Journal of

Materials Chemistry A

ELECTRONIC SUPPLEMENTARY INFORMATION (ESI†)

Rational design of forest-like nickel sulfide hierarchical architectures

with ultrahigh areal capacity as a binder-free cathode material for

hybrid supercapacitors†

G. Seeta Rama Raju,a E. Pavitra,b Goli Nagaraju,c S. Chandra Sekhar,d Seyed Majid Ghoreishian,b

Cheol Hwan Kwak,b Jae Su Yu,*d Yun Suk Huh,*b and Young-Kyu Han,*a

aDepartment of Energy and Materials Engineering, Dongguk University–Seoul, Seoul 04620,

Republic of Korea

bDepartment of Biological Engineering, Biohybrid Systems Research Center (BSRC), Inha

University, Incheon, 22212, Republic of Korea

cDepartment of Chemical Engineering, College of Engineering, Kyung Hee University, 1732

Deogyeong-daero, Gihung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea

dDepartment of Electronic Engineering, Institute for Wearable Convergence Electronics, Kyung

Hee University, 1732 Deogyeong-daero, Gihung-gu, Yongin-si, Gyeonggi-do 17104, Republic of

Korea

Corresponding Authors

*Email: jsyu@khu.ac.kr (J. S. Yu)

*Email: yunsuk.huh@inha.ac.kr (Y. S. Huh)

*Email: ykenergy@dongguk.edu (Y.-K. Han)

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2018

2

Fig. S1 FE-SEM images of pristine Ni foam, showing its porous conductive frames with smooth

surface.

3

Fig. S2 (a) XRD patterns of NiS-based samples synthesized under different time intervals [i) 1 h,

ii) 2 h, iii) 3 h and iv) 5 h], (b) HR-Raman, and (c–e) XPS survey scan spectrum, high-resolution

Ni 2p and S 2p XPS spectra, respectively, of forest-like NiS NTs/Ni foam sample under the optimal

growth condition of 85 C for 3 h.

4

Section 1: Structural, morphological and electrochemical properties of NiS on

Ni foam without using the nickel salt in the growth solution:

Fig. S3a-c shows the low and high-magnification FE-SEM images of the nanostructured NiS on

Ni foam, which was developed without Ni salt (Ni(NO3)2∙6H2O source) in the growth solution.

Interestingly, NiS nanoparticles were observed on the Ni foam with a mass loading of 0.9 mg/cm2

at the reaction temperature of 85 ºC for 3 h. This indicates that, forest-like NiS NTs on Ni foam

were not formed without the addition of nickel salt in the growth solution. The structural and

electrochemical properties of the corresponding sample was also examined. From the EDX (taken

from FE-SEM equipment) and XRD results (Fig. S3d-e), it is evident that the prepared sample

(without the addition of nickel salt) composed of Ni and S elements has pure NiS phase without

any impurities. The XRD pattern of NiS/Ni foam showed low intense peaks, which may be due to

the less amount material deposited on the spectrum. Furthermore, when tested the electrochemical

properties in 1 M KOH solution, the NiS nanoparticles coated Ni foam exhibited a battery-type

redox behavior, confirmed from the CV and GCD curves (Fig. S3f-g and Fig. S4a-b), which is

similar to the forest-like NiS NTs electrode behavior. However, NiS nanoparticles coated Ni foam

sample exhibited relatively low electrochemical performance compared to the forest-like NiS

NTs/Ni foam electrode, as shown in Fig. S4a-b. The obtained results indicate that the inclusion of

nickel salt in growth solution help to increase the nucleation and precipitation rate to form the

hierarchically designed forest-like NiS NTs for the enhancement of energy storage performance.

5

Fig. S3. Physical and electrochemical properties of NiS nanoparticles coated Ni foam, which was

prepared without addition of nickel salt in the growth solution. (a-c) low- and high-magnification

FE-SEM images of NiS nanoparticles, (d-e) EDX and XRD pattern of the same sample. (f-h) CV

curves, GCD curves and calculated areal capacity values of NiS nanoparticles coated Ni foam

electrode, respectively.

Matrix

Correction:

ZAF Element

Wt.% At.%

NiL 91.16 84.92

S K 08.84 15.08

5 m 200 nm 50 nm

(a) (b) (c)

0 100 200 300 400 500 600 7000.0

0.1

0.2

0.3

0.4

40 mA cm-2

Po

ten

tia

l (V

vs

. A

g/A

gC

l)

Time (s)

4 mA cm-2

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-60

-40

-20

0

20

40

60

Cu

rre

nt

De

ns

ity

(m

A/c

m2)

2 mV s-1

5 mV s-1

7 mV s-1

10 mV s-1

15 mV s-1

20 mV s-1

30 mV s-1

Potential (V vs. Ag/AgCl)

0 5 10 15 20 25 300

50

100

150

200

250

Are

al C

ap

acit

y (A

h c

m-2)

Current Density (mA cm-2)

(f) (g) (h)

Ni

10 20 30 40 50 60 70 80 90

NiS

Ni foam

(200)

(101)

(100)

Inte

ns

ity

(a

.u.)

2 (degree)

(d) (e)

OS

Ni

Ni

Energy (keV)

6

Fig. S4. Comparative electrochemical properties of NiS nanoparticles and forest-like NiS NTs,

which were prepared with and without inclusion of nickel salt in the growth solution. (a) CV curves

(b) GCD curves and calculated capacity values of the both samples. This results indicate that the

sample prepared with an inclusion of nickel salt (i.e., forest-like NiS NTs) ensued superior capacity

values than the sample synthesized without addition of nickel salt in the growth solution.

Section 2: Effect of growth temperature on the morphological and electrochemical properties

of NiS nanostructures on Ni foam: The effect of growth time on the structural and

electrochemical properties of NiS on Ni foam were carried out under different temperatures of 50-

115 C with a constant growth time of 3 h. At the low growth temperature (50 C), as shown in

FE-SEM images of Fig. S5a, NiS with nanosheet like morphology was started to grew on Ni foam

substrate. This means that the growth temperature is not enough to form the vertically aligned

forest-like nanoarchitectures. With increasing the growth temperature to 85 C, the forest-like NiS

NTs were uniformly distributed on Ni foam due to the increased nucleation and growth rate of the

added reactants (see FE-SEM images of Fig. 2). Further increasing the growth temperature to 115

C (Fig. S5b), NiS nanostructures were densely integrated on Ni foam in the form of lumps with

high mass loading. Also, several cracks were observed due to the extreme growth rate and

0 5 10 15 20 25 30 35 400

200

400

600

800

NiS nanoparticles

Forest-like NiS NTs

Without nickel salt

Are

al

Ca

pa

cit

y (A

h c

m-2)

Current Density (mA cm-2)

With nickel salt

15.1%

0 300 600 900 1200 15000.0

0.1

0.2

0.3

0.4

I: 4 mA cm-2

Forest-like NiS NTs

NiS

nanoparticles

(With nickel salt)

Po

ten

tia

l (V

vs

. A

g/A

gC

l)

Time (s)

(Without

nickel salt)

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-150

-100

-50

0

50

100

150

Scan rate: 10 mV s-1

(Without

nickel salt)

NiS nanoparticles

(With nickel salt)

Forest-like NiS NTs

Cu

rre

nt

(mA

)

Potential (V vs. Ag/AgCl)

(a) (b) (c)

7

precipitation of added reactants. This kind of cracks may not useful for improving the capacity and

rate capability of the prepared samples.

Fig. S5. FE SEM images of NiS nanostructures prepared at the growth temperatures of (a) 50 C

and (b) 115 C.

The electrochemical properties of the prepared samples under different temperatures were

included in Fig. S6. The comparative CV curves (measured at a scan rate of 10 mV/s), shown in

Fig. S6a displayed the dynamic redox peaks, indicating the battery-type mechanism of NiS-based

samples. Compared to other samples, the forest-like NiS NTs synthesized at 85 C exhibited higher

redox current and large enclosed CV area, revealing the high capacity contribution of the material.

To estimate the capacity of the prepared samples, the GCD curves (Fig. S6b) also measured as a

function of synthesis temperature. As shown in the comparative GCD curves (measured at a

constant current density of 4 mA/cm2), the sample synthesized at high temperature (115 C)

demonstrated uneven charge-discharge times, where the material showed high charge time and

small discharge time, which indicates the low columbic efficiency of the prepared sample and this

could be due to the surface cracks and over mass loading of the material. On the other hand, as

Lumps

Cracks

300 nm3 m10 m

(b) (ii) (iii)NiS/Ni foam at 115 C(i)

8

shown in discharge curves of the prepared electrodes, the NiS synthesized at 85 C demonstrated

high discharge time compared to the other growth temperature samples. The calculated discharge

capacities of these samples were plotted in Fig. S6c, which showed the areal capacities of 287.37,

752.71 and 386.88 Ah/cm2 for the NiS nanostructures prepared at various growth temperatures

of 50, 85, and 115 C, respectively. Thus, we have chosen 85 C and 3 h were the optimal growth

conditions in the development of forest-like NiS NTs as a high capacity cathode material for the

hybrid supercapacitors. The overall electrochemical properties, including CV at various scan rates,

GCD at different current densities and calculated capacity plots, of NiS samples developed at 50

and 115 C, were presented in Fig. S7.

9

Fig. S6. Comparative electrochemical properties of NiS nanostructures prepared under various

growth temperatures.

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-120

-80

-40

0

40

80

120

160C

urr

en

t D

en

sit

y (

mA

/cm

2)

Potential (V vs. Ag/AgCl)

50 C

85 C

115 C

0 300 600 900 1200 15000.0

0.1

0.2

0.3

0.4

Po

ten

tial (V

vs. A

g/A

gC

l)

Time (s)

50 C

85 C

115 C

NiS/Ni foamNiS/Ni foam

Scan rate: 10 mV/s

I : 4 mA/cm2

0 100 200 300 400 500 600 7000.0

0.1

0.2

0.3

0.4

Po

ten

tial (V

vs. A

g/A

gC

l)

Time (s)

50 C

85 C

115 C

40 60 80 100 1200

200

400

600

800

Are

al C

ap

acit

y (A

h c

m-2)

Growth Temperature (C)

Discharge Curves

(a) (b)

(c)

752.71 Ah/cm2

386.88 Ah/cm2

287.37 Ah/cm2

10

Fig. S7. CV curves, GCD curves and calculated areal capacity values of the NiS-based samples

synthesized at various growth temperatures of (a) 50 C and (b) 115 C, respectively.

0 5 10 15 20 25 300

100

200

300

Are

al C

ap

acit

y (A

h c

m-2)

Current Density (mA cm-2)

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

-120

-80

-40

0

40

80

120

160 2 mV s

-1

5 mV s-1

7 mV s-1

10 mV s-1

15 mV s-1

20 mV s-1

30 mV s-1C

urr

en

t D

en

sit

y (

mA

/cm

2)

Potential (V vs. Ag/AgCl)0 300 600 900 1200 1500

0.0

0.1

0.2

0.3

0.4

40 mA cm-2

Po

ten

tial (V

vs. A

g/A

gC

l)

Time (s)

4 mA cm-2

0 5 10 15 20 25 300

100

200

300

400

Are

al C

ap

acit

y (A

h c

m-2)

Current Density (mA cm-2)

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7-100

-75

-50

-25

0

25

50

75

100 2 mV s-1

5 mV s-1

7 mV s-1

10 mV s-1

15 mV s-1

20 mV s-1

30 mV s-1C

urr

en

t D

en

sit

y (

mA

/cm

2)

Potential (V vs. Ag/AgCl)0 100 200 300 400 500

0.0

0.1

0.2

0.3

0.4

40 mA cm-2

Po

ten

tia

l (V

vs

. A

g/A

gC

l)

Time (s)

4 mA cm-2

(a) (ii) (iii)(i)

(b) (ii) (iii)(i)

11

Fig. S8. Electrochemical performance of NiS-based sampled deposited under different growth

times of (a-b) 1 h, (c-d) 2 h and (e-f) 5 h, respectively with a constant growth temperature of 85

C.

0 5 10 15 20 25 30 35 400

100

200

300

400

500

600

700

Are

al

Ca

pa

cit

y (A

h c

m-2)

Current Density (mA cm-2)

0 200 400 600 800 1000 12000.0

0.1

0.2

0.3

0.4

40 mA cm-2

Po

ten

tial

(V v

s.

Ag

/Ag

Cl)

Time (s)

4 mA cm-2

0 100 200 300 400 500 600 700 8000.0

0.1

0.2

0.3

0.4

40 mA cm-2

P

ote

nti

al

(V v

s.

Ag

/Ag

Cl)

Time (s)

4 mA cm-2

0 5 10 15 20 25 30 35 400

100

200

300

400

Are

al C

ap

ac

ity

(A

h c

m-2)

Current Density (mA cm-2)

0 300 600 900 12000.0

0.1

0.2

0.3

0.4

40 mA cm-2

Po

ten

tial

(V v

s.

Ag

/Ag

Cl)

Time (s)

4 mA cm-2

0 5 10 15 20 25 30 35 400

100

200

300

400

500

600

700

Are

al C

ap

ac

ity

(A

h c

m-2)

Current Density (mA cm-2)

(a)

(b)

(c)

(d)

(e)

(f)

12

Fig. S9 FE-SEM images of the forest-like NiS NTs/Ni foam after cycling test in three-electrode

system.

Fig. S10 (a) CV (b) GCD curves of PAC/Ni foam electrode in 1 M KOH solution.

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

-80

-60

-40

-20

0

20

40

60

80

Cu

rre

nt

De

nsit

y (

mA

/cm

2)

Potential (V, vs. Ag/AgCl)

5 mV/s

100 mV/s

0 50 100 150 200 250 300 350-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Po

ten

tial

(V, v

s. A

g/A

gC

l)

Time (s)

5 mA/cm2

40 mA/cm2

(a) (b)

13

Table S1. Comparative electrochemical properties of previously reported metal sulfide/selenide

based nanostructures with forest-like NiS NTs/Ni foam electrode.

Electroactive material Current

collector Electrolyte

Test

condition

(mA/cm2)

Area

(cm2)

Areal

capacity

(Ah/cm2)

Ref.

Ni3S2 nanoparticles Carbon

fiber paper 2 M KOH 2 1 119.44 S1

NiSe microspheres Ni foam 2 M KOH 3 0.6 1250 S2

Ni3S2 nanosheets Ni foam 1 M KOH 1 1 154.16 S3

NiS box-in-box Ni foam 3 M KOH 1 1 63.8 S4

Ni3S2@MWCNTs

composite Ni foam 2 M KOH 1.2 1 191.6 S5

NiSe nanowires Ni foam 2 M KOH 5 1 700.1 S6

NiS nanoframes Ni foam 6 M KOH 1 1 279.16 S7

NiS hollow spheres Ni foam 2 M KOH 4.08 1 147.3 S8

CoS hollow tubes Ni foam 6 M KOH 5 1.13 472.2 S9

CuS nanonedles@CNT Ni foam 2 M KOH 2.9 1 40.7 S10

NiS nanostructures Graphene-

Cotton 6 M KOH 0.5 1 172.1 S11

Forest-like NiS NTs Ni foam 1 M KOH 4 1 752.71 This

work

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