revised supporting information · 2011-10-24 · each element. rheological tests were conducted on...

Supporting Information for

Alkali-treated graphene oxide as a solid base catalyst: synthesis and electrochemical

capacitance of graphene/carbon composite aerogels

Fanchang Meng, Xuetong Zhang,* Bin Xu, Shufang Yue, Hui Guo and Yunjun Luo

School of Materials Science & Engineering, Beijing Institute of Technology, Beijing 100081, P. R. China

Research Institute of Chemical Defence, Beijing 100191, P. R. China

Aerospace Institute of Special Materials & Technology, China Aerospace Science & Industry Corp., Beijing 100074, P. R. China

Experimental

Materials: All reagents, including Resorcinol (99%) and formaldehyde (37% in water), absolute ethyl

alcohol, sodium hydroxide (NaOH), TFA (trifluoroacetic acid) and acetone, were purchased from Beijing

Chemical Reagents Company with their purity being of analytical grade and used as received. Graphene

oxide (GO) was synthesized in our lab according to the procedure reported in our previous study (J. Mater.

Chem., 2011, 21, 6494-6497).

Synthesis:

General procedure for synthesis of graphene/carbon composite aerogels is shown in Scheme 1. The

details are as follows:

Scheme 1: The synthetic route for graphene/carbon composite aerogles

Synthesis of alkali treated graphene oxide (AGO): 23.7 mL NaOH aqueous solution (0.1 M) was added

AGO nanosheet

Graphene nanosheet

Organic aerogel skeleton

Carbon aerogel skeleton

Electronic Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is © The Royal Society of Chemistry 2011

into 17 mL of GO dispersion (7 mg/mL) with stirring for ca. 10 minutes, then AGO was coagulated and

filtered from above mixture. Finally the solid AGO was washed repeatedly with ethanol, and then dialyzed

with DI water at least over 3 times.

Synthesis of graphene/carbon composite aerogels: we have made products with different content of

AGO in total solid content of 10 wt. %. All samples were with the molar ratio of resorcinol to

formaldehyde of 0.5. Quantitative AGO with respective portion of 1.0, 2.0, 5.0, 10.0 wt. % of the total solid

content was sonicated in an aqueous solution until homogeneous dispersion was obtained. If more GO, e. g.,

15 wt. % of the total solid content, was added in, only inhomogeneous dispersion was obtained. Resorcinol

(R) and Formaldehyde (F) were added in sequence into the AGO dispersion. The resulting mixture was

then sealed and reacted in water bath at 80 for 72 h. Then, the composite gel precursors were placed in ℃

solution of 0.125% TFA at 45 for 3 days. ℃ The TFA wash assisted in further condensation of

hydroxymethyl groups (-CH2OH) remaining in the gels to form ether bridges between resorcinol molecules

(Journal of Materials Science, 1989, 24, 3221-3227). The resulting gels were then removed from the TFA

solution and soaked in acetone for 4 times (changing the acetone every 8 h) to exchange all the reaction

media from the pores of the gel network. The wet gels were subsequently dried with supercritical CO2 and

pyrolyzed at 1000 (℃ heating rate: 3 /min) under a N℃ 2 atmosphere for 3 h, then the temperature was

naturally lowered down to room temperature. Each final product keeping the original shape was recognized

as a black cylindrical monolith.

Instrumentation: X-Ray photoelectron spectroscopy (XPS) was performed using an AXIS Ultra

spectrometer with a high-performance Al monochromatic source operated at 15 kV. The XPS spectra were

taken after all binding energies were referenced to the C 1s neutral carbon peak at 284.8 eV, and the

elemental compositions were determined from peak area ratios after correction for the sensitivity factor for


each element. Rheological tests were conducted on a Physica MCR 301 Rheometer with 25mm diameter

parallel-plate geometry. The gap distance between two plates was fixed to 2 mm and the frequency sweep

was in the range from 0.1 to 100 rad/s at a fixed oscillatory strain of 0.2%. To avoid the solvent evaporation

during the testing process, we used a plastic jacket to cover the hydrogel, and kept the test time as short as

possible (~15 min) at the room temperature. Atomic force microscope (AFM, Veeco NanoScope III, Veeco

Co., USA, operated in tapping mode) was used to characterize the surface topography of the samples. TEM

was conducted at a FEI Tecnai 20 transmission electron microscopy. The imaging was performed at 200

kV. Nitrogen sorption measurements were performed with ASAP 2010 (Micromeritics, USA) to obtain

pore properties such as the BET-specific surface area, pore size distribution, and total pore volume. Before

measurement, the sample was outgassed under vacuum at 250℃ for ca. 10 h until the pressure less than

0.665 Pa. UV-Vis spectroscopy was performed on UV-6100 double beam spectrophotometer (Shanghai

Mapada). Fourier transformed infrared (FT-IR, Bruker Tensor 27) spectra were recorded between 400 and

4000 cm-1. Raman spectra were recorded on a Renishaw system 1000 with a 50 mW He-Ne laser operating

at 514.5 nm with a CCD detector. XRD patterns of samples were measured with a X’Pert Pro MPD

(PANalytical, The Netherlands) diffractometer with monochromatic Cu Kα1 radiation (λ = 1.5406 Å) at 40

kV and 40 mA. The diffraction patterns were optimized with a step length of 0.01° (2θ) over an angular

range 4.5-90° (2θ) with a scanning speed of 0.01°/s. The compression tests were carried out by a

single-column system (FPZ100) with loading capacity from 100 to 1000 N at a constant loading speed of 1

mm/min. The electrochemical performances of the samples were measured in a two-electrode cell. The

electrodes were prepared by pressing a mixture of 87 wt% of sample, 10 wt% of acetylene black and 3 wt%

of PTFE binder into pellets (11 mm in diameter) and then drying at 120 °C for 12 h. The capacitor was

assembled into two-electrode system, among which two electrodes were separated by polypropylene


membrane using 6 mol.L-1 KOH aqueous solutions as electrolyte. The cyclic voltammetry (CV) was

recorded by Solartron 1280B electrochemical workstation. The galvanostatic charge/discharge test was

carried out on an Arbin cell tester (CT2001A) between 0 and 1 V. The specific capacitance (C) of a single

electrode was determined with the formula 2 /C It Vm= Δ ，where I is the discharge current (A), t is the

discharge time (s)， VΔ is the potential change in discharge (V) and m is the mass of the active material in a

single electrode (g). A Keithley 4200 Semiconductor Characterization System was used to measure

electrical conductivities (four-probe method) of the samples. Furthermore, the density of the resulting

products calculated in Table 1 was determined as the mass of the aerogel divided by its volume, and the

porosity of the resulting products was calculated as 100)2.2

1( ×−ρ

, where 2.2 (in the unit of g/cm3)

means the density of the graphite.


Figures

Fig. SI1 (a) full scan spectra of GO and AGO. Elements for GO: O: 32.44%, C: 65.97%, S: 1.48%, Cl:

0.11%.. Elements for AGO: O: 26.32%, C: 67.71%, S: 0.47%, Cl: 0.19%, Na: 5.31%. (b) high-resolution

Na 1s XPS spectrum of AGO, (c) high-resolution O 1s XPS spectrum of GO and (d) high-resolution O 1s

XPS spectrum of AGO.

1000 800 600 400 200 0

Na

2pN

a 2s

S 2p

S 2 s

C 1

s

Na

KLL

O 1

s

O K

LL

Na

1s

Binding Energy (eV)

S 2p

S 2s

O 2

s

AGO GO

1065 1070 1075 1080

Binding Energy(ev)

COONa1071.6

538 536 534 532 530 528 526

Sum O-C O=C O=C-OH

Binding Energy(ev)

530.7

531.8

532.5

538 536 534 532 530 528 526

Binding Energy(ev)

Sum O-C O=C O=C-ONa

530.4

531.8

532.5

1000 800 600 400 200 0

Na

2pN

a 2s

S 2p

S 2 s

C 1

s

Na

KLL

O 1

s

O K

LL

Na

1s

Binding Energy (eV)

S 2p

S 2s

O 2

s

AGO GO

1065 1070 1075 1080

Binding Energy(ev)

COONa1071.6

538 536 534 532 530 528 526

Sum O-C O=C O=C-OH

Binding Energy(ev)

530.7

531.8

532.5

538 536 534 532 530 528 526

Binding Energy(ev)

Sum O-C O=C O=C-ONa

530.4

531.8

532.5

538 536 534 532 530 528 526

Sum O-C O=C O=C-OH

Binding Energy(ev)

530.7

531.8

532.5

538 536 534 532 530 528 526

Binding Energy(ev)

Sum O-C O=C O=C-ONa

530.4

531.8

532.5

a b

c d


Fig. SI2 UV spectra of GO and AGO in ultra-pure water. The absorption peak of the GO at 230 nm slightly

red-shifts to 234 nm, suggesting that the electronic conjugation within the graphene sheets is partially

restored after treating with alkali as the partial reduction happened from graphene oxide to graphene in the

presence of NaOH (please see ref. Adv. Mater. 2008, 20, 4490-4493).

200 400 600 800

0.0

0.5

1.0

1.5234

Abs

orba

nce

Wavelength(nm)

AGO GO

230


Fig. SI3 FT-IR spectra of GO and AGO. The peak at 3402 cm-1 shows a strong and broad absorption due to

the –OH stretching vibration (J. Phys. Chem, 2010, 114, 10368-10373), and an absorption band at 1728

cm-1 is typical of carbonyl stretching (Carbon, 2009, 47, 68-72). The peak at 1224 cm-1 due to C–OH

stretching and one at 1052 cm-1 arises from C–O stretching, respectively (J. Phys. Chem. B, 2010, 114,

5723-5728).

4000 3500 3000 2500 2000 1500 1000

1728

3402

1224

Tra

nsm

ittan

ce(%

)

Wavenumber(cm-1)

GO AGO

17281622

13901052

3404

16211384

12321054


Fig. SI4 Raman spectra of GO and AGO. The relative intensity ratio ID/IG of AGO is higher than that of

GO, resulting from a decrease in the average size of the sp2 domains upon reduction of the exfoliated GO

(Carbon, 2007, 45, 1558-1565).

1000 1500 2000 2500 3000

ID/IG=1.03

G

Inte

nsity

(Arb

. Uni

ts)

Raman Shift (cm -1)

AGOD

ID/IG=1.14

1583

GO

1350


Fig. SI5 AFM images of GO (a, the same as Fig. SI1 (a) in ref. 6(a) of the manuscript) and AGO (b). The

height (<1.2 nm) of both GO and AGO measured by AFM has confirmed the single-layer nature of the

chemically modified graphene (Angew. Chem. Int. Ed. 2009, 48, 4785-4787).

1.154nm1.173nm

GO AGO

1.154nm1.173nm

GO AGO

1.154nm1.173nm

GO AGO


Fig. SI6 TEM images of GO (a, the same as the Fig. SI1(c) in ref. 6(a) of the manuscript) and AGO (b)

0.5 um 0.2 um

(a) (b)


Fig. SI7 Proposed mechanism on polymerization of R with F in the presence of AGO as a solid base

catalyst, very similar to that of using NaCO3 as a catalyst (see Adv. Mater., 2003, 15, 101-114).

HO OHHO O 2 H C H

OOH

OHCH2OH

HOH2C

1. Addition Reaction

2. Condensation Reaction

OH

OH

CH2OH

HOH2C

HOH

OH

CH2

H2C

OH

OH

CH2OH

HOH2C

+

OH

OH

H2C

HOH2C

OH

CH2OH

CH2OH

HO

HO

CH2OH

CH2OCH2

H

OH

OH

H2C

CH2

HO

OH

CH2

OH2C

H2C

CH2

O

OH

HOH2C

HO

CH2OHOHOH

+

HO

HO

OH2C

HOHOCH2

COONa

COONa COOH

COOH

HO OHHO O 2 H C H

OOH

OHCH2OH

HOH2C

1. Addition Reaction

2. Condensation Reaction

OH

OH

CH2OH

HOH2C

HOH

OH

CH2

H2C

OH

OH

CH2OH

HOH2C

+

OH

OH

H2C

HOH2C

OH

CH2OH

CH2OH

HO

HO

CH2OH

CH2OCH2

H

OH

OH

H2C

CH2

HO

OH

CH2

OH2C

H2C

CH2

O

OH

HOH2C

HO

CH2OHOHOH

+

HO

HO

OH2C

HOHOCH2

COONa

COONa COOH

COOH


Fig. SI8 TGA curves of the RF aerogel and AGO/RF composite aerogels.

200 400 600 800 100040

50

60

70

80

90

100

Wei

ght P

erce

nt/ %

Temperature/℃

RF organic aerogel RF organic aerogel containing 2.0 wt% AGO RF organic aerogel containing 10.0 wt% AGO


Fig. SI9 XRD patterns of the composite aerogels before (a) and after (b) carbonization. No characteristic

peaks of AGO in the composite aerogels before carbonization and peaks of graphene in the composte

aerogels after carbonization indicate that AGO or graphene sheets were well dispersed in the organic or

carbon matrix (similar deduction see ACS Nano, 2011, 5, 4720-4728).

10 20 30 40 50 60

Inte

nsity

(a.u

.)

2θ (degree)

RF organic aerogel RF organic aerogel containing 1.0 wt.% AGO RF organic aerogel containing 10.0 wt.% AGO

10 20 30 40 50 60

Inte

nsity

(a.u

.)

2θ (degree)

carbon aerogel pyrolyzed composite aerogels identified by CA-1 pyrolyzed composite aerogels identified by CA-4

(a) (b)

10 20 30 40 50 60

Inte

nsity

(a.u

.)

2θ (degree)


10 20 30 40 50 60

Inte

nsity

(a.u

.)

2θ (degree)


(a) (b)


Fig. SI10 Raman spectra of the composite aerogels before carbonization (a) and after carbonization

(b).The ratio of ID/IG was increased after carbonization, indicating that the AGO have been converted

into graphene during carbonization (the intensity ratio of ID/IG for the pure graphene is 1.34 in our

case).

1000 1500 2000 2500


ID/IG=0.98

1586

Inte

nsity

(Arb

. Uni

ts)

Raman Shift (cm -1)

1340

D G

ID/IG=0.96

750 1000 1250 1500 1750 2000


D

Inte

nsity

(Arb

. Uni

ts)

Raman Shift (cm -1)

1325

1590G

ID/IG=1.28

ID/IG=1.16

ID/IG=1.14

(a) (b)

1000 1500 2000 2500


ID/IG=0.98

1586

Inte

nsity

(Arb

. Uni

ts)

Raman Shift (cm -1)

1340

D G

ID/IG=0.96

750 1000 1250 1500 1750 2000


D

Inte

nsity

(Arb

. Uni

ts)

Raman Shift (cm -1)

1325

1590G

ID/IG=1.28

ID/IG=1.16

ID/IG=1.14

(a) (b)


Fig. SI11 Low magnification TEM image of graphene/carbon composite aerogels


Fig. SI12 Compressive stress-strain curves of the resulting graphene/carbon composite aerogels with

different amount of original AGO.

0.0 1.2 2.4 3.6 4.8 6.00.0

0.8

1.6

2.4

3.2C

ompr

essi

ve st

ress

(MPa

)

Comprssive strain (%)

1% AGO 2% AGO 5% AGO 10% AGO

E10=29.558MPaE5=17.632MPaE2=5.707MPaE1=3.633MPa


revised supporting information · 2011-10-24 · each element. rheological tests were conducted on...

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