High-efficiency extraction synthesis for high-purity copper nanowires and their applications in flexible transparent electrodes

Copper nanowires(Cu NWs)are considered an excellent alternative to indium tin oxide(ITO)in flexible transparency electrodes(FTEs).However,the mixed particles and surface oxidation of Cu NWs degrade the transmittance and conductivity of the electrodes.Therefore,highly purified Cu NWs without oxidation are vital for high-performance FTEs.Herein,a facile and effective purification process is introduced to purify Cu NWs in a water and n-hexane system,which takes advantage of the differences in hydrophilicity between Cu NWs and Cu NPs caused by their different adsorption affinities to octadecylamine(ODA).At the same sheet resistance,the transmittance of the purified Cu NW-based FTEs improved approximately 2%compared to that of non-purified Cu NW-based FTEs.Immersion of the electrode in glacial acetic acid removed the surface organics and oxides.After only 40 s of treatment,the sheet resistance dramatically decreased from 10^5 Ohm/sq to 31 Ohm/sq with a transmittance of 85%.In addition,the Cu NW-based FTE conductors showed excellent flexibility(remaining stable after 1000 bending cycles).The Cu NW-based FTEs were further applied to fabricate a flexible transparent heater.At a voltage of 10 V,the temperature of the heater reached 73℃,demonstrating the potential applications of this material in various fields.

Evolution of copper nanowires through coalescing of copper nanoparticles induced by aliphatic amines and their electrical conductivities in polyester films

Copper nanowires were synthesized by the wet chemical reduction method using copper sulfate as the copper precursor,aliphatic amines(methylamine,ethanediamine,1,2-propanediamine)as the inducing reagents,and hydrazine hydrate as the reductant through the aging and reduction processes.The high-resolution transmission electron microscopy(HRTEM)images reveal that the copper nanowires were synthesized by coalescing extremely small-sized copper nanoparticles with the particle sizes of1–6 nm in copper complex micelles.A longer aging time period favored the coalescing of the copper nanoparticles to form thinner copper nanowires in the following reduction process.The coalescing extent of copper nanoparticles in copper nanowires was highly enhanced by ethanediamine and 1,2-propanediamine as compared with that by methylamine.The copper nanowire-filled polyester films had higher electrical conductivity than the copper nanoparticle-filled ones.

In situ carbon coating for enhanced chemical stability of copper nanowires

Copper nanowires(CuNWs)are promising electrode materials,especially for used in flexible and transparent electrodes,due to their advantages of earth-abundant,low-cost,high conductivity and flexibility.However,the poor stability of CuNWs against oxidation and chemic-al corrosion seriously hinders their practical applications.Herein,we propose a facile strategy to improve the chemical stability of CuNWs by in situ coating of carbon protective layer on top of them through hydrothermal carbonization method.The influential factors on the growth of carbon film including the concentration of the glucose precursor(carbon source),hydrothermal temperature,and hydrothermal time are sys-tematically studied.By tailoring these factors,carbon layers with thickness of 3-8 nm can be uniformly grown on CuNWs with appropriate glucose concentration around 80 mg·mL−1,hydrothermal temperature of 160-170°C,and hydrothermal time of 1-3 h.The as-prepared carbon-coated CuNWs show excellent resistance against corrosion and oxidation,and are of great potential to use broadly in various optoelectronic devices.

Synthesis and purification of long copper nanowires. Application to high performance flexible transparent electrodes with and without PEDOT：PSS

We demonstrate the hydrothermal synthesis of long copper nanowires based on a simple protocol. We show that the purification of the nanowires is very important and can be achieved easily by wet treatment with glacial acetic acid. Fabrication of random networks of purified copper nanowires leads to flexible transparent electrodes with excellent optoelectronic performances （e.g., 55 Ω/sq. at 94% transparency）. The process is carried out at room temperature and no post-treatment is necessary. Hybrid materials with the conductive polymer PEDOT：PSS show similar properties （e.g., 46 Ω/sq, at 93% transparency）, with improved mechanical properties. Both electrodes were integrated in capacitive touch sensors.

Synthesis of ultrathin semicircle-shaped copper nanowires in ethanol solution for low haze flexible transparent conductors

Copper nanowires （CuNWs） are becoming an indispensable item for next- generation transparent optical devices due to their excellent conductivity and transparency. In this work, ultrathin semicircle-shaped copper nanowires （SCuNWs） with a diameter of - 15 nm and a length of - 30 μm （aspect ratio of -2,000） were synthesized in ethanol solution. The mechanism and factors that affect the morphology and dispersity of the SCuNWs were investigated. The prepared SCuNWs were coated on polyethylene terephthalate （PET） or polyd- imethylsiloxane （PDMS） substrate to fabricate flexible transparent conductors （FTCs）. The fabricated FTCs exhibited excellent optoelectrical performance and low haze. In addition, the fabricated FTCs showed high mechanical stability during stretching and bending, indicating their great potential in flexible optical devices.

Soft piezoresistive pressure sensing matrix from copper nanowires composite aerogel

We report on a simple yet efficient approach to fabricate soft piezoresistive pressure sensors using copper nanowires-based aerogels.The sensors exhibit excellent sensitivity and durability and can be easily scalable to form large-area sensing matrix for pressure mapping.This opens a low-cost strategy to wearable biomedical sensors.

First-principles study of the adsorption of oxygen atoms on copper nanowires

By using first-principles calculations,we have systematically investigated the structural stability and electronic properties of a single oxygen atom adsorbed on the surface of foursquare Cu nanowires for a wide range of adsorption sites.In view of binding energy maximization,we found that the long bridge site at the edge of the Cu nanowires is the most stable site for oxygen adsorption,which is always slightly energetically favorable compared with the hollow site at the surface.The electron transferring from Cu atoms to O adatom and a significant polarization indicate the O-Cu chemical bond,showing some degree of ionic character.In addition,the hybridization between O-2p and Cu-3d states implies the O-Cu bond which also shows some degree of covalence character.The main factors which affect the oxygen preferred adsorption site are analyzed from the local geometrical configurations and electronic properties.

A core-shell copper oxides-cobalt oxides heterostructure nanowire arrays for nitrate reduction to ammonia with high yield rate

Electrochemical nitrate reduction to ammonia(NRA) can realize the green synthesis of ammonia(NH3) at ambient conditions, and also remove nitrate contamination in water. However, the current catalysts for NRA still face relatively low NH3yield rate and poor stability. We present here a core-shell heterostructure comprising cobalt oxide anchored on copper oxide nanowire arrays(CuO NWAs@Co_(3)O_(4)) for efficient NRA. The CuO NWAs@Co_(3)O_(4)demonstrates significantly enhanced NRA performance in alkaline media in comparison with plain CuO NWAs and Co_(3)O_(4)flocs. Especially, at-0.23 V vs. RHE, NH_(3) yield rate of the CuO NWAs@Co_(3)O_(4)reaches 1.915 mmol h^(-1)cm^(-2),much higher than those of CuO NWAs(1.472 mmol h^(-1)cm^(-2)), Co_(3)O_(4)flocs(1.222 mmol h^(-1)cm^(-2)) and recent reported Cu-based catalysts.It is proposed that the synergetic effects of the heterostructure combing atom hydrogen adsorption and nitrate reduction lead to the enhanced NRA performance.

Refit Silver Nanostructures Using a Convergent Electron Beam

Using a superionic conductor AgI thin film and a direct current electric field, we synthesize silver nanowires in diameter of about lOOnm. In order to refit the prepared nanowires, the samples are irradiated by a convergent electron beam （200 k V） inside a transmission electron microscope to prepare new small silver nanostructures. The new nanostructures are investigated in situ by high-resolution transmission electron microscope. This electron- induced crystal growth method is useful for technical applications in fabrication of nanodevices.

Formation of copper oxide nanowires and nanoparticles via electrospinning

Copper oxide nanowires and nanoparticles were fabricated through electrospinning followed by calcinations in different heating conditions.It was found that the solution viscosity and environment humidity had great impact on the morphologies of precursor nanowires,and the parameters of heat treatment,including final temperature and heating rate,significantly affected the product morphologies.

Large-scale Growth of Copper Oxide Nanowires on Various Copper Substrates

Large-scale growth of copper oxide nanowires was realized on surfaces of various copper-containing substrates, including copper grids, high-purity copper foils, and small copper blocks, by the stress-induced method. A relatively low heating temperature of 340 ~C was demonstrated to give rise to dense nanowire growth with fine crystal structures and high aspect ratio of approximately 300. Gradual cooling process, which is positive for the growth of nanowires on multi-layer substrates, is shown to have no effect on the nanowire growth on other pure copper substrates. Diameter of as-obtained nanowires is mainly dependent on the heating temperature. Moreover, the nanowires growing on copper grids are much longer than those growing on two other substrates.

Solution-processed copper nanowire flexible transparent electrodes with PEDOT：PSS as binder, protector and oxide-layer scavenger for polymer solar cells

The easy oxidation and surface roughness of Cu nanowire （NW） films are the main bottlenecks for their usage in transparent conductive electrodes （TCEs）. Herein, we have developed a facile and scaled-up solution route to prepare Cu NW-based TCEs by embedding Cu NWs into pre-coated smooth poly（3,4-ethylenedioxythiophene）：poly（styrenesulfonate） （PEDOT：PSS） films on poly（ethylene terephthalate） （PET） substrates. The so obtained Cu NW- PEDOT：PSS/PET films have low surface roughness （-70 nm in height）, high stability toward oxidation and good flexibility. The optimal TCEs show a typical sheet resistance of 15Ω·sq-1 at high transparency （76% at A = 550 nm） and have been used successfully to make polymer （poly（3-hexylthiophene）：phenyl-C61- butyric acid methyl ester） solar cells, giving an efficiency of 1.4%. The overall properties of Cu NW-PEDOT：PSS/PET films demonstrate their potential application as a replacement for indium tin oxide in flexible solar cells.

Fabrication of sintering-free flexible copper nanowire/ polymer composite transparent electrodes with enhanced chemical and mechanical stability

The thermal decomposition synthesis of long copper nanowires （CuNWs） was achieved by controlling the synthesis parameters. A detailed study was performed to determine the effect of the molar ratio of copper chloride to nickel acetylacetonate, temperature, and stirring rate on the final shape of the products. Transparent electrodes （TEs） were fabricated by wet treatment with acetic acid （AA）, without using a sintering process. The low oxidation stability and high surface roughness are the main disadvantages of the CuNW TEs, which limit their applications. In order to overcome these issues, we prepared CuNW/polymer composite TEs by partial embedding of the CuNWs into poly（methyl methacrylate） （PMMA） on poly（ethylene terephthalate） （PET） substrates. The CuNW/PMMA composite TEs exhibit excellent optoelectronic performance （91.3% at 100.7 ff2/sq）, low surface roughness （4.6 nm in height）, and good mechanical and chemical stability as compared with CuNW TEs. On the basis of these properties, we believe that CuNW-based composite TEs could serve as low-cost materials for a wide range of new optoelectronic devices.

Copper nanowire with enriched high‐index facets for highly selective CO_(2) reduction

Electroreduction of carbon dioxide into fuels and feedstocks with renewable energy is an attractive route to mitigate carbon emission and solve energy crisis.However,how to improve the selectivity of high‐value multicarbon products is still challenging.Here,we demonstrate that the high‐index crystalline surface of copper could be designed and obtained through a simple square‐wave potential treatment on copper nanowires,which is beneficial to improve the selectivity of multi‐carbon products,especially the reaction route towards ethylene.The Faradaic efficiency of C_(2+)products can reach nearly 60%,and hydrogen can be suppressed to below 20%.Density functional theory(DFT)calculations reveal that(311)high‐index facet can activate CO_(2) effectively and promote adsorption of the*COCOH intermediate on copper for ethylene formation,therefore improves the selectivity of ethylene and inhibits the competing hydrogen evolution reaction.This method can be extended to the design of other catalytic systems and has inspirations for other electrochemical catalytic reactions.

Copper nanowire-TiO2-polyacrylate composite electrodes with high conductivity and smoothness for flexible polymer solar cells

Copper nanowire （Cu NW） transparent electrodes have attracted considerable attention due to their outstanding electrical properties, flexibility and low cost. However, complicated post-treatment techniques are needed to obtain good electrical conductivity, because of the organic residues and oxide layers on the surface of the Cu NWs. In addition, commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, a TiO2 sol treatment was introduced to obtain Cu NW transparent electrodes with superb performance （13 Ω/sq @ 82% T） at room temperature within one minute. Polymer solar ceils with excellent flexibility were then fabricated on the copper nanowire- TiO2-polyacrylate composite electrode. The power conversion efficiency （PCE） of the cells based on a blend of poly（3-hexylthiophene） （P3HT） and phenyl-C61- butyric acid methyl ester （PC61BM） reached 3.11%, which was better than the control devices that used indium tin oxide （ITO）-PET electrodes, and outperforms other Cu NW based organic solar cells previously reported. The PCE of the solar cells based on Cu NW electrodes remained at 90% after 500 cycles of bending, while the PET/ITO solar cells failed after 20 and 200 cycles, with sheet resistance of 35 and 15 Ω/sq, respectively.

Enhanced disinfection of Escherichia coli and bacteriophage MS2 in water using a copper and silver loaded titanium dioxide nanowire membrane

Titanium dioxide （TiO2） is a widely used photocatalyst that has been demonstrated for microorganism disinfection in drinking water. In this study, a new material with a novel structure, silver and copper loaded TiO2 nanowire membrane （Cu-Ag-TiO2） was prepared and evaluated for its efficiency to inactivate E. coli and bacteriophage MS2. Enhanced photo-activated bactericidal and virucidal activities were obtained by the Cu-Ag-TiO2 membrane than by the TiO2, Ag-TiO2 and Cu-TiO2 membranes under both dark and UV light illumination. The better performance was attributed to the synergies of enhanced membrane photoacfivity by loading silver and copper on the membrane and the synergistic effect between the free silver and copper ions in water. At the end of a 30 min test of dead- end filtration under 254 nm UV irradiation, the Cu-Ag-TiO2 membrane was able to obtain an E. coli removal of 7.68 log and bacteriophage Ms2 removal of 4.02 log, which have met the US EPA standard. The free metal ions coming offthe membrane have concentrations of less than 10 ppb in the water effluent, far below the US EPA maximum contaminant level for silver and copper ions in drinking water. Therefore, the photo-activated disinfection by the Cu-Ag-Ti02 membrane is a viable technique for meeting drinking water treatment standards of microbiological water purifiers.

Transparent heaters based on highly stable Cu nanowire films

In spite of the recent successful demonstrations of flexible and transparent film heaters, most heaters with high optical transmittance and low applied direct current （DC） voltage are silver nanowire （Ag NW）-based or silver grid-based. In this study, flexible and stretchable copper nanowire （Cu NW）-based transparent film heaters were fabricated through a solution-based process, in which a thin layer of hydrophobic polymers was encapsulated on the Cu NW films. The thin polymer layer protected the films from oxidation under harsh testing conditions, i.e., high temperature, high humidity, and acidic and alkaline environments. The films exhibited remarkable performance, a wide operating temperature range （up to 150 ℃）, and a high heating rate （14 ℃/s）. Defrosting and wearable thermotherapy demonstrations of the Cu NW film heaters were carried out to investigate their practicality. The Cu NW-based film heaters have potential as reliable and low-cost film heaters.