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Page S1
Supplementary Information
Thermally induced nanostructuring for the synthesis of core/shell-structured CoO/CoSx electrocatalyst
Min Soo Kima†, Muhammad Awais Abbasb†, Raju Thotab† and Jin Ho Bang*abc
aDepartment of Bionano Technology, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan,
Gyeonggi-do 15588, Republic of Korea
bNanosensor Research Institute, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan,
Gyeonggi-do 15588, Republic of Korea
cDepartment of Chemical and Molecular Engineering, Hanyang University, 55 Hanyangdaehak-ro,
Sangnok-gu, Ansan, Gyeonggi-do 15588, Republic of Korea
Author Contributions:
†These authors contributed equally to this work.
*Corresponding Author
E-mail: [email protected]
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019
Page S2
Fig. S1 XRD patterns of intermediates obtained during a hot H2 treatment of Co3O4 at various
temperatures for 1 h.
Fig. S2 SEM images of Co3O4 (a,b) before and (c,d) after a hot H2 treatment at 300 oC for 1 h.
Co3O4
220 °C, 1 h
240 °C, 1 hIn
tens
ity (a
.u.) 245 °C, 1 h
250 °C, 1 h
300 °C, 1 h
Co3O4
Co
20 30 40 50 60 70 802-Theta (degree)
CoO
Page S3
Fig. S3 The crystal structure of cobalt oxides and cobalt sulfides.
Scheme S1 Schematic representation of the grain fracture of Co3O4 and the formation of mesoporous
CoO with smaller crystallites from bulk Co3O4 under a reducing environment of hot NH3.
Co3O4
CoO
Co3O4 Co3O4/CoO CoO
Page S4
Fig. S4 Cyclic voltammograms of (a) CoO/CoSx and (b) Pt electrodes at various scan rates. (c) Tafel
polarization curves of CoO/CoSx and Pt counter electrodes. Equivalent circuits used for fitting the
Nyquist plots of (d) CoO/CoSx and (e) Pt counter electrodes. Rs is the equivalent series resistance, Rct is
the charge transfer resistance, ZN is the Nernst diffusion impedance, Rtrns is the electron transport
resistance in the carbon layer, and CPE2 and CPE3 are the constant phase elements associated with
resistances.
Table S1 Various resistance values extracted from fitting the Nyquist plots of CoO/CoSx and Pt
electrodes. EIS was carried out with symmetric dummy cells.
Counter Electrode Rs (Ω∙cm2)
Rtrns (Ω∙cm2)
Rct (Ω∙cm2)
ZN (Ω∙cm2)
CoO/CoSx 3.30 0.57 0.91 1.35
Pt 3.31 - 0.97 1.32
Page S5
Fig. S5 XRD pattern of CoO/CoSx and Rietveld refinement result that determines the composition of
each component (CoO: 86.2%, CoS: 11.9%, and Co3S4: 1.9%).
Observed Calculated Background Difference
Inte
nsity
(a.u
.)
CoO
CoS
20 30 40 50 60 70 802-Theta (degree)
Co3S4
Inte
nsity
(a.u
.)
CoSx
Co3S4
20 30 40 50 60 70 802-Theta (degree)
CoS
Page S6
Fig. S6 XRD pattern of CoSx obtained at 300 oC for 1 h. The compositional percentages of CoS and Co3S4
determined by Rietveld refinement were 76.5 and 23.5%, respectively.
Fig. S7 (a) N2 physisorption isotherms and (b) pore size distributions of CoSx. The BET surface area was
7.34 m2·g-1 and the total pore volume was 0.047 cm3·g-1.
Fig. S8 (a-c) TEM images and (d) FFT patterns of CoSx.
0 0.2 0.4 0.6 0.8 1.00
5
10
15
20
25
30
Volu
me
Ads
orbe
d (c
m3 g
-1)
Relative Pressure (P/P0)
Adsorption Desorption
1 10 1000
0.01
0.02
0.03
0.04
0.05
dV/d
logD
Pore Diameter (nm)
(a) (b)
0 0.2 0.4 0.6 0.80
5
10
15
20
Cur
rent
Den
sity
(mA
·cm
-2)
Voltage (V)
CoO/CoSx
Pt CoSx
· ·
Page S7
Fig. S9 J–V curve of DSSCs assembled with various CEs made of CoO/CoSx, Pt, and CoSx.
Table S2 J–V parameters of DSSCs fabricated with the above CEs.
CE Jsc (mA·cm2) Voc (V) FF PCE (%)
CoO/CoSx 15.5 ± 0.3 0.73 ± 0.01 0.66 ± 0.02 7.27 ± 0.06
Pt 15.9 ± 0.2 0.70 ± 0.01 0.65 ± 0.01 7.12 ± 0.05
CoSx 15.1 ± 0.5 0.71 ± 0.02 0.62 ± 0.03 6.73 ± 0.16
Fig. S10 (a) XRD patterns of CoO/CoSx obtained at various reaction conditions and (b) CoS and Co3S4
composition ratios determined by Rietveld refinement.
12.91%
87.09%
4.33%
95.67%CoSCo3S4
17.38%
82.62%
41.76%
58.24%
31.19%
68.81%
32.73%
67.27%
71.34%
28.66%
17.54%
82.46%
300 ºC, 10 min 400 ºC, 10 min
270 ºC, 1 h 400 ºC, 30 min
300 ºC, 30 min 300 ºC, 1 h
450 ºC, 10 min 400 ºC, 1 h
CoO
270 °C, 1 h
300 °C, 10 min
300 °C, 30 min
300 °C, 1 h
400 °C, 10 min
Inte
nsity
(a.u
.)
400 °C, 30 min
400 °C, 1 h
450 °C, 10 min
CoO
CoS
20 30 40 50 60 70 802-Theta (degree)
Co3S4
(a) (b)
Page S8
Fig. S11 (a) SEM and (b) TEM images of commercially available IrO2.
Page S9
Fig. S12 Cyclic voltammograms of of (a) Bare GC, (b) Co3O4, (c) CoO, (d) CoO/CoSx, and (e) IrO2 electrodes
in 0.1 M KOH at various scan rates to determine the electrochemical double layer capacitance (Cdl). (f)
Linear scan voltammograms of CoO/CoSx as an electrocatalyst for OER before and after 1000 CV scans,
demonstrating excellent stability of CoO/CoSx.
0.84 0.87 0.90 0.93 0.96 0.99-0.010
-0.005
0.005
0.010
0.015
0
0.81 0.84 0.87 0.90 0.93 0.96 0.99-0.015-0.010-0.005
0.0050.0100.0150.020
0
0.78 0.81 0.84 0.87 0.90 0.93 0.96-0.06
-0.03
0.03
0.06
0.09
0.12
0
0.8 1.0 1.2 1.4 1.6 1.8
10
20
30
40
50
60
0
0.84 0.86 0.88 0.90 0.92 0.94 0.96 0.98-0.0045
-0.0030
-0.0015
0.0015
0.0030
0.0045
0
0.84 0.87 0.90 0.93 0.96-0.09
-0.06
-0.03
0.03
0.06
0.09
0.12
0
Cur
rent
Den
sity
(mA
⋅cm
-2)
Potential (V vs RHE)
2 mV·s-1 20 mV·s-1
5 mV·s-1 25 mV·s-1
10 mV·s-1 15 mV·s-1
2 mV⋅s-1
25 mV⋅s-1
(b)
Cur
rent
Den
sity
(mA
⋅cm
-2)
Potential (V vs RHE)
2 mV·s-1 15 mV·s-1
5 mV·s-1 20 mV·s-1
10 mV·s-1 25 mV·s-1
2 mV⋅s-1
25 mV⋅s-1
(c)C
urre
nt D
ensi
ty (m
A⋅c
m-2
)
Potential (V vs RHE)
2 mV·s-1 15 mV·s-1
5 mV·s-1 20 mV·s-1
10 mV·s-1 25 mV·s-1
(d)
Cur
rent
Den
sity
(mA
⋅cm
-2)
Potential (V vs RHE)
Initial After 1000 CV Cycles
(a)
Cur
rent
Den
sity
(mA
⋅cm
-2)
Potential (V vs RHE)
2 mV·s-1 20 mV·s-1
5 mV·s-1 25 mV·s-1
10 mV·s-1
15 mV·s-1
2 mV⋅s-1
(f)(e)
25 mV⋅s-1
25 mV⋅s-1
2 mV⋅s-1
2 mV⋅s-1
25 mV⋅s-1
Cur
rent
Den
sity
(mA
⋅cm
-2)
Potential (V vs RHE)
2 mV·s-1 20 mV·s-1
5 mV·s-1 25 mV·s-1
10 mV·s-1 15 mV·s-1
Page S10
Table S3 The ECSA calculations of each catalyst.
Sample Slope (mF∙cm-2) Cdl (mF∙cm-2) Rf ECSA (cm2)
Bare GC 0.154 0.077 - -
CO3O4 0.427 0.214 2.77 0.54
CoO 0.458 0.229 2.98 0.58
CoO/CoSx 3.7 1.85 23.99 4.70
IrO2 4.85 2.425 31.45 6.16
Fig. S13 Equivalent circuit used for fitting the impedance spectra of OER electrocatalysts. Rs represents
the solution resistance. R1 and C1 denote the diffusion/adsorption of reaction intermediates due to slow
diffusion through the reaction interface in the porous electrode. R2 and Cdl are ascribed to the charge
transfer resistance the capacitance associated with OER, respectively.
Table S4 Various resistance values extracted by fitting the equivalent circuit in Fig. S5 to the Nyquist
plots of various cobalt oxides and IrO2 when employed as OER electrocatalysts.
Catalyst Rs (Ω∙cm2) R1 (Ω∙cm2) Rct (Ω∙cm2)
Co3O4 2.30 111.82 952.36
CoO 1.19 0.97 185.24
CoO/CoSx 1.87 0.38 21.77
IrO2 2.11 1.77 40.68
Rs
C1
R1
Cdl
Rct
Page S11
Fig. S14 XRD patterns taken during the synthesis of (a) nanostructured MoN/MoS2 and (b)
nanostructured W0.62(N,O)/WS2.
Fig. S15 TEM images of taken during the synthesis of nanostructured MoN/MoS2: (a,b) MoO3, (c,d) MoN,
(e,f) MoN/MoS2, and (g) STEM-EDS mapping analysis results of MoN/MoS2.
WO3
NH3, 600°C, 1 h
Inte
nsity
(a.u
.)
H2S, 300°C, 1 h
W0.62(N,O)
20 30 40 50 60 70 802-Theta (degree)
WS2
MoO3
NH3, 600°C, 1 h
Inte
nsity
(a.u
.)
H2S, 300°C, 1 h
MoN
20 30 40 50 60 70 802-Theta (degree)
MoS2
(a) (b)
Page S12
Fig. S16 TEM images of taken during the synthesis of nanostructured W0.62(N,O)/WS2: (a,b) WO3, (c,d)
W0.62(N,O), (e,f) W0.62(N,O)/WS2, and (g) STEM-EDS mapping analysis results of W0.62(N,O)/WS2.