Promising wet chemical strategies to synthesize Cu nanowires for emerging electronic applications

Progress in photocatalytic CO2 reduction based on single-atom catalysts

Reduced CO2 emissions, conversion, and reuse are critical steps toward carbon peaking and carbon neutrality. Converting CO2 into high-value carbon-containing compounds or fuels may effectively address the energy shortage and environmental issues, which is consistent with the notion of sustainable development. Photocatalytic CO2 reduction processes have become one of the research focuses, where single-atom catalysts have demonstrated significant benefits owing to their excellent percentage of atom utilization. However, among the crucial challenges confronting contemporary research is the production of efficient, low-cost, and durable photocatalysts. In this paper, we offer a comprehensive overview of the study growth on single-atom catalysts for photocatalytic CO2 reduction reactions, describe several techniques for preparing single-atom catalysts, and discuss the advantages and disadvantages of single-atom catalysts and present the study findings of three single-atom photocatalysts with TiO2, g-C3N4 and MOFs materials as carriers based on the interaction between single atoms and carriers, and finally provide an outlook on the innovation of photocatalytic CO2 reduction reactions.

Room Temperature Curable Copper Nanowire-Based Transparent Heater

Copper nanowires (Cu NWs) are a promising alternative to silver NWs to develop transparent conducting films (TCFs) due to their comparable electrical conductivity and relative abundance. Postsynthetic modifications of the ink and high-temperature postannealing processes for obtaining conducting films are significant challenges that need to be addressed before commercial deployment of these materials. In this work, we have developed an annealing-free (room temperature curable) TCF with Cu NW ink that requires minimal postsynthetic modifications. Organic acid pretreated Cu NW ink is used for spin-coating to obtain a TCF with a sheet resistance of 9.4 Ω/sq. and optical transparency of 67.4% at 550 nm. For oxidation protection, the Cu NW TCF is encapsulated with polydimethylsiloxane (PDMS). The encapsulated film is tested as a transparent heater at various voltages and shows good repeatability. These results demonstrate the potential of Cu NW-based TCFs as a replacement for Ag-NW based TCFs for a variety of optoelectronic applications, such as transparent heaters, touch screens, and photovoltaics.

A crack templated copper network film as a transparent conductive film and its application in organic light-emitting diode

In this paper, a highly transparent, low sheet resistance copper network film fabricated by a crack template, which made by drying an acrylic based colloidal dispersion. The fabricated copper network film shows excellent optoelectronic performances with low sheet resistance of 13.4 Ω/sq and high optical transmittance of 93% [excluding Polyethylene terephthalate (PET) substrate] at 550 nm. What’s more, the surface root mean square of the copper network film is about 4 nm, and the figure of merit is about 380. It’s comparable to that of conventional indium tin oxide thin film. The repeated bending cycle test and adhesive test results confirm the reliability of the copper network film. As a transparent conductive film, the copper network film was used as an anode to prepare organic light-emitting diode (OLED). The experiment results show that the threshold voltage of the OLED is less than 5 V and the maximum luminance is 1587 cd/m2.

Synthesis of Copper Nanostructures for Non-Enzymatic Glucose Sensors via Direct-Current Magnetron Sputtering

In this paper, Cu nanocolumnar structure electrodes are synthetized using a clean and easy-to-scale-up direct-current magnetron sputtering (DC-MS) technique for non-enzymatic glucose sensing. The nanocolumnar structure increases the active surface area of the deposit, with the nanocolumns showing a mean size diameter of 121.0 nm ± 27.2 and a length of 2.52 µm ± 0.23. A scanning transmission electron (STEM) analysis shows the presence of Cu and a small amount of Cu2O. The behavior of the electrodes in alkaline environments and the electrochemical affinity of the Cu nanocolumns (CuNCs) towards the electro-oxidation of glucose are investigated using cyclic voltammetry (CV). After performing CV in NaOH solution, the columnar structures present corrosion products containing Cu2O, as revealed by STEM and X-ray diffraction (XRD) analyses. The amperometric responses of the CuNCs to the successive addition of glucose show a linear range up to 2 mM and a limit of detection of 5.2 µM. Furthermore, the electrodes are free from chloride poisoning, and they are insensitive to dopamine, uric acid, ascorbic acid, and acetaminophen at their physiological concentrations.

Copper inks for printed electronics: a review

Conductive inks have attracted tremendous attention owing to their adaptability and the convenient large-scale fabrication. As a new type of conductive ink, copper-based ink is considered to be one of the best candidate materials for the conductive layer in flexible printed electronics owing to its high conductivity and low price, and suitability for large-scale manufacturing processes. Recently, tremendous progress has been made in the preparation of cooper-based inks for electronic applications, but the antioxidation ability of copper-based nanomaterials within inks or films, that is, long-term reliability upon exposure to water and oxygen, still needs more exploration. In this review, we present a comprehensive overview of copper inks for printed electronics from ink preparation, printing methods and sintering, to antioxidation strategies and electronic applications. The review begins with an overview of the development of copper inks, followed by a demonstration of various preparation methods for copper inks. Then, the diverse printing techniques and post-annealing strategies used to fabricate conductive copper patterns are discussed. In addition, antioxidation strategies utilized to stabilize the mechanical and electrical properties of copper nanomaterials are summarized. Then the diverse applications of copper inks for electronic devices, such as transparent conductive electrodes, sensors, optoelectronic devices, and thin-film transistors, are discussed. Finally, the future development of copper-based inks and the challenges of their application in printed electronics are discussed.

Anisotropic Growth of Copper Nanorods Mediated by Cl- Ions

Anisotropic growth to form Cu particles of rod and wire shapes has been obtained typically in a complex system that involves both organic capping agents and Cl- ions. However, the sole effect of Cl- ions on the formation of Cu wires has yet to be fully understood, especially in an organic system. This present work determines the effect of Cl- ions on the morphologies of Cu particles in an organic phase without any capping agents. The results revealed that anisotropic Cu rods could be grown with the sole presence of Cl- ions. The rods have the (011) facets as the long axis, the (111) facets as the tip, and the (100) facets as the side surface. By increasing the Cl- ion concentration, more Cu atoms contributed to the formation of Cu rods and the kinetic growth of the length and the diameter of the rods varied. This suggests that Cl- ions have preferential adsorption on the (100) Cu surfaces to promote the anisotropic growth of Cu. Meanwhile, the adsorption of Cl- to the (111) and (100) surfaces at high Cl- concentrations regulates the relative growth of the particle length and diameter.

Novel Fabrication of Silver-Coated Copper Nanowires with Organic Compound Solution

Copper nanowires and Cu-Ag nanowires have various potential applications, such as transparent conductive film, flexible electronics, and conductive filler. In this study, we developed a new green fabrication method for silver-coated copper nanowires using methylsulfonylmethane (DMSO2), which is an environmentally friendly chemical at the food-grade level, to replace toxic chemicals, including ammonia, in the silver coating process. Copper nanowires were synthesized under various reaction temperatures and concentrations of hydrazine (N2H4), ethylenediamine (EDA), sodium hydroxide (NaOH), and copper precursor. The reaction temperature higher than 70 °C caused the oxidation of copper products and evaporation of the sample solution. The optimal conditions to synthesize copper nanowires more than 18 µm in length and 25-45 nm in diameter were determined: 9 M of NaOH, 50 µL of EDA, 17 mM of CuCl2, 5.7 mM of N2H4, and 70 °C reaction temperature. Cu-Ag nanowires, which have about a 12 nm thick silver shell, were successfully fabricated at room temperature under 1 mM of silver nitrate (AgNO3) and 1 wt % of DMSO2. Synthesis conditions for copper and silver-coated copper nanowires have been optimized.

Designable Integration of Silicide Nanowire Springs as Ultra-Compact and Stretchable Electronic Interconnections

Stretchable electronics are finding widespread applications in bio-sensing, skin-mimetic electronics, and flexible displays, where high-density integration of elastic and durable interconnections is a key capability. Instead of forming a randomly crossed nanowire (NW) network, here, a large-scale and precise integration of highly conductive nickel silicide nanospring (SiNi_x -NS) arrays are demonstrated, which are fabricated out of an in-plane solid-liquid-solid guided growth of planar Si nanowires (SiNWs), and subsequent alloy-forming process that boosts the channel conductivity over 4 orders of magnitude (to 2 × 10⁴ S cm^-1 ). Thanks to the narrow diameter of the serpentine SiNi_x -NS channels, the elastic geometry engineering can be accomplished within a very short interconnection distance (down to ≈3 µm), which is crucial for integrating high-density displays or logic units in a rigid-island and elastic-interconnection configuration. Deployed over soft polydimethylsiloxane thin film substrate, the SiNi_x -NS array demonstrates an excellent stretchability that can sustain up to 50% stretching and for 10 000 cycles (at 15%). This approach paves the way to integrate high-density inorganic electronics and interconnections for high-performance health monitoring, displays, and on-skin electronic applications, based on the mature and rather reliable Si thin film technology.

Green synthesis of submicron copper powder with narrow particle size distribution via a simple methanol thermal reduction

In this work, submicron copper powder with narrow particle size distribution was synthesized via a simple methanol thermal reduction method without using any surfactants. Smaller copper powder with narrower particle size distribution could be realized by increasing the reaction temperature. Submicron copper powder with an average particle size of 206.6 nm and a particle size distribution of 100-300 nm could be obtained when the reaction temperature was 200 °C. Methyl formate was the only organic product found in the reaction. No organic products could be realized when the reaction temperature increased to 180 °C and above, which was environmentally friendly and was conducive to the subsequent copper powder extraction and washing. The synthesis of submicron copper powder via methanol thermal reduction was found to be a top-down process, which was beneficial for ultrafine copper powder production via wet chemical approaches.

Recent Advancement of Emerging Nano Copper-Based Printable Flexible Hybrid Electronics

Printed copper materials have been attracting significant attention prominently due to their electric, mechanical, and thermal properties. The emerging copper-based flexible electronics and energy-critical applications rely on the control of electric conductivity, current-carrying capacity, and reliability of copper nanostructures and their printable ink materials. In this review, we describe the growth of copper nanostructures as the building blocks for printable ink materials on which a variety of conductive features can be additively manufactured to achieve high electric conductivity and stability. Accordingly, the copper-based flexible hybrid electronics and energy-critical devices printed by different printing techniques are reviewed for emerging applications.

Copper(I)-alkylamine mediated synthesis of copper nanowires

Formation of a Cu(i)-alkylamine complex is found to be the key step for Cu(ii) ions to reduce to Cu(0) in the presence of glucose. Also, alkylamines in Cu nanowire synthesis serve triple roles as a reducing, complexation and capping agent. Alkylamines reduce Cu(ii) to Cu(i) at above 100 °C and protect the Cu(i) by forming a Cu ion-alkylamine coordination complex with a 1 : 2 ratio in an aqueous solution. With respect to the 1 : 2 complex ratio, the additional free alkylamines ensure a stable Cu(i)-alkylamine complex. After completion of Cu(i)-Cu(0) reduction by glucose, alkylamines remain on Cu(0) seeds to regulate the anisotropic growth of Cu nanocrystals. Long-chain (≥C16) alkylamines are found to help produce high-quality Cu nanowires, while short-chain (≤C12) alkylamines only produce CuO products. Furthermore, Cu nanowire synthesis is found to be sensitive to additional chemicals as they may destabilize Cu ion-alkylamine complexes. By comparing the Cu(i)-alkylamine and Maillard reaction mediated mechanism, the complete Cu nanowire synthesis process using glucose is revealed.

Nanowire Genome: A Magic Toolbox for 1D Nanostructures

1D nanomaterials with high aspect ratio, i.e., nanowires and nanotubes, have inspired considerable research interest thanks to the fact that exotic physical and chemical properties emerge as their diameters approach or fall into certain length scales, such as the wavelength of light, the mean free path of phonons, the exciton Bohr radius, the critical size of magnetic domains, and the exciton diffusion length. On the basis of their components, aspect ratio, and properties, there may be imperceptible connections among hundreds of nanowires prepared by different strategies. Inspired by the heredity system in life, a new concept termed the "nanowire genome" is introduced here to clarify the relationships between hundreds of nanowires reported previously. As such, this approach will not only improve the tools incorporating the prior nanowires but also help to precisely synthesize new nanowires and even assist in the prediction on the properties of nanowires. Although the road from start-ups to maturity is long and fraught with challenges, the genetical syntheses of more than 200 kinds of nanostructures stemming from three mother nanowires (Te, Ag, and Cu) are summarized here to demonstrate the nanowire genome as a versatile toolbox. A summary and outlook on future challenges in this field are also presented.

Stirring revealed new functions of ethylenediamine and hydrazine in the morphology control of copper nanowires

Cu nanowires, as promising candidates in many fields because of their merits, are commonly prepared by the solution phase based synthesis which is a simple and scalable method. However, precise control of the morphology, particularly surface roughness, of Cu nanowires is still challenging; and moreover, detailed formation mechanisms of Cu nanowires, in solution phase based synthesis, are still unclear. We here show the morphology manipulation of Cu nanowires by adjusting the stirring rate and the amounts of ethylenediamine and hydrazine (N2H4), yielding Cu nanowires with either smooth or rough surface. Importantly, according to our experimental results and theoretical investigation, new functions of ethylenediamine and N2H4 are found, and a growth process of Cu nanowires is proposed accordingly. In addition to typically accepted roles of ethylenediamine and N2H4, we find that ethylenediamine can facilitate the growth of Cu nanowires by etching Cu oxides and even Cu on the surface of Cu nanowires. Meanwhile, N2H4 molecules can modulate the growth of Cu nanowires as a capping agent, which can be easily influenced by stirring. Additionally, the as-synthesized Cu nanowires with different morphologies exhibit different optical and catalytic properties. This study provides new fundamental insights into the growth mechanism of Cu nanowires, and thus can facilitate controlled synthesis of Cu nanowires for further applications, including electronics, catalysis, and sensing.

Emergence of Flexible White Organic Light-Emitting Diodes

Flexible white organic light-emitting diodes (FWOLEDs) have considerable potential to meet the rapidly growing requirements of display and lighting commercialization. To achieve high-performance FWOLEDs, (i) the selection of effective flexible substrates, (ii) the use of transparent conducting electrodes, (iii) the introduction of efficient device architectures, and iv) the exploitation of advanced outcoupling techniques are necessary. In this review, recent state-of-the-art strategies to develop FWOLEDs have been summarized. Firstly, the fundamental concepts of FWOLEDs have been described. Then, the primary approaches to realize FWOLEDs have been introduced. Particularly, the effects of flexible substrates, conducting electrodes, device architectures, and outcoupling techniques in FWOLEDs have been comprehensively highlighted. Finally, issues and ways to further enhance the performance of FWOLEDs have been briefly clarified.

All-Solution-Processed Thermally and Chemically Stable Copper-Nickel Core-Shell Nanowire-Based Composite Window Electrodes for Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have recently attracted tremendous attention because of their excellent efficiency and the advantage of a low-cost fabrication process. As a transparent electrode for PSCs, the application of copper nanowire (CuNW)-network was limited because of its thermal/chemical instability, despite its advantages in terms of high optical/electrical properties and low-cost production. Here, the copper-nickel core-shell nanowire (Cu@Ni NW)-based composite electrode is proposed as a bottom window electrode for PSCs, without the involvement of a high-cost precious metal and vacuum process. The dense and uniform Ni protective shell for CuNWs is attainable by simple electroless plating, and the resulting Cu@Ni NWs exhibit outstanding chemical stability as well as thermal stability compared with bare CuNWs. When the Ni layer with the optimal thickness is introduced, the Cu@Ni NW electrode shows a high transmittance of 80.5% AVT at 400-800 nm, and a sheet resistance of 49.3 ± 5 Ω sq^-1. Using the highly stable Cu@Ni NWs, the composite electrode structure is fabricated with sol-gel-derived Al-doped zinc oxide (AZO) over-layer for better charge collection and additional protection against iodine ions from the perovskite. The PSCs fabricated with AZO/Cu@Ni NW-based composite electrode demonstrate a power conversion efficiency (PCE) of 12.2% and excellent long-term stability maintaining 91% of initial PCE after being stored for 500 h at room temperature. Experimental results demonstrate the potential of highly stable Cu@Ni NW-based electrodes as the cost-effective alternative transparent electrode, which can facilitate the commercialization of PSCs.

Seeds screening aqueous synthesis, multiphase interfacial separation and in situ optical characterization of invisible ultrathin silver nanowires

We report a multi-step synthetic method to obtain ultrathin silver nanowires (Ag NWs) from an aqueous solution with a ∼17 nm diameter average, and where some of them decreased down to 9 nm. Carefully designed seed screening processes including LED irradiation at high temperature for a short time, and then continuous H2O2 etching, and relative growth mechanisms of high-yield five-twinned pentagonal seeds and ultrathin Ag NWs in aqueous environment are detailed. Then, a rapid and simple multiphase interfacial assembly method particularly suitable for the separation of ultrathin Ag NWs from various by-products was demonstrated with a clear mechanism explanation. Next, a unique optical interaction between light and individual AG NWs, as well as feature structures in the AG NWs film, was investigated by a micro-domain optical confocal microscope measurement in situ together with a theoretical explanation using modal transmission theory. That revealed that the haze problem of AG NWs films was not only arising from the interaction between light and individual or crossed Ag NWs but was also greatly dependent on a weak coupling effect of leaky modes supported by adjacent Ag NWs with large distances which had not been considered before. We then provided direct experimental evidence and concluded how to obtain haze-free films with 100% transparency in the whole visible range based on ultrathin Ag NWs. This breakthrough in diameter confinement and purification of Ag NWs is a highly expected step to overcome the well-focused light diffusion and absorption problems of Ag NWs-based devices applied in various fields such as flexible electronics, high-clarity displays, visible transparent heaters, photovoltaics and various optoelectronic technologies.

Synthesis, Spray Deposition, and Hot-Press Transfer of Copper Nanowires for Flexible Transparent Electrodes

We report a solution-phase approach to the synthesis of crystalline copper nanowires (Cu NWs) with an aspect ratio >1000 via a new catalytic mechanism comprising copper ions. The synthesis involves the reaction between copper(II) chloride and copper(II) acetylacetonate in a mixture of oleylamine and octadecene. Reaction parameters such as the molar ratio of precursors as well as the volume ratio of solvents offer the possibility to tune the morphology of the final product. A simple low-cost spray deposition method was used to fabricate Cu NW films on a glass substrate. Post-treatment under reducing gas (5% H₂ + 95% N₂) atmosphere resulted in Cu NW films with a low sheet resistance of 24.5 Ω/sq, a transmittance of T = 71% at 550 nm (including the glass substrate), and a high oxidation resistance. Moreover, the conducting Cu NW networks on a glass substrate can easily be transferred onto a polycarbonate substrate using a simple hot-press transfer method without compromising on the electrical performance. The resulting flexible transparent electrodes show excellent flexibility ( R/ R_o < 1.28) upon bending to curvatures of 1 mm radius.

Advancements in Copper Nanowires: Synthesis, Purification, Assemblies, Surface Modification, and Applications

Copper nanowires (CuNWs) are attracting a myriad of attention due to their preponderant electric conductivity, optoelectronic and mechanical properties, high electrocatalytic efficiency, and large abundance. Recently, great endeavors are undertaken to develop controllable and facile approaches to synthesize CuNWs with high dispersibility, oxidation resistance, and zero defects for future large-scale nano-enabled materials. Herein, this work provides a comprehensive review of current remarkable advancements in CuNWs. The Review starts with a thorough overview of recently developed synthetic strategies and growth mechanisms to achieve single-crystalline CuNWs and fivefold twinned CuNWs by the reduction of Cu(I) and Cu(II) ions, respectively. Following is a discussion of CuNW purification and multidimensional assemblies comprising films, aerogels, and arrays. Next, several effective approaches to protect CuNWs from oxidation are highlighted. The emerging applications of CuNWs in diverse fields are then focused on, with particular emphasis on optoelectronics, energy storage/conversion, catalysis, wearable electronics, and thermal management, followed by a brief comment on the current challenges and future research directions. The central theme of the Review is to provide an intimate correlation among the synthesis, structure, properties, and applications of CuNWs.

A high-response transparent heater based on a CuS nanosheet film with superior mechanical flexibility and chemical stability

Transparent heaters are widely used in technologies such as window defrosting/defogging, displays, gas sensing, and medical equipment. Apart from mechanical robustness and electrical and optical reliabilities, outstanding chemical stability is also critical to the application of transparent heaters. In this regard, we first present a highly flexible and large-area CuS transparent heater fabricated by a colloidal crackle pattern method with an optimized sheet resistance (Rs) as low as 21.5 Ω sq-1 at a ∼80% transmittance. The CuS transparent heater exhibits remarkable mechanical robustness during bending tests as well as high chemical stability against acid and alkali environments. In the application as a transparent heater, the CuS heater demonstrates a high thermal resistance of 197 °C W-1 cm2 with a fast switching time (<30 s), requiring low input voltages (<4.5 V) to achieve uniform temperatures of ∼110 °C across large areas. The temperature of the wearable CuS heater, which is stuck on the skin, can be real-time controlled through a Bluetooth device in a cell phone wirelessly. Based on the wireless control system, we demonstrated an application of the CuS heater in snow removal for solar panels. These CuS network TCEs with high flexibility, transparency, conductivity, and chemical stability could be widely used in wearable electronic products.

Hyperthemia-Promoted Cytosolic and Nuclear Delivery of Copper/Carbon Quantum Dot-Crosslinked Nanosheets: Multimodal Imaging-Guided Photothermal Cancer Therapy

Copper-containing nanomaterials have been applied in various fields because of their appealing physical, chemical, and biomedical properties/functions. Herein, for the first time, a facile, room-temperature, and one-pot method of simply mixing copper ions and sulfur-doped carbon dots (CDs) is developed for the synthesis of copper/carbon quantum dot (or CD)-crosslinked nanosheets (CuCD NSs). The thus-obtained CuCD NSs with the size of 20-30 nm had a high photothermal conversion efficiency of 41.3% and good photothermal stability. Especially, after coating with thiol-polyethylene glycol and fluorescent molecules, the resultant CuCD NSs could selectively target tumor tissues and realize multimodal (photoacoustic, photothermal, and fluorescence) imaging-guided cancer therapy. More importantly, our CuCD NSs exhibited laser-triggered cytosolic delivery, lysosomal escape, and nuclear-targeting properties, which greatly enhanced their therapeutic efficacy. The significantly enhanced tumor accumulation of CuCD NSs after in situ tumor-site laser irradiation was also observed in in vivo experiments. These in vitro and in vivo events occurring during the continuous laser irradiation have not been observed. Overall, this work develops a CD-assisted synthetic method of photothermal nanoagents for triple-modal imaging-guided phototherapy and deepens our understanding of the action mechanism of photothermal therapy, which will promote the development of nanomedicine and beyond.

Enhanced compatibility between a copper nanowire-based transparent electrode and a hybrid perovskite absorber by poly(ethylenimine)

Copper nanowires (CuNWs) have been applied to hybrid perovskite solar cells (PSCs) as a window electrode. By sandwiching the CuNW network between aluminum-doped zinc oxide and adopting a poly(ethylenimine) buffer layer, the compatibility between the CuNWs and the perovskite layer could be dramatically improved. PSCs containing the CuNW-based composite electrode exhibited an average power conversion efficiency of 8.65%.

UV Treatment of Flexible Copper Nanowire Mesh Films for Transparent Conductor Applications

Copper nanowires have the potential to reach and even exceed the indium tin oxide performances as flexible transparent conductive electrodes. However, for a large-scale production, they need to be fabricated in a high-speed, low-cost way, without degrading the flexible substrate. One of the major bottlenecks resides in the post-treatment used to remove organic residues from the surface of the nanowires after forming the transparent electrode, which is necessary to obtain high optoelectronic performances. Here, we propose an ultra-violet irradiation and a subsequent acetic acid bath as an easy, scalable, fast post-treatment. After only 2 min of ultra-violet treatment, followed by 10 min of acid bath, an Rs of 42 Ω sq^-1 and a T _550 nm of 87% were measured. Besides, copper nanowire electrodes maintained their high transparency in the range 750-2500 nm, which makes them good candidates for applications such as infrared solar cells.

1D copper nanowires for flexible printable electronics and high ampacity wires

This paper addresses the synthesis and a detailed electrical analysis of individual copper nanowires (CuNWs). One dimensional CuNWs are chemically grown using bromide ions (Br^-) as a co-capping agent. By partially replacing alkyl amines with Br^-, the isotropic growth on Cu seeds was suppressed during the synthesis. To study the electrical properties of individual CuNWs, a fabrication method is developed which does not require any e-beam lithography process. Chemically grown CuNWs have an ampacity of about 30 million amps per cm², which is more than one order of magnitude larger than bulk Cu. These good quality, easy to synthesize CuNWs are excellent candidates for creating high ampacity wires and flexible printable electronics.

A Simple Silver Nanowire Patterning Method Based on Poly(Ethylene Glycol) Photolithography and Its Application for Soft Electronics

Hydrogel-based flexible microelectrodes have garnered considerable attention recently for soft bioelectronic applications. We constructed silver nanowire (AgNW) micropatterns on various substrates, via a simple, cost-effective, and eco-friendly method without aggressive etching or lift-off processes. Polyethylene glycol (PEG) photolithography was employed to construct AgNW patterns with various shapes and sizes on the glass substrate. Based on a second hydrogel gelation process, AgNW patterns on glass substrate were directly transferred to the synthetic/natural hydrogel substrates. The resultant AgNW micropatterns on the hydrogel exhibited high conductivity (ca. 8.40 × 103 S cm-1) with low sheet resistance (7.51 ± 1.11 Ω/sq), excellent bending durability (increases in resistance of only ~3 and ~13% after 40 and 160 bending cycles, respectively), and good stability in wet conditions (an increase in resistance of only ~6% after 4 h). Considering both biocompatibility of hydrogel and high conductivity of AgNWs, we anticipate that the AgNW micropatterned hydrogels described here will be particularly valuable as highly efficient and mechanically stable microelectrodes for the development of next-generation bioelectronic devices, especially for implantable biomedical devices.

Biomimetic synthesis of Ag3PO4-NPs/Cu-NWs with visible-light-enhanced photocatalytic activity for degradation of the antibiotic ciprofloxacin

Cu-NWs/Ag₃PO₄-NPs can be used as photocatalysts under visible light irradiation and have high photocatalytic performance for degradation of CPFX.

Reduced graphene oxide wrapped core-shell metal nanowires as promising flexible transparent conductive electrodes with enhanced stability

Transparent conductive electrodes (TCEs) are widely used in a wide range of optical-electronic devices. Recently, metal nanowires (NWs), e.g. Ag and Cu, have drawn attention as promising flexible materials for TCEs. Although the study of core-shell metal NWs, and the encapsulation/overcoating of the surface of single-metal NWs have separately been an object of focus in the literature, herein for the first time we simultaneously applied both strategies in the fabrication of highly stable Ag-Cu NW-based TCEs by the utilization of Ag nanoparticles covered with reduced graphene oxide (rGO). The incorporation of Ag nanoparticles by galvanic displacement reaction was shown to significantly increase the long term stability of the electrode. Upon comparison with a CuNW reference, our novel rGO/Cu-AgNW-based TCEs unveiled remarkable opto-electrical properties, with a 3-fold sheet resistance decrease (from 29.8 Ω sq^-1 to 10.0 Ω sq^-1) and an impressive FOM value (139.4). No detrimental effect was noticed in the relatively high transmittance value (T = 77.6% at 550 nm) characteristic of CuNWs. In addition, our rGO/Cu-AgNW-based TCEs exhibited outstanding thermal stability up to 20 days at 80 °C in air, as well as improved mechanical flexibility. The superior performance herein reported compared with both CuNWs and AgNWs, and with a current conventional ITO reference, is believed to highlight the great potential of these novel materials as promising alternatives in optical-electronic devices.

Highly Stretchable and Conductive Copper Nanowire Based Fibers with Hierarchical Structure for Wearable Heaters

Wearable heaters have been increasingly attracting researchers' great interest due to their efficient utility in maintaining warmth and in thermotherapy. Nowadays carbon nanomaterials and metallic nanowires tend to become the mainstream heating elements in wearable heaters considering their excellent electrical and mechanical properties. Though considerable progress has been made, there still exist challenging issues that need to be addressed in practical applications, including bad breathability and poor endurance to mechanical deformations. Here, we devise a copper nanowire based composite fiber with a unique hierarchical structure. This fiber possesses not only excellent heating performance, but also fantastic tolerance to mechanical impact, such as bending, twisting, and stretching. We further weave these fibers into a wearable heating fabric and realize smart personal heating management through an Android phone by integrating with a microcontroller unit. Two practical applications are demonstrated including a heating kneepad for articular thermotherapy and a heating coat on an infant model for maintaining warmth.

Cu Nanowires with Clean Surfaces: Synthesis and Enhanced Electrocatalytic Activity

Low activity and high cost of electrocatalysts are the major challenge for the commercialization of the direct fuel cells (DFCs) and biofuel cells. In this work, we demonstrate the desirable "clean surfaces" effect of Cu nanocrystals in electrocatalysis. By a new reaction route of Cu₂O nanospheres (Cu₂O NSs), Cu nanowires (Cu NWs) with high purity and "clean surfaces" are first obtained under mild conditions. Benefiting from the path directing effects and abundant (100) facets, the as-prepared Cu NWs exhibit a lower overpotential to achieve the methanol electro-oxidation reaction (MOR) than that of analogous Cu nanoparticles (Cu NPs). Moreover, the "clean surfaces" provide more available active sites for the efficient transfer of electrons, enabling the Cu NWs to show their enhanced electrocatalytic activity. In the MOR, forward peak current density for the surface-cleaned Cu NWs is 2839 μA cm^-2, which is ca. 6.45-fold higher than that of the Cu NWs with residual capping molecules on their surface. The "clean surfaces" effect can also be extended to the glucose electro-oxidation reaction (GOR), and the enhancement in specific surface area activity for the Cu NWs is 11.3-fold. This work enhances the electrocatalytic performance of Cu nanocrystals without the need for additional noble metals, which opens up new avenues for utilizing non-noble metals in the DFC or biofuel cell applications.

PEGylated Copper Nanowires as a Novel Photothermal Therapy Agent

Metal nanowires are promising for their applications including electrical connectors, transparent conductive electrodes and conductive additives, but the use of metal nanowires as photothermal agents to convert light to heat has yet to be reported. Here we synthesized dispersible polyethylene glycol-coated (PEGylated) copper nanowires (CuNWs) and showed for the first time that PEGylated CuNWs were able to convert near-infrared (NIR, 808 nm) light into heat at a photothermal efficiency of 12.5%. The PEGylated CuNWs exhibited good reusability and enabled rapid temperature rise to >50 °C in 6 min by NIR irradiation. The PEGylated CuNWs were flexible and intertwined around the cancer cells, which, upon NIR irradiation, allowed for direct heat transmission to cells and effectively triggered cancer cell ablation in vitro. Intratumoral injection of PEGylated CuNWs into colon tumor-bearing mice and ensuing NIR irradiation for 6 min significantly raised the local temperature to >50 °C, induced necrosis, and suppressed tumor growth. Compared with other NIR light absorbing noble metal-based nanomaterials, PEGylated CuNWs are relatively easy to synthesize in both laboratory and large scales using the low cost copper. This study demonstrated the potential of PEGylated CuNWs as a new cost-effective photothermal agent, and paved a new avenue to using CuNWs for cancer therapy.

Roll-to-roll-compatible, flexible, transparent electrodes based on self-nanoembedded Cu nanowires using intense pulsed light irradiation

Copper nanowire (Cu NW)-based flexible transparent conductive electrodes (FTCEs) have been investigated in detail for use in various applications such as flexible touch screens, organic photovoltaics and organic light-emitting diodes. In this study, hexadecylamine (HDA) adsorbed onto the surface of NWs is changed into polyvinylpyrrolidone (PVP) via a ligand exchange process; the high-molecular-weight PVP enables high dispersion stability. Intense pulsed light (IPL) irradiation is used to remove organic species present on the surface of the NWs and to form direct connections between the NWs rapidly without any atmospheric control. NWs are self-nanoembedded into a plastic substrate after IPL irradiation, which results in a smooth surface, strong NW/substrate adhesion, excellent mechanical flexibility and enhanced oxidation stability. Moreover, Cu NW FTCEs with high uniformities are successfully fabricated on a large area (150 mm × 200 mm) via successive IPL irradiation that is synchronized with the motion of the sample stage. This study demonstrates the possibility of roll-to-roll-based, large-scale production of low-cost, high-performance Cu NW-based FTCEs.