Ranran Wang

Synthesis of Ultralong Copper Nanowires for High-Performance Transparent Electrodes

Cu nanowires hold great promise for the fabrication of low-cost transparent electrodes. However, their current synthesis is mainly performed in aqueous media with poor nanowire dispersibility. We report herein the novel synthesis of ultralong single-crystalline Cu nanowires with excellent dispersibility, providing an excellent candidate material for high-performance transparent electrode fabrication.

Highly Thermal Conductive Copper Nanowire Composites with Ultralow Loading: Toward Applications as Thermal Interface Materials

Thermal interface materials (TIMs) are of ever-rising importance with the development of modern microelectronic devices. However, traditional TIMs exhibit low thermal conductivity even at high loading fractions. The use of high-aspect-ratio material is beneficial to achieve low percolation threshold for nanocomposites. In this work, single crystalline copper nanowires with large aspect ratio were used as filling materials for the first time. A thermal conductivity of 2.46 W/mK was obtained at an ultralow loading fraction, ∼0.9 vol %, which was enhanced by 1350% compared with plain matrix. Such an excellent performance makes copper nanowires attractive fillers for high-performance TIMs.

Copper nanowire based transparent conductive films with high stability and superior stretchability

In contrast to traditional “rigid and brittle” electronics, nowadays new electronic materials tend to be flexible, curvilinear, and even stretchable to meet the demands of wearable or body conformal electronic devices. Herein, a facile strategy has been demonstrated to synthesize copper nanowires with fewer particles and higher yield (promoted by 3 times). Through an artful fabrication and transfer technique, copper nanowires are constructed into stretchable conductive films, which not only possess good conductivity-transmittance performance (91% for 220 Ω □−1), but also exhibit excellent mechanical robustness against adhesion, friction and bending. Besides, the partly-embedding structure of nanowire network gives rise to chemical resistance (stable conductivity through acid/alkali test), and most significantly, extremely superb stability against oxidation (no degradation of conductivity after 50 days in ambient condition). This work opens a way for Cu nanowire-based transparent conductive films into various practical applications, especially when harsh environmental conditions are inevitable.

Fibrous nanocomposites of carbon nanotubes and graphene-oxide with synergetic mechanical and actuative performance

Fibrous nanocomposites of carbon nanotubes, graphene-oxide or graphene were prepared by a simple coagulation spinning technique exhibiting synergetic enhancement of mechanical strength, electronic conductivity and electrical actuation performance.

Controllable synthesis of 3D binary nickel–cobalt hydroxide/graphene/nickel foam as a binder-free electrode for high-performance supercapacitors

Binder-free electrodes based on 3D porous nickel–cobalt binary hydroxides (NCH)/graphene (G) composites on nickel foam (NF) for supercapacitors are fabricated via a chemical vapor deposition (CVD) process combined with an electrochemical deposition (ED) method. High quality graphene grown on NF makes the surface more suitable for deposition of 3D porous NCH and simultaneously enhances the electrode conductivity. The 3D structure can improve the electron transport ability and increase the contact of the active sites with electrolyte. The morphology and electrochemical performance of NCH/G/NF electrodes can be readily manipulated by adjusting the deposition current density and the Ni–Co ratio of the deposition solution. High capacitance with enhanced stability and rate capability is achieved and is attributed to the synergetic effect of the above factors. Specifically, at the deposition current density of 0.625 mA cm−2 and Ni–Co ratio of 1 : 1, the NCH11/G/NF electrode exhibits a maximum specific capacitance of 1410 F g−1 at 2 A g−1. When the current density increases to 4 A g−1, the capacitance is still 1328 F g−1 with a high capacitance retention of 94.2%. After 2500 cycles, the capacitance retention is 92.1%, which is higher than that of a common slurry-coated electrode. To research its practical applications, an asymmetric supercapacitor was fabricated with a NCH11/G/NF electrode as the positive electrode and activated carbon as the negative electrode. The asymmetric device exhibits a prominent energy density of 33.75 W h kg−1 at a power density of 750 W kg−1. The binder-free electrode with superior performance has been proven to be very promising for energy storage.

Plasma-induced nanowelding of a copper nanowire network and its application in transparent electrodes and stretchable conductors

Copper nanowires (Cu NWs) have attracted increasing attention as building blocks for electronics due to their outstanding electrical properties and low cost. However, organic residues and oxide layers ubiquitously existing on the surface of Cu NWs impede good inter-wire contact. Commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, hydrogen plasma treatment at room temperature has been demonstrated to be effective for simultaneous surface cleaning and selective welding of Cu NWs at junctions. Transparent electrodes with excellent optical-electrical performance (19 O·sq–1 @ 90% T) and enhanced stability have been fabricated and integrated into organic solar cells. Besides, Cu NW conductors with superior stretchability and cycling stability under stretching speeds of up to 400 mm·min–1 can also be produced by the nanowelding process, and the feasibility of their application in stretchable LED circuits has been demonstrated.

Synthesis of Metal/Bimetal Nanowires and Their Applications as Flexible Transparent Electrodes

As a potential alternative to indium oxide (ITO), metal nanowire transparent conductive electrodes (TCEs) have attracted more and more attention. Here, a facile method that can be applied to the synthesis of a variety of metal/bimetallic nanowires has been proposed. Metal/bimetallic nanowires synthesized through this method show high aspect ratios and great dispersibility, which makes them ideal building blocks for transparent electrodes. The synthesis mechanism is discussed in-depth to give a theoretical basis of morphology control of metal nanostructures in organic synthesizing systems. TCEs with high flexibility, excellent optical-electrical performance as well as outstanding anti-thermal and anti-moisture stability are constructed. To the best of our knowledge, this is the first work on synthesizing multiple metal/bimetallic nanowires through one method.

A high-performance flexible and weavable asymmetric fiber-shaped solid-state supercapacitor enhanced by surface modifications of carbon fibers with carbon nanotubes

To meet the demands of high energy storage and low productive cost as well as the ability to be incorporated into wearable electronics, we developed a flexible and weavable asymmetric fiber-shaped solid-state supercapacitor (a-FSSC) based on carbon fiber bundle@CNT–NiCo(OH)x (CF@CNC) and carbon fiber bundle@activated carbon (CF@AC) electrodes with increased operating voltage (1.4–1.6 V) and capacitance. For the positive electrode of CF@CNC, great electrochemical performance enhancement brought about by surface modifications with air plasma and carbon nanotube (CNT) coating is demonstrated. For the negative electrode of CF@AC, a facile and effective way of incorporating activated carbon into carbon fiber bundles is developed. The resultant assembled a-FSSC showed an areal energy and power density of 33.0 μW h cm−2 and 0.75 mW cm−2 at 1.6 V, which are better than those of most of the present fiber-shaped supercapacitors. The volumetric energy and power density of 0.84 mW h cm−3 and 19.1 mW cm−3 are also comparable to the reported results. Its long cycle life (100% capacitance retention after 8000 charge–discharge cycles) reveals its high electrochemical stability. High capacitance retention in the repeated bending (20% decay after 1000 bending times) and torsion (107% retention after 1000 twisting times) tests demonstrated the great flexibility, structural stability and potential utilization of the a-FSSC in wearable electronics. As a demonstration, a woolen fabric woven with three a-FSSCs connected in series can light a blue LED and be worn on the arm.

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 °C), and a high heating rate (14 °C/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.

Base and acid treatment of SWCNT-RNA transparent conductive films.

RNA was used to exfoliate single-walled carbon nanotubes (SWCNTs) in aqueous solution, and the ratio of it was optimized to obtain the best dispersion state. The obtained homogeneous SWCNT solution with small bundle size was used to prepare flexible transparent conductive films by filtration method. Sodium hydroxide treatment combining short-time acid treatment was used to remove the RNA molecules. After treatment, the sheet resistance of the films decreased significantly, while the change on the transmittance was negligible. Besides, the polyethylene terephthalate substrate would not turn brittle through this treatment process. Flexible films with outstanding performance (190 Omega/sq, 85%) and good stability were obtained after treatment. X-ray photoelectron spectroscopy and scanning electron microscope were used to analyze the role of base and acid treatment in detail.