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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Investigating the Role of Copper in Arsenic Doped Cd(Se,Te) Photovoltaics

The open circuit voltage (VOC) deficit in Cd(Se,Te)-based photovoltaics remains a critical obstacle for pushing the technology closer to theoretical performance limits. Arsenic doping has become a dominant and promising route to achieve the higher p-type carrier concentrations necessary for higher VOC, but challenges associated with this alternate defect chemistry and higher doping density have hindered progress. Here we show that while arsenic doping enables high carrier concentrations (>1016 cm-3), co-doping with copper can provide a boost to VOC without a significant change to carrier concentration. A large data set is initially used to explore current-voltage and capacitance-voltage trends associated with arsenic doped devices with and without copper. A smaller subset is then used to probe these trends using a wide variety of characterization techniques. Copper is found to facilitate reduced interface recombination and potentially improved bulk absorber characteristics, though the mechanisms for these improvements are not yet clear. Despite the improved performance of co-doped devices, VOC is still far below its potential especially for highly doped devices. Low emitter doping in conjunction with high absorber doping seems to be a plausible cause for this significant deficit, though other device properties may exacerbate this problem.

CdSeTe↗
DOE OSTI2017

Neutron and Atomic Resolution X-ray Structures of a Lytic Polysaccharide Monooxygenase Reveal Copper-Mediated Dioxygen Binding and Evidence for N-Terminal Deprotonation

A 1.1 Å resolution, room-temperature X-ray structure and a 2.1 Å resolution neutron structure of a chitin-degrading lytic polysaccharide monooxygenase domain from the bacterium Jonesia denitrificans (JdLPMO10A) show a putative dioxygen species equatorially bound to the active site copper. We found that both structures show an elongated density for the dioxygen, most consistent with a Cu(II)-bound peroxide. The coordination environment is consistent with Cu(II). Furthermore, in the neutron and X-ray structures, difference maps reveal the N-terminal amino group, involved in copper coordination, is present as a mixed ND 2 and ND – , suggesting a role for the copper ion in shifting the pK a of the amino terminus.

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

Two-Dimensional Copper Iodide-Based Inorganic–Organic Hybrid Semiconductors: Synthesis, Structures, and Optical and Transport Properties

A group of copper iodide-based hybrid semiconductors with the general formula of 2D-CuI(L) 0.5 (L = organic ligands) are synthesized and structurally characterized. All compounds are two-dimensional (2D) networks made of one-dimensional (1D) copper iodide staircase chains that are interconnected by bidentate nitrogen-containing ligands. Results from optical absorption and emission experiments and density functional theory (DFT) calculations reveal that their photoluminescence (PL) can be systematically tuned by adjusting the lowest unoccupied molecular orbital (LUMO) energies of the organic ligands. Charge carrier transport measurements were carried out for the first time on single crystals of selected 2D-CuI(L) 0.5 structures, and the results show that they possess p-type conductivity with a Hall mobility of ~1 cm 2 V -1 s -1 for 2D-CuI(pm) 0.5 and 0.13 cm 2 V -1 s -1 for 2D-CuI(pz) 0.5 , respectively. These values are comparable to or higher than the mobilities of typical highly luminescent organic semiconductors. Finally, this work suggests that robust, high-dimensional copper iodide hybrid semiconductors are promising candidates to be considered as a new type of emissive layer for light-emitting diode (LED) devices.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Remote Stabilization of Copper Paddlewheel Based Molecular Building Blocks in Metal-Organic Frameworks

Copper paddlewheel based molecular building blocks (MBBs) are ubiquitous and have been widely employed for the construction of highly porous metal–organic frameworks (MOFs). However, most copper paddlewheel based MOFs fail to retain their structural integrity in the presence of water. This instability is directly correlated to the plausible displacement of coordinating carboxylates in the copper paddlewheel MBB, [Cu₂(O₂C-)₄], by the strongly coordinating water molecules. In this comprehensive study, we illustrate the chemical stability control in the rht-MOF platform via strengthening the coordinating bonds within the triangular inorganic MBB, [Cu₃O(N 4–x (CH) x C-)₃] (x = 0, 1, or 2). Remotely, the chemical stabilization propagated into the paddlewheel MBB to afford isoreticular rht-MOFs with remarkably enhanced water/chemical stabilities compared to the prototypal rht-MOF-1.

Gao, Wen-Yang↗
DOE OSTI2018

Formation and Ripening of Self-Assembled Multilayers from the Vapor-Phase Deposition of Dodecanethiol on Copper Oxide

Here, the vapor-phase reaction of dodecanethiol (DDT) with copper oxide surfaces and the molecular level composition and structure of the resulting films were examined. Atomic force microscopy, cross-sectional transmission electron microscopy, and electron energy loss/electron dispersive spectroscopy reveal that, instead of forming self-assembled monolayers, DDT etches CuO surfaces to create ~8 nm thick Cu-thiolate multilayers. These layers are composed of surprisingly well-ordered crystallites, oriented either parallel or perpendicular to the substrate surface. Pre-etching of the CuO to expose the underlaying copper metal is shown to prevent the formation of multilayers and instead allow for the formation of the expected monolayers. Water contact angle and Fourier transform infrared spectroscopy are further shown to be ineffective at distinguishing the multilayer and monolayer thiol films. Interestingly, the multilayer films are unstable in air, ripening into particles 20 μm wide and several hundred nanometers tall over the course of a week. Air exposure also leads to the slow oxidation of the sulfur and copper within the films at a rate similar to what has been seen before for DDT monolayers. As a result, the multilayers show no significant improvement over monolayers in the prevention of oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Rational Design of Metalorganic Complexes for the Deposition of Solid Films: Growth of Metallic Copper with Amidinate Precursors

A fourth-generation copper metalorganic compound, Cu(I)-2-(tert-butylimino)-5,5,-dimethylpyrrolidinate, was designed, and its chemistry on nickel surfaces characterized, for use as a precursor for the atomic layer deposition (ALD) of thin solid metal films. On the basis of surface-science studies with similar acetamidinate, guanidinate, and iminopyrrolidinate complexes, it was concluded that the high (and undesirable) reactivity of those when adsorbed on metal surfaces is due to the lability of their C–N bonds, which can be triggered by β-hydrogen elimination steps. Accordingly, a ligand was designed without any available hydrogen atoms at those positions. The result is a much more stable reactant. Temperature programed desorption (TPD) experiments indicated that dehydrogenation from the new compound on Ni(110) starts only at 450 K, an increase of about 200 K in comparison with any of the earlier-generations ALD precursors. TPD and X-ray photoelectron spectroscopy (XPS) data were used to establish the details of the decomposition mechanism of the ligands, which appears to be initiated by the scission of the imino-pyrrolidine C–N bond. Many byproducts are produced, including HCN, N 2 , iso-butene, and possibly pyrroline and other olefins such as pentenes. However, all of that occurs at relatively high temperatures, leaving an acceptable temperature window for the use of this complex for the deposition of copper films. An increased stability of the new ligands in our new copper ALD precursor was also observed on SiO 2 thin films, attesting to the generality of our conclusions. We suggest that our methodology for the rational design of this ALD precursor, based on studies of its surface chemistry, can be easily extended to other cases.

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

Nanomolar Copper Enhances Mercury Methylation by Desulfovibrio desulfuricans ND132

Methylmercury (MeHg) is produced by certain anaerobic microorganisms, such as the sulfate-reducing bacterium Desulfovibrio desulfuricans ND132, but environmental factors affecting inorganic mercury [Hg(II)] uptake and methylation remain unclear. We report that the presence of a small amount of copper ions [Cu(II), <100 nM] enhances Hg(II) uptake and methylation by washed cells of ND132, while Hg(II) methylation is inhibited at higher Cu(II) concentrations because of the toxicity of copper to the microorganism. The enhancement or inhibitory effect of Cu(II) is dependent on both time and concentration. The presence of nanomolar concentrations of Cu(II) facilitates rapid uptake of Hg(II) (within minutes) and doubles MeHg production within a 24 h period, but micromolar concentrations of Cu(II) completely inhibit Hg(II) methylation. Metal ions such as zinc [Zn(II)] and nickel [Ni(II)] also inhibit but do not enhance Hg(II) methylation under the same experimental conditions. Furthermore, these observations suggest a synergistic effect of Cu(II) on Hg(II) uptake and methylation, possibly facilitated by copper transporters or metallochaperones in this organism, and highlight the fact that complex environmental factors affect MeHg production in the environment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Sterically Encumbered Heteroleptic Copper(I) β-Diketiminate Complexes with Extended Excited-State Lifetimes

One of the main challenges in developing effective copper(I) photosensitizers is their short excited-state lifetimes, usually attributed to structural distortion upon light excitation. We have previously introduced copper(I) charge-transfer chromophores of the general formula Cu(N^N)(ArNacNac), where N^N is a conjugated diimine ligand and ArNacNac is a substituted β-diketiminate ligand. These chromophores were promising regarding their tunable redox potentials and intense visible absorption but were ineffective as photosensitizers, presumably due to short excited-state lifetimes. Here, we introduce sterically crowded analogues of these heteroleptic chromophores with bulky alkyl substituents on the N^N and/or ArNacNac ligand. Structural analysis was combined with electrochemical and photophysical characterization, including ultrafast transient absorption (UFTA) spectroscopy to investigate the effects of the alkyl groups on the excited-state lifetimes of the complexes. The molecular structures determined by single-crystal X-ray diffraction display more distortion in the ground state as alkyl substituents are introduced into the phenanthroline or the NacNac ligand, showing smaller τ 4 values due to the steric hindrance. UFTA measurements were carried out to determine the excited-state dynamics. Sterically encumbered Cu5 and Cu6 display excited-state lifetimes 15–20 times longer than unsubstituted complex Cu1, likely indicating that the incorporation of bulky alkyl substituents inhibits the pseudo-Jahn–Teller (PJT) flattening distortion in the excited state. Furthermore, this work suggests that the steric properties of these heteroleptic copper(I) charge-transfer chromophores can be readily modified and that the excited-state dynamics are strongly responsive to these modifications.

14 SOLAR ENERGY↗
DOE OSTI2025

Etch Products of Copper Atomic Layer Etching by Oxidation and Formic Acid Vapor

Atomic layer etching (ALE) of metals offers a path to greater control of selectivity, etch rate, and etch profile. However, tailoring a process to meet these demands requires an understanding of the volatile etch product, which is challenging to detect due to low product concentrations and the paramagnetism of many metalorganic products. Here, in this work, several complementary analysis techniques were used to determine the volatile etch product and residual surface species of a Cu ALE process based on plasma oxidation and formic acid vapor etching of the oxidized layer. It was shown that the volatile product was copper formate with a Cu 2+ paramagnetic center, in concordance with prior density functional theory (DFT) calculations. While copper formate tetrahydrate was formed, it was determined that the tetrahydrate product was confined to the surface, with anhydrous copper formate being the volatile etch product.

Smith, Taylor G. [Univ. of California, Los Angeles↗
DOE OSTI2017

Optimizing C–C Coupling on Oxide-Derived Copper Catalysts for Electrochemical CO 2 Reduction

Here, copper electrodes, prepared by reduction of oxidized metallic copper, have been reported to exhibit higher activity for the electrochemical reduction of CO 2 and better selectivity toward C 2 and C 3 (C 2+ ) products than metallic copper that has not been preoxidized. We report here an investigation of the effects of four different preparations of oxide-derived electrocatalysts on their activity and selectivity for CO 2 reduction, with particular attention given to the selectivity to C 2+ products. All catalysts were tested for CO 2 reduction in 0.1 M KHCO 3 and 0.1 M CsHCO 3 at applied voltages in the range from –0.7 to –1.0 V vs RHE. The best performing oxide-derived catalysts show up to ~70% selectivity to C 2+ products and only ~3% selectivity to C 1 products at –1.0 V vs RHE when CsHCO 3 is used as the electrolyte. In contrast, the selectivity to C 2+ products decreases to ~56% for the same catalysts tested in KHCO 3 . By studying all catalysts under identical conditions, the key factors affecting product selectivity could be discerned. These efforts reveal that the surface area of the oxide-derived layer is a critical parameter affecting selectivity. A high selectivity to C 2+ products is attained at an overpotential of –1 V vs RHE by operating at a current density sufficiently high to achieve a moderately high pH near the catalyst surface but not so high as to cause a significant reduction in the local concentration of CO 2 . On the basis of recent theoretical studies, a high pH suppresses the formation of C 1 relative to C 2+ products. At the same time, however, a high local CO 2 concentration is necessary for the formation of C 2+ products.

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

Nature and Distribution of Stable Subsurface Oxygen in Copper Electrodes During Electrochemical CO 2 Reduction

Oxide-derived copper (OD-Cu) electrodes exhibit higher activity than pristine copper during the carbon dioxide reduction reaction (CO 2 RR) and higher selectivity toward ethylene. The presence of residual subsurface oxygen in OD-Cu has been proposed to be responsible for such improvements, although its stability under the reductive CO 2 RR conditions remains unclear. This work sheds light on the nature and stability of subsurface oxygen. Our spectroscopic results show that oxygen is primarily concentrated in an amorphous 1–2 nm thick layer within the Cu subsurface, confirming that subsurface oxygen is stable during CO 2 RR for up to 1 h at –1.15 V vs RHE. Besides, it is associated with a high density of defects in the OD-Cu structure. In conclusion, we propose that both low coordination of the amorphous OD-Cu surface and the presence of subsurface oxygen that withdraws charge from the copper sp- and d-bands might selectively enhance the binding energy of CO.

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

Is Subsurface Oxygen Necessary for the Electrochemical Reduction of CO 2 on Copper?

It has recently been proposed that subsurface oxygen is crucial for the adsorption and subsequent electroreduction of CO 2 on copper. Using density functional theory, we have studied the stability and diffusion of subsurface oxygen in single crystals of copper exposing (111) and (100) facets. Oxygen is at least 1.5 eV more stable on the surface than beneath it for both crystal orientations; interstitial sites are too small to accommodate oxygen. Here, the rate of atomic oxygen diffusion from one layer below a Cu(111) surface to the surface is 5 × 10 3 s –1 . Oxygen can survive longer in deeper layers, but it does not promote CO 2 adsorption there. Diffusion of subsurface oxygen is easier to the less-dense Cu(100) surface, even from lower layers (rate ≈ 1 × 107 s–1). Finally, once the applied voltage and dispersion forces are properly modeled, we find that subsurface oxygen is unnecessary for CO 2 adsorption on copper.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Copper-Intercalated Birnessite as a Water Oxidation Catalyst

Here, we report a synthetic method to increase the catalytic activity of birnessite toward water oxidation by intercalating copper in the interlayer region of the layered manganese oxide. Intercalation of copper, verified by XRD, XPS, ICP, and Raman spectroscopy, was accomplished by exposing a suspension of birnessite to a Cu + -bearing precursor molecule that underwent disproportionation in solution to yield Cu 0 and Cu 2+ . Electrocatalytic studies reflected that the Cu-modified birnessite exhibited an overpotential for water oxidation of ~490 mV (at 10 mA/cm 2 ) and a Tafel slope of 126 mV/decade compared to ~700 mV (at 10 mA/cm 2 ) and 240 mV/decade, respectively, for birnessite without copper. Impedance spectroscopy results suggested that the charge transfer resistivity of the Cu-modified sample was significantly lower than Cu-free birnessite, suggesting that Cu in the interlayer increased the conductivity of birnessite leading to an enhancement of water oxidation kinetics. Density functional theory calculations show that the intercalation of Cu 0 into a layered MnO 2 model structure led to a change of the electronic properties of the material from a semiconductor to a metallic-like structure. This conclusion from computation is in general agreement with the aforementioned impedance spectroscopy results. X-ray photoelectron spectroscopy (XPS) showed that Cu 0 coexisted with Cu 2+ in the prepared Cu-modified birnessite. Control experiments using birnessite that was decorated with only Cu 2+ showed a reduction in water oxidation kinetics, further emphasizing the importance of Cu 0 for the increased activity of birnessite. The introduction of Cu 0 into the birnessite structure also increased the stability of the electrocatalyst. At a working current of 2 mA, the Cu-modified birnessite took ~3 times longer for the overpotential for water oxdiation to increase by 100 mV compared to when Cu was not present in the birnessite.

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

Polysulfides capture-copper additive for long cycle life lithium sulfur batteries

Copper powder was introduced into the lithium sulfur battery system to capture intermediate polysulfides and Cu x S (x = 1 or 2) species was generated depending on the chain length of polysulfides. This phenomenon was verified by X-ray absorption near edge structure technique. The results indicated that copper can be oxidized to CuS by Li 2 S x (x ≥ 6), and a mixture of Cu 2 S and CuS was obtained when x ranges from 3 to 6. While Cu 2 S is eventually formed in the presence of Li 2 S 3 . After several cycles activation, the polysulfide-shuttle effect and self-discharge phenomenon which hinder the application of lithium sulfur batteries are found nearly eliminated Further experiments demonstrated that in the case of Cu 2 S generation, a high specific sulfur capacity of 1300 mAh g –1 could be delivered, corresponding to 77.6% sulfur utilization, while the Coulombic efficiency approximates around 100%. As a result, self-discharge experiment further demonstrated that polysulfides almost disappear in the electrolyte, which verified the polysulfide-capture capability of copper.

25 ENERGY STORAGE↗
DOE OSTI2018

Mechanism of CO 2 Reduction at Copper Surfaces: Pathways to C 2 Products

On the basis of constraints from reported experimental observations and density functional theory simulations, in this paper we propose a mechanism for the reduction of CO 2 to C 2 products on copper electrodes. To model the effects of an applied potential bias on the reactions, calculations are carried out with a variable, fractional number of electrons on the unit cell, which is optimized so that the Fermi level matches the actual chemical potential of electrons (i.e., the applied bias); an implicit electrolyte model allows for compensation of the surface charge so that neutrality is maintained in the overall simulation cell. Our mechanism explains the presence of the seven C 2 species that have been detected in the reaction, as well as other notable experimental observations. Furthermore, our results shed light on the difference in activities toward C 2 products between the (100) and (111) facets of copper. Finally, we compare our methodologies and findings with those in other recent mechanistic studies of the copper-catalyzed CO 2 reduction reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Single-Particle Emission Spectroscopy Resolves d-Hole Relaxation in Copper Nanocubes

Resolving the dynamics of photoexcited d-holes in metallic nanostructures is one step in the rational design of plasmonic photocatalysis. In this work, we track the creation and relaxation of charge carriers in catalytically important plasmonic copper nanocubes using single-particle spectroscopy. We show that interband transitions dominate the absorption and emission of 60–160 nm copper nanocubes, and in contrast to gold nanorods, the LSPR is less important to the emission. Furthermore, we uncover the plasmonic enhancement of emission hidden in ensemble measurements by resolving the size-dependent line shape and quantum yield. Quantum yield analysis reveals the energy dependence of d-hole lifetimes. We demonstrate that the effect of excitation energy on quantum yield is stronger in copper nanocubes than in gold nanocubes of equivalent size due to differences in the band structure and the probabilities of hole scattering. Finally, we establish that emission spectroscopy is useful to understand the physical chemistry of d-holes in plasmonic photocatalysts.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Atomically Dispersed Copper Sites in a Metal–Organic Framework for Reduction of Nitrogen Dioxide

Metal-organic framework (MOF) materials provide an excellent platform to fabricate single-atom catalysts due to their structural diversity, intrinsic porosity, and designable functionality. However, the unambiguous identification of atomically dispersed metal sites and the elucidation of their role in catalysis are challenging due to limited methods of characterization and lack of direct structural information. Here, we report a comprehensive investigation of the structure and the role of atomically dispersed copper sites in UiO-66 for the catalytic reduction of NO 2 at ambient temperature. The atomic dispersion of copper sites on UiO-66 is confirmed by high-angle annular dark-field scanning transmission electron microscopy, electron paramagnetic resonance spectroscopy, and inelastic neutron scattering, and their location is identified by neutron powder diffraction and solid-state nuclear magnetic resonance spectroscopy. The Cu/UiO-66 catalyst exhibits superior catalytic performance for the reduction of NO 2 at 25 °C without the use of reductants. A selectivity of 88% for the formation of N2 at a 97% conversion of NO 2 with a lifetime of >50 h and an unprecedented turnover frequency of 6.1 h-1 is achieved under nonthermal plasma activation. In situ and operando infrared, solid-state NMR, and EPR spectroscopy reveal the critical role of copper sites in the adsorption and activation of NO 2 molecules, with the formation of {Cu(I)···NO} and {Cu···NO 2 } adducts promoting the conversion of NO 2 to N 2 . This study will inspire the further design and study of new efficient single-atom catalysts for NO 2 abatement via detailed unravelling of their role in catalysis.

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

Lattice-Hydride Mechanism in Electrocatalytic CO 2 Reduction by Structurally Precise Copper-Hydride Nanoclusters

Copper electrocatalysts can reduce CO2 to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO2 reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as Cu32H20L12 (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO2 reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential. The HCOOH formation proceeds via the lattice-hydride mechanism: first, surface hydrides reduce CO2 to HCOOH product, and then the hydride vacancies are readily regenerated by the electrochemical proton reduction. DFT calculations further predict that hydrogen evolution is less competitive than HCOOH formation at the low overpotential. Confirming the predictions, electrochemical tests of CO2 reduction on the Cu32H20L12 cluster demonstrate that HCOOH is indeed the main product at low overpotential, while H2 production dominates at higher overpotential. The unique selectivity afforded by the lattice-hydride mechanism opens the door for further fundamental and applied studies of electrocatalytic CO2 reduction by copper-hydride nanoclusters and other metal nanoclusters that contain hydrides.

Tang, Qing↗