Matter, Volume 3

Supplemental Information

CVD Growth of Porous Graphene Foam in Film Form

Ming Huang, Chunhui Wang, Le Quan, Thi Hai-Yen Nguyen, Hanyang Zhang, YiJiang, Gangil Byun, and Rodney S. Ruoff

Supplemental Experimental Procedures Synthesis of the porous Cu/Ni foil: Porous Ni layers were electrodeposited onto Cu foils by the

hydrogen bubble dynamic template method.[1] Prior to electrodeposition, the Cu foils (Nilaco Co., 99.9% purity)

with a typical area of 4 × 4 cm2 were washed by ultrasonic treatment first with acetone and then with isopropanol

several times to remove any surface contamination. The electrodeposition of Ni was performed in an aqueous

solution containing 0.2 M NiCl2 and 2 M NH4Cl for different times (from 15 to 30 minutes) with a 0.3 A cm-2

current density with a Ni foil as the counter electrode and a Cu foil as the working electrode (target substrate).

After washing and drying, the Ni-plated Cu foils were placed in a quartz furnace and heated at 1050°C (heating

rate of 17°C/min) for 4-8 h in a gas flow of Ar (50 sccm) and H2 (50 sccm) at atmospheric pressure (760 Torr)

and finally cooled by sliding the heating zone away from the sample substrate (average cooling rate of

25°C/min) to obtain porous Cu/Ni alloy foils.

Synthesis of the porous graphene foam: The Cu/Ni alloy foils were loaded into a CVD chamber and

the system was pumped down to ~2.4 × 10-4 Torr followed by two purges with pure Ar, and then a flow of an

Ar/H2 (30 sccm/30 sccm) mixture was introduced to reach atmospheric pressure (1 atm). The system was then

heated to 1050 °C in 1 h (heating rate of 17°C/min) and held for another 30 minutes at this temperature. A CH4

flow (10 sccm) was then introduced into the system for the graphene growth and the sample was cooled down

by sliding the sample from the heating-zone (average cooling rate of 25°C/min). Finally, the free-standing few-

layer graphene foam was obtained after removal of the Cu/Ni template in a FeCl3/HCl mixture solution (1M/1M)

at 80 ºC.

Preparation of the porous Cu foil and the porous graphene foam: Before the electroplating, a 4 × 4

cm2 Cu foil (Nilaco Co., 99.9% purity) with thickness of 80 µm was cleaned in acetone and used as the cathode

for porous Cu deposition. A piece of the same Cu foil was used as the anode. The electrodeposition was

conducted in an aqueous solution containing 0.4 M CuSO4, 1.5 M H2SO4 and 0.1 M CH3COOH at a current

density of 1.5 A cm-2 for 60-90 s. The porous Cu foils were washed and dried in a vacuum oven (80 °C) for 12

hours and then heat-treated at 1050 °C (heating rate of 17°C/min and average cooling rate of 25°C/min) for 4-

8 h in a gas flow of Ar (50 sccm) and H2 (50 sccm) at atmospheric pressure.

Organic solvent and oil absorption test: Graphene foams were soaked in the solvent (ethanol, n-

hexane, acetone, isopropanol, dimethylformamide, olive oil, pump oil or chloroform) for 5 minutes to measure

the saturation absorption capacity which was calculated by the ratio of the maximum absorbed solvent quantity

to the weight of the graphene foam. The original few-layer graphene foam sample was weighed, and its mass

recorded as mg. Next, the sample, after being saturated with organic solvent, was weighed and recorded as

ma. In the case of volatile solvents such as chloroform, the weight measurements were done just after 15-20

seconds to avoid evaporation of the absorbed liquid, and after configuring the carbon film so that excess liquid

would “drip off” its surface. For more viscous solvents such as pump oil, the weight was measured after excess

solvent was removed by allowing it to drip off, i.e. after around 60 s. The absorption capacity (Q, g g–1) was

calculated as:

𝑄 =𝑚𝑎 − 𝑚𝑔

𝑚𝑔

Characterization: X-ray diffraction (XRD, Rigaku SmartLab), scanning electron microscopy (SEM, FEI

Verios 460), and high-resolution transmission electron microscopy (HR-TEM, FEI Titan3 G2 60−300) were

used to analyze the crystallinity and morphology of the prepared graphene foams. Raman spectroscopy

(WITec, 532 nm wavelength) and X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250

Xi) were used for their further characterization. Nitrogen adsorption-desorption isotherms were measured at

77 K with a Micromeritics ASAP 2020 sorptometer. Standard tensile tests were performed in a dynamic

mechanical analyser (DMA Q800, TA Instruments). The dimensions of the samples (PDMS and graphene

foam/PDMS) were 12 × 5.3 mm2 (gauge length × gauge width). The tensile loading was done at a constant

displacement (strain rate) of 500 µm min−1 in air at room temperature. An Instron 5982 was used to measure

the compressive strength of polydimethylsiloxane (PDMS) and the graphene foam/PDMS composite. The

compressive behavior was studied at a strain of 30.0% for several compression cycles at a speed of 3.5 mm

min-1 (load capacity: 100 kN).

Mechanism for the preparation of the porous Cu/Ni foil

Gas bubbles (especially H2 bubbles) have been extensively used as a dynamic template for the fabrication of

self-supported 3D porous metals (Ni, Cu, Sn)[2-4] with highly porous dendritic walls by an electroplating method.

This simple but effective technique involving H2 evolution is suppressed in electroplating processes for the

preparation of smooth and dense metal films. We have previously reported smooth Ni film deposition on

Cu(111) foil for the preparation of single crystal Cu/Ni(111) foils.[5] In our current work, we used a bare Cu foil

as the substrate for the Ni deposition and the procedure for the preparation of the porous Cu/Ni foil is

schematically shown in Figure 1A of our main text. As shown in this Figure, a large number of H2 bubbles

formed mostly from the Cu foil substrate due to its lower overpotential for hydrogen evolution compared to that

of the newly electrodeposited Ni in an acidic medium and at high current density.[6] Thus, only Ni can

electrodeposit and grow within the interstitial spaces between the H2 bubbles (no Ni ions are available in the

bubbles). In other words, the hydrogen bubbles function as a dynamic template during the Ni deposition. After

Ni deposition onto the Cu foil, we performed a further heat-treatment of the porous Ni-plated Cu foil at 1050°C

in a gas flow of Ar (50 sccm) and H2 (50 sccm) at atmospheric pressure for 4-8 h to obtain the porous Cu/Ni

foil (the morphology and the shape of the pores are well maintained during the heat treatment).

Porosity (pore volume fraction) measurement of porous few-layer graphene foam (GF)

The pore volume fraction (δ) is calculated by

𝛿(%) = (1 −𝜌𝐺𝐹

𝜌𝐺𝑟𝑎𝑝ℎ𝑖𝑡𝑒) × 100

Where ρGF and ρGraphite are the apparent densities of the graphene foam and true density of graphite (2.2 g

cm-3), respectively.

Electrical conductivity measurement

The porous graphene foam (GF) is a new material with many unknown physical properties. Here, we

characterized the electricial conductivity of GFs on a surface resistivity measurement system (AIT Co., Ltd.,

CMT-2000N, Seoul, Korea) with a four point-probe head unit at room temperature. According to the Lemlich

model, the conductivity of the thin graphene itself within the porous graphene foam is given by

𝜎𝐺 =3𝜎𝐺𝐹

𝜑𝐺𝐹

Where σGF is the electrical conductivity of GF and φGF is the volume fraction (calculated from Table S1). The

Lemlich model has been shown to adequately describe electrical transport in low volume fraction, open celled

metal foams.[7, 8]

Preparation of the GF/PDMS composite

Pure PDMS is almost transparent to electromagnetic waves, exhibiting little shielding capability. Thus,

graphene foams were infiltrated with PDMS for easier manipulation during testing. The PDMS pre-polymer

was prepared by mixing the base and curing agents (10:1 in weight; Sylgard 184, Dow Corning) and the

graphene foam was immersed in the pre-polymer for 2 hours followed by curing at 80 ºC for 3 hours to obtain

the GF/PDMS composites. The samples were cut into 22.9 mm × 10.2 mm rectangular plates to fit the

waveguide sample holder. For comparison, pure PDMS plates of the same size were prepared as control

samples.

EMI shielding effectiveness measurement

The EMI shielding effectiveness (EMI SE) was measured in the X-band frequency range of 8-12 GHz using a

WILTRON 54169A scalar measurement system.

The EMI SE was used to measure the ability of the material to attenuate the electromagnetic wave strength,

which is defined as the logarithm of incoming power (Pi) to transmitted power (Pt) of an electromagnetic wave

in decibels (dB).[9-11]

𝑆𝐸𝑡𝑜𝑡𝑎𝑙 = 10log (𝑃𝑖

𝑃𝑡) (1)

When an electromagnetic wave encounters a shielding material, the reflection (R), absorption (A), and

transmission (T) fractions must add up to 1, that is,

𝑅 + 𝐴 + 𝑇 = 1 (2)

The reflection (R) and transmission (T) coefficients were obtained from the network analyzer in the form of

scattering parameters, “Smn”, which measure how the energy is scattered from a material or device. The first

letter “m” designates the network analyzer port receiving the EMI radiation and the second letter “n”, represents

the port that is transmitting the incident energy. A vector network analyzer directly gives the output in the form

of four scattering parameters (S11, S12, S21, S22), which can be used to find the R and T coefficients as:

R = |𝑆11|2 = |𝑆22|2 (3)

T = |𝑆12|2 = |𝑆21|2 (4)

The total EMI SE (EMI SET) is the sum of the contributions from reflection (SER), absorption (SEA) and multiple

internal reflections (SEM). At higher EMI SE values, and with a multilayer EMI shield (as in the case of the few-

layer graphene foam), multi-reflected waves become absorbed or dissipated as heat in the same way as the

absorption mechanism. The total SEtotal can be written as:[11]

𝑆𝐸𝑡𝑜𝑡𝑎𝑙 = 𝑆𝐸𝑅 + 𝑆𝐸𝐴 (5)

SER and SEA can be expressed in terms of reflection and effective absorption considering the power of the

incident electromagnetic waves inside the shielding material as:

𝑆𝐸𝑅 = 10log (1

1−𝑅) = 10log (

1

1−|𝑆11|2) (6)

𝑆𝐸𝐴 = 10log (1−𝑅

𝑇) = 10log (

1−|𝑆11|2

|𝑆21|2 ) (7)

𝑆𝐸𝑡𝑜𝑡𝑎𝑙 = 10log (1

|𝑆21|2) (8)

The specific shielding effectiveness (SSE; dB cm3 g-1) was derived to compare the effectiveness of the

shielding materials (SEtotal) taking into account the density (ρ) and is obtained as follows:[12]

SSE =𝑆𝐸𝑡𝑜𝑡𝑎𝑙

𝜌 (9)

The SSE has a basic limitation in that it does not account for the thickness dependence. Higher values of SSE

can simply be obtained at larger thickness while maintaining the low density. However, a larger thickness

increases the net weight and is disadvantageous. To account for the thickness contribution (t; cm), the

following equation is used to evaluate the absolute effectiveness (SSEt; dB cm2 g-1) of a material in relative

terms:[12]

SSE𝑡 =𝑆𝑆𝐸

𝑡 (10)

The EMI shielding efficiency is the material’s ability to block waves in terms of percentage. For example, a EMI

Shielding Efficiency of 10 dB corresponds to 90% blockage of the incident radiation, and 30 dB corresponds

to 99.9% blockage of the incident radiation. The EMI shielding effectiveness [dB] is converted into the EMI

shielding efficiency [%] using the following equation:

EMI shielding efficiency (%) = 100 − (1

10𝑆𝐸𝑡𝑜𝑡𝑎𝑙

10

) × 100 (11)

Figure S1. (A) A photograph showing the bubble-assisted electroplating of porous Ni onto Cu foil. (B) Photos

of the bare Cu foil and Cu foil with the porous Ni-deposit. (C) XRD patterns of the bare Cu foil and the Cu foil

with the porous Ni-deposit. (D and E) SEM images of the Cu foil with the porous Ni-deposit at different

magnifications, showing a very wide range of pore sizes. (F and G) Cross-sectional SEM image and EDS

maps of the Cu foil with the porous Ni-deposit.

Figure S2. (A and B) SEM top surface view of the porous Cu/Ni alloy foil (after the 1050°C heat treatment)

and EDS maps of the region marked in (A). (C and D) Cross-section SEM image of the porous Cu/Ni foil (after

the 1050°C heat treatment) and EDS maps of the region marked in (C). Both sets of maps indicate the

successful inter-diffusion between Cu and Ni, forming a gradient alloy.

Figure S3. Photograph of a large piece of porous graphene coated Cu/Ni foil (around 7 cm × 7 cm).

Figure S4. (A-D) SEM images of the graphene-coated porous Cu/Ni foil at different magnifications showing a

porous structure with pore sizes in the range of a few hundred nanometers to less than 100 microns. (D) shows

the wrinkling of the graphene.

Figure S5. (A) SEM image of the porous Cu/Ni alloy after coating with graphene. (B-D) EDS maps of the

region marked in (A), indicating uniform distributions of C, Ni and Cu.

Figure S6. (A) Nitrogen adsorption–desorption isotherms and (B) pore size distribution plot of the porous few-

layer graphene foam.

Figure S7. (A) Typical stress–strain curves of PDMS and a graphene foam/PDMS composite (GF/PDMS) with

∼0.29 wt.% graphene content (tensile test). (B) Average tensile strength and tensile modulus of PDMS and a

graphene foam/PDMS composite, calculated from the stress–strain curves of five specimens. (C and D)

Stress-strain curves of PDMS and a graphene foam/PDMS composite repeatedly subjected to a 30.0%

compressive strain, for 20 cycles.

Figure S8. (A and B) SEM top view of the porous graphene foam and the corresponding EDS map of the

region marked in (A). (C and D) Cross-sectional SEM image of the porous graphene foam and the EDS map

of the region marked in (C). The EDS maps indicates a very pure and clean graphene foam without any

impurities.

Figure S9. (A) Optical image and (B) Raman spectra of the graphene foam. Seven regions were randomly

selected and tested with a 532-nm Raman laser.

Figure S10. Cross-sectional SEM images of graphene foams with different thicknesses.

Figure S11. Cross-sectional SEM image of a graphene foam with a thickness of ~450 μm.

Figure S12. (A) Photograph showing the H2 bubble-assisted electroplating of porous Cu onto Cu foil. (B) Photo

of the bare Cu foil and the Cu foil plated with porous Cu. (C) SEM image of the surface of the bare Cu foil. (D-

F) SEM images of the Cu foam at different magnifications, indicating a porous structure with a wide range of

pore sizes. The deposited Cu foam consists of numerous dendrites in all directions, forming the pore walls.

(G-I) SEM images of graphene-coated Cu foam at different magnifications. A partial collapse of the Cu foam

structure was observed due to annealing but the skeleton and the pore structure are still maintained. The

yellow arrows in (I) indicate wrinkles in the graphene grown on the porous Cu.

Figure S13. (A and B) SEM images of the graphene foam without a support layer. The foam walls are broken

and collapsed into randomly stacked graphene sheets. (C and D) SEM images of the graphene foam with a

PMMA support layer. The pore structure and pore walls of the graphene foam are maintained.

Figure S14. TGA curve of graphene foam measured in air with a heating rate of 10°C min-1. A weight loss of

~3 wt.% below 180°C results from the removal of adsorbed water. The graphene is stable with no

decomposition, even when the temperature is increased to ~600°C.

Figure S15. (A and B) XPS survey scan and C1s XPS spectrum of the graphene foam before combustion of

the absorbed n-hexane. (C and D) XPS survey scan and C1s XPS spectrum of the foam after combustion of

the absorbed n-hexane. No significant difference was found in the foam after recycling it and using it to absorb

n-hexane again several times.

Figure S16. (A) EMI shielding effectiveness of a pure PDMS (1 mm in thickness) sample. (B) EMI shielding

effectiveness of one to three stacked graphene foam/PDMS composite layers. Each piece of graphene

foam/PDMS composite layer is about 1 mm thick and the total thickness of the three stacked pieces is around

3 mm (with some small physical gaps that are present between each piece due to the soft nature of the

graphene foam/PDMS composite).

Table S1. The size and weight of the graphene foams used for calculating the apparent density and pore

volume fraction.

Sample Area

(cm2)

Thickness

(cm)

Volume

(cm3)

Mass

(mg)

Apparent density

(mg cm-3)

Pore volume

fraction (%)

1 7.24 1.00×10-2 7.24×10-2 1.61 22.24 98.99

2 15.96 1.10×10-2 17.56×10-2 3.55 20.22 99.08

3 10.14 1.20×10-2 12.17×10-2 2.66 21.86 99.01

4 11.28 1.40×10-2 15.79×10-2 3.87 24.51 98.88

5 9.46 1.50×10-2 14.19×10-2 3.64 25.65 98.83

6 16.92 1.60×10-2 27.07×10-2 6.77 25.01 98.86

7 12.74 1.60×10-2 20.38×10-2 5.12 25.12 98.86

8 14.00 1.60×10-2 22.40×10-2 5.50 24.55 98.88

9 18.27 1.80×10-2 32.89×10-2 9.19 27.94 98.73

10 10.80 1.80×10-2 19.44×10-2 5.33 27.42 98.75

11 9.00 2.00×10-2 18.00×10-2 5.24 29.11 98.68

12 7.40 2.00×10-2 14.80×10-2 4.19 28.31 98.71

13 7.80 2.00×10-2 15.60×10-2 4.65 29.81 98.64

14 8.12 2.50×10-2 20.30×10-2 5.88 28.96 98.68

15 10.26 2.50×10-2 25.65×10-2 7.44 29.00 98.68

16 14.15 2.50×10-2 35.38×10-2 10.97 31.01 98.59

17 15.48 3.00×10-2 46.44×10-2 14.87 32.02 98.54

18 10.64 3.00×10-2 31.92×10-2 10.18 31.89 98.55

19 14.80 3.20×10-2 47.36×10-2 14.98 31.63 98.56

20 9.60 3.50×10-2 33.60×10-2 10.89 32.41 98.53

21 14.30 3.50×10-2 50.05×10-2 16.76 33.49 98.48

Table S2. Electrical conductivity of GF and the normalized conductivity of graphene-like walls made from

porous Cu/Ni foil.

Sample Sample 1

conductivity

(S m-1)

Sample 2

conductivity

(S m-1)

Sample 3

conductivity

(S m-1)

Sample 4

conductivity

(S m-1)

Sample 5

conductivity

(S m-1)

Average

conductivity

(S m-1)

Normalized

conductivity

(S m-1)

GF 668.9 638.9 631.5 564.3 618.3 624.4 1.6 × 105

Table S3. Comparison of various graphene-based absorbents for oil and solvent absorption.

3D absorbent material Preparation method Absorbates Absorption capacity

[g g-1]

Ref.

1 Graphene sponge Hydrothermal reduction and freeze drying

Gasoline, machine oil, chloroform, etc.

20-35 [13]

2 rGO-coated PU sponge Dip-coating and solvothermal method

n-hexane, gasoline, pump oil, etc.

25-37 [14]

3 Fluorinated polydopamine/chitosan/rGO

Hydrothermal treatment, immersion and freeze-

drying

Gasoline, ethanol, hexane, etc.

8-20 [15]

4 N-doped GO foam Hydrothermal reaction, freeze drying and annealing

Chloroform, corn oil, acetone, etc.

135-380 [16]

5 Copolymer-modified GO foam

Silanization and quaternization process

Pump oil, gasoline, chloroform, etc.

40-196 [17]

6 Magnetic polymer-based graphene foam

Hydrothermal and self-assembly

Hexane, peanut oil, lubricating oil, etc.

8-20 [18]

7 Spongy graphene Hydrothermal reduction and freeze-drying

Chloroform, hexane, pump oil, etc.

20-86 [19]

8 GO-modified melamine foam

Ultrasonic and microwave irradiation

n-hexane, chloroform,

petroleum, etc.

60-112 [20]

9 rGO foam Autoclaved leavening and steaming

Motor oil, chlorobenzene, petroleum, etc.

10-37 [21]

10 Graphene-CNT hybrid foam Two-step CVD method Compressor oil, sesame oil,

chloroform, etc.

80-130 [22]

11 CNT-Graphene hybrid aerogel

Ultrafast microwave irradiation

Pump oil, gasoline, ethyl acetate, etc.

100-135 [23]

12 3D graphene foam Seashell-based CVD method

Ethanol, n-hexane, pump oil, etc.

130-230 [24]

13 Silica-coated rGO foam Hydrothermal reduction and sol-gel approach

Chloroform, motor oil, gasoline, etc.

15-30 [25]

14 Fe3O4-decorated rGO foam Hydrothermal reduction and hydrothermal reaction

Motor oil 36 [26]

15 rGO-coated polyurethane sponge

Immersion and reduction with hydrazine

Acetone, chloroform, pump oil, etc.

80-160 [27]

16 graphene foam Autoclaved leavening of PS particles

Chloroform, hexane, olive oil, etc.

14-33 [28]

17 PU sponge-reinforced graphene aerogel

Pre-compaction and ice-templated assembly

n-hexane, bean oil, DMF, etc.

30-50 [29]

18 Functionalized rGO aerogel One-step solution immersion method

Chlorobenzene, chloroform, pump oil,

etc.

40-110 [30]

19 rGO-PU sponge Reduction and surface functionalization

Gasoline, chloroform, pump oil, etc.

30-45 [31]

20 Fe3O4-GO foam Hydrothermal reaction Hexane, chloroform, motor oil, etc.

12-27 [32]

21 Graphene/PVDF aerogel Solvothermal method Pump oil, hexane, chloroform, etc.

20-70 [33]

22 rGO foam Reduction and freeze drying

Gasoline, pump oil, olive oil, etc.

50-120 [34]

23 GO aerogel Chemical reduction Acetone, pump oil, chloroform, etc.

100-260 [35]

24 GO/Carbon black/melamine sponge

Dip-coating, thermal reduction, and immersion

Hexane, pump oil, chloroform, etc.

50-130 [36]

25 Porous graphene foam Cu/Ni-templated CVD method

n-hexane, pump oil, chloroform, etc.

50-112 This work

Table S4. Comparison of the EMI shielding performance for various materials

Type Material Filler

content

Thickness

[mm]

EMI SE in X

band [dB]

SSE

[dB cm3g

-1]

SSEt

[dB cm2g

-1]

Ref.

Metal-

based

Cu / 3.1 90 10 32 [37]

Ni / / 82 9.2 / [37]

Stainless steel / 4 89 11 28 [37]

Ag foil / 0.01 58 5.6 5576 [38]

Al foil / 0.05 63 23.2 4630 [38]

Cu-Ni foam / 1.5 25 100 667 [39]

Cu-Ni/CNT foam / 1.5 48 207 1377 [39]

AgNW/WPU foam 28.6 wt.% 2.3 64 1422 6183 [40]

Ag-hollow sphere/epoxy

foam 30.5 wt.% 1.5 60 46 309 [41]

Ag NW/PANI 43.4 wt.% 0.013 48 / / [42]

Cu nanowires/PS 2.1 vol.% 0.21 35 / / [43]

Carbon

-based

Graphene film / 0.0084 20 / / [44]

CNT mat / 4.634 81 370 798 [45]

Carbon fabric / 0.109 47 43 3929 [38]

GO/WPU fiber 7.5 wt.% 1 34 / / [46]

GO/PPy coated wool fabric / 2.236 22 227 1013 [47]

Graphene/PDMS foam 0.8 wt.% 1 20 333 3333 [48]

MWCNT/polymer foam 50 wt.% 2.3 47 2400 10400 [49]

Carbon nanotube

sponge/epoxy 0.66 wt.% 2 33 1320 6600 [50]

Carbon foam / 2 51 341 1706 [51]

CDG/PMMA foam 5 wt.% 2.4 17 22 92 [52]

MWCNT/fluorocarbon foam 12 wt.% 3.8 48 40 105 [53]

CNT/PS foam 7 wt.% 1.2 19 33 275 [54]

CNF/PS foam 15 wt.% / 19 / / [55]

Graphene/epoxy 15 wt.% / 21 / / [56]

Graphene/PEI foam 10 wt.% 2.3 11 38 165 [10]

rGO/PU foam 10 wt.% 2 20 663 3316 [57]

rGO/PI foam 16 wt.% 0.8 21 75 937 [58]

Porous graphene/PS 5.6 wt.% 2.5 29 64 258 [59]

MWCNT/WPU foam 76.2 wt.% 2.3 1 541 5410 [60]

CNT-Multilayer graphene / 1.6 38 6600 40000 [61]

Porous graphene/PDMS foam 0.45 wt.% 0.16 18 723 45188 This

work 1.0 wt.% 0.35 24 728 20800

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