CuO Square Research Articles

Amorphous‐Confined Crystalline CuO Nanoflakes for Enhanced Ethylene Production from CO2 Electroreduction

AbstractThe electrocatalytic reduction of CO2 to high value‐added chemicals is one of the effective technologies to achieve the goal of carbon neutralization. However, highly selective production of hydrocarbon via electrochemical conversion of CO2 still has great challenges. Herein, a unique CuO phase composition is constructed that consists of rectangular nanoflakes possessing crystalline/amorphous structures by the facile strategy. Crystalline CuO square nanoblocks are confined in amorphous nanoflakes and form crystalline/amorphous hybrid phase. The results of electrocatalytic CO2 reduction demonstrate that this crystalline/amorphous CuO material exhibits superior CO2 conversion ability with ethylene Faradaic efficiency of 58.3 % at −1.08 V vs. RHE, which is ascribed to nanoflake structures and fast electron transfer on the crystalline/amorphous interfaces because of superior conductivity of amorphous CuO. The present research provides an effective route to reconstruct novel crystalline/amorphous interfaces of CuO for catalysis applications.

Effect of Coordinatively Unsaturated Sites in MOF‐Derived Highly Porous CuO for Catalyst‐Free ppb‐Level Gas Sensors

AbstractHerein, the authors successfully synthesize diamond‐ and square‐type Cu‐metal–organic frameworks (MOFs) and then convert them to highly porous CuO nanostructures with maintaining their morphology. Both the CuO‐diamond (CuO‐D) and CuO‐square (CuO‐S) gas sensors can detect a tiny concentration of acetone gas up to 50 ppb. However, the gas sensitivity depends on the morphology and the CuO‐D exhibits a higher gas response (Rg/Ra: 3.3) for 1 ppm of acetone as compared with CuO‐S sensors (Rg/Ra: 2.5). The mainly exposed crystal facet on the surface significantly affects the sensor performance. Especially, coordinatively unsaturated metal sites in an exposed facet can allow enhancing the sensitivity. The (111) facet is the main exposed facet of CuO‐D and it includes Cu3‐fold which is a coordinatively unsaturated metal site. These relatively unstable Cu3‐fold sites are favorable to react with other molecules to stabilize themselves as compared with coordinatively saturated Cu4‐fold. Thus, CuO‐D demonstrates higher sensitivity as compared to CuO‐S, which is the main reaction surface as (020) facet composed only of Cu4‐fold.

Ultrasound assisted quick synthesis of square-brick-like porous CuO and optical properties

Square-brick-like CuC2O4 intermediate was synthesized quickly by an ultrasound and microwave assisted solution route in the presence of sodium dodecyl benzene sulfonate (SDBS) surfactant using CuCl2 and K2C2O4 as raw materials. The CuC2O4 was transformed into CuO with a preserved morphology by heating at 300°C for 2h. The products were characterized by XRD, TG-DTA, XPS, SEM, TEM, HRTEM and N2 adsorption–desorption measurement. The light harvesting capability, photoluminescence and surface photovoltage properties of the CuO were investigated. The width and thickness of the obtained porous CuO square bricks are ca. 0.5–1μm and 200nm, respectively. Its average primary particle size is 12nm. The formation mechanism of this square-brick-like CuO was investigated on the basis of series of controlling experiments. The results show that SDBS, C2O42− and ultrasonic processing play important roles in the formation of this square-brick-like morphology.

Structural units of cuprates in natural Cu-oxysalts.

The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme developed earlier for synthetic cuprates. The copper-oxygen compounds were considered as the salts of hypothetical copper acids with characteristic Cu-containing structural units of various dimensions formed by a polymerization of the CuO squares. The results of magnetic susceptibility measurements performed recently were analyzed from the viewpoint of the developed extended structural classification scheme. The dimerization of magnetic moments was considered as a property of cuprates which was strongly dependent on the type of Cu-containing structural unit. A further extension of the structural classification scheme for cuprates is also discussed.

Layered Cuprates

AbstractLayered copper-oxide superconductors exhibit the highest critical transition temperatures of any materials. Yet all of the known double perovskites A′A″B′B″O6 containing copper have a random or rock salt distribution of the B cations with the exception of the unique layered arrangement found in La2CuSnO6. Only the layered arrangement contains the CuO22- planes which are necessary for high-temperature superconductivity. The occurrence of layered or two dimensional structures increases markedly when vacancies are introduced on the oxygen sublattice, as evidenced in Ln2AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4). Similarities among oxygen-deficient structures, especially those with two-dimensional solid-state features, are discussed. Combined conductivity and thermopower analysis are presented to elucidate their unique internal chemistry, defect structure, and conduction parameters. In particular, data for La2-xSrxCuSnO6 are presented and related to the crystal chemistry of the copper-oxygen layer. These data are compared with La2Ba2Cu2Sn2O11 and La2Ba2Cu2Ti2O11 to illustrate the significance of oxygen vacancies on the properties of the copper oxygen planes. New layered cuprates are discussed including the mixed A-site stoichiometries Ln′Ln″AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4) which contain the smaller lanthanide (Ln″) ordered between the closely spaced, facing sheets of Cu-O square pyramids.

Intermediate steps in YBa2Cu3O7?x synthesis by sol-gel method: YBaCuO oxycarbonate

High T c -superconducting powders of the Y-Ba-Cu-O system are prepared by a solution-polyacrylamide gel using citric acid as a complexing agent. This method provides an easy way to prepare reactive YBaCuO powders by sol-gel synthesis. However this synthesis involves intermediate phases formation which impedes the obtention of the pure phase at low temperature. An intermediate oxycarbonate phase forms between 800° and 850°C in flowing oxygen. From powder X-ray diffraction, thermal analysis and IR spectroscopy, it is concluded that the intermediate oxycarbonate has an average tetragonal structure—SG P4/mmm—similar to that of the parent oxide with a stoichiometry close to YBa2Cu2.95(CO3)0.35O6.6. The carbonate group is located in the center of the basal CuO square. This compound has superconducting properties. A pure 123 phase is obtained when the xerogel precursor is annealed at 925°C in O2 or at 800°C in Ar, then in O2. The grain growth and microstructure development of YBaCuO have also been investigated and compared using two different powders, i.e. sol-gel route and commercial powder from Hoechst.

Synthesis of YBa 2Cu 3O 7−x by sol-gel route formation of YBaCuO oxycarbonate intermediate

High- T c superconducting powders of the Y-Ba-Cu-O system are prepared by a solution-polyacrylamide gel using citric acid as a complexing agent. This method provides an easy way to prepare reactive YBaCuO powders. However, sol-gel synthesis of this oxide involves the formation of intermediate phases which impedes the obtaining of the pure phase at low temperature. An intermediate oxycarbonate phase forms between 800 and 850°C in flowing oxygen. From powder X-ray diffraction, thermal analysis and IR spectroscopy, it is concluded that the intermediate oxycarbonate has an average tetragonal structure — SG P4/ mmm — similar to the parent oxide with a stoichiometry close to YBa 2Cu 2.95(CO 3) 0.35O 6.6. The carbonate group is located in the center of the basal CuO square. This compound has superconducting properties. A pure 123 phase is obtained when the sol-gel precursor is annealed at 925°C in O 2.

Mössbauer study of quadrupole interaction at the different Cu sites in the Bi-system superconductor

57Fe Mössbauer measurements have been performed on Fe-doped samples of Bi 1.6Pb 0.4Sr 2Ca 3Cu 4- x Fe x O y ( x=0.06 and 0.08) at room temperature. The Mössbauer spectra show three quadrupole doublets that can be related to different Cu sites. Two doublets (B and C) with larger quadrupole splitting (QS) are assigned with a 57Fe probe atom on the Cu-O square planar sites of the compound with different local charge environments. Another doublet A with smallest quadrupole splitting is associated with a Fe atom in a planar pyramid site. the doublet with smallest QS possesses relatively the smaller area indicating that the Fe atom preferentially occupies a square planar site rather than a pyramid site. To assure our assignment, we calculated the EFG (electric field gradient) on different Cu sites with the use of the point charge model and of the calculation of an effective ions valence.

Crystal structure of nonsuperconducting Pb 2(Sr 0.94Nd 0.06) 2(Nd 0.76Sr 0.24)Cu 3O 8

The crystal structure of Pb 2(Sr 0.94Nd 0.06) 2(Nd 0.76Sr 0.24)Cu 3O 8 was determined by single crystal X-ray diffraction. The compound was found to be orthorhombic ( Cmmm) with a = 5.437(3), b = 5.472(2), c = 15.797(7)Å and Z = 2. In the structure double layers of CuO square pyramids are separated by (Nd, Sr) oxygen deficient layers which are stacked between (PbO)Cu(PbO) slabs. The oxygen in the Pb planes is shifted toward a pair of Pb atoms resulting in an orthorhombic distortion of the tetragonal unit cell. The possibilities for modulations and superlattices are discussed as is the role of the PbO planes in superconductivity.

Nuclear quadrupole resonance of [formula omitted]Cu in the 2223 phase of Tl-Ba-Ca-Cu-O and (Bi, Pb)-Sr-Ca-Cu-O

Nuclear quadrupole resonance (NQR) of 63 65 Cu is observed in the 2223-phase of Tl 2Ba 2Ca 2Cu 2O 10 ( T c=121 K) and (Bi 1.6Pb 0.4)Sr 2Ca 2Cu 3O 10 ( T c=110 K). The electric quadrupole interactions at two Cu sites (in the Cu-O pyramid and in the Cu-O square plane) are distinguished and are compared with those in other T c superconductors.

Electron and hole doping in Nd-based cuprates with single-layer CuO2 sheets: Role of doped Ce ions and 30-K superconductivity.

We have attempted electron and hole doping in Nd-based cuprates with single-layer sheets of Cu-O squares and pyramids. It was found that partial substitution of Nd/sup 3+/ sites with Ce/sup 4+/ ions introduces mobile electrons into the Nd/sub 2/CuO/sub 4/ structure which shows two-dimensional (2D) sheets of Cu-O squares with no apical oxygens. With further Sr doping into Nd/sub 2-//sub x/Ce/sub x/CuO/sub 4/, the crystalline lattice undergoes a structural transformation into the new hole-conductive compound with 2D sheets of Cu-O pyramids, which is identical with the superconducting phase discovered recently by Akimitsu et al. The hole concentration in Nd/sub 2-//sub x//sub -//sub y/ Ce/sub x/Sr/sub y/CuO/sub 4-//sub delta/ can be increased by controlling the composition (x,y) of non-copper cations and filling oxygen vacancies (delta) as well, which give rise to superconductivity with T/sub c/ up to 30 K.

Superconductivity produced by electron doping in CuO2-layered compounds.

We have discovered that the Ce4+doping and subsequent annealing in reducing atmosphere give rise to 24-K superconductivity in the Nd2CuO4-type structure with sheets of Cu-O squares. In contrast to the previously reported high-Tccuprates, the charge carriers in the new superconductors are doped electrons, not holes; this was confirmed by the measurements of Hall and Seebeck coefficients as well as by chemical analysis of the effective copper valence. An anomalous dependence ofTcon the concentration of doped electrons is shown for these electron-doped superconducting cuprates.