CuO Nanowires Research Articles

Enhanced field emission of CuO nanowires by aluminum coating for volatile organic compound detection

This work reports-a novel ionization gas sensor assembled by the building blocks of CuO nanowires coated with a thin layer of aluminum. The superficial aluminum is then partially oxidized to alumina forming an Al2O3/Al/CuO hybrid nanocomposite. It is revealed that this nanocomposite enables the discharge of volatile organic compound at ppm level at an ultralow ionization voltage (several tens of volts) with high stability. Typical organic gases, including toluene, acetone, isopropanol, and methanol can be identified by this sensor with the specific threshold voltages in the cleanroom. In addition, the concentration of isopropanol gas has also been detected at a low limit down to 5 ppm. The gas sensing mechanism is due to the variation of voltages that are required to ionize a specific gas as the fingerprint. Based on the comparative discharge experiments along with the energy band analysis, the high enhancement of gas ionization is attributed to the optimized low work function and intermediate energy interlayer in combination with the tip effect of Al2O3, Al, and CuO. This work may pave a new way for the design of the similar material system to advance ionization gas sensing.

Hierarchical Structure of CuO Nanowires Decorated with Ni(OH)2 Supported on Cu Foam for Hydrogen Production via Urea Electrocatalysis.

Owing to the low theoretical potential of the urea oxidation reaction (UOR), urea electrolysis is an energy-saving technique for the generation of hydrogen. Herein, a hierarchical structure of CuO nanowires decorated with nickel hydroxide supported on 3D Cu foam is constructed. Combined theoretical and experimental analyses demonstrate the high reactivity and selectivity of CuO and Ni(OH)2 toward the UOR instead of the oxygen evolution reaction. The hierarchical structure creates a synergistic effect between the two highly active sites, enabling an exceptional UOR activity with a record low potential of 1.334V (vs the reversible hydrogen electrode) to reach 100mA cm-2 and a low Tafel slope of 14mV dec-1 in 1 m KOH and 0.5 m urea electrolyte. Assembling full urea electrolysis driven by this developed UOR electrocatalyst as the anode and a commercial Pt/C electrocatalyst as the cathode provides a current density of 20mA cm-2 at a cell voltage of ≈1.36V with promising operational stability for at least 150 h. This work not only enriches the UOR material family but also significantly advances energy-saving hydrogen production.

The Synergetic Effect Induced High Electrochemical Performance of CuO/Cu2O/Cu Nanocomposites as Lithium-Ion Battery Anodes.

Due to the high theoretical capability, copper-based oxides were widely investigated. A facile water bath method was used to synthesis CuO nanowires and CuO/Cu2O/Cu nanocomposites. Owing to the synergetic effect, the CuO/Cu2O/Cu nanocomposites exhibit superior electrochemical performance compared to the CuO nanowires. The initial discharge and charge capacities are 2,660.4 mAh/g and 2,107.8 mAh/g, and the reversible capacity is 1,265.7 mAh/g after 200 cycles at 200 mA/g. Moreover, the reversible capacity is 1,180 mAh/g at 800 mA/g and 1,750 mAh/g when back to 100 mA/g, indicating the excellent rate capability. The CuO/Cu2O/Cu nanocomposites also exhibit relatively high electric conductivity and lithium-ion diffusion coefficient, especially after cycling. For the energy storage mechanism, the capacitive controlled mechanism is predominance at the high scan rates, which is consistent with the excellent rate capability. The outstanding electrochemical performance of the CuO/Cu2O/Cu nanocomposites indicates the potential application of copper-based oxides nanomaterials in future lithium-ion batteries.

Structural and Compositional Investigations on the Stability of Cuprous Oxide Nanowire Photocathodes for Photoelectrochemical Water Splitting.

Cuprous oxide (Cu2O) is a promising photocathode material for photoelectrochemical (PEC) water splitting. Recently, the PEC performances of Cu2O-based devices have been considerably improved by introducing nanostructures, semiconductor overlayers, and hydrogen evolution reaction (HER) catalysts. However, Cu2O devices still suffer from poor stability in aqueous solution, especially in strong acidic or alkaline conditions, despite the use of an intrinsically stable oxide overlayer as a protection layer. Thus, it is essential to fully understand the stability of the entire Cu2O photocathodes in these conditions for establishing suitable protection strategies to achieve durable PEC water splitting. In this work, the stability of bare and protected Cu2O nanowire (NW) photocathodes was evaluated in detail using microscopy techniques and compositional analyses. The insights gained in this work will guide the design and synthesis of durable photoelectrodes for PEC water splitting.

Photoelectrocatalytic Reduction of CO2 to Syngas via SnOx‐Enhanced Cu2O Nanowires Photocathodes

AbstractPhotoelectrochemical (PEC) reduction of CO2 with H2O into syngas is an effective way to relieve the greenhouse effect and produce valuable chemicals. In this study, controllable PEC reduction of CO2 with H2O to syngas is achieved by the Cu2O‐SnOx hybrid nanowires (NWs) photocathode, which can effectively produce the mixture of syngas (CO and H2) with a total Faradaic efficiency of 90.32% at −0.35 V versus RHE. In addition, the CO/H2 ratio of syngas can be adjusted in a wide range from 2.2:1 to 4.6:1. The investigations of linear sweep voltammetry, incident photon to current efficiency, electrochemical impedance spectroscopy, and temperature programmed desorption indicate that the charge transfer efficiency and CO2 adsorption capacity are highly enhanced by the electrodeposition of SnOx on the Cu2O NWs electrode. In situ diffuse reflectance Fourier transformed infrared spectroscopy spectra results indicate that visible light irradiation can accelerate the accumulation of CO2 reduction intermediates and thus facilitate the release of CO. This study provides an available way for the rational development of high‐performance PEC systems for CO2 reduction to valuable carbon‐based compounds, as well as a new strategy for atmospheric CO2 treatment.

Efficient UV–visible photodetector based on single CuO/Cu2O core-shell nanowire

One-dimensional nanostructures such as nanowires show better photoresponse than that of their bulk counterparts because of unidirectional transport that significantly reduces recombination and scattering of photo-generated charge carriers. CuO and Cu2O are relatively abundant transition metal oxides with optical band gaps suitable for efficient detection of UV and visible radiation. In addition, they form type-II heterojunction for efficient charge separation. Here, we report the fabrication of CuO/Cu2O core-shell nanowire arrays by chemical bath deposited Cu2O layer over thermally grown CuO nanowires. Photodetector devices based on individual CuO and CuO/Cu2O core-shell nanowire are fabricated through photolithography using Pd metal contact for studying response under UV and visible light illumination. Core-shell nanostructures show better performance in terms of responsivity, detectivity, external quantum efficiency, faster response, and recovery times over that of bare CuO nanowires. This is attributed to the Ohmic junction formed at the Pd-Cu2O interface that ensures barrierless hole transport for the core-shell photodetector. Further, the type-II heterojunction formed at CuO/Cu2O interface enhances hole concentration in the Cu2O shell layer, which is responsible for better photoresponse in core-shell nanostructures. The results establish that CuO/Cu2O core-shell nanowires offer simplified design and highly efficient photodetectors that can be used in several optoelectronic devices.

Atomic bonding-engineered heterogeneous integration of semiconductor nanowires by femtosecond laser irradiation for a miniaturized photodetector

Heterogeneous integration of semiconductor nanowires (NWs) incorporating the advantages of various materials is vital for developing new generation nanoscale devices. To date, the integration issues, especially the atomic bonding integration, remain a grand challenge due to the high melting point and lattice mismatches of heterogeneous materials. Herein, atomic bonding-engineered heterogeneous integration of semiconductor NWs is successfully achieved based on femtosecond (fs) laser irradiation. The nanobraze-welding mechanism is revealed for the formation of atomic-level bonding between CuO and ZnO NWs. A laser irradiation-induced diffusion region is observed at the CuO/ZnO hetero-interface, which remarkably broadens the carrier transport channels to optimize the electrical properties of the CuO/ZnO NWs p-n junction. Further simulation and band gap calculation reveal the absorption of laser energy via single-photon excitation in CuO NWs and two-photon excitation in ZnO NWs. A high-performance photodetector based on laser-nanobrazed CuO/ZnO NWs p-n junction is fabricated, which exhibits a high responsivity (9.86 A/W), fast rise and decay time (0.560 s and 2.056 s). This semiconductor NWs atomic-level bonding integration may inspire the widespread application of 1D nanomaterials and reveals a prospective pathway to develop miniaturized and multi-functional electronic devices by semiconductor NWs integration.

Crystalline-to-Amorphous Phase Transformation in CuO Nanowires for Gaseous Ionization and Sensing Application.

We report a dramatic reduction of operation voltage of a CuO nanowire-based ionization gas sensor due to the crystalline-to-amorphous phase transformation. The structural change is attributed to the ion bombardment and heating effect during the initial discharge, which brings about the formation of abundant nanocrystallites and surface states favoring gaseous ionization. The gas-sensing properties of the CuO nanowire sensor are confirmed by differentiating various types or concentrations of volatile organic compounds diluted in nitrogen, with a low detection limit at the ppm level. Moreover, a sensing mechanism is proposed on the basis of charge redistribution by electron-gas collision related to the specific ionization energy. The insightful study of the electrode microstructure delivers an exploratory investigation to the effect of gas ionization toward the discharge system, which provides new approaches to develop advanced ionization gas sensors.

Role of crystallographic textures on the growth of CuO nanowires via thermal oxidation

To investigate the influence of crystallographic textures on the growth of CuO nanowires, nanocrystalline coppers with distinct textures were fabricated using an electrodeposition. Thermogravimetric analysis, x-ray diffraction analysis, and scanning electron microscopy equipped with an electron backscattered diffraction detector were employed to investigate the growth of CuO nanowires at 200 °C and 300 °C. While a high number-density of nanowires was clearly observed in the (100) and (101)-textured coppers, it was not the case for the copper with strong (111) texture, indicating that the growth of CuO nanowires via a low-temperature thermal oxidation can be achieved by tailoring the texture. Data availabilityThe raw and processed data required to reproduce these findings are available to download from [https://data.mendeley.com/datasets/6zjnhgk7vc/draft?a=8057336c-389a-451d-95e0–756b5e93cb99].

Preparation of copper nanowires and thermal oxidation behaviour in dry oxygen

Copper (Cu) nanowires are a promising functional and structural material in electronics, optoelectronic devices and integrated circuits. The preparation and thermal stability of Cu nanowires are crucial for the functional realisation and performance stability of related devices. In this work, the authors particularly prepared Cu nanowires by a two-step approach and further studied the thermal oxidation behaviour of Cu nanowires in dry oxygen. It was found that the as-prepared Cu nanowires have a good (111)-oriented single crystal structure with a smooth and clean surface. With the increase of annealing temperature and time, the Cu nanowires were oxidised gradually in dry oxygen and the crystal phase of Cu nanowires underwent the evolution of Cu (111)→Cu2O (111)→CuO (−111)+(111). Furthermore, when the temperature was not higher than 400°C, the as-formed Cu2O and CuO layers or nanowires were slightly crystallised or nearly amorphous. However, when the temperature was higher than 400°C, the as-formed CuO nanowires were greatly crystallised. It was further observed that the oxidation of Cu nanowires arose from the wire surface and formed a non-dense, nearly amorphous layer of Cu2O nanoparticles therein. Such Cu2O layer on the surface of Cu nanowires greatly reduces optical transmittance.

High mass loading NiCo–OH nanothorns coated CuO nanowire arrays for high-capacity nickel–zinc battery

The rational design of cathode materials with core–shell heterostructures is significant to develop a Ni//Zn battery with both high gravimetric and areal energy density under high mass loading. In this work, the NiCo–OH nanothorns with a mass loading of 11.6 mg cm−2 were coated on CuO nanowire arrays via a chemical bath deposition method. Thanks to the construction of 3D core–shell nanowire arrays and appropriate cobalt doping, as-fabricated Ni//Zn battery based on the NiCo–OH as cathode achieved the maximum specific capacity of 383 mAh g−1 at 5 mA cm−2 with high energy density of 649 Wh kg−1 at 0.73 kW kg−1, indicating good energy storage performance in Ni//Zn battery.

Verification of Carrier Concentration-Dependent Behavior in Water-Infiltration-Induced Electricity Generation by Ionovoltaic Effect.

Water-infiltration-induced power generation has the renewable characteristic of generating electrical energy from ambient water. Importantly, it is found that the carrier concentration in semiconductor constituting the energy generator seriously affect the electricity generation. Nevertheless, few studies are conducted on the influence of semiconductor carrier concentration, a crucial factor on electricity generation. Due to this, understanding of the energy harvesting mechanism is still insufficient. Herein, the semiconductor carrier concentration-dependent behavior in water-infiltration-induced electricity generation and the energy harvesting mechanism by ionovoltaic effect are comprehensively verified. A clue to enhance the electric power generation efficiency is also proposed. When 20 µL of water (NaCl, 0.1 m) infiltrates into a porous CuO nanowires film (PCNF), electric power of ≈0.5V and ≈1 µA are produced for 25 min. Moreover, the PCNF shows good practicability by generating electricity using various ambient water, turning on LEDs, and being fabricated as a curved one.

Synthesis of super-hydrophobic CuO/ZnO layered composite nano-photocatalyst

The introduction of super-hydrophobicity into the field of photocatalysis has attracted the attention of many researchers nowadays. Here, CuO nanowires were synthesized via thermal oxidation method. The flower-like ZnO nanostructures were self-assembled with CuO nanowires by hydrothermal growth method. The functionalized super-hydrophobic CuO/ZnO layered composite nano-photocatalyst was obtained though polydimethylsiloxane (PDMS) grafting. We analyzed the effects of zinc sources, hydrothermal reaction time, solution concentration and surfactant concentration on the properties of the composite nano-photocatalyst. FESEM micrographs revealed CuO/ZnO layered composite nanostructures, which were composed of CuO nanowires with uniform morphology and carnation-like ZnO nanoflowers. XRD spectrum showed CuO/ZnO layered composite nano-photocatalyst possessed pure CuO phase and the wurtzite structure of ZnO. UV–vis spectrum manifested that the composite nanostructures had desired light absorption for ultraviolet light band and the contact angle (CA) results confirmed the successful modification of super-hydrophobic functionalization. After the modification of PDMS, the CuO/ZnO layered composite nano-photocatalyst prepared with the optimal conditions shows desired photocatalytic properties and super-hydrophobicity. The stable super-hydrophobic property after photocatalytic degradation is expected to improve self-cleaning and broaden the application field of photocatalyst.

Enhancing Water Splitting Activity of Photocathode Using MoS2 Flakes Deposited on Copper Oxide Nanowire

In this work, we report the synthesis of copper oxide (CuO) nanowires on indium tin oxide (ITO) coated with a few–layers of MoS2 flakes by the thermal annealing and metal–organic chemical vapour deposition (MOCVD) methods at a temperature of 200 °C. As a result, the CuO/MoS2 photocathode gave the maximum photocurrent density (PCD) of −9.8 mA/cm2 (η = 0.75%) at –1.2 V (vs. RHE), which is higher than that of the pristine CuO nanowires photocathode (−6.08 mA/cm2, η = 0.44%). The high PCD of CuO/MoS2 photocathode is attributed to the high stability and more active sites of MoS2 flakes, lowering the electrochemical proton reduction over potential, as well as the built–in potential of CuO–MoS2 heterojunction, and minimizing the dark current of the photoelectrochemical (PEC) cell. Based on these findings, we advance the fabrication of the hybrid PEC device (MoS2 and traditional photocatalytic materials) for enhancing efficient hydrogen evolution reaction.

Cu2O nanowires with exposed {111} facet for nonenzymatic detection of glucose in complex biological fluids

Accurate glucose sensing in complex biological fluids could enable diagnostics for home healthcare. However, glucose oxidase (GOx) has been suffered from poor reproducibility and chemical instability due to intrinsic nature of enzymes. Here, we report a free-standing and robust reduced graphene oxide wrapped Cu foam (rGO/CuF)-supported Cu2O nanowires (Cu2O NWs) with exposed {111} facet via facile electrodeposition route. When being used as an electrode for nonenzymic glucose detection, Cu2O NWs@rGO/CuF exhibited the distinguished performances with powerful reliability for analyzing human plasma and even whole blood samples. These unprecedented performances could be ascribed to nanoscale hydrophilic structure of Cu2O NWs, which could control the fouling level especially for protein. Moreover, taking into account the Cu2O NWs with exposed {111} facet, Cu2O NWs {111} could reduce ion diffusion distance and couple with improved electronic conductivity, thus leading to high glucose sensitivity. Through the theoretical calculations, a reliable interpretation of the catalytic mechanism with Cu2O NWs {111} has been provided. This study deepens the understanding of hydrophilic nanostructure and facet-dependent activity of Cu2O NWs and points out a strategy to improve their sensitivity and stability.

Formation of metal–semiconductor nanowire heterojunctions by nanosecond laser irradiation

Laser nano-joining has emerged as a preferred technique for better device performance as it can result in stronger mechanical contacts and enhance the electrical properties between nanocomponents. It is often used to bond metallic nanostructures, but there is little information available on the applicability of the corresponding processes for creating hybrid bonds between metal and semiconductor nanomaterials. In this article, we show that Nd:YAG nanosecond (ns) laser irradiation is an effective tool for use in the nano-joining of metal–semiconductor nanowire (NW) combinations. We show that photothermal, electron–hole pair creation and plasmonic effects combine to facilitate nano-joining with Nd:YAG ns laser radiation, producing similar interfacial structures to those occurring under femtosecond laser irradiation. We find that Nd:YAG laser irradiation is effective in the production of bonds between Ag–TiO2 and Ag–CuO NW structures but that the detailed mechanism involved in the creation of these bonds depends on the bandgap energy of the semiconductor NW. Direct heating of the semiconductor through photoexcitation of excitons and electron transfer to the conduction band is significant in the Nd:YAG laser nano-joining of low bandgap materials such as CuO. Coupling of surface plasmon resonance energy to electrical carriers in the semiconductor NW at the Ag-semiconductor interface is found to be important in all hybrid systems, including those involving a wide bandgap material such as TiO2. Since the Nd:YAG ns laser is widely available, these results suggest that nano-joining of heterogeneous materials with ns laser pulses is a practical alternative to joining with ultrashort laser radiation.

Hierarchical shell/core electrodes with CuO nanowires based on carbon cloths for high performance asymmetric supercapacitors

Transition metal oxides/hydroxides are important pseudocapacitive materials for supercapacitors, however, low electron transfer capability and poor long-term cycle stability limit their applications. Constructing transition metal oxide/hydroxide nanoarrays on conducting collectors is an effective way to solve the above problems. In this thesis, CuO nanowires based on carbon cloths (CuO–CCs) were firstly grown by chemical copper plating and thermal oxidation, and then Ni(OH)2@CuO–CCs and Fe2O3@CuO–CCs were constructed by chemical bath deposition and hydrothermal methods, respectively. The ASC device using Ni(OH)2@CuO–CCs as positive electrodes and Fe2O3@CuO–CCs as negative electrodes were assembled. The results demonstrate that the optimal specific capacities of Ni(OH)2@CuO–CCs and Fe2O3@CuO–CCs are 2.282 F cm−2 (at 1 mA cm−2) and 0.772 F cm−2 (at 2.5 mA cm−2), respectively. The ASC device reaches the energy density of 81.12 Wh kg−1 at a power density of 2.88 kW kg−1, and exhibit the capacitance maintenance of 97.9% after 10,000 cycles.

3D coating layers of polyhydroquinone di-imidazopyridine (PIPD) fibers to improve their mechanical, interfacial and antimicrobial properties

The effect of growing CuO nanowires decorated with Ag nanoparticle in the presence of poly(dopamine) (PDA) as intermediate agent on PIPD fiber surface was evaluated. This treatment exhibited significant enhancement of the interfacial and mechanical performance, along with increment of the antimicrobial activity against E. coli as a model for Gram-negative bacteria. The scanning electron microscopy (SEM) validates the growth of CuO NWs and Ag NPs on the surface of PIPD fiber. The X-ray diffraction (XRD), The X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and the ratio of weight loss analyses supported the above results. The interface shear strength (IFSS) between the PIPD fiber and epoxy resin was improved by 72%; and the coated Ag nanoparticles raised the fiber tensile strength (TS) by 13%. The influence of UV radiation and hydrothermal degradation on PIPD fiber was studied, and the UV and hydrothermal aging resistance were both increased by 15% and 22% respectively. The antimicrobial activity analysis results strong efficiency of the coated PIPD fibers by Ag NPs against gram negative bacteria E. coli.

Ultrafast epitaxial growth of CuO nanowires using atmospheric pressure plasma with enhanced electrocatalytic and photocatalytic activities

AbstractThis work reports an environment friendly alternative to epitaxially grow copper oxide nanowires (NWs) on copper substrates using single step atmospheric pressure plasma jet assisted oxidation. NWs of average length 300 nm are grown rapidly in 5 minutes along with transforming the surface to superhydrophilic. This method introduces defects in the nanowire structure which is otherwise difficult to achieve due to the highly isotropic nature of nanowire growth. High resolution transmission electron microscopy reveals vacancies and structural defects such as lattice twinning and kinks. Theoretical investigations using density functional theory calculations indicated that oxygen vacancies reduces the adsorption energy of methanol molecules onto the CuO (111) surface and shifts the Fermi level towards conduction band. During electrocatalysis, these defect‐rich nanowires exhibit twice the catalytic activity toward oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) in comparison to the traditionally thermally grown nanowires. Moreover, retreating the electrodes after each stability test drops the contact resistance similar to the prisitine sample. Additionally, these NW photocathodes demonstrate an exceptional photocurrent of 2.2 mAcm–2 and have an excellent degradation activity towards organic pollutants namely phenol and paracetamol. This facile growth method can be used to engineer nanowires of other transition metals with enhanced activities.

Hybrid liquid crystalline zinc phthalocyanine@Cu2O nanowires for NO2 sensor application

A novel organic-inorganic hybrid conductometric NO2 sensor has been introduced by depositing liquid-crystalline zinc oktakisalkylthiophthalocyanine [(C6S)8PcZn] on the surface of Cu2O nanowires. Cu2O nanowires were synthesized by electrochemical anodization of Cu films on glass substrates. Surface structures of bare Cu2O and (C6S)8PcZn@Cu2O nanowires hybrid structures were monitored by scanning electron microscope (SEM). UV–vis spectrophotometer measurements revealed the heterostructure formation by comparing the absorption profiles of bare Cu2O nanowires, (C6S)8PcZn thin film, and (C6S)8PcZn@Cu2O hybrid nanowires. The interdigitated transducers (IDT) were used for conductometric gas measurements. The sensing properties of all samples were investigated towards 500 ppb, 1 ppm, 2 ppm, and 5 ppm NO2 under dry airflow in 30 °C, 50 °C, 100 °C, and 150 °C. The measurements at 150 °C were repeated for (C6S)8PcZn film and hybrid sample using the same concentrations of NO2 gas under 38 % relative humidity airflow. In addition, selectivity of hybrid sensor was confirmed with carbon monoxide (CO), hydrogen (H2) and ethanol (C2H5OH) measurements. Our density functional theory calculations indicate that S atoms play a crucial role in improving the sensor response. The sensing properties and sensing mechanisms of samples were compared and discussed.