Bridging Oriented Copper NanowireâGraphene Composites for

Subscriber access provided by NEW MEXICO STATE UNIV

Article

Bridging Oriented Copper Nanowire-Graphene Composites for SolutionProcessable, Annealing-Free and Air-Stable flexible Electrodes Wang Zhang, Zhenxing Yin, Alvin Chun, Jeeyoung Yoo, Youn Sang Kim, and Yuanzhe Piao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b09337 • Publication Date (Web): 31 Dec 2015 Downloaded from http://pubs.acs.org on January 7, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Bridging Oriented Copper Nanowire-Graphene Composites for Solution-Processable, Annealing-Free and Air-Stable flexible Electrodes Wang Zhang,‡ab Zhenxing Yin,‡a Alvin Chun,a Jeeyoung Yoo,a Youn Sang Kim,*ab and Yuanzhe Piao,

∗

ab

Abstract One-dimensional flexible metallic nanowires (NWs) are considerable interest for next-generation wearable devices. The unavoidable challenge for wearable electrode is the assurance of high conductivity, flexibility, and durability with economically feasible materials and simple manufacturing processes. Here, we use a straightforward solvothermal method to prepare a flexible conductive material that contains reduced graphene oxide (RGO) nanosheets bridging oriented copper NWs. The GO-assistance route can successfully meet the criteria listed above and help the composite films maintain high conductivity and durable flexibility without any extra treatment, such as annealing or acid process. The composite film exhibits a high electrical performance (0.808 Ω·sq-1) without considerable change over 30 days under ambient conditions. Moreover, the Cu NW-RGO composites can be deposited on polyester cloth as a lightweight wearable electrode with high durability and simple processability and are very promising for a wide variety of electronic devices. Keywords: Copper nanowire, reduced graphene oxide, solvothermal procedure, flexible electrode

a

Graduate School of Convergence Science and Technology, Seoul National University, Seoul,

151-742, Republic of Korea. E-mail: [email protected]; Tel: +82 318889148 b

Advanced Institutes of Convergence Technology, Suwon, 443-270, Republic of Korea

‡ These authors contributed equally to this work. 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 40

1. Introduction Solution-processable, flexible, and durable conductive electrodes have been widely researched because of the stringent requirements for the rapid development of wearable electronic devices, such as smart clothes, wearable energy-storage devices, and epidermal medical devices.1-2 Compared with conventional conducting electrodes, next-generation wearable electrodes must be designed for high electrical conductivity and mechanical durability under human motional deformation.2-4 Currently, solution processes as one of best choices have been widely used in the fabrication of wearable devices because of their convenience and low cost.5-6 In general, these novel electrodes have been based on polymers and carbon materials that can be directly knitted into different types of fabrics, which has attracted interest from people. Recently,

conductive

fiber-based

poly(3,4-ethylenedioxythiophene)

and

poly(styrenesulfonate) were prepared by the wet spinning method,7 and these polymers were easily solution-processed into conductive fibers with good mechanical properties. However, these materials typically have low conductivity and poor durability, resulting in their limited application to wearable electronic devices. Therefore, how to decrease the electrical resistance of the fiber electrode is still a big challenge currently.8-9 Conductive carbon materials, such as carbon nanotubes and graphene, are viable for use as wearable electronics because of their low sheet resistance (~1 Ω·sq-1) and good mechanical properties. In spite of their processability and conductivity, the large-scale production of carbon nanomaterials requires a complicated process with a high cost.10 Although many composites have been

2


Page 3 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


prepared to address these shortcomings,11-13 their conductivities are still much lower than those of metals. To address the urgent requirements for high-performance electrical devices, much research effort is currently focused on areas such as low-cost manufacturing techniques and their application to cheap wearable electronics. Therefore,

both

academic

and

industrial

laboratories

are

researching

a

solution-processable way to prepare conductive metal electrodes.14 To date, most solution-processable metallic electrodes reported are composed of conductive metallic nanoparticles (NPs) and nanowires (NWs) of silver or copper, which are promising for the development of wearable and portable electronics.15-16 These nanocomposite electrodes show low sheet resistance (∼0.01 Ω·sq-1), facile manufacturability, and superior mechanical performance compared to carbon, polymers, and other conductive materials.17-19 Currently, Ag NW-based percolation networks have shown promise in flexible electronics.2, 20 Although Ag NWs have excellent electrical conductivity and flexibility,21 the scarcity and high cost of silver are difficult to address. Cu NWs with high-temperature treatment are as electrically conductive as Ag, and thus, Cu, which is cheaper, has gained more attention than Ag recently.22-25 Our previous studies focused on the novel synthesis and low-temperature treatment of oxidation-resistant Cu NW electrodes by straightforward solution methods.26-27 Unfortunately, the excessive post-treatment process of Cu nanomaterials is still an obstacle for many applications for wearable electronics. In addition, the problems with Cu NWs, including easy oxidation and harsh preparation, must be resolved.

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The invention of lightweight and wearable electrodes with a convergence of high conductivity, high machinability, and high flexibility with low cost materials and scalable manufacturing processes is still a challenge.28-30 In this work, we designed low-cost reduced graphene oxide (RGO)-Cu NW composite electrodes using a one-pot solvothermal method that led to high-performance flexible electrodes (Scheme 1). After deposition on polyester clothes, the Cu NWs in the composites maintained their high intrinsic conductivity and flexibility, while the RGO nanosheets connecting the oriented Cu NWs not only provided remarkable pathways for charge transfer but also acted as an anti-oxidation layer to protect the Cu NWs from harsh environments.

2. Experimental Section 2.1. Reagents CuCl, NH4Cl, oleylamine, ethylene glycol (EG), and graphite (100>111,37 the shape of seeds was closely related to the crystal planes, which exposed the crystal surface with the lowest surface energy.38 The capping effect of NH4Cl changed the surface energy and induced the exposure of the relatively stable 100 plane of Cu on the surface. As a result, the seed grew along the [110] direction, forming straight Cu NWs. In the solvothermal system, GO was not only adsorbed on oleylamine because of electrostatic interaction but also aggregated Cu+ by the coordination between Cu+ and oxygen groups on GO. The synergistic

effect

induced

the

formation

of

the

ternary

complex

of

oleylamine-GO-Cu+, resulting in the growth of Cu NWs. When the concentration of GO was low, a sufficient amount of Cu+ caused the GO sheets to fold.39 Consequently, the steric hindrance of GO actuated the formation of arc-shaped Cu NWs instead of straight Cu NWs. Under the optimized reaction condition, first, a sufficient amount of oxygen groups bonded to the edges of GO could effectively stabilize the Cu seeds. Then, under the co-influence of the capping and reducing agents, the regular Cu NWs were reduced, and the nanostructures were elongated in the [110] direction to connect the RGO nanosheets, which assembled 2D Cu NW-RGO embedded nets with oriented Cu NWs bridging RGOs. However, excess GOs as a mild reducing agent could accelerate the reduction of Cu+ and prevent the capping effect of oleylamine simultaneously.33 Therefore, the growth of Cu NWs was blocked and stopped midway

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 40

through the reaction, while irregularly shaped Cu NPs with a few Cu NWs were formed. Moreover, the addition of oleylamine to the reaction was an essential factor in the formation of Cu NW-RGO composites. When oleylamine was not used in the reaction, only irregular polyhedrons with diameters ranging from 1 to 10 µm were present (Figure 4a). At a low concentration of oleylamine (0.05 mol·L-1), Cu NWs gradually started to appear from the RGO edge and nearly grew across the RGO boundary (Figure 4b), which suggested that the amine groups of oleylamine were bound to the surface of copper nanostructures in the reaction.27,

40

When Cu

complexes enriched the edge of GO because of its plentiful oxygen groups, oleylamine could preferentially bind to the side facets of the Cu complexes, which caused preferential growth of Cu NWs along the axial [110] direction from the edge of the GO. Increasing the amount of oleylamine to 0.1 mol·L-1 led to further growth of the Cu NWs along the parallel axis, which formed 2D embedded nets with RGOs (Figure 4 c). Interestingly, increasing the amount of oleylamine further (0.15 mol·L-1) resulted in the formation of ultra-long Cu NWs covering the RGOs in a disordered manner (Figure 4d). Although higher concentrations of oleylamine caused the capping effect of Cu NWs, which more easily formed longer wires with larger diameters, excessive oleylamine also led to the aggregation of RGOs accompanied with the disappearance of the RGO boundary containing 1D ordered Cu NWs. In addition to the conditions above, the nucleation rate with different heating rates was another important condition in the preparation of Cu NW-RGO composites.

10


Page 11 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Heating from 25 to 180 °C at different rates (6 and 3 °C·min-1) was performed under the optimum conditions of 0.1 L EG, 0.006 mol CuCl, 0.075 g GO, 0.01 mol oleylamine, and 0.001 mol NH4Cl. When the heating rate was 6 °C·min-1, the precursor was quickly reduced by EG before the formation of oriented Cu NWs on RGO. As a result, few Cu NWs emerged in spite of the connected edges of RGO (Figure S3 a). Otherwise, at the slow heating rate of 3 °C·min-1 (Figure S3 b), oriented Cu NWs bridging RGOs were assembled because the precursor had sufficient time to form quasi-stable decahedral shaped Cu and the Cu seeds grew along the [110] direction to form the nanowires.26 High-quality Cu NW-RGO composites offer ideal building blocks for wearable electrodes. The sheet resistances of Cu NW-RGO composite films prepared with different concentrations of GO are listed in Figure 5a. The sheet resistance of the Cu NW-RGO composite film decreased significantly from nearly ten thousand Ω·sq-1 to less than 1 Ω·sq-1 when the concentration of GO increased from 0 to 0.75 g·L-1 GO. In general, the oxidation of Cu NWs could strongly militate against the conductivity. To achieve the ideal performance, high-temperature sintering or acid washing of Cu NW films is indispensable,26,

41

but these methods are difficult to apply to wearable

substrates such as polyester and nylon. In this system, the addition of a small amount of GO (no more than 0.75 g·L-1) not only led to excellent electrical conductivity and flexibility without any added treatment but also led to durability attributed to the nanostructure. When the concentration of GO reached 1 g·L-1, the sheet resistance of the Cu NW-RGO composite films increased, because the excessive GO restricted the

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

growth of the Cu NWs. By optimizing the experimental conditions above, the ideal synthetic conditions for preparing Cu NW-RGO composite films were confirmed as follows: 0.006 mol CuCl, 0.075 g GO, 0.01 mol oleylamine, 0.001 mol NH4Cl, 0.1 L EG, and a heating rate of 3 °C·min-1 from 25 to 180 °C. In Figure 5b, the sheet resistance of the Cu NW-RGO composite film was controlled by varying the concentration of the deposition, which led to the formation of continuous nanowire networks. The sheet resistance decreased significantly (0.808 Ω·sq-1 at 5 mg·cm-2) with the concentration of Cu NW-RGO composites because a greater number of contact points between the Cu NWs and RGO were generated at higher concentrations. Normally, nanoscale Cu-based electrodes have plenty point-to-point contacts that serve as current pathways through partial sintering at a temperature greater than 180 °C.26, 42 However, the Cu NW-RGO composites had outstanding structural advantages without sintering. A film of overlapped and stacked RGO platelets as large as several micrometres can provide a growth platform for Cu NWs and bridge initially unconnected Cu NWs, which provide two-dimensional conductive platforms for charge delivery and decrease the contact resistance compared to that of Cu NW films. Furthermore, every RGO platelet separated laterally by 1D ordered Cu NWs showed unique boundaries. This might have resulted in the higher electrical conductivity of the hybrid films due to the absence of the inter-platelet junction resistances of RGO. The results were suggested that the cooperative interaction between Cu NWs and RGO led to the annealing-free fabrication of hybrid films with better electrical conductivity than pure Cu NW films.

12


Page 12 of 40

Page 13 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For the further discussion of the RGO effect in the composite, we compared the sheet resistances of Cu NW-RGO, Cu NW/RGO (physical mixed), Cu NW without annealing, and Cu NW annealing at 200 ºC with different surface density (1-5 mg·cm-2), which was listed in Table 1. For the Cu NW-RGO by the solvothermal method and Cu NW/RGO (physical mixed), the RGO concentration was same (0.75 g·L-1). The density of Cu NWs in Cu NW-RGO and Cu NW/RGO (physical mixed) were a little less than those of the pure Cu NW films (annealing or without annealing) due to small amounts of RGO in the composites. In Table 1, the sheet resistance of every sample decreased with the increasing surface density, because a greater number of contact points in the composites were generated at higher concentrations. In addition, the sheet resistance of Cu NW-RGO prepared by the solvothermal method without annealing was close to that of pure Cu NW annealing at 200 ºC. Usually, Cu NW electrodes with annealing at a temperature greater than 180 ºC have many contacts as electron pathways.26 However, the Cu NW-RGO composites obtain good conductivity without sintering due to the outstanding structural advantages, as shown in Figure S4 a. Actually, the exposed parts of Cu NWs were oxidized, but the contact parts of Cu NWs that connected on the graphene sheets could not be oxidized. Because RGOs as anti-oxidation layers protected the contact parts of Cu NWs which was connected on the graphene surfaces from harsh environment. The electrons could be transported between Cu NWs and graphene by the protection of graphene leading to less junction resistance of the composite. The resistance of Cu NW-RGO films was mainly determined by the contact

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

resistance of junctions between Cu NWs and RGOs. For pure Cu NWs without any treatment, the oxide layer could quickly generate and tightly cover on the surface of Cu NWs in air condition, which attributed to high resistance due to the barrier of contacts between nanowires.26, 43-44 However, in the preparation of Cu NW-RGO, RGOs offered large platforms that helped the Cu NWs to grow on the surface of RGOs, resulting in the formation of close contacts between them. The firm contacting parts provided anti-oxidation layers for the Cu NWs bridging RGOs, as similar to the acid treatment and annealing method of Cu NWs,26, 41 which was expected to facilitate the electron transfer between Cu NWs and RGOs. Furthermore, the filtration transfer process applied the external pressure to make direct and tight contacts in the composites. For those reasons, the Cu NW-RGO composite films achieved a low contact resistance by RGO. Compared to Cu NW/RGO (physical mixed) and Cu NW without annealing, the Cu NW-RGO also showed the excellent conductivity. Without annealing, the surface on the Cu NWs could form Cu oxide layer, which hindered electron transference between nanowires due to the high junction resistance, as shown in Figure S4 b and c. The RGOs also improved stability of the Cu NW-RGO in the air condition. Figures 5 c1, c2, and c3 show the change of the relative resistance over time of pure Cu NWs and Cu NW-RGO films under ambient conditions at room temperature, 60, and 100 °C, respectively. The room-temperature resistance ratio (R/R0) of Cu NW films increased to 6 after 30 days, the R/R0 of the samples at 60 °C increased to 19.4 after 5 h, and the R/R0 of the samples at 100 °C increased to 38.6 after 150 min; this is

14


Page 14 of 40

Page 15 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


because Cu is more sensitive to oxygen and moisture than other noble metals and the faster kinetics of oxidation at higher temperatures gave rise to a more rapid increase in R/R0.45 However, the R/R0 of the Cu NW-RGO composite films showed no significant change in Figure 5C, which indicates the extraordinary oxidation resistance of Cu NW-RGO composites. The R/R0 of the Cu NW-RGO composites only increased to 3.8 after 150 min at 100 °C due to the irreversible nature of Cu. Without RGO, the Cu NWs were generally prepared surrounded by residual oleylamine, and the oxides/hydroxide on their surface critically obstructed the electron mobility between the Cu NWs. During the addition of GO in the reaction, these Cu NWs could grow on the overlapped and stacked RGOs, which acted as a diffusion barrier to air, water, and oleylamine to protect the surface of Cu NWs from oxidation,46 as shown in Figure S4. Furthermore, the subtle change of Cu NW-RGO composites was found that the R/R0 was increased in the shorter time when the temperature was higher. It was meant that RGOs could not cover the Cu NWs fully as shown in Figure 1, leading to the surface oxidation was not suppressed completely. If the temperature was high in air condition, the Cu NWs in the Cu NW-RGO composite would be oxidized, which was similar to the pure Cu NWs. In Table 2, the film thickness, sheet resistance, and electrical conductivity and resistivity of Cu NW/RGO physical mixture and Cu NW-RGO composite films with different GO concentration were listed. It was found that the electrical conductivity reached the maximum without additional post-treatments when the GO concentration was increased to 0.75 g·L-1, which suggested that RGOs partially prevented oxidation

15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

leading to the slight surface oxide involved in composite materials. Compared with conventional metal wires, wearable conducting materials must have excellent mechanical and electrical properties and light weight. Currently, wearable conducting devices are fabricated from an extensive variety of nanomaterials, including carbon nanotubes (CNTs), Ag NWs, aligned-CNT/Ag, and Ni-coated cotton composite.2, 28, 47-48 However, most of these strategies require many complicated and high-cost production processes (such as coating, assembling, and weaving), and the productions are easily damaged under bending, folding, or other deformations that often occur during the daily use, resulting in equipment malfunctions.49 Although the Cu NW cost in per gram was nearly 1000 times the cost of bulk Cu and the cost of our production was a little higher than the reference,50 we chose the cheap CuCl as the Cu source and used the GO by a chemical method in order to control our cost. Furthermore, we only used the filtration process to deposit Cu NW-RGO composites on polyester fabric, which simplified the production process and decreased the expense of wearable electrodes. In our study, the facile and simple filtration method was exploited to deposit Cu NW-RGO composites on polyester fabric as high-conductivity electrodes to overcome the above-mentioned drawbacks of conventional conducting wearable materials, as shown in Figures 6a and b. The Cu NW-RGO composites were also filtered on polyester fabric for a special pattern in Figure S5. The Cu NW-RGO composites deposited on the cloth were strongly dependent on random connections and stacking. In addition, the combination of Cu NWs and RGO maintained a high intrinsic

16


Page 16 of 40

Page 17 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electrical conductivity and fabric-like flexibility. In comparison with metallic wearable materials, Cu NW-RGO-based electrodes prepared with the direct coating method could easily be mended, had no metallic contacts, and were ultraportable as a thin paper. Therefore, the flexible and antioxidant composite has great potential for application to next-generation smart wearable electronics. The conductivity of the Cu NW-RGO composites remained suitable when the fabric was bended (Figure S6), which clearly showed that the electrode was suitable for human motion applications. A laboratory designed bending machine was used to study the flexibility of the Cu NW-RGO composites. The composite was stressed by different bending cycles and bending radius, which was bended by 5 mm of bending radius under 20 mm s-1 of motion speed from 1 to 1000 cycles. In Figure 6c, the resistance ratio still kept below 1.08 after 1000 bending cycles. The good durability of Cu NW-RGO film was likely attributed to their stable nanostructure. The Cu NW bridged between RGO nanosheets to form a continuous conducting network that had the collaborative effect of the intrinsic conductivity and the good durability between RGOs and Cu NWs. The resistance ratio of different bending radius (5, 10, 15, and 20 mm) of Cu NW-RGO composite films is shown in Figure 6d, which has a little variation of the resistance ratio (R/R0180 ºC, it cannot be directly coated on polyester clothes), the extra treatment usually resulted in the brittle Cu NWs with poor mechanical property. Although the addition of graphene affected the flexibility and durability of the Cu NW-RGO, our method overcame the defect of the annealing treatment for directly coating on polyester fabric. As the result, it retained the good mechanical property and simplified the production process, which provided the composite with potential applications in wearable devices.

4. Conclusions In conclusion, we directly synthesized Cu NW-RGO composites for flexible, durable, and air-stable electrodes using the GO-assisted solvothermal method. Furthermore, the Cu NW-RGO composites directly deposited on polyester cloth by simple filtration method, and this film showed a low sheet resistance without any extra treatment, such as annealing or acid process. The aligned Cu NWs can bridge disconnected RGO networks and act as significant pathways for charge transfer, and RGO offered an anti-oxidation layer protecting the Cu NWs from harsh environments. Therefore, the Cu NW-RGO composite film was superior to other flexible materials because of the combination of high conductivity, stable resistance to oxidation, and durable flexibility. We envision that this composite will be applicable to various types of ideal wearable smart clothes.

Supporting Information 18


Page 18 of 40

Page 19 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TEM image and SAED pattern of Cu NW-RGO, SEM images of Cu NW-RGO composites prepared by the different heating rate, SEM image of Cu NW, Schematic illustration of the electron transference, and Photographs of Cu NW-RGO composites deposited on polyester fabric for wearable conductive electrode

Acknowledgements This work was supported by Nano Material Technology Development Program (NRF-2015M3A7B6027970) of MSIP/NRF and by the Center for Integrated Smart Sensors funded by the Ministry of Science, ICT and Future Planning,

Republic

of

Korea,

as

Global

Frontier

Project

(CISS-012M3A6A6054186). Also, this work was supported by the Center for Advanced

Soft

Electronics

as

Global

Frontier

Research

Program

(2013M3A6A5073177) of the Ministry of Science, ICT and Future Planning of Korea.

References 1.

Choi, S.; Park, J.; Hyun, W.; Kim, J.; Kim, J.; Lee, Y. B.; Song, C.; Hwang, H. J.; Kim, J. H.;

Hyeon, T.; Kim, D.-H., Stretchable Heater Using Ligand-Exchanged Silver Nanowire Nanocomposite for Wearable Articular Thermotherapy. ACS Nano 2015, 9 (6), 6626-6633. 2.

Lee, S.; Shin, S.; Lee, S.; Seo, J.; Lee, J.; Son, S.; Cho, H. J.; Algadi, H.; Al-Sayari, S.; Kim, D. E.;

Lee, T., Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics. Adv. Funct. Mater. 2015, 25 (21), 3114-3121. 3.

Ahn, B. Y.; Duoss, E. B.; Motala, M. J.; Guo, X.; Park, S.-I.; Xiong, Y.; Yoon, J.; Nuzzo, R. G.;

Rogers, J. A.; Lewis, J. A., Omnidirectional Printing of Flexible, Stretchable, and Spanning Silver Microelectrodes. Science 2009, 323 (5921), 1590-1593. 4.

Wu, J.; Zang, J.; Rathmell, A. R.; Zhao, X.; Wiley, B. J., Reversible sliding in networks of

nanowires. Nano lett. 2013, 13 (6), 2381-2386. 5.

Shin, D.-H.; Woo, S.; Yem, H.; Cha, M.; Cho, S.; Kang, M.; Jeong, S.; Kim, Y.; Kang, K.; Piao,

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 40

Y., A Self-Reducible and Alcohol-Soluble Copper-Based Metal–Organic Decomposition Ink for Printed Electronics. ACS appl. mater. interfaces 2014, 6 (5), 3312-3319. 6.

Yang, H.-J.; He, S.-Y.; Chen, H.-L.; Tuan, H.-Y., Monodisperse Copper Nanocubes: Synthesis,

Self-Assembly, and Large-Area Dense-Packed Films. Chem. Mater. 2014, 26 (5), 1785-1793. 7.

Seyedin,

M.

Z.;

Razal,

J.

M.;

Innis,

P.

C.;

Wallace,

G.

G.,

Strain-Responsive

Polyurethane/PEDOT:PSS Elastomeric Composite Fibers with High Electrical Conductivity. Adv. Funct. Mater. 2014, 24 (20), 2957-2966. 8.

Ren, J.; Bai, W.; Guan, G.; Zhang, Y.; Peng, H., Flexible and Weaveable Capacitor Wire Based

on a Carbon Nanocomposite Fiber. Adv. Mater. 2013, 25 (41), 5965-5970. 9.

Sun, H.; You, X.; Deng, J.; Chen, X.; Yang, Z.; Ren, J.; Peng, H., Novel Graphene/Carbon

Nanotube Composite Fibers for Efficient Wire-Shaped Miniature Energy Devices. Adv. Mater. 2014, 26 (18), 2868-2873. 10. Hu, L.; Pasta, M.; Mantia, F. L.; Cui, L.; Jeong, S.; Deshazer, H. D.; Choi, J. W.; Han, S. M.; Cui, Y., Stretchable, Porous, and Conductive Energy Textiles. Nano Lett. 2010, 10 (2), 708-714. 11. Yang, Z.; Sun, H.; Chen, T.; Qiu, L.; Luo, Y.; Peng, H., Photovoltaic Wire Derived from a Graphene Composite Fiber Achieving an 8.45 % Energy Conversion Efficiency. Angew. Chem. Int. Ed. 2013, 125 (29), 7693-7696. 12. Boland, C. S.; Khan, U.; Backes, C.; O’Neill, A.; McCauley, J.; Duane, S.; Shanker, R.; Liu, Y.; Jurewicz, I.; Dalton, A. B.; Coleman, J. N., Sensitive, High-Strain, High-Rate Bodily Motion Sensors Based on Graphene–Rubber Composites. ACS Nano 2014, 8 (9), 8819-8830. 13. Zhao, X.; Zheng, B.; Huang, T.; Gao, C., Graphene-Based Single Fiber Supercapacitor with a Coaxial Structure. Nanoscale 2015, 7 (21), 9399-9404. 14. Yao, S.; Zhu, Y., Nanomaterial-Enabled Stretchable Conductors: Strategies, Materials and Devices. Adv. Mater. 2015, 27 (9), 1480-1511. 15. Atwa, Y.; Maheshwari, N.; Goldthorpe, I. A., Silver Nanowire Coated Threads for Electrically Conductive Textiles. J. Mater. Chem. C 2015, 3 (16), 3908-3912. 16. Hong, S.; Lee, H.; Lee, J.; Kwon, J.; Han, S.; Suh, Y. D.; Cho, H.; Shin, J.; Yeo, J.; Ko, S. H., Highly Stretchable and Transparent Metal Nanowire Heater for Wearable Electronics Applications. Adv. Mater. 2015, 27 (32), 4744-4751. 17. Park, M.; Im, J.; Shin, M.; Min, Y.; Park, J.; Cho, H.; Park, S.; Shim, M.-B.; Jeon, S.; Chung, D.-Y.; Bae, J.; Park, J.; Jeong, U.; Kim, K., Highly Stretchable Electric Circuits from a Composite Material of Silver Nanoparticles and Elastomeric Fibres. Nat. Nanotech. 2012, 7 (12), 803-809. 18. Ye, S.; Rathmell, A. R.; Chen, Z.; Stewart, I. E.; Wiley, B. J., Metal Nanowire Networks: The Next Generation of Transparent Conductors. Adv. Mater. 2014, 26 (39), 6670-6687. 19. Song, J.; Zeng, H., Transparent Electrodes Printed with Nanocrystal Inks for Flexible Smart Devices. Angew. Chem. Int. Ed. 2015, 54, 9760-9774. 20. Liang, J.; Li, L.; Tong, K.; Ren, Z.; Hu, W.; Niu, X.; Chen, Y.; Pei, Q., Silver Nanowire Percolation Network Soldered with Graphene Oxide at Room Temperature and Its Application for Fully Stretchable Polymer Light-Emitting Diodes. ACS Nano 2014, 8 (2), 1590-1600. 21. Ge, J.; Yao, H.-B.; Wang, X.; Ye, Y.-D.; Wang, J.-L.; Wu, Z.-Y.; Liu, J.-W.; Fan, F.-J.; Gao, H.-L.; Zhang, C.-L.; Yu, S.-H., Stretchable Conductors Based on Silver Nanowires: Improved Performance through a Binary Network Design. Angew. Chem. Int. Ed. 2013, 52 (6), 1654-1659. 22. Bhanushali, S.; Ghosh, P.; Ganesh, A.; Cheng, W., 1D Copper Nanostructures: Progress, Challenges and Opportunities. Small 2015, 11 (11), 1232-1252.

20


Page 21 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


23. Borchert, J. W.; Stewart, I. E.; Ye, S.; Rathmell, A. R.; Wiley, B. J.; Winey, K. I., Effects of Length Dispersity and Film Fabrication on the Sheet Resistance of Copper Nanowire Transparent Conductors. Nanoscale 2015, 7, 14496-14504. 24. Jason, N. N.; Shen, W.; Cheng, W., Copper Nanowires as Conductive Ink for Low-Cost Draw-On Electronics. ACS appl. mater. interfaces 2015, 7 (30), 16760-16766. 25. Han, S.; Hong, S.; Ham, J.; Yeo, J.; Lee, J.; Kang, B.; Lee, P.; Kwon, J.; Lee, S. S.; Yang, M.-Y.; Ko, S. H., Fast Plasmonic Laser Nanowelding for a Cu-Nanowire Percolation Network for Flexible Transparent Conductors and Stretchable Electronics. Adv. Mater. 2014, 26 (33), 5808-5814. 26. Yin, Z.; Lee, C.; Cho, S.; Yoo, J.; Piao, Y.; Kim, Y. S., Facile Synthesis of Oxidation-Resistant Copper Nanowires toward Solution-Processable, Flexible, Foldable, and Free-Standing Electrodes. Small 2014, 10 (24), 5047-5052. 27. Yin, Z.; Song, S. K.; You, D.-J.; Ko, Y.; Cho, S.; Yoo, J.; Park, S. Y.; Piao, Y.; Chang, S. T.; Kim, Y. S., Novel Synthesis, Coating, and Networking of Curved Copper Nanowires for Flexible Transparent Conductive Electrodes. Small 2015, 11 (35), 4576–4583. 28. Libin, L.; You, Y.; Casey, Y.; Kan, L.; Zijian, Z., Wearable Energy-Dense and Power-Dense Supercapacitor Yarns Enabled by Scalable Graphene-Metallic Textile Composite Electrodes. Nat. Commun. 2015, 6, 7260. 29. Xu, H.; Wang, H.; Wu, C.; Lin, N.; Soomro, A. M.; Guo, H.; Liu, C.; Yang, X.; Wu, Y.; Cai, D.; Kang, J., Direct Synthesis of Graphene 3D-Coated Cu Nanosilks Network for Antioxidant Transparent Conducting Electrode. Nanoscale 2015, 7 (24), 10613-10621. 30. Kholmanov, I. N.; Domingues, S. H.; Chou, H.; Wang, X.; Tan, C.; Kim, J.-Y.; Li, H.; Piner, R.; Zarbin, A. J. G.; Ruoff, R. S., Reduced Graphene Oxide/Copper Nanowire Hybrid Films as High-Performance Transparent Electrodes. ACS Nano 2013, 7 (2), 1811-1816. 31. Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S., Synthesis of Graphene-Based Nanosheets via Chemical Reduction of Exfoliated Graphite Oxide. Carbon 2007, 45 (7), 1558-1565. 32. Hummers, W. S.; Offeman, R. E., Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80 (6), 1339-1339. 33. Zhang, W.; Quan, B.; Lee, C.; Park, S.-K.; Li, X.; Choi, E.; Diao, G.; Piao, Y., One-Step Facile Solvothermal Synthesis of Copper Ferrite–Graphene Composite as a High-Performance Supercapacitor Material. ACS appl. mater. interfaces 2015, 7 (4), 2404-2414. 34. Jin, M.; He, G.; Zhang, H.; Zeng, J.; Xie, Z.; Xia, Y., Shape-Controlled Synthesis of Copper Nanocrystals in an Aqueous Solution with Glucose as a Reducing Agent and Hexadecylamine as a Capping Agent. Angew. Chem. Int. Ed. 2011, 50 (45), 10560-10564. 35. Yang, H.-J.; He, S.-Y.; Tuan, H.-Y., Self-Seeded Growth of Five-Fold Twinned Copper Nanowires: Mechanistic Study, Characterization, and SERS Applications. Langmuir 2014, 30 (2), 602-610. 36. Meng, F.; Jin, S., The Solution Growth of Copper Nanowires and Nanotubes is Driven by Screw Dislocations. Nano Lett. 2012, 12 (1), 234-239. 37. Zhang, D.; Wang, R.; Wen, M.; Weng, D.; Cui, X.; Sun, J.; Li, H.; Lu, Y., Synthesis of Ultralong Copper Nanowires for High-Performance Transparent Electrodes. J. Am. Chem. Soc. 2012, 134 (35), 14283-14286. 38. Guo, H.; Chen, Y.; Ping, H.; Jin, J.; Peng, D.-L., Facile Synthesis of Cu and Cu@Cu-Ni Nanocubes and Nanowires in Hydrophobic Solution in the Presence of Nickel and Chloride Ions.

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nanoscale 2013, 5 (6), 2394-2402. 39. Yang, S.-T.; Chang, Y.; Wang, H.; Liu, G.; Chen, S.; Wang, Y.; Liu, Y.; Cao, A., Folding/Aggregation of Graphene Oxide and its Application in Cu2+ Removal. J. Colloid Interf. Sci. 2010, 351 (1), 122-127. 40. Rathmell, A. R.; Bergin, S. M.; Hua, Y.-L.; Li, Z.-Y.; Wiley, B. J., The Growth Mechanism of Copper Nanowires and Their Properties in Flexible, Transparent Conducting Films. Adv. Mater. 2010, 22 (32), 3558-3563. 41. Yulim, W.; Areum, K.; Donggyu, L.; Wooseok, Y.; Kyoohee, W.; Sunho, J.; Jooho, M., Annealing-Free Fabrication of Highly Oxidation-Resistive Copper Nanowire Composite Conductors for Photovoltaics. NPG Asia Materials 2014, 6 (6), e105. 42. Ishizaki, T.; Watanabe, R., A New One-Pot Method for the Synthesis of Cu Nanoparticles for Low Temperature Bonding. J. Mater. Chem. 2012, 22 (48), 25198-25206. 43. Wu, H.; Kong, D.; Ruan, Z.; Hsu, P.-C.; Wang, S.; Yu, Z.; Carney, T. J.; Hu, L.; Fan, S.; Cui, Y., A Transparent Electrode Based on a Metal Nanotrough Network. Nat. Nano. 2013, 8 (6), 421-425. 44. Ding, S.; Jiu, J.; Tian, Y.; Sugahara, T.; Nagao, S.; Suganuma, K., Fast Fabrication of Copper Nanowire Transparent Electrodes by a High Intensity Pulsed Light Sintering Technique in Air. Phys. Chem. Chem. Phys. 2015, 17 (46), 31110-31116. 45. Rathmell, A. R.; Nguyen, M.; Chi, M.; Wiley, B. J., Synthesis of Oxidation-Resistant Cupronickel Nanowires for Transparent Conducting Nanowire Networks. Nano Letters 2012, 12 (6), 3193-3199. 46. Kang, D.; Kwon, J. Y.; Cho, H.; Sim, J.-H.; Hwang, H. S.; Kim, C. S.; Kim, Y. J.; Ruoff, R. S.; Shin, H. S., Oxidation Resistance of Iron and Copper Foils Coated with Reduced Graphene Oxide Multilayers. ACS Nano 2012, 6 (9), 7763-7769. 47. Behabtu, N.; Young, C. C.; Tsentalovich, D. E.; Kleinerman, O.; Wang, X.; Ma, A. W. K.; Bengio, E. A.; ter Waarbeek, R. F.; de Jong, J. J.; Hoogerwerf, R. E.; Fairchild, S. B.; Ferguson, J. B.; Maruyama, B.; Kono, J.; Talmon, Y.; Cohen, Y.; Otto, M. J.; Pasquali, M., Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity. Science 2013, 339 (6116), 182-186. 48. Sun, H.; You, X.; Jiang, Y.; Guan, G.; Fang, X.; Deng, J.; Chen, P.; Luo, Y.; Peng, H., Self-Healable Electrically Conducting Wires for Wearable Microelectronics. Angew. Chem. Int. Ed. 2014, 53 (36), 9526-9531. 49. Sun, H.; You, X.; Deng, J.; Chen, X.; Yang, Z.; Chen, P.; Fang, X.; Peng, H., A Twisted Wire-Shaped Dual-Function Energy Device for Photoelectric Conversion and Electrochemical Storage. Angew. Chem. Int. Ed. 2014, 126 (26), 6782-6786. 50. Wei, Y.; Chen, S.; Lin, Y.; Yang, Z.; Liu, L., Cu-Ag Core-Shell Nanowires for Electronic Skin with a Petal Molded Microstructure. J. Mater. Chem. C 2015, 3 (37), 9594-9602.

22


Page 22 of 40

Page 23 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Fabrication of Cu NW-RGO composite wearable electrode. .

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. (a, b) SEM images of Cu NW-RGO composites. (c) TEM image of Cu NW-RGO composites. (d) XRD pattern of Cu NW-RGO composites.

24


Page 24 of 40

Page 25 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a, c) HR-TEM images and (b, d) corresponded FFT patterns of Cu NW on composites with different incident electron beam.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. SEM images of Cu NW-RGO composites prepared by the different concentrations of GO: (a) 0.25, (b) 0.75, (c) 1.25, and (d) 1.75 g·L-1. Other conditions: 0.06 mol·L-1 CuCl, 0.1 mol·L-1 oleylamine, 0.01 mol·L-1 NH4Cl, 180 °C, 10 h

26


Page 26 of 40

Page 27 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. SEM images of Cu NW-RGO composites prepared by the different concentrations of oleylamine: (a) 0, (b) 0.05, (c) 0.1, and (d) 0.15 mol·L-1. Other conditions: 0.06 mol·L-1 CuCl, 0.75 g·L-1 GO, 0.01 mol·L-1 NH4Cl, 180 °C, 10 h

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5. (a) The sheet resistance of Cu NW-RGO composite films (5 mg·cm-2) with different GO concentration: 0, 0.25, 0.5, 0.75, and 1.00 g·L-1. (b) The sheet resistance of Cu NW-RGO composite films with different surface density: 1, 2, 3, 4, and 5 mg·cm-2. (c) Changes in the resistance ratio of pure Cu NW films and Cu NW-RGO films kept at (c1) room temperature for 30 days, (c2) 60 °C for 5 h, and (c3) 100 °C for 150 min.

28


Page 28 of 40

Page 29 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. (a) Photograph of the Cu NW-RGO composites filtered on a polyester cloth, (b) Photograph of the Cu NW-RGO composites on a polyester cloth with strong bending, lighting of a LED with an external power supply. (c) The relative resistance of Cu NW-RGO film under 1000 times of bending cycle. (d) The relative resistance of Cu NW-RGO film under 20, 15, 10, and 5 mm of bending radius.

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 40

Table 1 The sheet resistances in the different surface density. Sheet resistances (Ω·sq-1) in different surface density Sample

a

1 mg·cm-2

2 mg·cm-2

3 mg·cm-2

4 mg·cm-2

5 mg·cm-2

Cu NW/RGO physical mixture a

3.09×105

2.24×105

1.54×105

7.68×104

3.38×104

Cu NW without annealing

2.18×104

9.47×103

6.47×103

4.25×103

1.83×103

Cu NW with annealing b

5.12

1.28

9.29×10-1

5.30×10-1

1.14×10-1

Cu NW-RGO without annealing c

4.90×102

6.01

4.33

2.61

8.08×10-1

The mixture is without annealing, and the RGO concentration was same to that of Cu NW-RGO prepared with 0.75 g·L-1 GO.

b

Annealing temperature was 200 ºC

c

The Cu NW-RGO was prepared with 0.75 g·L-1 GO.

30


Page 31 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2 The film thicknesses, sheet resistances, and electrical conductivities and resistivities of Cu NW/RGO physical mixture and Cu NW-RGO composite films with different GO concentration: 0, 0.25, 0.5, 0.75, and 1.00 g·L-1. (Surface density: 5 mg·cm-2) Sheet

Sheet

Electric

thickness

resistance

conductivity

(m)

(Ω·sq-1)

(S·m-1)

Cu NW without annealing

1.456×10-5

1.83×103

3.75×101

2.66×10-2

Cu NW-RGO with 0.25 g·L-1 GO

1.471×10-5

6.69

1.02×104

9.84×10-5


1.537×10-5

1.66

3.91×104

2.55×10-5


1.512×10-5

8.08×10-1

8.19×104

1.22×10-5

Cu NW-RGO with 1 g·L-1 GO

1.576×10-5

7.55

8.40×103

1.19×10-4

Cu NW/RGO physical mixture b

1.458×10-5

3.38×104

2.03

4.93×10-1

Sample

a

a

All samples were without annealing.

b

The RGO concentration was same to that of Cu NW-RGO prepared with 0.75 g·L-1 GO.

31


Resistivity (Ω·m)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC

32


Page 32 of 40

Page 33 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Fabrication of Cu NW-RGO composite wearable electrode. 433x121mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. (a, b) SEM images of Cu NW-RGO composites. (c) TEM image of Cu NW-RGO composites. (d) XRD pattern of Cu NW-RGO composites. 337x260mm (96 x 96 DPI)


Page 34 of 40

Page 35 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a, c) HR-TEM images and (b, d) corresponded FFT patterns of Cu NW on composites with different incident electron beam. 326x296mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. SEM images of Cu NW-RGO composites prepared by the different concentrations of GO: (a) 0.25, (b) 0.75, (c) 1.25, and (d) 1.75 g·L-1. Other conditions: 0.06 mol·L-1 CuCl, 0.1 mol·L-1 oleylamine, 0.01 mol·L-1 NH4Cl, 180 °C, 10 h 342x241mm (96 x 96 DPI)


Page 36 of 40

Page 37 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. SEM images of Cu NW-RGO composites prepared by the different concentrations of oleylamine: (a) 0, (b) 0.05, (c) 0.1, and (d) 0.15 mol·L-1. Other conditions: 0.06 mol·L-1 CuCl, 0.75 g·L-1 GO, 0.01 mol·L-1 NH4Cl, 180 °C, 10 h 351x250mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. (a) Photograph of the Cu NW-RGO composites filtered on a polyester cloth, (b) Photograph of the Cu NW-RGO composites on a polyester cloth with strong bending, lighting of a LED with an external power supply. (c) The relative resistance of Cu NW-RGO film under 1000 times of bending cycle. (d) The relative resistance of Cu NW-RGO film under 20, 15, 10, and 5 mm of bending radius. 317x246mm (96 x 96 DPI)


Page 38 of 40

Page 39 of 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC 91x47mm (120 x 120 DPI)


Bridging Oriented Copper NanowireâGraphene Composites for

Recommend Documents

Bridging Oriented Copper NanowireâGraphene Composites for