reports the fabrication of a fourth-order line-by-line fiber Bragg grating (FBG) array using femtosecond laser inscription within a highly multimode coreless optical fiber, with a particular focus on achieving substantial multiplexing capabilities. An ultrafast annealing procedure is employed, resulting in an impressive enhancement of the FBG sensor’s fringe visibility by approximately 13 dB, signifying a notable improvement of approximately ~4 dB. This substantial enhancement contributes to the long-term stability and performance of the multiplexed FBG array in extreme-temperature conditions. The systematic fabrication approach employed for the multiplexed FBG array guarantees a high signal-to-noise ratio (SNR) for each individual FBG within the array. This FBG array is intended for extreme-temperature applications, addressing limitations associated with traditional FBGs based on doped optical fibers, including SNR degradation and temperature-induced fringe drift. Testing at temperatures up to 1120 °C demonstrates the FBG array’s stability without fluctuations in readings. Furthermore, it endures seven heat cycles, spanning from 500 °C to 1120 °C, over 60 h, exhibiting outstanding thermal stability. Furthermore, this highly multiplexed FBG array with an ultrafast annealing approach holds promise for extreme-temperature environments, such as steelmaking, where precise and reliable distributed temperature monitoring is imperative.

47 OTHER INSTRUMENTATION↗
NASA NTRS1990

Instabilities and subharmonic resonances of subsonic heated round jets, volume 2

When a jet is perturbed by a periodic excitation of suitable frequency, a large-scale coherent structure develops and grows in amplitude as it propagates downstream. The structure eventually rolls up into vortices at some downstream location. The wavy flow associated with the roll-up of a coherent structure is approximated by a parallel mean flow and a small, spatially periodic, axisymmetric wave whose phase velocity and mode shape are given by classical (primary) stability theory. The periodic wave acts as a parametric excitation in the differential equations governing the secondary instability of a subharmonic disturbance. The (resonant) conditions for which the periodic flow can strongly destabilize a subharmonic disturbance are derived. When the resonant conditions are met, the periodic wave plays a catalytic role to enhance the growth rate of the subharmonic. The stability characteristics of the subharmonic disturbance, as a function of jet Mach number, jet heating, mode number and the amplitude of the periodic wave, are studied via a secondary instability analysis using two independent but complementary methods: (1) method of multiple scales, and (2) normal mode analysis. It is found that the growth rates of the subharmonic waves with azimuthal numbers beta = 0 and beta = 1 are enhanced strongly, but comparably, when the amplitude of the periodic wave is increased. Furthermore, compressibility at subsonic Mach numbers has a moderate stabilizing influence on the subharmonic instability modes. Heating suppresses moderately the subharmonic growth rate of an axisymmetric mode, and it reduces more significantly the corresponding growth rate for the first spinning mode. Calculations also indicate that while the presence of a finite-amplitude periodic wave enhances the growth rates of subharmonic instability modes, it minimally distorts the mode shapes of the subharmonic waves.

Ng, Lian Lai↗
DOE OSTI2020

Solving Recent Challenges for Wrought Ni-Base Superalloys

This paper reviews the status of technology in design and manufacture of new wrought 21 polycrystalline Ni-base superalloys for critical engineering applications. There is a strong 22 motivation to develop new alloys that are capable of operating at higher temperatures to 23 realise improvements in thermal efficiency, which are necessary to achieve environmental 24 targets for reduced emissions of harmful green-house gases. From the aerospace sector, 25 the development of new powder metallurgy and ingot metallurgy alloys are discussed for 26 disk rotor and static applications. New compositions for powder metallurgy contain about 27 50-55% of gamma prime (γ') strengthening precipitates to ensure components operate 28 successfully at temperatures up to 788°C (1450°F). In contrast, new compositions for ingot 29 metallurgy aim to occupy a design space in temperature capability between Alloy 718 and 30 current powder alloys that are in-service, and show levels of γ' of about 30-44%. The focus 31 in developing these alloys was design for manufacturability. To complement the aerospace 32 developments, a review of work to understand the suitability of candidate alloys for multiple 33 applications in Advanced-Ultra Supercritical (AUSC) power plants has been undertaken by 34 Detrois, Jablonski and Hawk from the National Energy Technology Laboratory. In these 35 power plants, steam temperatures are required to reach 700-760°C. The common thread is 36 to develop alloys that demonstrate a combination of high temperature properties, which are 37 reliant on both the alloy composition and microstructure and can be produced readily at the 38 right price. For the AUSC applications, the emphasis is on high temperature strength, long 39 term creep life, phase stability, oxidation resistance and robust welding for fabrications. 40 Whereas for powder disk rotors in aircraft engines, the priority is enhanced resistance to 41 time dependent crack growth, phase stability and resistance to environmental damage, while 42 extending the current strength levels, which are shown by existing alloys, to higher 43 temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis and characterization of magnetic ionic liquids containing multiple paramagnetic lanthanide and transition metal centers and functionalized diglycolamide ligands

Magnetic ionic liquids (MILs) containing paramagnetic centers have gained widespread recognition as sustainable solvents due to their ability to respond to an external magnetic field. The physico-chemical properties of MILs are dependent on the choice of anion/cation ligands and metal centers; the search for highly tunable ligands and precursors that can confer favorable characteristics, such as low viscosity, is ongoing. Diglycolamides employed as cationic ligands have been previously shown to form hydrophobic MILs that can simultaneously incorporate multiple lanthanide metal centers in both the anion/cation. Despite their enhanced magnetic susceptibility, the effect of diglycolamide chemical structure modifications on the physico-chemical properties of MILs has not been thoroughly studied. Additionally, the possibility of forming diglycolamide-based MILs with popularly employed transition metals has not been investigated and combinations that can simultaneously embed two different types of metal centers in both the anion/cation have not been explored. In this study, thirty (30) MILs comprised of lanthanide and transition metals were synthesized by examining their chelation to both straight-chained and branched diglycolamides. Here, transition metal-based MILs were found to possess high thermal stabilities up to 235 °C compared to 192 °C for those comprised of lanthanides. While MILs comprised of rare-earth metal centers exhibited the lowest viscosities, substituting lanthanides with transition metals in just the anion or cation resulted in enhanced thermal stability and reduced viscosity. The effective magnetic moment for these MILs varied between 4.71 and 21.08 µ B and was much higher compared to all previous classes of MILs prepared using the same metals. Results from this study explore all possible modifications that can be made to these MILs in an effort to demonstrate their structural tunability, which is often highly desirable in various applications, including organic synthesis and chemical separations.

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

Stabilization of Ultrasmall Platinum Nanoparticles by Nitrogen-Doped Carbon: Implications for Catalysis and Electrocatalysis

Heterogeneous materials comprising platinum nanoparticles on carbon supports have numerous applications including fuel cell electrodes and heterogeneous catalysts. The effective application of these materials for fuel cells and catalysis will be greatly advanced by the ability to control the oxidation and sintering of the nanoparticles by modifications of the carbon support. One attempt of such control has been doping carbon supports with nitrogen. Here, in this work, a cutting-edge, high-sensitivity, in situ XRD instrument, which allows observation of ultrasmall Pt nanoparticles, has been combined with in situ XPS to provide unprecedented clarity in the characterization of supported Pt nanoparticles in oxidizing and high-temperature environments. On a nitrogen-doped carbon support derived from poly-phenylporphyrin, Pt nanoparticles show increased stability to oxidation and thermal sintering. The enhanced Pt–support interaction arising from the N dopant versus the N-free carbon is manifested by (1) decreased initial Pt particle sizes, (2) small particle size at higher surface densities, (3) increased resistance of Pt nanoparticles to oxidation, (4) increased electron binding energy of Pt0, and (5) increased resistance of Pt nanoparticles to sintering. It is expected that the higher stability of Pt on NC will be manifested in higher activity in fuel cells and high-temperature catalytic reactions.

catalytic reactions↗