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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Copper Vacancies and Heavy Holes in the Two-Dimensional Semiconductor KCu 3– x Se 2

The two-dimensional material KCu 3–x Se 2 was synthesized using both a K 2 Se 3 flux and directly from the elements. It crystallizes in the CsAg 3 S 2 structure (monoclinic space group C2/m with a = 15.417(3) Å, b = 4.0742(8) Å, c = 8.3190(17) Å, and β = 112.94(3)°), and single-crystal refinement revealed infinite copper-deficient [Cu 3–x Se 2 ]– layers separated by K + ions. Thermal analysis indicated that KCu 3–x Se 2 melts congruently at ~755 °C. UV–vis spectroscopy showed an optical band gap of ~1.35 eV that is direct in nature, as confirmed by electronic structure calculations. Electronic transport measurements on single crystals yielded an in-plane resistivity of ~6 × 10 –1 Ω cm at 300 K that has a complex temperature dependence. The results of Seebeck coefficient measurements were consistent with a doped p-type semiconductor (S = +214 μV K –1 at 300 K), with doping being attributed to copper vacancies. Transport is dominated by low-mobility (on the order of 1 cm 2 V –1 s –1 ) holes caused by relatively flat valence bands with substantial Cu 3d character and a significant concentration of Cu ion vacancy defects (p ~ 10 19 cm –3 ) in this material. In conclusion, electronic band structure calculations showed that electrons should be significantly more mobile in this structure type.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines

8-Hydroxyquinolines (8HQs) are a family of lipophilic metal ion chelators that have been used in a range of analytical and pharmaceutical applications over the last 100 years. More recently, CQ (clioquinol; 5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) have undergone clinical trials for the treatment of Alzheimer’s disease and Huntington’s disease. Because CQ and PBT2 appear to redistribute metals into cells, these compounds have been redefined as copper and zinc ionophores. Despite the attention surrounding the clinical trials and the clear link between 8HQs and metals, the fundamental solution chemistry of how these compounds bind divalent metals such as copper and zinc, as well as their mechanism(s) of action in mammalian systems, remains poorly understood. Here, we used a combination of X-ray absorption spectroscopy (XAS), high-energy resolution fluorescence detected (HERFD) XAS, electron paramagnetic resonance (EPR), and UV–visible absorption spectroscopies to investigate the aqueous solution chemistry of a range of 8HQ derivatives. To circumvent the known solubility issues with 8HQ compounds and their complexes with Cu(II), and to avoid the use of abiological organic solvents, we have devised a surfactant buffer system to investigate these Cu(II) complexes in aqueous solution. Our study comprises the first comprehensive investigation of the Cu(II) complexes formed with many 8HQs of interest in aqueous solution, and it provides the first structural information on some of these complexes. We find that halogen substitutions in 8HQ derivatives appear to have little effect on the Cu(II) coordination environment; 5,7-dihalogenated 8HQ conformers all have a pseudo square planar Cu(II) bound by two quinolin-8-olate anions, in agreement with previous studies. Conversely, substituents in the 2-position of the 8HQ moiety appear to cause significant distortions from the typical square-planar-like coordination of most Cu(II)-bis-8HQ complexes, such that the 8HQ moieties in the Cu(II)-bis-8HQ complex are rotated approximately 30–40° apart in a “propeller-like” arrangement.

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

Trifluoromethylated Phenanthroline Ligands Reduce Excited-State Distortion in Homoleptic Copper(I) Complexes

Herein, we report the synthesis and excited-state dynamics for a series of homoleptic copper(I) trifluoromethylated phenanthroline complexes with two, three, and four trifluoromethyl functional groups. Our analysis of the steady-state absorbance and emission, transient-absorption spectroscopy, and electronic-structure-theory calculations results enable in-depth analysis of the pseudo-Jahn–Teller distortion inhibition from increased steric hindrance of the trifluoromethyl functional group relative to the prototypical dimethyl phenanthroline complex. Surprisingly, our results demonstrate that the greatest degree of pseudo-Jahn–Teller distortion inhibition is achieved with trifluoromethylation of only the 2 and 9 positions by an unusual combination of steric hindrance and stabilization of a nondistorted 1 MLCT manifold observed by transient kinetic lifetimes and optimized excited-state structures. The intersystem-crossing (ISC) lifetime for the 2,9-bis(trifluoromethyl)-1,10-phenanthroline Cu(I) complex is 69 ps, while the triplet excited-state lifetime and emission quantum yield are 106 ns and 4 × 10 –3 , respectively. Further trifluoromethylation of the phenanthroline yields a greater σ bond inductive withdrawing force on the phenanthroline nitrogens, ultimately resulting in weaker coordination to the copper. Last, the surprising success of the 2,9-bis(trifluoromethyl)-1,10-phenanthroline Cu(I) complex by adjusting both ligand sterics and electronic properties outlines a new strategy for developing long-lived Cu(I) charge-transfer complexes.

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

Advanced Catalysts for Olefin Synthesis: Copper(II) Quinoline-Fused Oxazolidines in Alcohol Dehydration

The new copper(II) catalyst [Cu( Q FOX)- (CH 3 CN)][OTf] 2 has been synthesized and found to be active for alcohol dehydration to give olefins at 120 °C with a 1% catalyst loading ( Q FOX = di-2-quinolinyl-fused-oxazolidine). Benzylic, allylic, and tertiary alcohols are all dehydrated. In some cases, ethers are observed to be produced, but these are re-entrained into the catalytic cycle. Unactivated secondary alcohols are also dehydrated. Similar catalysts employing Mn II , Fe II , Co II , and Ni II were also synthesized but showed reduced dehydration activity compared to the copper(II) derivative. A Cu I analog was also prepared but did not show improved dehydration activity.

Alcohols↗
DOE OSTI2017

Water Adsorption and Dissociation on Polycrystalline Copper Oxides: Effects of Environmental Contamination and Experimental Protocol

We use ambient-pressure X-ray photoelectron spectroscopy (APXPS) to study chemical changes, including hydroxylation and water adsorption, at copper oxide surfaces from ultrahigh vacuum to ambient relative humidities of ~5%. Polycrystalline CuO and Cu 2 O surfaces were prepared by selective oxidation of metallic copper foils. For both oxides, hydroxylation occurs readily, even at high-vacuum conditions. Hydroxylation on both oxides plateaus near ~0.01% relative humidity (RH) at a coverage of ~1 monolayer. In contrast to previous studies, neither oxide shows significant accumulation of molecular water; rather, both surfaces show a high affinity for adventitious carbon contaminants. Results of isobaric and isothermic experiments are compared, and the strengths and potential drawbacks of each method are discussed. We also provide critical evaluations of the effects of the hot filament of the ion pressure gauge on the reactivity of gas-phase species, the peak fitting procedure on the quantitative analysis of spectra, and rigorous accounting of carbon contamination on data analysis and interpretation. Lastly, this work underscores the importance of considering experimental design and data analysis protocols during APXPS experiments with water vapor in order to minimize misinterpretations arising from these factors.

36 MATERIALS SCIENCE↗
DOE OSTI2025

In Situ Studies of Copper-Zirconia-Zinc Oxide Model Catalysts for CO 2 Hydrogenation

A combination of in situ X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRAS) was used to investigate the formation of surface intermediates from CO 2 hydrogenation on copper-zirconia-zinc oxide model catalysts under reaction conditions. Copper clusters with different numbers of atoms (n = 1, 4, 13) were deposited onto bare and ZrO 2 -modified ZnO powder supports to systematically examine the effects of Cu cluster size and the synergy between metal and metal-oxide components. Under low pressure CO 2 hydrogenation conditions (CO 2 :H 2 = 1:9, 0.4 mbar, 300–600 K), XPS and IRAS identify the most prominent intermediates as carbonate (CO 3 *), formate (HCOO*) and methoxy (CH 3 O*), which is the final surface-bound intermediate leading to methanol. The temperature profiles are consistent with a mechanism in which CO 2 is adsorbed as carbonate species (HCO 3 *, CO 3 *) followed by hydrogenation reactions to formate (HCOO*) and methoxy (CH 3 O*), but the relative yields strongly depend on surface composition. Specifically, the presence of ZrO 2 promotes CO 2 adsorption and activation and improves the thermal stability of the Cu clusters against loss of surface area. Moreover, the ternary Cu 4 /ZrO 2 /ZnO surface is significantly more active than Cu 4 /ZnO and ZrO 2 /ZnO surfaces for the formation of methoxy (CH 3 O*), indicating that Cu–ZrO 2 interfaces promote the formation of key intermediates leading to methanol. Finally, the yields of intermediates are similar for all Cu cluster sizes (Cu 1 , Cu 4 and Cu 13 ), indicating that the primary role of Cu is to provide H atoms via H 2 dissociation and spillover. In conclusion, these molecular-level insights provide a fundamental understanding of the enhanced efficiency of ternary Cu–ZrO 2 –ZnO catalysts and establish design principles for developing improved catalysts for CO 2 conversion.

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

One electron changes everything: a multispecies copper redox shuttle for dye-sensitized solar cells.

Dye-sensitized solar cells (DSCs) are an established alternative photovoltaic technology that offers numerous potential advantages in solar energy applications. However, this technology has been limited by the availability of molecular redox couples that are both noncorrosive/nontoxic and do not diminish the performance of the device. In an effort to overcome these shortcomings, a copper-containing redox shuttle derived from 1,8-bis(2'-pyridyl)-3,6-dithiaoctane (PDTO) ligand and the common DSC additive 4-tert-butylpyridine (TBP) was investigated. Electrochemical measurements, single-crystal X-ray diffraction, and absorption and electron paramagnetic resonance spectroscopies reveal that, upon removal of one metal-centered electron, PDTO-enshrouded copper ions completely shed the tetradentate PDTO ligand and replace it with four or more TBP ligands. Thus, the Cu(I) and Cu(II) forms of the electron shuttle have completely different coordination spheres and are characterized by widely differing Cu(II/I) formal potentials and reactivities for forward versus reverse electron transfer. Notably, the coordination-sphere replacement process is fully reversed upon converting Cu(II) back to Cu(I). In cells featuring an adsorbed organic dye and a nano- and mesoparticulate, TiO2-based, photoelectrode, the dual species redox shuttle system engenders performance superior to that obtained with shuttles based on the (II/I) forms of either of the coordination complexes in isolation.

Hoffeditz, William L.↗
DOE OSTI2018

Enhanced Reactivity of Lithium and Copper at High Pressure

High pressure can profoundly affect the electronic structure and reactivity, creating compounds between elements that do not react at ambient conditions. Lithium is known to react with gold and silver; however, no copper compounds are known to date. Here, by compressing mixtures of the elements in diamond-anvil cells, compounds of lithium and copper have been synthesized and characterized by X-ray diffraction for the first time. Pressures as low as 1 GPa lead to the formation of a complex layered phase LiCu, displaying two-dimensional kagomé lattice layers of Cu atoms. With increasing pressure, the layered Cu–Cu bonding is replaced by linear chains of Cu atoms in the high-pressure phase Li 2 Cu. Here we show the powerful effects of even modest pressures on the reactivity of lithium, leading to structures of remarkable complexity and low-dimensional transition metal bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Electrochemical Control of Copper Intercalation into Nanoscale Bi 2 Se 3

Intercalation of exotic atoms or molecules into the layered materials remains an extensively investigated subject in current physics and chemistry. However, traditionally melt-growth and chemical interaction strategies are either limited by insufficiency of intercalant concentrations or destitute of accurate controllability. Here, we have developed a general electrochemical intercalation method to efficaciously regulate the concentration of zerovalent copper atoms into layered Bi 2 Se 3 , followed by comprehensive experimental characterization and analyses. Up to 57% copper atoms (Cu 6.7 Bi 2 Se 3 ) can be intercalated with no disruption to the host lattice. Meanwhile the unconventional resistance dip accompanied by a hysteresis loop below 40 K, as well as the emergence of new Raman peak in Cu x Bi 2 Se 3 , is a distinct manifestation of the interplay between intercalated Cu atoms with Bi 2 Se 3 host. Furthermore, our work demonstrates a new methodology to study fundamentally new and unexpected physical behaviors in intercalated metastable materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modification of Carbon Nitride/Reduced Graphene Oxide van der Waals Heterostructure with Copper Nanoparticles To Improve CO 2 Sensitivity

Carbon nitride/reduced graphene oxide (rGO) van der Waals heterostructures (vdWH) have previously shown exceptional oxygen sensitivity via a photoredox mechanism, making it a potential material candidate for various applications such as oxygen reduction reaction catalysis and oxygen sensing. In this work, the electronic structure of a carbon nitride/rGO composite is modified through the introduction of copper nanoparticles (NPs). When incorporated into a chemiresistor device, this vdWH displayed a newfound CO 2 sensitivity. The effects of humidity and light were investigated and found to be crucial components for the CO 2 sensitivity. Density functional theory calculations performed on a carbon nitride/copper NP@rGO model system found an enhanced stabilization of CO 2 caused by H-bonds between the carbon nitride layer and chemisorbed CO 2 on copper, pointing to the important role played by humidity. The synergetic effect between the carbon nitride layer interfaced with CuNP@rGO, in combination with humidity and light (395 nm) irradiation, is found to be responsible for the newfound sensitivity toward CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

High Conductivity Copper–Carbon Nanotube Hybrids via Site-Specific Chemical Vapor Deposition

In this work, site-selective copper nanometal seeding through chemical vapor deposition (CVD) is demonstrated as a viable method in concert with solution electrodeposition of bulk Cu to enhance the electrical conductivity of a porous, low-density (0.12 g/cm 3 , ~9 mg/m) CNT roving. An electrical bias applied directly to the CNT roving promotes Joule heating, which provides the thermal energy necessary for the decomposition of a bis(tert-butylacetoacetato)copper (Cu(tBAOAC) 2 ) precursor. Localized changes in the resistance within the bulk CNT conductor were used to selectively deposit the precursor at thermally active sites, which were evaluated through thermal imaging. The deposition varies from localized Cu deposits at currents producing average temperatures of ~225 °C to a consistent deposition of 10–40 nm Cu particles at applied currents producing average temperatures >300 °C, far above the threshold for the decomposition of the Cu(tBAOAC) 2 precursor. Scanning electron microscopy of a cross section of the roving reveals Cu depositions on the interior of the roving, demonstrating the penetration of the vapor into the CNT network and subsequent decomposition within the roving. A commercial acid-based Cu electroplating solution was used to deposit bulk Cu onto as-prepared and CVD seeded CNT wires, followed by planar densification and H 2 /Ar annealing. The finished conductors with Cu loadings from ~30 to 95% w/w which combine CVD Cu seeding and electrodeposition result in specific conductivity values 3-5 times higher than Cu-CNT conductors produced by electrodeposition alone. Ultimately, a CNT hybrid conductor with 94.2% w/w Cu achieved a specific conductivity of 5632 S m 2 /kg and electrical conductivity of 28.1 MS/m—approaching values previously only seen in metallic conductors. Overall, the present results demonstrate the potential of site-specific CVD toward both seeding metal prior to electroplating and as a possible method toward the enhanced nanometal interconnection of carbon conductors (NICCs).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Electrocatalytic Water Oxidation by a Copper(II) Complex of an Oxidation-Resistant Ligand

The copper(II) complex Cu(pyalk) 2 (pyalk = 2-pyridyl-2-propanoate) is a robust homogeneous water-oxidation electrocatalyst under basic conditions (pH > 10.4). Water oxidation occurs at a relatively low overpotential for copper of 520–580 mV with a turnover frequency of ~0.7 s –1 . Controlled potential electrolysis experiments over 12 h at 1.1 V vs NHE resulted in the formation of >30 catalytic turnovers of O 2 with only ~20% catalyst degradation. The robustness of the catalyst under fairly harsh conditions and the low overpotential further highlight the oxidation resistance and strong donor character of pyalk.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A New Type of Hybrid Copper Iodide as Nontoxic and Ultrastable LED Emissive Layer Material

Perovskite-based light-emitting diodes (PeLEDs) are promising candidates for next-generation solid-state lighting and display technologies. However, all current high-performance PeLEDs contain a toxic element (lead) and suffer from relatively low stability. Herein, we report a new type of lead-free LED using low-cost, eco-friendly, and robust copper(I) iodide hybrid material as the emissive layer (EML). Specifically, they are composed of copper iodide chains and organic ligands through ionic and coordinate bonds. Their remarkable stability and solution processability stem from this unique multifold bonding feature. High-quality thin films of 1D-Cu 4 I 6 (bttmp) 2 were fabricated by a simple, one-step spin-coating process. They exhibit high photoluminescence quantum yield (91%) and long-term air stability (>2000 h). An EQE of 5.02% was achieved for a prototype yellow LED using 1D-Cu 4 I 6 (bttmp) 2 EML. Its half-lifetime of 35.5 h obtained in open air outperforms that of most PeLEDs reported to date. Finally, this work opens a new direction for making LEDs based on ecofriendly and robust hybrid materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Identification of the Selective Sites for Electrochemical Reduction of CO to C 2+ Products on Copper Nanoparticles by Combining Reactive Force Fields, Density Functional Theory, and Machine Learning

Recent experiments have shown that CO reduction on oxide derived Cu nanoparticles (NP) are highly selective toward C 2+ products. However, understanding of the active sites on such NPs is limited, because the NPs have ~200 000 atoms with more than 10 000 surface sites, far too many for direct quantum mechanical calculations and experimental identifications. We show here how to overcome the computational limitation by combining multiple levels of theoretical computations with machine learning. This approach allows us to map the machine learned CO adsorption energies on the surface of the copper nanoparticle to construct the active site visualization (ASV). Furthermore, we identify the structural criteria for optimizing selective reduction by predicting the reaction energies of the potential determining step, $ΔE_{OCCOH}$, for the C 2+ product. Based on this structural criterion, we design a new periodic copper structure for CO reduction with a theoretical faradaic efficiency of 97%.

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

Copper-Based Two-Dimensional Conductive Metal–Organic Framework Thin Films for Ultrasensitive Detection of Perfluoroalkyls in Drinking Water

Perfluoroalkyls (PFAS) continue to emerge as a global health threat making their effective detection and capture extremely important. Though metal–organic frameworks (MOFs) have stood out as a promising class of porous materials for sensing PFAS, detection limits remain insufficient and a fundamental understanding of detection mechanisms warrants further investigation. Here, in this study, we show the use of a 2D conductive MOF film based on copper hexahydroxy triphenylene (Cu-HHTP) to fabricate chemiresistive sensing devices for detecting PFAS in drinking water. We further show ultrasensitive detection using electrochemical impedance spectroscopy. Owing to excellent electrostatic attractions and electrochemical interactions between the copper-based MOF and PFAS, confirmed by high-resolution spectroscopy and theoretical simulations, the MOF-based sensor reported herein exhibits excellent affinity and sensitivity toward perfluorinated acids at concentrations as low as 0.002 ng/L.

2D metal−organic frameworks↗
DOE OSTI2015

Platinum-ruthenium nanotubes and platinum-ruthenium coated copper nanowires as efficient catalysts for electro-oxidation of methanol

The sluggish kinetics of methanol oxidation reaction (MOR) is a major barrier to the commercialization of direct methanol fuel cells (DMFCs). In this study, we report a facile synthesis of platinum–ruthenium nanotubes (PtRuNTs) and platinum–ruthenium-coated copper nanowires (PtRu/CuNWs) by galvanic displacement reaction using copper nanowires as a template. The PtRu compositional effect on MOR is investigated; the optimum Pt/Ru bulk atomic ratio is about 4 and surface atomic ratio about 1 for both PtRuNTs and PtRu/CuNWs. Enhanced specific MOR activities are observed on both PtRuNTs and PtRu/CuNWs compared with the benchmark commercial carbon-supported PtRu catalyst (PtRu/C, Hispec 12100). Finally, x-ray photoelectron spectroscopy (XPS) reveals a larger extent of electron transfer from Ru to Pt on PtRu/CuNWs, which may lead to a modification of the d-band center of Pt and consequently a weaker bonding of CO (the poisoning intermediate) on Pt and a higher MOR activity on PtRu/CuNWs.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Methane Activation by a Mononuclear Copper Active Site in the Zeolite Mordenite: Effect of Metal Nuclearity on Reactivity

The direct conversion of methane to methanol would have a wide reaching environmental and industrial impact. Copper-containing zeolites can perform this reaction at low temperatures and pressures at a previously defined O 2 -activated [Cu 2 O] 2+ site. However, after autoreduction of the copper-containing zeolite mordenite and removal of the [Cu 2 O] 2+ active site, the zeolite is still methane reactive. In this study, we use diffuse reflectance UV–vis spectroscopy, magnetic circular dichroism, resonance Raman spectroscopy, electron paramagnetic resonance, and X-ray absorption spectroscopy to unambiguously define a mononuclear [CuOH] + as the CH 4 reactive active site of the autoreduced zeolite. The rigorous identification of a mononuclear active site allows a reactivity comparison to the previously defined [Cu 2 O] 2+ active site. We perform kinetic experiments to compare the reactivity of the [CuOH] + and [Cu 2 O] 2+ sites and find that the binuclear site is significantly more reactive. From the analysis of density functional theory calculations, we elucidate that this increased reactivity is a direct result of stabilization of the [Cu 2 OH] 2+ H-atom abstraction product by electron delocalization over the two Cu cations via the bridging ligand. This significant increase in reactivity from electron delocalization over a binuclear active site provides new insights for the design of highly reactive oxidative catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Electrochemical C–N Bond Formation within Boron Imidazolate Cages Featuring Single Copper Sites

Electrocatalysis expands the ability to generate industrially relevant chemicals locally and on-demand with intermittent renewable energy, thereby improving grid resiliency and reducing supply logistics. Herein, we report the feasibility of using molecular copper boron-imidazolate cages, BIF-29(Cu), to enable coupling between the electroreduction reaction of CO 2 (CO 2 RR) with NO 3 – reduction (NO 3 RR) to produce urea with high selectivity of 68.5% and activity of 424 μA cm –2 . Remarkably, BIF-29(Cu) is among the most selective systems for this multistep C–N coupling to-date, despite possessing isolated single-metal sites. The mechanism for C–N bond formation was probed with a combination of electrochemical analysis, in situ spectroscopy, and atomic-scale simulations. We found that NO 3 RR and CO 2 RR occur in tandem at separate copper sites with the most favorable C–N coupling pathway following the condensation between *CO and NH 2 OH to produce urea. In conclusion, this work highlights the utility of supramolecular metal–organic cages with atomically discrete active sites to enable highly efficient coupling reactions.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗