1

Supporting Information

MOFs-Derived Copper Sulfides Embedded within Porous Carbon Octahedra for Electrochemical Capacitor Applications

Renbing Wu,†ad Dan Ping Wang,†bc Vipin Kumar,c Kun Zhou,*a Adrian W. K. Law,de Pooi See

Lee,c Jun Lou,f and Zhong Chen*cb

a School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50

Nanyang Avenue, Singapore 639798, Singaporeb Energy Research Institute, Nanyang Technological University, 1 CleanTech Loop, Singapore

6371412, Singaporec School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang

Avenue, Singapore 639798, Singapored DHI-NTU Center, Nanyang Environmental and Water Research Institute , Nanyang Technological

University, 1 CleanTech Loop, Singapore 6371411, Singaporee School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang

Avenue, Singapore 639798, Singaporef Department of Materials Science and Nanoengineering, Rice University, Houston, Texas 77005,

United States

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2015

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Experimental Section

Preparation of HKUST-1 template. All chemicals and solvents were purchased from commercial

sources and used without purification. Briefly, 1.5 g copper nitrate (Cu(NO3)2·3H2O) and 3.5 g

benzene-1,3,5-tricarboxylic acid (C6H3(COOH)3) were dissolved in a 5 ml and 55 ml absolute

methanol under ultrasonication, respectively. Afterwards, the two solutions were mixed vigorously

for 10 s, and the resultant solution was kept at room temperature for 3 h until HKUST-1

precipitation finished. The blue precipitates were collected by centrifugation and washed with

methanol for three times and finally dried in vacuum at 60°C.

Synthesis of porous Cu1.96S/C octahedra and porous carbon. In a typical procedure, a

combustion boat loaded with 0.2 g HKUST-1 and 0.08 g S powder were put into a tube furnace and

then heated to the target temperature at the rate of 2 °C min-1 and maintained at this temperature for

2 h under an argon gas flow of 50 mL min-1. The resultant products were labeled as Cu1.96S/C-t,

where t indicates the target temperature. In comparison, porous carbon was prepared by removing

Cu1.96S from the Cu1.96S/C-650 composite using hydrochloric acid (HCl) solution (37%).

Characterization. X-ray diffraction patterns (XRD) were performed on an X-ray powder

diffractometer (Bruker D8 Advance) with Cu Kα radiation (λ=1.5406 Å). Raman spectra were

recorded using an inVia Raman microscope (RENISHAW). The electronic binding energy of the

sample was examined by X-ray photoelectron spectroscopy (XPS) on a PHI 5600 XPS instrument.

Field-emission scanning electron microscope (FESEM) images were obtained from a JEOL JSM-

7600F microscope. Transmission electron microscope (TEM) images, high-resolution TEM images,

high-angle annular dark-field scanning TEM (HAADF-STEM) images, and elemental mapping

images were taken on a JEOL JEM-2100F microscope, equipped with energy-dispersive X-ray

(EDX) spectroscopy. The BET specific surface areas of products were determined from the results

of N2 physisorption at 77 K using a Quantachrome Instruments Autosorb AS-6B instrument. The

carbon contents of composites were measured by Elementar Vario EL III Elemental Analyser.

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Electrochemical measurements. All electrochemical measurements were performed on an

electrochemical analyzer (Autolab Potentiostat, PGSTAT302N) in a three-electrode cell

configuration with Ag/AgCl as the reference electrode and using Pt plate as the counter electrode.

The working electrode was fabricated by mixing the as-prepared Cu1.96S/C composites with carbon

black and polyvinylidene difluoride (PVDF) at the weight ratio of 8:1:1 to yield paste before

spreading it onto graphite paper. The loading amount of active materials on the graphite paper was

about 1.5 mg. The electrolyte used was 1 M H2SO4 solution. Cyclic voltammetry (CV) curves were

recorded between 0 and 0.9 V versus Ag/AgCl at various scan rates ranging from 1 to 100 mV S-1.

Galvanostatic charging-discharging tests were obtained in the potential between 0 and 0.9 V versus

Ag/AgCl at different current densities from 0.5 to 5 A g-1. Electrochemical impedance

spectroscopic (EIS) experiments were performed within the frequency range of 100 KHz and 0.01

Hz. The specific capacitance can be calculated by integrating the area under the CV curve based C

on the following equation:

(1)1

21 2

1 ( )( )

V

V

QC I V dVV mv V V

where m is the mass of the active materials, v is the scan rate, V1 and V2 represent the switching

potentials in the CV curve, respectively, and I (V) represents the charge-discharge current and is a

function of the voltage.

In addition, can also be calculated from the galvanostatic charge-discharge curve by C

(2)I tCm V

where is the discharging time, and is the potential range upon discharging.t V

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Fig. S1 (a) Low-magnification and (b) high-magnification FESEM images of as-synthesized

HKUST-1 template.

5

10 15 20 25 30

(551

)

Inte

nsity

(a.u

.)

II

(751

)

(731

)

(444

)

(620

)(6

00)

(440

)(3

33)

(422

)

(331

)(4

00)

(200

)

(220

)

HKUST-1

2 (degree)

I

(222

)

Fig. S2 (I) Experimental and (II) simulated XRD patterns of HKSUT-1. The crystal data for

standard HKUST-1 is stored in the Cambridge Structural Database, deposit number 112954.

http://www.ccdc.cam.ac.uk/Community/Requestastructure/Pages/DataRequest.aspx

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Fig. S3 (a) Low- and (b) high-magnification FESEM images of porous Cu1.96S/C-350 octahedra; (c)

low- and (d) high-magnification FESEM images of porous Cu1.96S/C-500 octahedra.

7

980 970 960 950 940 930 920

(a)

Binding energy (eV)

Inte

nsity

(a.u

)

Cu 2p B

170 168 166 164 162 160 158 156

(b)

165.0

163.8

162.9

Inte

nsity

(a.u

)

Binding energy (eV)

161.7

S 2p

Fig. S4 High-resolution XPS characterization of Cu1.96S/C-650 octahedra: (a) Cu 2p region and (b)

S 2p region.

19.9 eV

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Fig. S5 HRTEM images of (a) Cu1.96S/C-650 octahedra and (b) Cu1.96S/C-350 octahedra. The bent

graphitic carbon layers marked with arrows can be observed in (a), whereas no graphitic carbon

layers can be found in (b).

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0.0 0.2 0.4 0.6 0.8 1.0

0

50

100

Relative pressure (P/P0)

Volu

me

adso

rbed

(cm

3 g-1) Cu1.96S/C-350

Cu1.96S/C-500 Cu1.96S/C-650

(a)

0 5 10 15 20 25 30 35 40 45 50

0.0000

0.0004

0.0008

0.0012

0.0016

Pore diameter (nm)

dV/d

D (c

m3 g

-1 n

m-1)

350

(b)

0 5 10 15 20 25 30 35 40 45 50

0.0000

0.0005

0.0010

0.0015

0.0020 (c)

dV/d

D (c

m3 g

-1 n

m-1)

Pore diameter (nm)

500

0 5 10 15 20 25 30 35 40 45 50

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

Pore diameter (nm)

(d)

dV

/dD

(cm

3 g-1 n

m-1)

650

Fig. S6 (a) Nitrogen adsorption-desorption isotherm of Cu1.96S/C composites and the corresponding

pore size distributions of (b) Cu1.96S/C-350, (c) Cu1.96S/C-500 and (d) Cu1.96S/C-650.

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Table S1. Pore properties of the Cu1.96S/C composites

Sample BET surface area

(m2/g)

BJH desorption pore diameter (nm) Total pore

volume

(cc/g)

Cu1.96S/C-350 14.8 2.3 0.0587

Cu1.96S/C-500 120.9 1.9 0.134

Cu1.96S/C-650 140.4 1.6 0.118

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0 20 40 60 80 1000

30

60

90

120

150

180

210

Scan rate (mV/s)

Spec

ific

capa

cita

nce

(F/g

)

Cu1.96S/C-650 porous carbon

Fig. S7 Correlation of the specific capacitance with the scan rate for Cu1.96S/C-650 and porous

carbon.

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0 150 300 450 600 7500.0

0.3

0.6

0.9

Pote

ntia

l (V)

Time (s)

Cu1.96S/C-350 Cu1.96S/C-500 Cu1.96S/C-650

Fig. S8 Charge-discharge curves of Cu1.96S/C-350, Cu1.96S/C-500 and Cu1.96S/C-650 at the current density of 0.5 A g-1.

13

0 50 100 150 200 2500.0

0.3

0.6

0.9(a)

Po

tent

ial (

V)

0.5 A/g 1 A/g 2 A/g 3 A/g 4 A/g 5 A/g

Time (sec)

0 150 300 450 600 7500.0

0.3

0.6

0.9(b)

Po

tent

ial (

V)

0.5 A/g 1 A/g 2 A/g 3 A/g 4 A/g 5 A/g

Time (sec)

Fig. S9 Charge-discharge curves of (a) Cu1.96S/C-350 and (b) Cu1.96S/C-500 at different current

densities.

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0 1 2 3 4 525

50

75

100

125

150

175

200

Current density (A/g)

Spec

ific

capa

cita

nce

(F/g

) Cu1.96S/C-350 Cu1.96S/C-500 Cu1.96S/C-650

Fig. S10 Specific capacitance of Cu1.96S/C-350, Cu1.96S/C-500 and Cu1.96S/C-650 electrodes at

different current densities.

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4 6 8 100

1

2

3

4

-Z'' (

Ohm

)

Z' (Ohm)

350 C 500 C 650 C

Fig. S11 Nyquist plots of Cu1.96S/C-350, Cu1.96S/C-500 and Cu1.96S/C-650, with the inset showing

the modeled equivalent circuit of EIS where Rs stands for the electrolyte resistance, Rct the charge

transfer resistance, Wd the “Warburg” resistance, and CPE the constant phase element, and Cp the

capacitance.

CPE

Rs

Rct Wd

Cp

16

Fig. S12 (a) TEM image and (b) HRTEM image of the Cu1.96S/C-650 composite electrode obtained

after 3000 cycles.

17

-0.6 -0.4 -0.2 0.0 0.2 0.4

-4

-2

0

2

4 (a)

Potential (V vs. Ag/AgCl)

Cu

rrent

des

nity

(mA/

cm2 )

1st cycle 100th cycle

-0.6 -0.4 -0.2 0.0 0.2 0.4-15

-10

-5

0

5

10 (b)

Potential (V vs. Ag/AgCl)

Curre

nt d

esni

ty (m

A/cm

2 )

1 mV/s 5 mV/s 10 mV/s 25 mV/s 50 mV/s 100 mV/s

0 20 40 60 80 1000

30

60

90

120

150

180 (c)

Spec

ific

capa

cita

nce

(F/g

)

Scan rate (mV/s)

Fig. S13 Electrochemical properties of the Cu1.96S/C-650 composite electrode in the 1M KOH

electrolyte: (a) CV curves at the scan rate of 50 mV S-1, (b) CV curves at different scan rates, and (c)

relationship between the specific capacitance and scan rate.