1

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.

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1683-1690.5 Z. Jiao, J. Wang, L. Ke, X. Liu, H. V. Demir, M. F. Yang and X. W. Sun, Electrochim. Acta, 2012,

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