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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Synergetic Effect of Ultrasmall Metal Clusters and Zeolites Promoting Hydrogen Generation

Abstract Taking advantage of the synergetic effect of confined ultrasmall metal clusters and zeolite frameworks is an efficient strategy for improving the catalytic performance of metal nanocatalysts. Herein, it is demonstrated that the synergetic effect of ultrasmall ruthenium (Ru) clusters and intrinsic Brønsted acidity of zeolite frameworks can significantly promote the hydrogen generation of ammonia borane (AB) hydrolysis. Ultrasmall Ru clusters are embedded onto the silicoaluminophosphate SAPO‐34 ( CHA ) and various aluminosilicate zeolites ( MFI, * BEA , and FAU ) with tunable acidities by a facile incipient wetness impregnation method. Evidenced by high‐resolution scanning transmission electron microscopy, the sub‐nanometric Ru clusters are uniformly distributed throughout the zeolite crystals. The X‐ray absorption spectroscopy measurements reveal the existence of Ru‐H species between Ru clusters and adjacent Brønsted acid sites of zeolites, which could synergistically activate AB and water molecules, significantly enhancing the hydrogen evolution rate of AB hydrolysis. Notably, the Ru/SAPO‐34‐0.8Si (Si/Al = 0.8) and Ru/FAU (Si/Al = 30) catalysts with strong acidities afford high turnover frequency values up to 490 and 627 min −1 , respectively. These values are more than a 13‐fold enhancement than that of the commercial Ru/C catalyst, and among the top level over other heterogeneous catalysts tested under similar conditions.

08 HYDROGEN↗
DOE OSTI2015

Magnetic Field Enhancement of Organic Light‐Emitting Diodes Based on Electron Donor–Acceptor Exciplex

Reverse intersystem crossing (RISC) from triplet to singlet states has been recently introduced to photophysics of organic chromophores. One type of RISC occurs in donor (D)–acceptor (A) composites that form an exciplex manifold in which the energy difference, Δ E ST between the lowest singlet (S 1 ) and triplet (T 1 ) levels of the exciplex is small (<100 meV) thus allowing RISC at room temperature. This adds a delayed component to the photoluminescence emission that is widely known as thermally activated delayed fluorescence. Here, it is found that the electroluminescence in organic light‐emitting diodes (OLED) based on electron D–A exciplex is significantly enhanced (up to ≈40%) by applying magnetic field, due to the existence of an additional spin‐mixing channel between singlet and triplet states in the exciplex. The large magneto‐electroluminescence (MEL) in N , N , N ′, N ′‐tetrakis(4‐methoxyphenyl)benzidine: tris‐[3‐(3‐pyridyl)mesityl]borane [D–A] based OLEDs is demonstrated. These results are supported by magneto‐photoluminescence (MPL) measurements, and density functional theory calculations. Importantly, it is found that both MEL and MPL are thermally activated indicating the dominant role of the RISC process. The MEL( B ) response using the Δ g mechanism is analyzed, where the electron and hole g ‐values are different from each other because they reside in different molecules.

Basel, Tek↗
DOE OSTI2015

Air‐Stable (CAAC)CuCl and (CAAC)CuBH 4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH 3 NH 3

Abstract The first stable copper borohydride complex [(CAAC)CuBH 4 ] [CAAC=cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH 4 or BH 3 NH 3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air‐stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H 2 /BH 3 NH 3 with a turnover frequency of 8400 mol mol cat −1 h −1 at 25 °C. In a fifteen‐cycle experiment, the catalyst was reused without any loss of efficiency.

Hu, Xingbang↗
DOE OSTI2019

Readily Available Primary Aminoboranes as Powerful Reagents for Aldimine Synthesis

Abstract Primary aminoboranes (RNHBR 2 ), which are readily available by spontaneous dehydrocoupling of amines and boranes cleanly react at room temperature with aldehydes to give aldimines. The overall transformation from amines to aldimines can be conveniently performed by a sequential one‐pot reaction. This synthetic strategy is especially useful for electron poor and bulky amines which are reluctant to react with aldehydes under dehydration conditions. Using a Glorius robustness screen, we show that this methodology is chemoselective, and functional group tolerant. Computational and experimental data support the irreversible formation of the aldimine product in marked contrast with traditional methods.

Junor, Glen P.↗
DOE OSTI2020

Dihydrogen Adduct (Co–H 2 ) Complexes Displaying H‐Atom and Hydride Transfer

Abstract The prototypical reactivity profiles of transition metal dihydrogen complexes (M‐H 2 ) are well‐characterized with respect to oxidative addition (to afford dihydrides, M(H) 2 ) and as acids, heterolytically delivering H + to a base and H − to the metal. In the course of this study we explored plausible alternative pathways for H 2 activation, namely direct activation through H‐atom or hydride transfer from the σ‐H 2 adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S = and an anionic S =0 Co‐H 2 adduct, both supported by a trisphosphine borane ligand (P 3 B ). The thermally stable metalloradical, (P 3 B )Co(H 2 ), serves as a competent precursor for hydrogen atom transfer to t Bu 3 ArO ⋅ . What is more, its anionic derivative, the dihydrogen complex [(P 3 B )Co(H 2 )] 1− , is a competent precursor for hydride transfer to BEt 3 , establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M‐H 2 complexes known.

Deegan, Meaghan M.↗
DOE OSTI2015

Air‐Stable (CAAC)CuCl and (CAAC)CuBH 4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH 3 NH 3

Abstract The first stable copper borohydride complex [(CAAC)CuBH 4 ] [CAAC=cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH 4 or BH 3 NH 3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air‐stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H 2 /BH 3 NH 3 with a turnover frequency of 8400 mol mol cat −1 h −1 at 25 °C. In a fifteen‐cycle experiment, the catalyst was reused without any loss of efficiency.

Hu, Xingbang↗
DOE OSTI2019

Readily Available Primary Aminoboranes as Powerful Reagents for Aldimine Synthesis

Primary aminoboranes (RNHBR 2 ), which are readily available by spontaneous dehydrocoupling of amines and boranes cleanly react at room temperature with aldehydes to give aldimines. The overall transformation from amines to aldimines can be conveniently performed by a sequential one-pot reaction. This synthetic strategy is especially useful for electron poor and bulky amines which are reluctant to react with aldehydes under dehydration conditions. Using a Glorius robustness screen, we show that this methodology is chemoselective, and functional group tolerant. Finally, computational and experimental data support the irreversible formation of the aldimine product in marked contrast with traditional methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Impact of Advances in Anion Exchange Membranes and Ionomers on Alkaline Fuel Cells

Abstract The operation of low‐temperature electrochemical energy conversion systems (fuel cells, electrolyzers) at high pH values is of perennial interest due to the possibility of moving away from expensive platinum group metal catalysts and reducing cost. Historically, the anion exchange membranes (AEMs) and ionomers have been hampered by performance (ionic conductivity, mechanical strength) and chemical stability issues. In this context, select developments over the past decade in alternate AEM chemistries, water management methods, and production of membrane electrode assemblies (MEAs) that have enabled a significant leap in performance of alkaline fuel cells are examined. These developments are linked to performance improvements in alkaline H 2 /O 2 fuel cells and also consider developments in alkaline fuel cells using nitrogen‐containing fuels (ammonia, hydrazine), carbon‐containing fuels (alcohols, glycols), and boron‐containing fuels (sodium borohydride, ammonia borane). Finally, current challenges and bottlenecks are identified, and potential solutions are proposed.

Chemistry↗
DOE OSTI2025

Redox‐Active Frustrated Lewis Pair‐Mediated B—H Bond Activation: From Proton Transfer to THF Ring Opening

The CAAC-stabilized dithiolene (L 0 ) zwitterion (1), an unusual redox-active intramolecular frustrated Lewis pair (FLP), activates the B─H bond of boranes via hydride-coupled reverse electron transfer processes. The reactions of 1 with catecholborane in THF give a zwitterionic bis(dithiolene)-based spiroborate ( 2 ), in which one sulphur atom (at the C2 carbon) bonds to the (CH 2 ) 4 OB(O) 2 C 6 H 4 chain due to the catecholborane (CatBH)/S thiourea Lewis pair-mediated THF ring opening. In addition to 2 , [CAAC(H)] + [(Cat) 2 B] − , ( 3 ), CAAC(H) 2 , ( 4 ), and [CAAC(H) 3 ] + [(Cat) 2 B] − , ( 5 ), are also isolated from these reactions. In addition to synthetic, structural, and spectroscopic data, a plausible reaction mechanism is proposed. This finding provides compelling experimental evidence of FLP-mediated B─H activation via net proton transfer.

carbenes↗
DOE OSTI2014

Interface Modifications by Anion Acceptors for High Energy Lithium Ion Batteries

Li-rich, Mn-rich (LMR) layered composite, for example, Li[Li0.2Ni0.2Mn0.6]O2, has attracted extensive interests because of its highest energy density among all cathode candidates for lithium ion batteries (LIB). However, capacity degradation and voltage fading are the major challenges associated with this series of layered composite, which plagues its practical application. Herein, we demonstrate that anion receptor, tris(pentafluorophenyl)borane ((C6F5)3B, TPFPB), substantially enhances the cycling stability and alleviates the voltage degradation of LMR. In the presence of 0.2 M TPFPB, Li[Li0.2Ni0.2Mn0.6]O2 shows capacity retention of 81% after 300 cycles. It is proposed that TPFPB effectively confines the highly active oxygen species released from structural lattice through its strong coordination ability and high oxygen solubility. The electrolyte decomposition caused by the oxygen species attack is therefore largely mitigated, forming reduced amount of byproducts on the cathode surface. Additionally, other salts such as insulating LiF derived from electrolyte decomposition are also soluble in the presence of TPFPB. The collective effects of TPFPB mitigate the accumulation of parasitic reaction products and stabilize the interfacial resistances between cathode and electrolyte during extended cycling, thus significantly improving the cycling performance of Li[Li0.2Ni0.2Mn0.6]O2.

anion receptor↗
DOE OSTI2014

Slurry-Based Chemical Hydrogen Storage Systems for Automotive Fuel Cell Applications

In this paper, the system designs for hydrogen storage using chemical hydrogen materials in an 80 kWe fuel cell, light-duty vehicle are described. Ammonia borane and alane are used for these designs to represent the general classes of exothermic and endothermic materials. The designs are then compared to the USDRIVE/DOE developed set of system level targets for on-board storage. While most of the DOE targets are predicted to be achieved based on the modeling, the system gravimetric and volumetric densities were more challenging and became the focus of this work. The resulting system evaluation determined that the slurry is majority of the system mass. Only modest reductions in the system mass can be expected with improvements in the balance of plant components. Most of the gravimetric improvements will require developing materials with higher inherent storage capacity or by increasing the solids loading of the chemical hydrogen storage material in the slurry.

chemical hydrogen storage↗
DOE OSTI2025

Probing the elastic modulus and hardness of superionic boron cluster solid electrolytes

Polyhedral borane salts are highly tunable compounds with the potential to be used as solid electrolytes due to their high Li and Na superionic conductivity and relatively wide electrochemical stability window. In considering their application to all solid-state batteries, their mechanical properties play a critical role in their operation due to stresses the solid electrolyte is subjected to during battery operation. Density functional theory (DFT) calculations have provided an initial assessment of bulk and elastic moduli for some selected boron cluster solid electrolytes, but direct measurements are still scarce. Here, in this paper, we report the elastic moduli and hardnesses of LiCB 11 H 12 , LiCB 9 H 10 , NaCB 11 H 12 , and NaCB 9 H 10 for the first time using nanoindentation continuous stiffness method (CSM) measurements under inert atmosphere. Experimental modulus values ranging 8.8–12.3 GPa and hardness values ranging 0.15–0.38 GPa are lower than that of other inorganic solid-state electrolytes such as oxide- and sulfide-based solid electrolytes. DFT calculations on the expected moduli of these compounds are also presented and discussed. Analysis of the indentation plasticity index reveals that these compounds have higher plasticity index compared to other common oxide and sulfide solid electrolytes. According to the calculated Pugh's ratio, all compounds in this study except LiCB 11 H 12 are considered ductile.

25 ENERGY STORAGE↗
DOE OSTI2014

A biotemplated nickel nanostructure: Synthesis, characterization and antibacterial activity

Highlights: • Nickel nanostructure-encapsulated bacteria were prepared using electroless deposition. • Bacterium surface was activated by red-ox reaction of its surface amino acids. • Interfacial changes at cell surfaces were investigated using fluorescence spectroscopy. • TEM and AFM depicted morphological changes. • Antibacterial activity of nanostructure was examined against different bacteria strains. - Abstract: Nickel nanostructure-encapsulated bacteria were prepared using the electroless deposition procedure and activation of bacterium cell surface by red-ox reaction of surface amino acids. The electroless deposition step occurred in the presence of Ni(II) and dimethyl amine boran (DMAB). Interfacial changes at bacteria cell surfaces during the coating process were investigated using fluorescence spectroscopy. Fluorescence of tryptophan residues was completely quenched after the deposition of nickel onto bacteria surfaces. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) depicted morphological changes on the surface of the bacterium. It was found that the Ni coated nanostructure was mechanically stable after ultrasonication for 20 min. Significant increase in surface roughness of bacteria was also observed after deposition of Ni clusters. The amount of coated Ni on the bacteria surface was calculated as 36% w/w. The antibacterial activity of fabricated nanostructure in culture media was examined against three different bacteria strains; Escherichia coli, Bacillus subtilis and Xantomonas campestris. The minimum inhibitory concentrations (MIC) were determined as 500 mg/L, 350 mg/L and 200 mg/L against bacteria, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A facile route to high-purity BN nanoplates with ultraviolet cathodoluminescence emissions at room temperature

Highlights: • We present a novel and simple approach to great-scale fabrication of BN nanoplates. • The as-synthesized products are extensively characterized. • The formation mechanism of BN nanoplates are elucidated based on experimental observations. • A growth model was proposed according to our experimental observations and analysis. • BN nanoplates’ CL performance envisions its applications such as UV emitters. - Abstract: We present a novel and notably simple approach to fabricate BN nanoplates in large scale employing ammonia borane as a single-source precursor. The structure and chemical composition of the as-synthesized products are extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). XRD analysis indicates that the products are hexagonal BN crystal. SEM images confirm that the BN nanoplates have an average diameter of about 200 nm and thickness of tens of nanometers. HRTEM results illustrate the BN nanoplates to be single-crystals. EELS result suggests the nanoplates are composed of boron and nitride elements. The formation mechanism of the BN nanoplates has been elucidated based on our experimental observations, and a growth model has been proposed accordingly. Cathodoluminescence spectroscopic analysis is performed and strong ultraviolet (UV) emissions are detected. Our method provides a simple route towards the large-scale fabrication of high-quality BN nanoplates, for which various promising applications such as compact UV emitters can be envisioned.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Boron nitride hollow nanospheres: Synthesis, formation mechanism and dielectric property

Highlights: • BN hollow nanospheres are fabricated in large scale via a new CVD method. • Morphology and structure are elucidated by complementary analytical techniques. • Formation mechanism is proposed based on experimental observations. • Dielectric properties are investigated in the X-band microwave frequencies. • BN hollow nanospheres show lower dielectric loss than regular BN powders. - Abstract: Boron nitride (BN) hollow nanospheres have been successfully fabricated by pyrolyzing vapors decomposed from ammonia borane (NH{sub 3}BH{sub 3}) at 1300 °C. The final products have been extensively characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The BN hollow nanospheres were ranging from 100 to 300 nm in diameter and around 30–100 nm in thickness. The internal structure of the products was found dependent on the reaction temperatures. A possible formation mechanism of the BN hollow nanospheres was proposed on the basis of the experimental observations. Dielectric measurements in the X-band microwave frequencies (8–12 GHz) showed that the dielectric loss of the paraffin filled by the BN hollow nanospheres was lower than that filled by regular BN powders, which indicated that the BN hollow nanospheres could be potentially used as low-density fillers for microwave radomes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Aqueous Synthesis of Concave Rh Nanotetrahedra with Defect-Rich Surfaces: Insights into Growth-, Defect-, and Plasmon-Enhanced Catalytic Energy Conversion

The control of morphology in the synthesis of Rh nanocrystals can be used to precisely tailor the electronic surface structure; this in turn directly influences their performance in catalysis applications. Many works have brought attention to the development of Rh nanostructures with low-index surfaces, but limited effort has been devoted to the study of high-index and surface defect-enriched nanocrystals as they are not favored by thermodynamics because of the involvement of high-energy surfaces and increased surface-to-volume ratios. Here, we demonstrate an aqueous synthesis of concave Rh nanotetrahedra (CTDs) serving as efficient catalysts for energy conversion reactions. CTDs are surface defect-rich structures that form through a slow growth rate and follow the four-step model of metallic nanoparticle growth. Via the tuning of the surfactant concentration, the morphology of Rh CTDs evolved into highly excavated nanotetrahedra (HETDs) and twinned nanoparticles (TWs). Unlike the CTD surfaces with abundant adatoms and vacancies, HETDs and TWs have more regular surfaces with layered terraces. Each nanocrystal type was evaluated for methanol electrooxidation and hydrogen evolution from hydrolysis of ammonia borane, and the CTDs significantly showed the best catalytic performance because of defect enrichment, which benefits the surface reactivity of adsorbates. In addition, both CTDs and HETDs have strong absorption near the visible light region (382 and 396 nm), for which they show plasmon-enhanced performance in photocatalytic hydrogen evolution under visible light illumination. CTDs are more photoactive than HETDs, likely because of more pronounced localized surface plasmon resonance hot spots. Lastly, this facile aqueous synthesis of large-surface-area, defect-rich Rh nanotetrahedra is exciting for the fields of nanosynthesis and catalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electron Counting and High-Pressure Phase Transformations in Metal Hexaborides

Pressure-induced structural transitions of the alkaline earth hexaborides, CaB 6 , SrB 6 , and BaB 6 , are studied theoretically using electron counting rules and density functional theory calculations. Here, we demonstrate the applicability of gas-phase borane electron counting methods to solid-state metal borides under pressure and validate the assumptions of the rules by density functional theory (DFT) calculations. All three compounds share ambient-pressure and high-pressure structures, but BaB 6 differs from CaB 6 and SrB 6 at intermediate pressures. The unique BaB 6 phase is shown to break electron counting rules, while all other phases obey them. This anomaly is resolved by DFT, which reveals B–Ba covalency and unusual B–B π bonding under pressure. The relationships between structure and bonding can help us to understand the exotic behavior of lanthanide hexaborides and design new borides with desirable properties. Developing electron counting procedures for solids will enhance materials discovery efforts with chemical intuition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗