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Supplementary Information
Directly grown high-performance WO3 films by a novel one-step
hydrothermal method with significantly improved stability for
electrochromic applications
Jianbo Pan, Yi Wang, Rongzhong Zheng, Maotong Wang, Zhongquan Wan, Chunyang Jia,
Xiaolong Weng, Jianliang Xie and Longjiang Deng
State Key Laboratory of Electronic Thin Films and Integrated Devices, National Engineering Research Center of Electromagnetic Radiation Control Materials, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China
Scheme S1 shows the pertinent synthesis processes for hexagonal WO3 (hex-
WO3) and orthorhombic WO3·0.33H2O (ort-WO3·0.33H2O) crystals. First of all, the
yellow precipitate (H2WO4) was formed by adding HCl (3 M) solution to the sodium
tungstate solution. After H2WO4 dissolved in hydrogen peroxide (H2O2), a stable
peroxopolytungstic acid solution was obtained.1 Under acid hydrothermal condition,
WO2(OH)2 was precipitated from the precursor solution when solution reached
oversaturated state, and excess H+ ions made it transform into polycondensation
precursor monomers in hydration procedure, including WO(OH)4(OH2)2 and W(OH)6
monomers. Six monomers could be condensed to form a six-membered ring structure,
then further nucleated. Finally, after the crystal nucleus reached a critical size, the
crystals of ort-WO3·0.33H2O and hex-WO3 were obtained respectively by further
crystalized growth.
Corresponding author. Tel.: +86 28 83201991; Fax: +86 28 83202569. Email: cyjia@uestc.edu.cn (C. Y. Jia)
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019
2
OH W OH
O
OW OHOH
O
O
H2O H2O
W OHO
OH2
O
H2O
OH
W OHHO
OH2
O
OH
OHH+
W OO
O
OH2
OH
OH
WOH
OHO
W
OOH
HO
WO
OH2
OW
O
WOH
OH
HO
HOHO
HO
OHOH
OH
HO
OH
OH
HO
HO
W OHHO
OH2
O
OH
OH
W OHHO
OH
OH
OH
OH
+
Na2WO4 + 2HCl H2WO4(s) + 2NaCl
H2WO4 + H2O2 WO3 · H2O2 · H2O(l)
WO3 · H2O2 · H2O(l)Supersaturation
H+
( H2WO4 )
( Peroxotungstic acid )
(1)
(2)
(3)
(4) 2 4[H+]
-H2O
Excess
W OHOH
O
O
H2O H2O
W OHO
OH
O
H2O
OH2
W OHHO
OH
OH
OH
OH
W OO
OH
OH
OH
OH
WOH
OHO
W
OOH
HO
WO
OH
OHW
O
WOH
OH
HO
HOHO
HO
OHOH
OH
HO
OH
OH
HO
HO
W OHHO
OH
OH
OH
OH
6[H+, (NH4)2SO4]
-H2O(5)
Crystallization
Crystallization
WO3·0.33H2O
WO3
Orthorhomic
Hexagonal
H+
Excess
(NH4)2SO4
Scheme S1. Proposed synthetic route for the formation of orthorhombic WO3·0.33H2O and hexagonal WO3.
The chemical composition of FTO-coated glass surface was characterized by FT-
IR spectra, as shown in Fig. S1. An obvious broad peak at 3370 cm-1 is ascribed to O-
H. The bands at regions between 2800-3650 cm-1 and 1700-1400 cm-1 are assigned to
O-H stretching and O-H bending, respectively,3, 4 which confirm that the surface of
FTO-coated glass is active and rich in hydroxyl (-OH) groups. Particularly, the peaks
of 2920 cm-1 and 2347 cm-1 can be attributed to some residual organic matter.
4000 3500 3000 2500 2000 1500
3370
FTO-coated glass
Tran
smitt
ance
/
Wavenumber (cm-1) Fig. S1 The FT-IR spectra of FTO-coated glass.
3
The adhesive force of WO3 films with (W-AS0) and without (pure-H2O) glycerol
were tested via a simple grid-sticking method. As shown in Fig. S2a, first of all, using
glass cutter to engrave girds (2mm * 2mm) on films. Secondly, sticking the tapes (3M
#600) firmly and covering at least one small grid. After 2-5 minutes, pulling down the
tapes at 150 degree, and evaluating the damage level of each film according to Table
S1. The damage of W-AS0 film occurred only at the intersection of cutting lines, but
pure-H2O film at the edges and intersection of cutting lines simultaneously.
Therefore, the damage of W-AS0 film and pure-H2O film could be judged as 4B and
3B, respectively. It could be confirmed that glycerol can strengthen the adhesive force
between WO3 film and FTO.
a
a
f
b
a
f
c
a
f
Fig. S2 (a) Schematic illustration of grid-sticking method; The contrast test of adhesive force of films: (b) with glycerol (W-AS0 film), (c) without glycerol (pure-H2O film).
4
Table S1 The damage grade check list of film
Damage grade Damage description5B The edge of the cutting line is smooth and the mesh does not fall off at all.
4BFine powder drops off at the intersection of cutting lines, and the affected area is less than 5%.
3BFine powder drops off at the edge and intersection of the cutting lines, and the affected area ranges from 5% to 15%.
2BFlakes fall off at the edge and grid of cutting lines, and the affected area ranges from 15% to 35%.
1BStrip flakes falling off and the whole grid falling off at the edge of the cutting line, and the affected area ranges from 35% to 65%.
0B More serious film shedding that 1B
10 20 30 40 50 60 70 80
Orthorhombic WO30.33H2OFTO
W-AS0
Pure-H2O
(220
)(2
20)
(002
)(0
02)
(111
)(1
11)
(020
)(0
20)
Inten
sity
/ a.u
.
2degree
FTO
Fig. S3 XRD patterns for FTO-coated glass, pure-H2O and W-AS0 films.
a b c d
Fig. S4 Cross-sectional SEM images of WO3 films: (a) W-AS0, (b) W-AS2, (c) W-AS4, (d) W-AS6.
Table S2 The thickness of each filmSample W-AS0 W-AS2 W-AS4 W-AS6Thickness (µm) 1.11 1.88 1.58 0.81
The pore size distribution of each structure as shown in Fig. S5, it can be found
that there are peaks at 3~5 nm in both W-AS0 and W-AS4 structures, but not in W-
5
AS2 structure, which indicates the W-AS2 structure does not contain 3~5 nm pore.
0.0 0.2 0.4 0.6 0.8 1.00
5
10
15
20W-AS0
Qua
ntity
Ads
orbe
d (c
m3 /
g)
Relative Pressure (P/P)
0 10 20 30 40 500.00
0.01
0.02
0.03
0.04
dV/d
log(
W)
(cm
3 /g)
Pore Width (nm)
0.0 0.2 0.4 0.6 0.8 1.0
0
10
20
30
40 W-AS2
Qua
ntity
Ads
orbe
d (c
m3 /
g)
Relative Pressure (P/P)
0 10 20 30 40 50 60 700.00
0.02
0.04
0.06
0.08
dV/d
log(
W)
(cm
3 /g)
Pore Width (nm)
0.0 0.2 0.4 0.6 0.8 1.00
10
20
30
40
Qua
ntity
Ads
orbe
d (c
m3 /
g)
Relative Pressure (P/P)
W-AS4
0 10 20 30 40 50 600.00
0.02
0.04
0.06
0.08
dV/d
log(
W)
(cm
3 /g)
Pore Width (nm)
Fig. S5 N2 (77 K) adsorption/desorption isotherms linear plots (inset: pore size distribution).
Table S3 The specific surface area of different structures
Sample W-AS0 W-AS2 W-AS4 W-AS6Specific Surface Area (m2/g)
10.1 10.3 22.5
Note: Due to the low yields of W-AS6 powder with low crystallinity, the surface area could not be tested.
6
0 200 400 600 800 1000
-1
0
1
2
3a
Curre
nt D
ensit
y (m
A/cm
2 )
Number of cycles0 200 400 600 800 1000
-1
0
1
2
3b
Curre
nt D
ensit
y (m
A/cm
2 )
Number of cycles
0 200 400 600 800 1000-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0d
Curre
nt D
ensit
y (m
A/cm
2 )
Number of cycles0 200 400 600 800 1000
-2
-1
0
1
2
3
4c
Curre
nt D
ensit
y (m
A/cm
2 )
Number of cycles
Fig. S6 The step chronoamperometric cyclic curves of WO3 films with different amounts of
(NH4)2SO4 at -1.5 V (colored, 10 s) and +2.0 V (bleached, 10 s): (a) W-AS0, (b) W-AS2, (c) W-
AS4, (d) W-AS6.
Fig. S7 Cross-sectional SEM image of W-AS4_seed film.
Fig. S8 shows the cyclic stability of W-AS4_seed film in 1000 cycles. As same as
W-AS4 film, the W-AS4_seed film is in activation stage within at least 1000 cycles.
7
0 200 400 600 800 1000-2
-1
0
1
2
3
Curre
nt D
ensit
y (m
A/cm
2 )
Number of cycles
Fig. S8 The step chronoamperometric cyclic curve of W-AS4_seed film at -1.5 V (colored, 10 s) and +2.0 V (bleached, 10 s).
Fig. S9 shows the electrochromic performance of W-AS4_seed film. At 630 nm
wavelength, the transmittance modulation range of W-AS4_seed film under ±1.0 V
voltages was about 75.1%, which was lower than W-AS4 film (78.1%). The bleaching
time (tb) and coloration time (tc) were calculated to be 8 s and 5 s, respectively, which
were slower than the ones of W-AS4 film (6/5 s for bleaching/coloration). The
coloration efficiency was calculated to be 45.1 cm2 C-1, while it was 56.5 cm2 C-1 in
W-AS4 film. Thus, we could conclude that the self-seeded hydrothermal method is
better than crystal-seed-assisted hydrothermal method.
400 500 600 700 800 900 1000 11000
20
40
60
80a
Tran
smitt
ance
/
Wavelength / nm
+1V bleached - 1V colored
8
0 20 40 60 80 100 120 1400
20
40
60
80
100b
Tran
smitt
ance
/
Time / s
tc = 5 s
tb = 8 s
0 10 20 30 40 500.0
0.5
1.0
1.5c
630 nm, CE = 45.1 cm2 C-1
OD
Charge density / mC cm-2
Fig. S9 The electrochromic performance of W-AS4_seed film: (a) UV-vis transmittance spectrum of colored and bleached states between 350 nm and 1100 nm, (b) Switching time and transmittance variation curves between colored and bleached states at 630 nm, ±1.0 V bias, (c) Variation of the optical density (ΔOD) versus charger density (Q); Digital photographs of the W-AS4_seed film at different stages: (d) colored at -1.0 V for 25 s, (e) colored at -2.0 V for 25 s, (f) bleached at 2.0 V for 25 s.
Table S4 The electrochromic performances comparison of W-AS4 film with and without crystal seed layer
NameΔT
[%/nm]Tc/Tb
[s]CE
[cm2 C-1]W-AS4 film 78.1 5.0/6.0 56.5W-AS4_seed film 75.1 5.0/8.0 45.1
Fig. S10 Schematic illustration of the possible interlocking force in coral-like nanostructure of W-AS4 film.
Fig. S11 shows the electrochemical and electrochromic properties of PB film. All
9
the above tests were carried out in 1 M LiClO4/PC electrolyte by conventional three-
electrode test method. In CV curve of PB film, there are two obvious peaks at -0.2 V
and +0.6 V, which correspond to the reduction and oxidation reactions, respectively.5
The electrochromic properties of PB film were tested at ±0.6 V. The switching time
and transmittance variation curve between colored and bleached states at 630 nm
shows tc/tb was 2.5/6 s.
-1 0 1-2
-1
0
1
2a
Cu
rrent
den
sity
( mA/
cm2 )
Voltage (V vs. Ag/AgCl)
400 500 600 700 800 900 1000 11000
20
40
60
80
100b
Tran
smitt
ance
/
Wavelength / nm
+0.6 V bleached - 0.6 V colored
0 20 40 60 80 100 1200
20
40
60
80
100c
tc = 2.5 s
tb = 6 s
Tran
smitt
ance
/
Time / s
Fig. S11 (a) CV curve of PB film; (b) UV-vis transmittance spectrum of PB film in colored and bleached states between 350 nm and 1100 nm; (c) Switching time and transmittance variation
curves between colored and bleached states at 630 nm, ±0.6 V bias.
References1 Z. Jiao, X. W. Sun, J. Wang, L. Ke and H. V. Demir, J. Phys. D: Appl. Phys., 2010, 43, 285501.2 D. Mandal, P. Routh and A. K. Nandi, Small, 2018, 14, 1702881.3 L. Zhu, W. L. Ong, X. Lu, K. Zeng, H. J. Fan and G. W. Ho, Small, 2017, 13, 1700084.4 A. Phuruangrat, D. J. Ham, S. J. Hong, S. Thongtem and J. S. Lee, J. Mater. Chem., 2010, 20,
1683-1690.5 Z. Jiao, J. Wang, L. Ke, X. Liu, H. V. Demir, M. F. Yang and X. W. Sun, Electrochim. Acta, 2012,
63, 153-160.
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