kasacrcfrcorppiv.c0
Attenuation Corrected reflectivity add to Ka-Band Scanning ARM Cloud Radar (KASACR) CF-Radial PPI scan
54 ENVIRONMENTAL SCIENCES↗
SEARCH · Engineering Papers
Results for “CF”
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.
Basal Plane Hydrogen Evolution Activity from Mixed Metal Nitride MXenes Measured by Scanning Electrochemical Microscopy
2D early transition metal carbide and nitride MXenes have intriguing properties for electrochemical energy storage and electrocatalysis. These properties can be manipulated by modifying the basal plane chemistry. Here, mixed transition metal nitride MXenes, M-Ti 4 N 3 T x (M = V, Cr, Mo, or Mn; T x = O and/or OH), are developed by modifying pristine exfoliated Ti 4 N 3 T x MXene with V, Cr, Mo, and Mn salts using a simple solution-based method. The resulting mixed transition metal nitride MXenes contain 6–51% metal loading (cf. Ti) that exhibit rich electrochemistry including highly tunable hydrogen evolution reaction (HER) electrocatalytic activity in a 0.5 m H 2 SO 4 electrolyte as follows: V-Ti 4 N 3 T x > Cr-Ti 4 N 3 T x > Mo-Ti 4 N 3 T x > Mn-Ti 4 N 3 T x > pristine Ti 4 N 3 T x with overpotentials as low as 330 mV at -10 mA cm -2 with a charge-transfer resistance of 70 O. Scanning electrochemical microscopy (SECM) reveals the electrochemical activity of individual MXene flakes. The SECM data corroborate the bulk HER activity trend for M-Ti 4 N 3 T x as well as provide the first experimental evidence that HER results from catalysis on the MXene basal plane. These electrocatalytic results demonstrate a new pathway to tune the electrochemical properties of MXenes for water splitting and related electrochemical applications.
2D materials↗
Solution–Doped Donor–Acceptor Copolymers Based on Diketopyrrolopyrrole and 3, 3'–Bis (2–(2–(2–Methoxyethoxy) Ethoxy) ethoxy)–2, 2'–Bithiophene Exhibiting Outstanding Thermoelectric Power Factors with p –Dopants
The design of polymeric semiconductors exhibiting high electrical conductivity (σ) and thermoelectric power factor (PF) will be vital for flexible large-area electronics. In this work, four polymers based on diketopyrrolopyrrole (DPP), 2,3-dihydrothieno[3,4-b][1,4]dioxine (EDOT), thieno[3,2-b]thiophene (TT), and 3, 3'-bis (2-(2-(2-methoxyethoxy) ethoxy) ethoxy)-2, 2'-bithiophene (MEET) are investigated as side-chains, with the MEET polymers newly synthesized for this study. These polymers are systematically doped with tetrafluorotetracyanoquinodimethane ( F 4 TCNQ), CF3SO3H, and the synthesized dopant Cp(CN) 3 -(COOMe) 3 , differing in geometry and electron affinity. The DPP-EDOT-based polymer containing MEET as side-chains exhibits the highest conductivity (σ) ≈700 S cm–1 in this series with the acidic dopant (CF 3 SO 3 H). This polymer also shows the lowest oxidation potential by cyclic voltammetry (CV), the strongest intermolecular interactions evidenced by differential scanning calorimetry (DSC), and has the most oxygen-based functionality for possible hydrogen bonding and ionic screening. Other polymers exhibit high σ ≈300–500 S cm–1 and power factor up to 300 µW m –1 K –2 . The mechanism of conductivity is predominantly electronic, as validated by time-dependent conductance studies and transient thermo voltage monitoring over time, including for those doped with the acid. Furthermore, these materials maintain significant thermal stability and air stability over ≈6 weeks. Density functional theory calculations reveal molecular geometries and inform about frontier energy levels. Raman spectroscopy, in conjunction with scanning electron microscopy (SEM-EDS) and x-ray diffraction, provides insight into the solid-state microstructure and degree of phase separation of the doped polymer films. Infrared spectroscopy enables this study to further quantify the degree of charge transfer from polymer to dopant.
36 MATERIALS SCIENCE↗
Operando Investigation of the Molecular Origins of Dipole Switching in P(VDF‐TrFE‐CFE) Terpolymer for Large Adiabatic Temperature Change
Abstract Relaxor ferroelectric polymers exhibiting a giant electrocaloric effect (ECE) can potentially be used to create next‐generation solid‐state coolers. Under an electric field, poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) terpolymer goes through a large dipolar entropy change producing a high adiabatic temperature change (Δ T ECE ). This work resolves the molecular origins of the large entropy change behind the electric field‐induced dipole switching. A Fourier transform infrared spectroscopy equipped with a high voltage source is used to operandoly observe the characteristic molecular vibrational modes. A short‐range trans (T) conformation of the CF 2 ‐CH 2 dyads interrupted by a gauche (G) conformation, e.g., TTTG in the terpolymer chain, undergoes a dynamic transformation that leads to a corresponding Δ T ECE whenever an electric field is applied. The molecular dynamics simulation also proves that the energy barrier that the transformation from TTTGs into a long T sequence overcomes is smaller than that for all other conformations. A mixed solvent system is used to obtain T3G‐enriched terpolymer films exhibiting a 4.02 K Δ T ECE at 60 MV m −1 and these films are employed to manufacture a 2‐layer‐cascaded cooling device that achieves a 6.7 K temperature lift, the highest reported value for a 2‐layer cascaded device made of fluoropolymers.
Zhu, Yuan↗
Dual-Solvent Li-Ion Solvation Enables High-Performance Li-Metal Batteries
Novel electrolyte designs to further enhance the lithium (Li) metal battery cyclability are highly desirable. Here, fluorinated 1,6-dimethoxyhexane (FDMH) is designed and synthesized as the solvent molecule to promote electrolyte stability with its prolonged –CF 2 – backbone. Meanwhile, 1,2-dimethoxyethane is used as a co-solvent to enable higher ionic conductivity and much reduced interfacial resistance. Combining the dual-solvent system with 1 m lithium bis(fluorosulfonyl)imide (LiFSI), high Li-metal Coulombic efficiency (99.5%) and oxidative stability (6 V) are achieved. Using this electrolyte, 20 µm Li||NMC batteries are able to retain ≈80% capacity after 250 cycles and Cu||NMC anode-free pouch cells last 120 cycles with 75% capacity retention under ≈2.1 µL mAh -1 lean electrolyte conditions. Such high performances are attributed to the anion-derived solid-electrolyte interphase, originating from the coordination of Li-ions to the highly stable FDMH and multiple anions in their solvation environments. This work demonstrates a new electrolyte design strategy that enables high-performance Li-metal batteries with multisolvent Li-ion solvation with rationally optimized molecular structure and ratio.
25 ENERGY STORAGE↗
Interfacial Strength in Hierarchical Carbon Fiber Composites: Interplay of Interphase Modulus and Roughness
A facile, direct deposition approach that exploits van der Waals interactions between carbonaceous materials is utilized to create unidirectional hybrid carbon fiber composites. Two small molecule crosslinkers, a trifunctional aromatic (TL) and a difunctional aliphatic (DL) acyl chloride, are first utilized to create a crosslinked interphase with a softer and stiffer modulus respectively. TL crosslinked interphase with a higher modulus improved the tensile strength by 50%, despite non-covalent linking between fiber and matrix, elucidating the critical role of the interphase in alleviating modulus mismatch between the high modulus carbon fiber and the rubbery matrix. Fractional quantities of carbon nanotubes are additionally dispersed in the small molecule crosslinkers which behaved as a dispersant, helping introduce nanoasperities on the carbon fiber surface. Strong “pi-pi” interactions between CNTs and CF contributed to tensile properties, which are increased by 66% compared to the control. A cohesive zone model suggests that a stiffer interphase is better able to exploit surface heterogeneities and roughness on the fiber, synergistically enhancing interfacial strength.
36 MATERIALS SCIENCE↗
Synthesis of Ln II ‐in‐Cryptand Complexes by Chemical Reduction of Ln III ‐in‐Cryptand Precursors: Isolation of a Nd II ‐in‐Cryptand Complex
Abstract Lanthanide triflates have been used to incorporate Nd III and Sm III ions into the 2.2.2‐cryptand ligand (crypt) to explore their reductive chemistry. The Ln(OTf) 3 complexes (Ln=Nd, Sm; OTf=SO 3 CF 3 ) react with crypt in THF to form the THF‐soluble complexes [Ln III (crypt)(OTf) 2 ][OTf] with two triflates bound to the metal encapsulated in the crypt. Reduction of these Ln III ‐in‐crypt complexes using KC 8 in THF forms the neutral Ln II ‐in‐crypt triflate complexes [Ln II (crypt)(OTf) 2 ]. DFT calculations on [Nd II (crypt)] 2+ ], the first Nd II cryptand complex, assign a 4f 4 electron configuration to this ion.
Huh, Daniel N.↗
2,4,6‐Triphenylpyridinium: A Bulky, Highly Electron‐Withdrawing Substituent That Enhances Properties of Nickel(II) Ethylene Polymerization Catalysts
Abstract The reactivity of Ni II and Pd II olefin polymerization catalysts can be enhanced by introduction of electron‐withdrawing substituents on the supporting ligands rendering the metal centers more electrophilic. Reported here is a comparison of ethylene polymerization activity of a classical salicyliminato nickel catalyst substituted with the powerful electron‐withdrawing 2,4,6‐triphenylpyridinium (trippy) group to the ‐CF 3 analogue. The trippy substituent is substantially more electron‐withdrawing (σ meta =0.63) than the trifluoromethyl group (σ meta =0.43) which results in a ca. 8‐fold increase in catalytic turnover frequency. An additional advantage of trippy is the high steric bulk relative to the trifluoromethyl group. This feature results in a four‐fold increase in polymer molecular weight owing to enhanced retardation of chain transfer. A significant increase in catalyst lifetime is observed as well.
Janeta, Mateusz↗
Fluoro‐nitrogen Cations
Abstract The crystal structures of [NH 3 F] + [CF 3 SO 3 ] − , [NH 2 F 2 ] + [SbF 6 ] − , and [N 2 F 3 ] + [Sb 3 F 16 ] − have been determined, representing the first structural characterizations of these simple fluoro‐nitrogen cations. The influences of the hybridization of the central nitrogen atom and of the number of fluorine substituents on the N−F bond lengths are evaluated for the series N 2 F + , N 2 F 3 + , NF 2 O + , NH 3 F + , NH 2 F 2 + , and NF 4 + . It is shown that the N−F bond length decreases from 1.40 Å to 1.26 Å with increasing fluorine substitution and increasing s‐character of the nitrogen atom, and that unusual N−F bond lengths reported in the previous literature are caused by disorder problems
Vij, Ashwani↗
Reversible CO 2 Hydrogenation, Neutron Crystallography, and Hydride Reactivity of a Triiridium Heptahydride Complex
Abstract The authors report the structure, reactivity, and catalytic utility of a triiridium complex, [Ir 3 H 6 ( μ 3 ‐H)(PN) 3 ] 2+ ( 2‐H , PN = (2‐pyridyl)CH 2 PBu t 2 ). Despite its unusual stability to unsaturated organics, electrophiles, and even CF 3 SO 3 D, they find that complex 2‐H catalyzes hydrogenation of CO 2 to formate (TON Ir = 9600) and reverse formic acid dehydrogenation (TON Ir = 54 400). The hydrogenation operates via a reactive intermediate [Ir 3 H 4 ( μ ‐H) 4 (PN) 3 ] + ( 5 ). Neutron crystallography and DFT‐supported neutron vibrational spectroscopy of 2‐H reveal Ir─H bond lengths and elucidate the vibration modes within the Ir 3 H 7 core. Stoichiometric oxidation of 2‐H produces four classes of iridium complexes of varied nuclearity and hydride structure: tetra‐ and pentanuclear clusters [Ir 3 H 6 ( μ 3 ‐AuPPh 3 )(PN) 3 ] 2+ ( 2‐Au ) and [Ag{Ir 2 H 4 ( μ ‐OAc)(PN) 2 } 2 ] 3+ ( 6 ) are generated using AuPPh 3 + and AgOAc, respectively. Further oxidation to class [Ir 2 H 3 ( μ ‐X) 2 (PN) 2 ] + is possible with AgOAc, Hg(OAc) 2 , or I 2 . Finally, a TEMPO/HCl system completely oxidizes the hydrides and gives [Ir 2 Cl 4 ( μ ‐Cl) 2 (PN) 2 ] ( 11 ).
Cherepakhin, Valeriy [Loker Hydrocarbon Research I↗
Fluoro–nitrogen Cations
The crystal structures of [NH 3 F] + [CF 3 SO 3 ] – , [NH 2 F 2 ] + [SbF 6 ] – , and [N 2 F 3 ] + [Sb 3 F 16 ] – have been determined, representing the first structural characterizations of these simple fluoro-nitrogen cations. The influences of the hybridization of the central nitrogen atom and of the number of fluorine substituents on the N–F bond lengths are evaluated for the series N 2 F + , N 2 F 3 + , NF 2 O + , NH 3 F + , NH 2 F 2 + , and NF 4 + . Here it is shown that the N–F bond length decreases from 1.40 Å to 1.26 Å with increasing fluorine substitution and increasing s-character of the nitrogen atom, and that unusual N–F bond lengths reported in the previous literature are caused by disorder problems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Reversible CO 2 Hydrogenation, Neutron Crystallography, and Hydride Reactivity of a Triiridium Heptahydride Complex
Here, the authors report the structure, reactivity, and catalytic utility of a triiridium complex, [Ir 3 H 6 (μ 3 -H)(PN) 3 ] 2+ (2-H, PN = (2-pyridyl)CH 2 PBu t 2 ). Despite its unusual stability to unsaturated organics, electrophiles, and even CF 3 SO 3 D, they find that complex 2-H catalyzes hydrogenation of CO 2 to formate (TON Ir = 9600) and reverse formic acid dehydrogenation (TON Ir = 54 400). The hydrogenation operates via a reactive intermediate [Ir 3 H 4 (μ-H) 4 (PN) 3 ] + (5). Neutron crystallography and DFT-supported neutron vibrational spectroscopy of 2-H reveal Ir─H bond lengths and elucidate the vibration modes within the Ir 3 H 7 core. Stoichiometric oxidation of 2-H produces four classes of iridium complexes of varied nuclearity and hydride structure: tetra- and pentanuclear clusters [Ir 3 H 6 (μ 3 -AuPPh 3 )(PN) 3 ] 2+ (2-Au) and [Ag{Ir 2 H 4 (μ-OAc)(PN) 2 } 2 ] 3+ (6) are generated using AuPPh 3 + and AgOAc, respectively. Further oxidation to class [Ir 2 H 3 (μ-X) 2 (PN) 2 ] + is possible with AgOAc, Hg(OAc) 2 , or I 2 . Finally, a TEMPO/HCl system completely oxidizes the hydrides and gives [Ir 2 Cl 4 (μ-Cl) 2 (PN) 2 ] (11).
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Influence of the Anions on the Interaction Energy between Water and Ionic Liquids
It is essential to understand the interaction energy between water and ionic liquids (ILs) in search of ILs for dehumidification applications. In this paper, the intermolecular interaction energy between water and 1-ethyl-3-methylimidazolium ([EMIM])-based ILs was investigated. The vapor-liquid equilibrium data were first measured for solutions of [EMIM][BF 4 ], [EMIM][N(CN) 2 ], [EMIM][CF 3 SO 3 ], and [EMIM][CH 3 SO 3 ] with water molar fractions of 8–95 % at temperatures of 303–343 K. The IL-IL and water-IL intermolecular interaction energies were determined by using the correlated non-random two-liquid model. The results revealed that fluorine atoms in anions reduce the attraction energy between IL and water, and thus, decrease the water affinity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Binding, Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes
The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu 2 (μ,η 1 : η 1 -MeCN)][X] 2 (X=weakly coordinating anion, NTf 2 (1 a), FAl[OC 6 F 10 (C 6 F 5 )] 3 (1 b), Al[OC(CF 3 ) 3 ] 4 (1 c)) was replaced by white phosphorus (P 4 ) or yellow arsenic (As 4 ) to yield [(DPFN)Cu 2 (μ,η 2 : η 2 -E 4 )][X] 2 (E=P (2 a-c), As (3 a-c)). The molecular structures in the solid state reveal novel coordination modes for E 4 tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E 4 tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E 4 tetrahedra with release of P 4 or As 4 and formation of [(DPFN)Cu 2 (μ,η 1 : η 1 - Me NHC)][X] 2 (4 a,b) or to an opening of one E-E bond leading to an unusual E 4 butterfly structural motif in [(DPFN)Cu 2 (μ,η 1 : η 1 -E 4 Dipp NHC)][X] 2 (E=P (5 a,b), E=As (6)). With a cyclic alkyl amino carbene ( Et CAAC), cleavage of two As-As bonds was observed to give two isomers of [(DPFN)Cu 2 (μ,η 2 : η 2 -As 4 Et CAAC)][X] 2 (7 a,b) with an unusual As 4 -triangle+1 unit.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Photochemical CO 2 Reduction Using Rhenium(I) Tricarbonyl Complexes with Bipyridyl-Type Ligands with and without Second Coordination Sphere Effects
In this study, the effect of phenyl, phenol, aniline, amino, and CF 3 substituents of the 2,2'-bipyridine ligand in fac-ReCl(L)(CO) 3 (L=2,2'-bipyridine derivative) catalysts on photochemical CO 2 reduction in dimethylacetamide is examined, in order to understand the structure-function relationships and to compare the catalytic activities with the previously published electrochemical results. All complexes including ReCl(bpy)(CO) 3 have similar excited-state lifetimes and emission spectra, but complex 1 with the Ph-NH 2 moiety exhibits a significantly larger molar absorption coefficient for its metal-to-ligand charge transfer (MLCT) band. All complexes we tested produce CO with only a negligible amount of H 2 and formate in self-sensitized systems in the presence of triethanolamine (TEOA) and in some cases, BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazole). The presence of the Ph-NH 2 moiety (complex 1) has a beneficial effect on both electrochemical and photochemical activity, allowing a turnover number (TON) of 32 and 120 for photochemical CO production (without and with BIH, respectively). In the case of the Ph-OH group in the second coordination sphere (complexes 4 and 6), these complexes are active for photochemical CO 2 reduction, despite the formation of a stable 6-coordinate Re-OPh intermediate via reductive deprotonation as previously observed under electrochemical conditions. Overall, BIH accelerates the rate of formation of the one-electron reduced species (OERS) of the Re catalysts and allows higher turnover frequency (TOF) and TON for CO formation. The X-ray structures of complexes 1 and 4 were determined to have distorted octahedral Re centres, and show π-π stacking interactions with neighboring molecules as well as intramolecular hydrogen bonds to the internal chloride ligands. The unusually high absorptivity of the MLCT absorption of complex 1 has been explained by TD-DFT calculations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Influence of Peripheral Substituents on Fe(II) Spin State in Complexes with Tridentate Schiff‐Base Ligands
Abstract Six Fe(II) complexes with substituted 6‐((quinoline‐8‐ylimino)methyl)phenolates (R 2 qsal) were synthesized. X‐ray crystal structure determination for [Fe(R 2 qsal) 2 ], where R=F ( 1 ), Cl ( 2 ), Br ( 3 ), I ( 4 ), CF 3 /H ( 5 ), or CN/H ( 6 ), revealed mononuclear complexes that crystallize either solvent‐free in case of 1 , 5 , and 6 or as CH 2 Cl 2 solvates in the case of 2 , 3 , and 4 . Complexes 1 – 4 , which contain π‐donating substituents, exhibit only high‐spin (HS) state, as shown by crystal structure analysis and magnetic measurements. In contrast, complexes 5 and 6 , which contain electron‐withdrawing substituents, exist in the low‐spin (LS) state at lower temperatures but exhibit crossover to the HS state above 300 K. Electronic structure calculations show a good correlation between the relative energies of the LS and HS states and the experimentally observed behavior.
Gakiya‐Teruya, Miguel↗
Scalable Detector Design for a High-Resolution Fast-Neutron Radiography Panel
Development of a scalable flat-panel neutron radiography device is needed to meet the nondestructive testing needs of a growing industrial market. Flood field images from a Cs-137 gamma source and a Cf-252 fission neutron source were generated using a detector composed of a 3-mm-thick sheet of EJ-200, and 3-mm-thick sheet of acrylic light spreader, an 8 $\times$ 8 array of SensL MICROFJ-60035-TSV SiPMs, and an IDEAS ROSSPAD readout module. The readout module can be tiled together with similar systems to create a panel of any size, and is only limited by the number of available Ethernet ports in a switching system. A collimated gamma line image demonstrated a 90% spatial resolution of approximately 0.47 line pairs per centimeter and a 10% spatial resolution of approximately 2.32 line pairs per centimeter. A neutron edge image demonstrated a 90% spatial resolution of approximately 0.70 line pairs per centimeter and a 10% spatial resolution of approximately 3.35 line pairs per centimeter. Both of these images show the ability to generate radiographs with sub-SiPM spatial resolution. Using these readout modules, a large-scale radiographic panel can be developed by tiling ROSSPAD modules together.
36 MATERIALS SCIENCE↗