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Results for “selective doping”

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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Triazine containing N-rich microporous organic polymers for CO{sub 2} capture and unprecedented CO{sub 2}/N{sub 2} selectivity

Targeted synthesis of microporous adsorbents for CO{sub 2} capture and storage is very challenging in the context of remediation from green house gases. Herein we report two novel N-rich microporous networks SB-TRZ-CRZ and SB-TRZ-TPA by extensive incorporation of triazine containing tripodal moiety in the porous polymer framework. These materials showed excellent CO{sub 2} storage capacities: SB-TRZ-CRZ displayed the CO{sub 2} uptake capacity of 25.5 wt% upto 1 bar at 273 K and SB-TRZ-TPA gave that of 16 wt% under identical conditions. The substantial dipole quadruple interaction between network (polar triazine) and CO{sub 2} boosts the selectivity for CO{sub 2}/N{sub 2}. SB-TRZ-CRZ has this CO{sub 2}/N{sub 2} selectivity ratio of 377, whereas for SB-TRZ-TPA it was 97. Compared to other porous polymers, these materials are very cost effective, scalable and very promising material for clean energy application and environmental issues. - Graphical abstract: We report two novel N-rich microporous polymeric materials by doping of triazine containing tripodal dopant in the organic framework. These materials showed excellent CO{sub 2} storage capacities as high as 25.5 wt% under 1 bar pressure with exceptional CO{sub 2}/N{sub 2} selectivity of 377. - Highlights: • Triazine containing trimodal moiety incorporated in polycarbazolic and poly triphenylamine networks. • N-rich crosslinked polymers with high BET surface area and 1.5–1.7 nm size large micropores. • CO{sub 2} uptake capacity of 25.5 wt% upto 1 bar at 273 K. • These crosslinked porous polymers showed exceptional CO{sub 2}/N{sub 2} selectivity.

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

Deep eutectic solvent approach towards nickel/nickel nitride nanocomposites

Nickel nitride is an attractive material for a broad range of applications including catalysis. However preparations and especially those targeting nanoscale particles remain a major challenge. Herein, we report a wet-chemical approach to produce nickel/nickel nitride nanocomposites using deep eutectic solvents. A choline chloride/urea deep eutectic solvent was used as a reaction medium to form gels containing nickel acetate tetrahydrate. Heat treatment of the gel in inert atmosphere forms nanoparticles embedded within a nitrogen-doped carbon matrix. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to understand the decomposition profile of the precursors and to select pyrolysis temperatures located in regions of thermal stability. X-ray diffraction (XRD) confirmed the presence of metallic nickel, whereas X-ray photoelectron spectroscopy (XPS) suggested the existence of a nickel nitride surface layer. According to transmission electron microscopy (TEM) analysis these mixed phase, possibly core-shell type nanoparticles, have very defined facets. Furthermore, these materials represent a unique opportunity to tune catalytic properties of nickel-based catalysts through control of their composition, surface structure, and morphology; in addition to employing potential benefits of a nitrogen-doped carbon support.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Free-standing membrane incorporating single-atom catalysts for ultrafast electroreduction of low-concentration nitrate

The release of wastewaters containing relatively low levels of nitrate (NO 3 ⁻) results in sufficient contamination to induce harmful algal blooms and to elevate drinking water NO 3 ⁻ concentrations to potentially hazardous levels. In particular, the facile triggering of algal blooms by ultra-low concentrations of NO 3 ⁻ necessitates the development of efficient methods for NO 3 ⁻ destruction. However, promising electrochemical methods suffer from weak mass transport under low reactant concentrations, resulting in long treatment times (on the order of hours) for complete NO 3 ⁻ destruction. In this study, we present flow-through electrofiltration via an electrified membrane incorporating nonprecious metal single-atom catalysts for NO 3 ⁻ reduction activity enhancement and selectivity modification, achieving near-complete removal of ultra-low concentration NO 3 ⁻ (10 mg-N L -1 ) with a residence time of only a few seconds (10 s). By anchoring Cu single atoms supported on N-doped carbon in a carbon nanotube interwoven framework, we fabricate a free-standing carbonaceous membrane featuring high conductivity, permeability, and flexibility. The membrane achieves over 97% NO 3 ⁻ removal with high N 2 selectivity of 86% in a single-pass electrofiltration, which is a significant improvement over flow-by operation (30% NO 3 ⁻ removal with 7% N 2 selectivity). This high NO 3 ⁻ reduction performance is attributed to the greater adsorption and transport of nitric oxide under high molecular collision frequency coupled with a balanced supply of atomic hydrogen through H 2 dissociation during electrofiltration. Overall, our findings provide a paradigm of applying a flow-through electrified membrane incorporating single-atom catalysts to improve the rate and selectivity of NO 3 ⁻ reduction for efficient water purification.

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

Zinc oxide doped graphene oxide films for gas sensing applications

Graphene Oxide (GO) is analogous to graphene, but presence of many functional groups makes its physical and chemical properties essentially different from those of graphene. GO is found to be a promising material for low cost fabrication of highly versatile and environment friendly gas sensors. Selectivity, reversibility and sensitivity of GO based gas sensor have been improved by hybridization with Zinc Oxide nanoparticles. The device is fabricated by spin coating of deionized water dispersed GO flakes (synthesized using traditional hummer’s method) doped with Zinc Oxide on standard glass substrate. Since GO is an insulator and functional groups on GO nanosheets play vital role in adsorbing gas molecules, it is being used as an adsorber. Additionally, on being exposed to certain gases the electric and optical characteristics of GO material exhibit an alteration in behavior. For the conductivity, we use Zinc Oxide, as it displays a high sensitivity towards conduction. The effects of the compositions, structural defects and morphologies of graphene based sensing layers and the configurations of sensing devices on the performances of gas sensors were investigated by Raman Spectroscopy, X-ray diffraction(XRD) and Keithley Sourcemeter.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Macrovoid-free high performance polybenzimidazole hollow fiber membranes for elevated temperature H 2 /CO 2 separations

Thermally robust membranes are required for H 2 production and carbon capture from hydrocarbon fuel derived synthesis (syn) gas. Polybenzimidaole (PBI) materials have exceptional thermal, chemical and mechanical characteristics and high H 2 perm-selectivity for efficient syngas separations at process relevant conditions. The large gas volumes processed mandate the use of a high-throughput, small footprint hollow fiber membrane (HFM) platform. Here in this work, an industrially attractive spinning protocol is developed to fabricate PBI HFMs with unprecedented H 2 /CO 2 separation performance. A unique dope composition incorporating an acetonitrile diluent is discovered enabling asymmetric macro-void free PBI HFM fabrication using a water coagulant. The influences of dope viscosity, coagulant chemistry, and air gap on HFM morphology are evaluated. Elevated temperature (up to 350 °C) H 2 permeances of 400 GPU with H 2 /CO 2 selectivities > 20 are achieved. This unprecedented separation performance is a ground breaking achievement at temperatures traditionally considered out-of-reach for polymeric membranes.

08 HYDROGEN↗
DOE OSTI2016

Synthesis of graphene and graphene nanostructures by ion implantation and pulsed laser annealing

In this paper, we report a systematic study that shows how the numerous processing parameters associated with ion implantation (II) and pulsed laser annealing (PLA) can be manipulated to control the quantity and quality of graphene (G), few-layer graphene (FLG), and other carbon nanostructures selectively synthesized in crystalline SiC (c-SiC). Controlled implantations of Si{sup −} plus C{sup −} and Au{sup +} ions in c-SiC showed that both the thickness of the amorphous layer formed by ion damage and the doping effect of the implanted Au enhance the formation of G and FLG during PLA. The relative contributions of the amorphous and doping effects were studied separately, and thermal simulation calculations were used to estimate surface temperatures and to help understand the phase changes occurring during PLA. In addition to the amorphous layer thickness and catalytic doping effects, other enhancement effects were found to depend on other ion species, the annealing environment, PLA fluence and number of pulses, and even laser frequency. Optimum II and PLA conditions are identified and possible mechanisms for selective synthesis of G, FLG, and carbon nanostructures are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Iron Single‐Atom Catalyzed N‐Alkylation of Amines with Alcohols via Solvent‐Free Borrowing Hydrogen Strategy

Abstract Industrial hydrogenation is a pivotal process in chemical synthesis. However, it has significant drawbacks, including high cost, safety risks associated with the use of molecular hydrogen gas, and substantial energy demands due to the need for elevated temperatures and pressures to achieve satisfactory yields. The borrowing hydrogen synthesis, which enables the transfer of hydrogen between molecules, offers a promising approach for green, one‐pot synthesis of industrially important chemicals and intermediates. Despite its potential, the broad application remains limited due to the reliance on toxic solvents, expensive noble metal catalysts, and the still restricted efficiency and substrate scope. In this study, the first solvent‐free strategy for theN‐alkylation of amines with alcohols is presented, employing an N‐doped graphene‐supported Fe single‐atom catalyst (Fe SA @N‐G; 1.06 wt.%). This approach achieves superior conversion and selectivity (up to 99%) along with record values for turnover number (TON, 1032.7) and turnover frequency (TOF, 413.1 h -1 ) for the coupling reaction of aniline with benzyl alcohol, surpassing all previously reported catalysts. DFT calculations, combined with experimental data, elucidated the reaction mechanism and identified the Fe 1 (III)‐N 4 active site participating in Fe‐H hydride transfer and containing two pyrrolic and two pyridinic nitrogens bound to the Fe center. The developed technology is further supported by the catalyst's excellent scalability, reusability, and performance under continuous‐flow conditions. Additionally, the exceptional efficiency of the single‐atom catalyst is demonstrated across more than 50 substrates, including reactions involving both aliphatic and aromatic amines with aliphatic and aromatic alcohols. The industrial applicability of this technology is validated through the synthesis of pharmaceutically relevant compounds, including stimulant drugs, antihistamines, and pharmaceutical intermediates.

Chemistry↗
DOE OSTI2019

Thermally Stable Perovskite Solar Cells by Systematic Molecular Design of the Hole-Transport Layer

With the burgeoning performance of metal halide perovskite solar cells (PSC), one of the biggest challenges to date is addressing device stability. Within the PSC device stack, charge-selective contact selection has been shown to considerably impact PSC stability. Recently, a triarylamine-based hole-transport layer (HTL) doped with its oxidized organic salt analogue (EH44/EH44-ox) has been shown to bypass the need for hygroscopic lithium salt dopants, enabling high PSC stability in ambient conditions. Despite these promising results, the improved stability came with a power conversion efficiency (PCE) penalty and poor performance above 30 degrees C. Broadening the applicability and understanding of this under-utilized dopant system, we report design criteria for stable, synthetically simple triarylamine-based organic hole transport materials (HTM) and their corresponding oxidized salts as HTL dopants for improved PSC efficiency and stability at elevated temperature. The triarylamine-based dopants must contain at least two para-electron donating groups for radical cation stabilization to prevent impurity formation (e.g., dopant reduction) which significantly reduces PSC fill factors (FF) and PCE. To further improve PSC FF and PCE, these dopants can be interchanged with respect to the HTL matrix. The stability of unencapsulated devices prepared with these three new HTLs, under constant load and illumination, considerably outperform both EH44/EH44-ox and Li+-doped spiro-OMeTAD controls at 50 degrees C. The ability to mix and match a stable dopant with a non-identical small-molecule-based HTL matrix for improved charge-transport properties broadens design scope for highly stable and cost-effective PSC without sacrificing performance.

14 SOLAR ENERGY↗
DOE OSTI2023

Cascade electrocatalysis via AgCu single-atom alloy and Ag nanoparticles in CO 2 electroreduction toward multicarbon products

Electrocatalytic CO 2 reduction into value-added multicarbon products offers a means to close the anthropogenic carbon cycle using renewable electricity. However, the unsatisfactory catalytic selectivity for multicarbon products severely hinders the practical application of this technology. In this paper, we report a cascade AgCu single-atom and nanoparticle electrocatalyst, in which Ag nanoparticles produce CO and AgCu single-atom alloys promote C-C coupling kinetics. As a result, a Faradaic efficiency (FE) of 94 ± 4% toward multicarbon products is achieved with the as-prepared AgCu single-atom and nanoparticle catalyst under ~720 mA cm -2 working current density at -0.65 V in a flow cell with alkaline electrolyte. Density functional theory calculations further demonstrate that the high multicarbon product selectivity results from cooperation between AgCu single-atom alloys and Ag nanoparticles, wherein the Ag single-atom doping of Cu nanoparticles increases the adsorption energy of *CO on Cu sites due to the asymmetric bonding of the Cu atom to the adjacent Ag atom with a compressive strain.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

Evaluation of the Effect of Microalloying on Cleavage of Monocrystalline NiAl Using a Miniaturized Disk-Bend Test

It was originally proposed to investigate the effect of microalloying on the ductility of monocrystalline NiAl. The idea was to deposit selected elements on oriented crystals of NiAl using magnetron sputtering, followed by annealing at high temperatures to produce the doped specimens. The project was terminated before that stage of the research was reached, but useful results needed for that study were obtained during the lifetime of the program. Those results are described in this report.

Ardell, Alan J.↗
NASA NTRS1997

Evaluation of the Effect of Microalloying on Cleavage of Monocrystalline NiAl using a Miniaturized Disk-Bend Test

It was originally proposed to investigate the effect of microalloying on the ductility of monocrystalline NiAl. The idea was to deposit selected elements on oriented crystals of NiAl using magnetron sputtering, followed by annealing at high temperatures to produce the doped specimens. The project was terminated before that stage of the research was reached, but useful results needed for that study were obtained during the lifetime of the program. Those results are described in this resort.

Ardell, Alan J.↗
DOE OSTI2017

ON-GOING STATUS OF KJRR FUEL (U-7MO) QUALIFICATION

In order to cope with global shortage of Mo-99 supplies and with growing demand of neutron transmutation doping, KJRR construction plan has been launched since April 2012 to provide self-sufficiency of domestic RI demand, and to extend Si doping capacity for power device market growth. Through comprehensive surveillance of the fuels in-reactor behavior, KAERI has selected the fuel meat of U-7%Mo dispersion in an aluminum matrix with 5wt%Si for the KJRR fuel. As part of the efforts for fuel licensing and qualification of the KJRR fuel, an LTA irradiation test at the ATR started from November 2015 was successfully completed by reaching at 219 EFPD in the end of February 2017. Together with the results of HAMP-1 already completed irradiation and PIE, the successful irradiation of the LTA also demonstrates the fuel integrity under more rigorous conditions than the KJRR operation conditions. This paper updates the current status of the KJRR U7Mo (8 g-U/cm3) LTA irradiation and PIE plan up to date as of February 2017.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Method of chemical doping that uses CMOS-compatible processes

A method of Atomic Precision Advanced Manufacturing (APAM) is provided, in which a substrate is doped from a dopant precursor gas. The method involves covering a surface of the substrate with a hard mask, selectively removing material from the hard mask such that selected areas of the substrate surface are laid bare, exposing the laid-bare areas to the dopant precursor gas, and heating the substrate so as to incorporate dopant from the dopant precursor gas into the substrate surface.

Misra, Shashank↗
DOE OSTI2024

Formation of functionally graded steel by laser powder bed fusion via in-situ carbon doping

Additive Manufacturing (AM) enables functional integration by combining multiple components into a single part to shorten assembly time, reduce weight, and improve performance. Laser Powder Bed Fusion (LPBF) is an important AM method due to excellent spatial resolution, surface finish, and material properties without the need for extensive post-processing. Functional integration could be enhanced by spatial tuning of properties, but LPBF cannot readily vary material composition. Here, this paper addresses a method to add spatial composition control by printing small quantities of dopants via liquid carrier prior to laser fusion. The impact of carbon black suspension added to select regions of a Stainless Steel 316 L powder bed on melt pool dimension, hardness, and porosity is reported. The distribution of the carbon between the doped and plain layers and the resulting spatial variation in hardness is measured. Optical microscopy and composition analysis show that the carbon dispersed uniformly within the layer of deposition and diffused as little as 50 μm in the build direction. Keyhole conditions dramatically increase the inter-layer transport of the dopant. The added carbon increased hardness by >50 %. Porosity increased in doped regions but remained below 1.5 % for the best processing parameters. These results demonstrate that the composition of LPBF parts could be controlled in 3-dimensions using a dopant that is soluble in the melt pool. Additional work will be required to evaluate different dopant materials and optimize processing conditions for full density, but microalloying with soluble dopants appears to be a plausible solution to enhance functional integration with LPBF.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Atomically Dispersed Transition Metals on Carbon Nanotubes with Ultrahigh Loading for Selective Electrochemical Carbon Dioxide Reduction

Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs suffer from a very low metal loading of 1–2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen-doped carbon nanotubes (MSA-N-CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA-N-CNTs, using a new multistep pyrolysis process. Among these materials, NiSA-N-CNTs show an excellent selectivity and activity for the electrochemical reduction of CO 2 to CO, achieving a turnover frequency (TOF) of 11.7 s -1 at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

GaN vertical-channel junction field-effect transistors with regrown p-GaN by metal organic chemical vapor deposition (MOCVD)

Fabricating a vertical-channel junction field-effect transistor includes forming an unintentionally doped GaN layer on a bulk GaN layer by metalorganic chemical vapor deposition, forming a Cr/SiO 2 hard mask on the unintentionally doped GaN layer, patterning a fin by electron beam lithography, defining the Cr and SiO 2 hard masks by reactive ion etching, improving a regrowth surface with inductively coupled plasma etching, removing hard mask residuals, regrowing a p-GaN layer, selectively etching the p-GaN layer, forming gate electrodes by electron beam evaporation, and forming source and drain electrodes by electron beam evaporation. The resulting vertical-channel junction field-effect transistor includes a doped GaN layer, an unintentionally doped GaN layer on the doped GaN layer, and a p-GaN regrowth layer on the unintentionally doped GaN layer. Portions of the p-GaN regrowth layer are separated by a vertical channel of the unintentionally doped GaN layer.

Zhao, Yuji↗