CuO nanostructures: Synthesis, characterization, growth mechanisms, fundamental properties, and applications

The Colloid Chemical Approach to Nanostructured Materials

Emerging electrosynthetic techniques such as electrogeneration of base, anodic oxidation, and ac (alternating current) synthesis provide simple and inexpensive alternative routes to the synthesis of ceramic thin films and coatings, nanoparticulate materials, and metastable phases. In this review, we survey illustrative examples to highlight the potential application of these techniques in meeting the goals of inorganic solid-state synthesis.

Electrochemical Synthesis of Metal Oxides and Hydroxides

A simple and efficient approach is developed for the synthesis of copper oxide nanorods with different morphology and crystallographic structure. Polycrystalline fine rods 10−20 nm thick and several hundred nanometers long and single crystalline thick rods 60−100 nm thick and up to 1 μm long were obtained from the reactions of copper hydrate with caustic soda solution at room temperature and 100 °C, respectively. The fine CuO nanorods as anode materials for Li ion battery exhibit a high electrochemical capacity of 766 mA h/g and relatively poor capacity retention as compared to thick nanorods with the single crystalline structure. The correlation between the structural features of the nanorods and their electrode performance is discussed in detail.

Preparation and Electrochemical Performance of Polycrystalline and Single Crystalline CuO Nanorods as Anode Materials for Li Ion Battery

Spherical cerium oxide nanoparticles and microsized rod-shaped and spindle-like CeO2 structures have been synthesized using a polyol method. When the duration of reaction and the concentration of cerium precursor are controlled, CeO2 products of different morphologies can be selectively produced. Results from XRD, XPS, SEM, and FT-IR measurements suggest that the CeO2 nanospheres are formed from the decomposition of the cerium precursor. Further reactions between the as-prepared CeO2 and ethylene glycol yield the rods/spindle-like cerium formate particles. These morphologies are preserved even after calcination. The order of band gap energy of these samples was found to be rod-shaped > spherical > spindle-like samples, as determined by the UV−Vis spectroscopic method. Compared to a nonoriented polycrystalline CeO2, these samples show an increase in band gap energy due to the quantum size effect. The higher catalytic activity on CO conversion in a spindle-like sample can be explained from the extent of Ce(...

Morphology-Controllable Synthesis of Mesoporous CeO2 Nano- and Microstructures

Electrochemical self-assembly of copper/cuprous oxide layered nanostructures

An electrochemical procedure is described for the anodic deposition of CuO thin films from solution precursors at 25-30°C in an alkaline medium (pH > 13). The deposition bath was similar to Fehling's solution using tartrate ions as a complexing agent for Cu(II). Cupric oxide deposited onto a platinum substrate at an anodic current density of 5 mA cm - 2 has a preferred orientation of [010]. Rietveld refinement of the powder diffraction pattern reveals pure Cu(II) oxide with no trace of other copper oxides. The suggested mechanism involves the irreversible electrochemical oxidation of the tartrate ligand of the Cu(II) complex leading to the CuO precipitation. The same bath can also be used to deposit Cu 2 O films using a cathodic electrodeposition process. In this case, cuprous oxide deposited onto a platinum electrode has a [111] preferred orientation.

https://iopscience.iop.org/article/10.1149/1.1535753/pdf

An Electrochemical Method for CuO Thin Film Deposition from Aqueous Solution

Layered nanostructures of copper metal and cuprous oxide are electrodeposited from alkaline solutions of Cu(II) lactate at room temperature. No subsequent heat treatment is necessary to effect crystallization. The electrode potential spontaneously oscillates during constant-current deposition. At a fixed current density the oscillation period decreases as either the pH or temperature is increased. The oscillations are periodic in stirred solution, but show period doubling and evidence of quasi-periodic or chaotic behavior in unstirred solution. The phase composition and resistivity of the films can be controlled by varying the applied current density. The resistivity of the films can be varied over ten orders of magnitude. Scanning electron microscopy shows that the films are layered.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400043612

Potential oscillations during the electrochemical self-assembly of copper/cuprous oxide layered nanostructures

Nanometer-scale layered structures based on thallium(III) oxide were electrodeposited in a beaker at room temperature by pulsing the applied potential during deposition. The conducting metal oxide samples were superlattices, with layers as thin as 6.7 nanometers. The defect chemistry was a function of the applied overpotential: High overpotentials favored oxygen vacancies, whereas low overpotentials favored cation interstitials. The transition from one defect chemistry to another in this nonequilibrium process occurred in the same potential range (100 to 120 millivolts) in which the rate of the back electron transfer reaction became significant. The epitaxial structures have the high carrier density and low electronic dimensionality of high transition temperature superconductors.

https://science.sciencemag.org/content/sci/264/5165/1573.full.pdf

Electrodeposited Defect Chemistry Superlattices

Thallium oxide is a degenerate n-type semiconductor which can be electrodeposited from aqueous solution at room temperature. Thin films were characterized by transmission and specular reflectance spectroscopy and by four-point resistivity and Hall measurements. Optical parameters were determined by fitting the observed specular reflectance to the Drude equation. Due to the high free carrier concentration, the material reflects strongly in the near-infrared, and the band-to-band optical transitions are shifted by up to 1.1 eV by the Moss-Burstein effect. The optical and electrical properties of the films were a function of the deposition overpotential. Films grown at 44 mV had an intrinsic bandgap of 0.66 eV, resistivity of 2.8 x 10{sup -4} ohm-cm, mobility of 27 cm{sup 2}Vs, and conduction band effective mass of 0.43m{sub o}. Films grown at 300 mV had an intrinsic band gap of 0.51 eV, resistivity of 7.8 x 10{sup -5} ohm cm, mobility of 93 cm{sup 2}V s, and conduction band effective mass of 0.29m{sub o}. Mobilities measured by contact and optical methods are similar, which shows the optical technique may be used for conditions in which contact methods might fail. 20 refs., 11 figs., 2 tabs.

Chen-Jen Hung

Papers

Electrochemical self-assembly of copper/cuprous oxide layered nanostructures

An Electrochemical Method for CuO Thin Film Deposition from Aqueous Solution

Potential oscillations during the electrochemical self-assembly of copper/cuprous oxide layered nanostructures

Electrodeposited Defect Chemistry Superlattices

Optical and Electronic Transport Properties of Electrodeposited Thallium(III) Oxide Films