Three-Dimensional Printed Graphene Foams

*Email: [email protected], [email protected], [email protected]. #. Authors have contributed equally. Abstract An automated metal powder three-dimensional (3D...
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Three-Dimensional Printed Graphene Foams Junwei Sha,†,⊥,∥,# Yilun Li,†,# Rodrigo Villegas Salvatierra,† Tuo Wang,† Pei Dong,§ Yongsung Ji,† Seoung-Ki Lee,† Chenhao Zhang,† Jibo Zhang,† Robert H. Smith,¶ Pulickel M. Ajayan,§ Jun Lou,*,§ Naiqin Zhao,*,⊥,∥ and James M. Tour*,†,‡,§ †

Department of Chemistry, ‡Smalley-Curl Institute and The NanoCarbon Center, and §Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, Texas 77005, United States ⊥ School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300350, China ∥ Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300350, China ¶ Qualified Rapid Products, 6764 Airport Road, West Jordan, Utah 84084, United States S Supporting Information *

ABSTRACT: An automated metal powder three-dimensional (3D) printing method for in situ synthesis of freestanding 3D graphene foams (GFs) was successfully modeled by manually placing a mixture of Ni and sucrose onto a platform and then using a commercial CO2 laser to convert the Ni/sucrose mixture into 3D GFs. The sucrose acted as the solid carbon source for graphene, and the sintered Ni metal acted as the catalyst and template for graphene growth. This simple and efficient method combines powder metallurgy templating with 3D printing techniques and enables direct in situ 3D printing of GFs with no high-temperature furnace or lengthy growth process required. The 3D printed GFs show high-porosity (∼99.3%), low-density (∼0.015g cm−3), high-quality, and multilayered graphene features. The GFs have an electrical conductivity of ∼8.7 S cm−1, a remarkable storage modulus of ∼11 kPa, and a high damping capacity of ∼0.06. These excellent physical properties of 3D printed GFs indicate potential applications in fields requiring rapid design and manufacturing of 3D carbon materials, for example, energy storage devices, damping materials, and sound absorption. KEYWORDS: 3D printing, powder metallurgy, graphene foam, laser sintering, high-porosity carbon raphene has drawn tremendous attention in the fields of energy storage devices,1−15 catalysis,16−18 transparent conductive films,19−24 and lightweight materi25 als due to its remarkable properties such as high thermal and electrical conductivity, high specific surface area, and good mechanical strength. 26−31 However, as most of these applications require a large mass or volume of graphene materials, two-dimensional (2D) graphene films or individual graphene nanosheets need to be extended into the third dimension to build a three-dimensional (3D) macroscopic structure.32 Several methods have been developed to prepare 3D graphene foams (GFs), such as chemical vapor deposition (CVD) using commercial Ni or Cu foams,33 pyrolysis using templates such as NaCl,34 polystyrene colloidal particles,35 or porous silica opal crystals,36 and self-assembly of graphene oxide (GO) by hydrothermal reactions.37 However, these methods still have limitations such as an inability to control pore structures, incapability to be free-standing, and low mechanical strength, and they often require complicated preparation processes. The GO-derived 3D GF is framed on discrete defective GO sheets rather than a single and uniform

G

© 2017 American Chemical Society

graphene structure. In our previous work, a powder metallurgy template method was developed to prepare 3D GFs.38,39 Yet, this process required the fabrication of a mold to contain the monolith that was formed. A 1000 °C CVD process as well as a ∼2.8 h heating and cooling process was required. Thus, a simple and efficient method to directly prepare 3D carbon materials was sought. 3D printing is a simple and efficient technique enabling the direct production of 3D bulk objects. In 3D printing, polymers, ceramics, or metals can be heated and deposited layer by layer under computer control to build 3D monoliths that are designed using software associated with the printer.40 However, when this 3D printing technique is used for carbon or carboncontaining objects, the as-prepared material is limited to microsized scales, with the precursors contained in inkjetprintable or UV-curable inks.40,41 Thus, for the fabrication of Received: March 22, 2017 Accepted: June 13, 2017 Published: June 13, 2017 6860

DOI: 10.1021/acsnano.7b01987 ACS Nano 2017, 11, 6860−6867

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Figure 1. (a) Schematic of in situ synthesis of 3D GF using a simulated 3D printing process. (b) Photographs of 3D printed GF before and after dissolving the Ni. The scale bars are 5 mm.

entire printing area, each laser spot (∼100 μm) exposure time is 10, the 2D band shifts to ∼2700 cm−1.56 With a 100P laser duty cycle and 2S rastering speed, the morphology and structure of 3D printed GFs after removing the Ni scaffolds were investigated by SEM and transmission electron microscope (TEM), as shown in Figure 4. Even after the three-step removal of the Ni scaffolds, the 3D printed GFs retained the structure of the sintered Ni scaffold, as shown in Figure 4a−c. The 3D printed GFs consist of graphene sheets and graphene shells that show structures similar to the Ni scaffolds and Ni particles since Ni acted as templates during growth, thereby permitting pore size commensurate with the metal particle sizes used. The porous structure of the 3D printed GFs could benefit applications in vibration damping and energy storage related fields.38,39,53 The density of 3D printed GFs was 0.015 ± 0.003 g cm−3, calculated by measuring the mass and volume of the CPD-dried monoliths. The porosity of 3D printed GFs was 99.3 ± 0.2%, calculated by the

details). As shown in the scanning electron microscope (SEM) images in Figures 2 and S2, although graphene sheets can be

(

equation θ = 1 − Figure 2. SEM images of 3D printed GFs with a Ni scaffold prepared using 100P and (a, b) 5S, (c, d) 3S, (e, f) 2S, and (g, h) 1S in a H2 atmosphere.

m Vd

) × 100%, where θ, m, V, and d are the

porosity, mass, volume, and density of graphite (which is 2.09 to 2.23 g cm−3), respectively.57 Both the density and porosity values of the 3D printed GFs are comparable to those of other carbon foam materials.58 The TEM image in Figure 4d shows a large graphene sheet; the inset is the selected area electron diffraction (SAED) pattern showing the hexagonal singlecrystal signal of the graphene. The carbon shells in Figure 4e are similar to those shown in the SEM images (Figure 4a−c). The high-magnification image in Figure 4f shows the fewlayered structure of 3D printed GFs, which can be observed from the edge of the graphene sheet, and is in good accordance with the results from the Raman spectra in Figure 3. The crystalline quality, elemental composition, phases, and purity of the 3D printed GFs were further investigated by Raman, X-ray photoelectron spectroscopy (XPS), X-ray

grown on the surface of sintered Ni scaffolds with 100P and 1S, 2S, 3S, and 5S, large amounts of unreacted sucrose were observed in Figure 2a,b at the highest 5S speed, indicating that the sucrose was not completely converted. When the rastering speed was decreased, the amount of unreacted sucrose decreased, and the sintered Ni scaffolds were larger and had smoother surfaces. With the slower rastering speed, the laser remained at each spot for more time, delivering more energy and heat to each particular spot. This increased energy and heat converted more sucrose to graphene and allowed the Ni crystalline grain to grow larger. While graphene wrinkles can be 6862

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Figure 3. Raman spectra of 3D printed GFs with a Ni scaffold prepared using (a) 10 to 100P with 5S and (b) 1 to 5S and 100P in a H2 atmosphere.

Figure 4. (a−c) SEM images and (d−f) TEM images of 3D printed GFs after removing Ni scaffolds prepared using 100P and 2S in a H2 atmosphere. The inset in (d) is the SAED pattern.

could be eliminated by using HCl as the etching reagent instead. TGA testing was performed in air from room temperature to 900 °C, as shown in Figure 5d. Only ∼1.9 wt % remained after testing, demonstrating that the Ni scaffolds and Fe etching residues were almost completely removed by the etching process. However, the rapid weight drop before ∼480 °C indicates the existence of amorphous carbon and unreacted sucrose, since the laser rastering process could still be too fast to completely convert the carbon from sucrose into graphene. The conductivity of 3D printed GFs was tested, as shown in Figure 6a. Pt contact pads (250 μm × 250 μm) were deposited directly onto the surface of 3D printed GFs using a shadow mask evaporation method. The distance between the contact pads is 120 μm. Figure 6b shows the room-temperature conductivity of 3D printed GFs. Figure 6c indicates the ohmic contact between the Pt pads and the 3D printed GFs. The average electrical conductivity of the 3D printed GFs is σ = IS / VA = 8.7 ± 1.8 S cm−1, where I, S , V, and A are the measured current, channel length, applied voltage, and cross-sectional area of 3D printed GFs, respectively. This value was comparable but lower than that of 3D GFs (13.8 S cm−1) prepared using powder metallurgy templates and other

diffraction (XRD), and thermogravimetric analyses (TGA), as shown in Figure 5. Similar to the spectra in Figure 3, typical D (∼1350 cm−1), G (∼1580 cm−1), and 2D (∼2670 cm−1) bands can be detected by Raman with a 633 nm laser, shown in Figure 5a. The ID/IG ratio of the purified GFs was 0.44, indicating a high quality of the 3D printed GFs. The IG/I2D ratio of 2.28 is indicative of multilayered graphene,51−54 which should contribute to the good mechanical properties of the 3D printed GFs. The 2D bands at ∼2670 cm−1 demonstrate that the content of the 3D printed GFs is indeed graphene, rather than graphite.56 The C 1s peak (284.5 eV) in the XPS elemental spectra, as shown in Figure 5b, indicates the material is graphene or graphite.51,54,59 Small amounts of Fe impurities (C 1s: 76.7 at. %; O 1s: 23.0 at. %; Fe 2p3: 0.3 at. %.) are also detected by XPS, which came from the FeCl3 etching solution and can be further removed with additional treatment if necessary.38 The XRD patterns in Figure 5c also indicate the low content of impurities in the 3D printed GFs. No obvious Ni peaks are detected, and most of the peaks match well with the expected peaks of a multilayered graphene phase.38,39,60 An additional small peak at ∼35° is also detected (as shown in Figure 5c). The small peak could be attributed to Fe2O3,61 arising from the FeCl3 etching solution. The Fe contamination 6863

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Figure 5. (a) Raman spectrum, (b) XPS curves with inset elemental scanning result of C 1s peak, (c) XRD pattern, and (d) TGA curve of 3D printed GFs after removing Ni prepared using 100P and 2S in a H2 atmosphere.

Figure 6. (a) Schematic diagram of electrical conductivity testing. The scale bar is 1 cm. (b) Current−voltage curves (I vs V) in semilogarithmic scale and (c) linear scale of 3D printed GFs after removing Ni, prepared using 100P and 2S in a H2 atmosphere.

Figure 7. DMA results of as-prepared 3D printed GF after removing Ni prepared using 100P and 2S in a H2 atmosphere: (a) storage modulus and loss modulus and (b) damping capacity at room temperature. The frequency of testing is 1 Hz.

methods.33,35,62−67 Although the high-quality and multilayered graphene features as demonstrated in Figure 5 indicate that the 3D printed GFs should possess high electrical conductivity, since the 3D printed GFs were prepared from loose powder rather than a hydraulic cold-pressing process, the resulting GFs have a relatively lower density, high-porosity structure with low conductivity. The 3D printed GFs were quite soft, so it was difficult to avoid damaging the Pt contact pads when touched

by the probe tips during testing, which would also lead to a lower conductivity value. However, the conductivity of the foamed GFs structure might be further improved by introducing CNTs to prepare 3D printed rebar GFs, which can also make the GFs mechanically stronger, as demonstrated in our previous work.39,54 To further investigate the mechanical properties of the 3D printed GFs, dynamic mechanical analysis (DMA) testing was 6864

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ion battery steel case was employed as the powder bed for 3D printing. The steel case was filled to ∼1 mm thick with the Ni/sucrose mixture and then transferred into a controlled atmosphere chamber, which allowed pure H2 gas (∼175 sccm) to flow through under ambient pressure.70 A ZnSe window (thickness 6 mm) was mounted on top of the chamber, which allowed an external CO2 laser to irradiate the Ni/ sucrose powder inside the chamber. The Ni/sucrose powder was irradiated with a 10.6 μm CO2 pulsed laser (75 W) on a XLS10MWH (Universal Laser Systems) laser platform with a maximum laser writing speed of 304.8 cm/s (120 in./s). The image density was 1000 pulses/ 2.54 cm (1000 pulses/inch) in both axes. The laser duty cycles used in this experiment are 10, 20, 50, and 100%, which are referred to as 10P, 20P, 50P, and 100P, respectively. Similarly, the rastering speeds are 1, 2, 3, and 5%, which are referred to as 1S, 2S, 3S, and 5S, respectively. After the first laser rastering, another thin layer of powder (∼50 to 100 μm) was manually added onto the top of the sample. Then the sample was irradiated by laser again in a H2 atmosphere. After repeating 20 times, the 3D printed GF/Ni was obtained. The 3D printed GF/Ni products were etched in a 1 M FeCl3 aqueous solution (∼200 mL) for 2 days to remove the Ni and then transferred into DI water. The foams were purified in DI water for 4 days (200 mL, refreshed with DI water 1×/day) and dried using a CPD (Supercritical Automegasamdri-915B) to obtain free-standing 3D printed GFs. During the entire process, no further heat treatment in a furnace was needed and no binder additive was applied. Characterization. The morphology and microscopic structures of 3D printed GFs were studied using a SEM (FEI Quanta 400 ESEM) operated at 5 kV and a high-resolution JEOL JEM-2100F TEM operated at 200 kV. Raman spectra were collected using a Renishaw inVia Raman microscope RE04 with a 633 nm laser. The XRD patterns were taken using a powder X-ray diffraction system (Rigaku D/Max Ultima II, Cu Kα radiation). TGA (Q-600 Simultaneous TGA/DSC from TA Instruments) were carried out from room temperature to 900 °C in air. XPS (PHI Quantera SXM scanning Xray microprobe) was tested with a 100 μm beam size and a 45° take-off angle. ATR-IR spectra were tested using a Nicolet Nexus 670 Fourier transform infrared spectrometer that is equipped with an attenuated total reflectance system (Nicolet, Smart Golden Gate) and an MCT-A detector. Under ambient atmosphere and room temperature, electrical conductivity was analyzed with an Agilent B1500A semiconductor parameter analyzer using a customized dc probe station by a twoprobe configuration measurement method. Pt contact pads (250 μm × 250 μm) were deposited onto 3D printed GFs using shadow mask evaporation; the distance between the contacts was 120 μm. The size of the GFs is ∼1 cm × 1 cm, the thickness of the original GFs is ∼2 mm, and it is pressed by hand to a film thickness of ∼70 μm before depositing the Pt contact pads. The mechanical properties of the 3D printed GFs were tested by using a DMA Q800 system (TA Instruments) under 1 Hz of constant frequency at room temperature. Tests were performed with a 20 μm amplitude (fixed displacement) by up to 70000 cycles.

carried out under a constant frequency of 1 Hz with an amplitude of 20 μm (fixed displacement) up to 70 000 cycles at room temperature. As shown in Figure 7a, the storage modulus of 3D printed GFs is ∼11 kPa, which is comparable with 3D GFs prepared by powder metallurgy templates and other methods.39,53,55 After testing for 70 000 cycles, no collapse was detected, indicating a good structural stability of the 3D printed GFs. The room-temperature damping capacity of 3D printed GFs was calculated using the following equation: Tanδ = loss modulus/storage modulus, where Tanδ is the damping capacity of the sample. As shown in Figure 7b, the damping capacity of the 3D printed GFs is 0.13 to 0.06, which is comparable with values reported previously, as listed in Table 1. The damping Table 1. Room-Temperature Damping Capacities Reported in the Literature material

damping capacity

ref

3D printed GF 3D GF 3D rebar GF with 10 wt % of CNTs 3D rebar GF with 18 wt % of CNTs graphene sponge CNTs/GO aerogels 20 vol % SiC reinforced A365 Al alloy pure Al foam CNT-reinforced 2024Al alloy

0.13−0.06 0.19 0.13 0.07 ∼0.04 ∼0.05−0.1 0.034−0.04 0.022 ∼0.005

this work 39 39 39 55 53 67 68 69

capacity of 3D printed GFs is also comparable to that of some foamed metal materials. Moreover, the 3D printing method reported here is much easier and faster than other reported 3D GF preparation methods,33−38,55 and there is no requirement for a high-temperature furnace or long growth process.

CONCLUSIONS An automated powder-bed 3D printing method for in situ synthesis of free-standing 3D GFs has been successfully modeled by manually feeding layer by layer a mixture of Ni and sucrose powder, with each layer treated by a CO2 laser. The 3D printed GFs have a large porosity of ∼99.3% and very low density of ∼0.015 g cm−3 and contain high-quality multilayered graphene. The 3D printed GFs also have a remarkable storage modulus of ∼11 kPa, as well as a high room-temperature damping capacity of ∼0.06, comparable to GFs made using other processes. This simple and efficient method for 3D printing of GFs negates the need for cold-press molds or high-temperature CVD treatment. In addition, by using carbon precursors other than sucrose, various 3D carbon composite materials including 3D printed rebar graphene and N-/S-doped graphene foam could be produced. The 3D GFs prepared by this method show promising applications in fields requiring rapid prototyping and manufacturing of 3D carbon materials, energy storage devices, damping materials, and sound absorption.

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.7b01987. ATR-IR spectra, SEM images, Raman spectra, and additional experimental information (PDF)

METHODS

AUTHOR INFORMATION

Synthesis. All chemicals were used as received without further purification. The procedures for preparing the Ni/sucrose mixture powders have been described.38 Briefly, 3 g of Ni powder (particle size: 2.2 to 3.0 μm) and 0.5 g of sucrose were mixed in 200 mL of DI water. Under mechanical stirring (300 rpm), the mixture was heated at ∼80 °C until the water was completely evaporated. The Ni/sucrose powders were dried at 75 °C in a vacuum oven (∼2 Torr) overnight and then ground using a mortar and pestle. A 2032 coin cell lithium

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Junwei Sha: 0000-0002-5211-8663 Yilun Li: 0000-0002-0750-2228 6865

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Rodrigo Villegas Salvatierra: 0000-0001-5050-4803 James M. Tour: 0000-0002-8479-9328 Author Contributions #

J. Sha and Y. Li have contributed equally.

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the AFOSR (FA9550-14-1-0111). We also thank the China Scholarship Council, the State Key Program of National Natural Science of China (51531004), the National Natural Science Foundation of China (51472177), and the Special Foundation for Science and Technology Major Program of Tianjin, China (16ZXCLGX00110) for their support. Rice University gratefully acknowledges the support of Universal Laser Systems and for their generously providing the XLS10MWH laser system with Multiwave Hybrid technology that was used for this research. Mr. J. Hillman of Universal Laser Systems kindly provided helpful advice. REFERENCES (1) Biswas, S.; Drzal, L. T. Multi Layered Nano-Architecture of Variable Sized Graphene Nanosheets for Enhanced Supercapacitor Electrode Performance. ACS Appl. Mater. Interfaces 2010, 2, 2293− 2300. (2) Botas, C.; Carriazo, D.; Singh, G.; Rojo, T. Sn- and SnO2Graphene Flexible Foams Suitable as Binder-Free Anodes for Lithium Ion Batteries. J. Mater. Chem. A 2015, 3, 13402−13410. (3) Dong, X.; Wang, X.; Wang, L.; Song, H.; Li, X.; Wang, L.; ChanPark, M. B.; Li, C. M.; Chen, P. Synthesis of a MnO2-Graphene Foam Hybrid with Controlled MnO2 Particle Shape and Its Use as a Supercapacitor Electrode. Carbon 2012, 50, 4865−4870. (4) Huang, L.; Wu, B.; Chen, J.; Xue, Y.; Geng, D.; Guo, Y.; Yu, G.; Liu, Y. Gram-Scale Synthesis of Graphene Sheets by a Catalytic ArcDischarge Method. Small 2013, 9, 1330−1335. (5) Lei, Z.; Shi, F.; Lu, L. Incorporation of MnO2-Coated Carbon Nanotubes between Graphene Sheets as Supercapacitor Electrode. ACS Appl. Mater. Interfaces 2012, 4, 1058−1064. (6) Liao, Q.; Li, N.; Jin, S.; Yang, G.; Wang, C. All-Solid-State Symmetric Supercapacitor Based on Co3O4 Nanoparticles on Vertically Aligned Graphene. ACS Nano 2015, 9, 5310−5317. (7) Luo, J.; Liu, J.; Zeng, Z.; Ng, C. F.; Ma, L.; Zhang, H.; Lin, J.; Shen, Z.; Fan, H. J. Three-Dimensional Graphene Foam Supported Fe3O4 Lithium Battery Anodes with Long Cycle Life and High Rate Capability. Nano Lett. 2013, 13, 6136−6143. (8) Qiu, H.; Zeng, L.; Lan, T.; Ding, X.; Wei, M. In Situ Synthesis of GeO2/Reduced Graphene Oxide Composite on Ni Foam Substrate as a Binder-Free Anode for High-Capacity Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3, 1619−1623. (9) Xie, B.; Yang, C.; Zhang, Z.; Zou, P.; Lin, Z.; Shi, G.; Yang, Q.; Kang, F.; Wong, C.-P. Shape-Tailorable Graphene-Based Ultra-HighRate Supercapacitor for Wearable Electronics. ACS Nano 2015, 9, 5636−5645. (10) Ye, S.; Feng, J.; Wu, P. Deposition of Three-Dimensional Graphene Aerogel on Nickel Foam as a Binder-Free Supercapacitor Electrode. ACS Appl. Mater. Interfaces 2013, 5, 7122−7129. (11) Zhang, C.; Kuila, T.; Kim, N. H.; Lee, S. H.; Lee, J. H. Facile Preparation of Flower-Like NiCo2O4/Three Dimensional Graphene Foam Hybrid for High Performance Supercapacitor Electrodes. Carbon 2015, 89, 328−339. (12) Li, X.; Sha, J.; Lee, S. K.; Li, Y.; Ji, Y.; Zhao, Y.; Tour, J. M. Rivet Graphene. ACS Nano 2016, 10, 7307−7313. (13) Ai, W.; Jiang, J.; Zhu, J.; Fan, Z.; Wang, Y.; Zhang, H.; Huang, W.; Yu, T. Supramolecular Polymerization Promoted in Situ Fabrication of Nitrogen-Doped Porous Graphene Sheets as Anode Materials for Li-Ion Batteries. Adv. Energy Mater. 2015, 5, 1500559. 6866

DOI: 10.1021/acsnano.7b01987 ACS Nano 2017, 11, 6860−6867

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DOI: 10.1021/acsnano.7b01987 ACS Nano 2017, 11, 6860−6867