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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Electronic structure Fermi liquid theory of high T(sub c) superconductors: Comparison with experiments

For years, there has been controversy on whether the normal state of the Cu-oxide superconductors is a Fermi liquid or some other exotic ground state. However, some experimentalists are clarifying the nature of the normal state of the high T(sub c) superconductors by surmounting the experimental difficulties in producing clean, well characterized surfaces so as to obtain meaningful high resolved photoemission data, which agrees with earlier positron-annihilation experiments. The experimental work on high resolution angle resolved photoemission by Campuzano et al. and positron-annihilation studies by Smedskjaer et al. has verified the calculated Fermi surfaces in YBa2Cu3O7 superconductors and has provided evidence for the validity of the energy band approach. Similar good agreement was found for Bi2Sr2CaCu2O8 by Olson et al. As a Fermi liquid (metallic) nature of the normal state of the high T(sub c) superconductors becomes evident, these experimental observations have served to confirm the predictions of the local density functional calculations and hence the energy band approach as a valid natural starting point for further studies of their superconductivity.

Freeman, A. J.↗
NASA NTRS1991

Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state

The bismuth based high T sub c superconductors can be processed via an amorphous Bi-Pb-Sr-Ca-Cu oxide. The amorphous oxides were prepared by melting the constituent powders in an alumina crucible at 1200 C in air followed by pouring the liquid onto an aluminum plate, and rapidly pressing with a second plate. In the amorphous state, no crystalline phase was identified in the powder x ray diffraction pattern of the quenched materials. After heat treatment at high temperature the amorphous materials crystallized into a glass ceramic containing a large fraction of the Bi2Sr2Ca2Cu3O(x) phase T sub c = 110 K. The processing method, crystallization, and results of dc electrical resistivity and ac magnetic susceptibility measurements are discussed.

Chiang, C. K.↗
NASA NTRS1992

Interaction of atomic oxygen with thin film and bulk copper: An XPS, AES, XRD, and profilometer study

The University of Alabama in Huntsville (UAH) experiment A-0114 was designed primarily to study degradation of material surfaces due to low earth orbital (LEO) atmospheric oxygen. The experiment contained 128 one inch circular samples: metals, polymers, carbons, and semiconductors. Among metal samples, copper has shown some interesting new results. Two types of copper samples, a film sputter coated on fused silica and a bulk piece of OFHC copper, were characterized employing a variety of techniques such as X-ray and Auger electron spectroscopies, X-ray diffraction, and high resolution profilometry. Cu 2p core level spectra were used to characterize the presence of Cu2O and CuO in addition to Cu Auger LMM lines. These results are supported by our recent X-ray diffraction studies which clearly establish the presence of Cu oxides which we were unable to prove in our earlier work. Profilometry showed an increase in thickness of the film sample where exposed to 106.7 +/- 0.5 nm from an initial thickness of 74.2 +/- 1.1 nm. Further studies with SEM and ellipsometry are underway.

Raikar, Genesh N.↗
NASA NTRS1991

Crystal growth of YBa2Cu3O(7-x) and reaction of gold crucible with Ba-Cu-rich flux

YBa2Cu3O(7-x) crystals are grown in a gold crucible by a self-flux method. The flux moves along the gold surface due to surface wetting and leaves Y123 crystals behind. The obtained crystals are clean and have a size up to two millimeters and a Tc is greater than 90 K. In an effort to recycle the used crucibles, it is found that the used gold is contaminated by copper. A CuO thin film is easily formed on the surface of the crucible that is made of the used gold. This film provides good surface wetting and a buffer layer, which reduces the reaction between gold and the Y-Ba-Cu-oxide melt.

Tao, Y. K.↗
DOE OSTI2025

Cu‐Catalyzed Aerobic Oxidative C─C Cleavage in Lignin‐Derived Oligomers and Biological Funneling of the Monomeric Products

Existing methods for lignin deconstruction to aromatic monomers primarily cleave carbon–oxygen bonds within the polymer, resulting in sub-optimal monomer yields and formation of oligomers that retain intact carbon–carbon bonds. Here, we demonstrate that copper-catalyzed aerobic oxidation under aqueous alkaline conditions promotes oxidative cleavage of carbon–carbon bonds in lignin oligomers derived from reductive catalytic fractionation (RCF) of pine and poplar biomass. Fundamental insights are gained from reactions of model compounds that resemble subunits present in RCF oligomers. Optimal results are achieved in a flow reactor that provides precise control over O2 delivery, temperature, and reaction residence time. The Cu-catalyzed aerobic oxidation conditions access aromatic monomers in 19 and 34 wt% monomer yields, respectively, from pine- and poplar-derived RCF oligomers. Overall, the sequence consisting of biomass RCF into monomers and oligomers followed by oxidative deconstruction of the RCF oligomers generates substantially higher yields of aromatic monomers from lignin. Engineered strains of Pseudomonas putida support biological funneling of the oligomer-derived oxygenated aromatic compounds into cis,cis-muconic acid from pine or 2-pyrone-4,6-dicarboxylic acid from poplar.

09 BIOMASS FUELS↗
DOE OSTI2025

CeO 2 Promoted CuO/MgO-Al 2 O 3 Catalyst with Enhanced Activity and Water-Resistance for CO Oxidation

Copper (Cu)-based catalysts have emerged as cost-effective and sustainable alternatives to noble metal systems (e.g., Pt, Pd) for catalytic CO oxidation. However, their practical application is hindered by insufficient low-temperature activity and rapid deactivation under wet conditions containing moisture. To address these challenges, this work introduces CeO 2 -modified CuO/MgO-Al 2 O 3 (Cu-Ce/MA) catalysts, strategically designed to enhance the catalytic performance and water resistance simultaneously. These catalytic materials were evaluated for CO oxidation under both dry and humid conditions, revealing that CeO 2 modification significantly improves the low-temperature activity. Specifically, the optimal catalyst, Cu-30Ce/MA, achieved a 50% CO conversion temperature (T 50 ) of 151 °C, a marked reduction from 218 °C on Cu/MA reference catalyst. Furthermore, the water resistance improves in a CeO 2 content-dependent manner, with higher CeO 2 loadings imparting greater stability in humid environments. Detailed characterizations demonstrate that CeO 2 promotes the dispersion of CuO and stabilizes Cu sites, while also enhancing the low-temperature reducibility and CO adsorption capacity. Crucially, CeO 2 modification suppresses the competitive H 2 O adsorption, mitigating water-induced deactivation. These synergistic effects collectively rationalize the superior activity and durability of Cu-Ce/MA catalysts. By elucidating the dual role of CeO 2 in optimizing Cu-based systems, this study advances the rational design of cost-effective catalysts for real-world CO emission control, particularly under water-rich industrial conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

Ternary and quaternary oxides of Bi, Sr, and Cu

Before the discovery of superconductivity in an oxide of Bi, Sr, and Cu, the system Bi-Sr-Cu-O had not been studied, although several solid phases had been identified in the two-component regions of the ternary system Bi2O3-SrO-CuO. The oxides Sr2CuO3, SrCu2O2, SrCuO2, and Bi2CuO4 were then well known and characterized, and the phase diagram of the binary system Bi2O3 -SrO had been established in the temperature range 620 to 1000 C. Besides nine solutions of compositions Bi(2-2x) Sr(x) O(3-2x) and different symmetries, this diagram includes three definite compounds of stoichiometries Bi(2)SrO4, Bi2Sr2O5, and Bi2Sr3O6 (x = 0.50, 0.67 and 0.75 respectively), only the second of which with known unit-cell of orthorhombic symmetry, dimensions (A) a = 14.293(2), b = 7.651(2), c = 6.172(1), and z = 4. The first superconducting oxide in the system Bi-Sr-Cu-O was initially formulated as Bi2Sr2Cu2O(7+x), with an orthorhombic unit-cell of parameters (A) a = 5.32, b = 26.6, c = 48.8. In a preliminary study the same oxide was formulated with half the copper content, Bi(2)Sr(2)CuO(6+x), and indexed its reflections assuming an orthorhombic unit-cell of dimensions (A) a = 5.390(2), b = 26.973(8), c = 24.69(4). Subsequent studies by diffraction techniques have confirmed the composition 2:2:1. A new family of oxygen-deficient perovskites, was characterized, after identifying by x ray diffraction the phases present in the products of thermal treatments of about 150 mixtures of analytical grade Bi2O3, Sr(OH)2-8H2O and CuO at different molar ratios. X ray diffraction data are presented for some other oxides of Bi and Sr, as well as for various quaternary oxides, among them an oxide of Bi, Sr, and Cu.

Casais, M. T.↗
NASA NTRS1991

Ternary and quaternary oxides of Bi, Sr and Cu

Before the discovery of superconductivity in an oxide of Bi, Sr, and Cu, the system Bi-Sr-Cu-O had not been studied, although several solid phases had been identified in the two-component regions of the ternary system Bi2O3-Si-O-CuO. The oxides Sr2CuO3, SrCu2O2, SrCuO2, and Bi2CuO4 were then well known and characterized, and the phase diagram of the binary system Bi2O3-SrO had been established in the temperature range 620 to 1000 C. Besides nine solutions of compositions Bi(2-2x) Sr(x) O(3-2x) and different symmetries, this diagram includes three definite compounds of stoichiometries Bi(2)BrO4. Bi2Sr2O5, and Bi2Sr3O6 (x - 0.50, 0.67 and 0.75 respectively), only the second of which with known unit-cell of orthorhombic symmetry, dimensions (A) a = 14.293(2), b = 7.651(2), c = 6.172(1), and z = 4. The first superconducting oxide in the system Bi-Sr-Cu-O was initially formulated as Bi2Sr2Cu2O(7+x), with an orthorhombic unit-cell of parameters (A) a = 5.32, b = 26.6, c = 48.8. In a preliminary study the same oxide was formulated with half the copper content, Bi(2)Sr(2)CuO(6+x), and index its reflections assuming an orthorhombic unit-cell of dimensions (A) a = 5.390(2), b = 26.973(8), c = 24.69(4). Subsequent studies by diffraction techniques have confirmed the composition 2:2:1. A new family of oxygen-deficient perovskites, was characterized, after identifying by x ray diffraction the phases present in the products of thermal treatments of about 150 mixtures of analytical grade Bi2O3, Sr(OH)2-8H2O and CuO at different molar ratios. X ray diffraction data are presented for some other oxides of Bi and Sr, as well as for various quaternary oxides, among them an oxide of Bi, Sr, and Cu.

Casais, M. T.↗
DOE OSTI2025

Cu Evolution over Bimetallic Cu‐Y/Beta Zeolite Under H 2 and Ethanol Atmospheres: Unveiling the Role of Diatomic Metal–Metal Interactions

Understanding the dynamic evolution of Cu species under varying environmental conditions is critical for addressing challenges related to the activity and the stability of copper‐based catalysts in thermo‐, photo‐, and electrocatalysis. However, metal–metal interactions between dual single atoms and their effects on Cu evolution after exposure to different environmental molecules remain underexplored. Herein, we synthesized bimetallic Cu‐Y/Beta catalysts with dual single‐atom Cu and Y sites and monometallic Cu‐Beta catalysts with isolated Cu sites in dealuminated Beta zeolites. By varying Cu and Y compositions, diatomic interactions were studied under H 2 and ethanol atmospheres. With 6 wt% Y loading, approximately 0.4 wt% of Cu species in Cu‐Y/Beta remained partially oxidized as Cu(I) after reduction in pure H 2 at 350 °C, in contrast to the full transition to metallic Cu observed in Cu‐Beta. Combining X‐ray absorption spectroscopy with kinetic studies revealed that metallic Cu became the predominant species after reduction with H 2 as Cu loading increased from 0.4 to 1.7 wt%, quadrupling the initial ethanol dehydrogenation rate and demonstrating the dominant role of Cu(0) sites. In conclusion, scanning transmission electron microscopy and density functional theory simulations indicated spatial proximity between dual single‐atom Cu and Y sites and elucidated Cu speciation controlled by diatomic interactions.

Copper↗
NASA NTRS2000

Oxidation Behavior of GRCop-84 (Cu-8Cr-4Nb) at Intermediate and High Temperatures

The oxidation behavior of GRCop-84 (Cu-8 at %Cr-4 at %Nb) has been investigated in air and in oxygen, for durations of 0.5 to 50 hours and temperatures ranging from 500 to 900 C. For comparison, data was also obtained for the oxidation of Cu and NARloy-Z (Cu-3 wt% Ag-0.5 wt% Zr) under the same conditions. Arrhenius plots of those data showed that all three materials had similar oxidation rates at high temperatures (> 750 C). However, at intermediate temperatures (500 to 750 C) GRCop exhibited significantly higher oxidation resistance than Cu and NARloy-Z. The oxidation kinetics of GRCop-84 exhibited a sharp and discontinuous jump between the two regimes. Also, in the high temperature regime GRCop-84 oxidation rate was found to change from a high initial value to a significantly smaller terminal value at each temperature, with progress of oxidation; the two different oxidation rates were found to correlate with a porous intial oxide and a dense final oxide, respectively.

Thomas-Ogbuji, Linus U.↗
DOE OSTI2026

In situ catalyst activation and regeneration enable energy-efficient high-current CO 2 reduction to ethanol-rich C 2+ mixtures

Electrochemical conversion of dissolved CO 2 in bicarbonate electrolytes, i.e., bicarbonate electrolysis, offers distinct advantages over gas diffusion electrode systems by enabling direct utilization of the CO 2 capture electrolyte while bypassing the energy-intensive CO 2 release step. However, bicarbonate electrolysis faces challenges such as CO 2 mass-transfer limitation, local pH-driven CO 2 depletion, and high cathodic potentials. The higher potential often causes catalyst surface reorganization, leading to a gradual loss of active sites and variations in selectivity during CO 2 reduction. Here, we report a directed, in situ activation and regeneration method that allows precatalysts to equilibrate under dynamic (pulsed) electrolysis conditions. We demonstrate in situ activation of a scalable Cu 2 O/Cu mesh that, under short-width (t = 4 s) pulsed electrolysis, provides stable mixed oxidation states of Cu, favoring the formation of an ethanol-rich crude mixture. The pulsed electrolysis waveform, consisting of six distinct segments, is tuned to form Cu + oxides, which are then reduced to generate local alkaline conditions favoring C–C coupling. This synergistic effect results in FEs of 73% for C2+ products and 39% for ethanol at an applied current density of −150 mA cm −2 and a cathodic potential of −1.45 V (vs. RHE). The overall half-cell energy efficiency is ∼30% for C 2+ products. The in situ Raman experiments confirm the role of pCO 2 R in dynamically regenerating Cu+-containing surface species during pulsed operation, thereby steering selectivity towards C 2+ products. A comprehensive multiscale, multiphysics model is developed to investigate the dynamic behavior of copper surface species (Cu, Cu + , and Cu 2+ ) and local microenvironmental conditions during the pCO 2 R. The results reveal that the coexistence of different copper oxidation states, especially the Cu+ intermediate, is critical in steering selectivity towards multicarbon (C 2+ ) products. The dynamic modulation of surface redox states via tailored pulsing strategies favors C–C coupling pathways by inducing localized alkaline conditions and stabilizing reactive intermediates. This work establishes a predictive modeling platform that links pulse waveform design with mechanistic insights into catalyst state evolution and product selectivity. Overall, this study provides valuable insights into the synergistic effect of in situ activation of pre-catalysts and pulsed electrolysis for higher selectivity towards C 2+ products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1988

Effects of oxidation and roughness on Cu contact resistance from 4 to 290 K

Knowledge of the factors influencing contact resistance is important for optimizing system design in cryogenic applications. In space cryogenics, indirect cooling of infrared components is the primary concern. The presence of bolted joints results in contact resistances which can dominate all other contributions to the overall heat transfer rate. Here, thermal and electrical contact resistances measured between 4 K and 290 K for a series of bolted OFHC Cu contacts are reported. Surface roughness is found to have little effect on the overall contact resistance within the experimental limits, while oxidation can increase the contact resistance by as much as a factor of 100. Thermal and electrical contact resistances measured on the same contact show that the contact resistance temperature dependence does not follow the bulk dependence. For example, the residual resistance ratio (RRR) of the OFHC Cu is 110, but for contacts made from this material, the RRR is about two.

Nilles, M. J.↗
DOE OSTI2025

The electrode–electrolyte interface of Cu via modulation excitation X-ray absorption spectroscopy

The development and application of modulation excitation X-ray absorption spectroscopy with sub-second resolution and better than 0.02% detection sensitivity unveils the kinetics of the anodic oxidation of Cu in bicarbonate electrolytes. Accessing the electrode–electrolyte interface under operating conditions and capturing time-resolved kinetics remain challenging in electrochemical studies. Copper's interfacial oxidation dynamics remain unclear despite extensive research. Modulation excitation X-ray absorption spectroscopy (ME-XAS) was used to probe Cu in 100 mM KHCO 3 with sub-second sensitivity, revealing that hydroxide forms 30 ± 10 ms before the appearance of Cu 2 O at positive potentials (0 to 0.5 V vs. RHE) near open-circuit conditions. From −0.4 to 0.8 V vs. RHE, hydroxide coverage reaches 49%, accompanied by a balanced presence of Cu( i ) and Cu( ii ) oxides. These insights into Cu interfacial redox behavior under intermittent renewable energy operation—relevant to CO 2 electrolyzer durability—enhance our fundamental understanding of electrochemical interfaces.

Garcia-Esparza, Angel T↗
DOE OSTI2025

Mechanism of O 2 Activation and Cysteine Oxidation by the Unusual Mononuclear Cu(I) Active Site of the Formylglycine-Generating Enzyme

The formylglycine-generating enzyme (FGE) catalyzes the selective oxidation of a peptidyl-cysteine to form formylglycine, a critical cotranslational modification for type I sulfatase activation and a useful bioconjugation handle. Previous studies have shown that the substrate peptidyl-cysteine binds to the linear bis-thiolate Cu(I) site of FGE to form a trigonal planar tris-thiolate Cu(I) structure that activates O 2 for the oxidation of the C β –H of the cysteine substrate via an unknown mechanism. Here, we employed a combination of stopped-flow kinetic, spectroscopic (UV–vis absorption, XAS, and EPR), and computational (DFT/TD-DFT calculations) methods to observe and characterize the key intermediates in this reaction for FGE from Streptomyces coelicolor. Our results define the reaction coordinate of FGE, which involves H-atom abstraction from the C β –H bond of the cysteine substrate by a reactive Cu(II)–O 2 •– species to form the now experimentally observed Cu(I)–OOH intermediate bound to a peptidyl-thioaldehyde, which proceeds to oxidize one of the protein-derived cysteine residues to a sulfenate that is end-on O-coordinated to Cu(I). These results provide fundamental insights into how the unusual mononuclear Cu(I) site of FGE activates O 2 for cysteine oxidation and stores oxidizing equivalents during catalysis by employing a Cu(I)–sulfenate intermediate with an end-on O-coordination that is unprecedented in biology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Shapeshifting Nanocatalyst for CO2 Conversion

The conversion of CO2 into high-value chemicals through a photoreduction reaction in water is a promising route to reduce the dependence on fossil fuels. Enhancing selectivity toward hydrocarbons or alcohols can be achieved by Ag-Cu alloys. However, the stabilized surface state created by Ag-Cu interactions is still poorly understood. In this work, multi-modal in situ X-ray experiments reveals underlying mechanisms and the evolution of Ag-Cu nanoparticles under CO2 reduction reaction (CO2RR) conditions. Both morphological and chemical changes of Ag and Cu species induced by diffusion mechanics are tracked during nanocatalyst operation. The initial spheroid Ag-Cu nanoparticles are composed of a Cu-rich shell and Ag-rich core. The reduction treatment promotes Ag migration toward the surface. During photocatalytic CO2 reduction reaction, Cu atoms migrate back to the surface, forming Ag-Cu-O species. The study observes the surface oxidation of Cu(0) to Cu+ and the presence of Ag at the sub-surface region. Furthermore, nanoparticles change their shape, decreasing their specific surface area, driven by Cu diffusion during the CO2 photoreduction reaction. The results provide invaluable insights into the dynamic restructuring of the catalyst under reaction conditions and into the active species responsible for CO2 conversion.

CO2 reduction reaction↗