Graphene-based electrochromic systems: The case of Prussian Blue nanoparticles on transparent graphene film

Article abstract of DOI:10.1039/c2cc30161j

Prussian Blue nanoparticles were electrodeposited on transparent grapheme film, which showed a promising electrochromism with response times in the range of 3.3-38 s. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2cc30161j

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COMMUNICATION
Graphene-based electrochromic systems: the case of Prussian Blue
nanoparticles on transparent graphene filmw
Ju Hong Ko,a Soojung Yeo,a Ji Hoon Park,a Jaewon Choi,a Changho Nohb and
Seung Uk Son*a
Received 9th January 2012, Accepted 21st February 2012
DOI: 10.1039/c2cc30161j
Prussian Blue nanoparticles were electrodeposited on transparent
grapheme film, which showed a promising electrochromism with
response times in the range of 3.3–38 s.
color and also as an electron-mediator9 in sensing devices.
Moreover, it can be diversified into sub-family materials via
incorporation of diverse transition metals instead of iron.10 Very
recently, Wang’s group prepared the graphene composites of PB
nanoparticles for sensor devices.9a In their work, graphene was
prepared by a wet-chemical method from graphite via a modified
Hummers method. The PB nanoparticles were deposited on
graphene by mixing the graphene suspension with a precursor
solution of PB nanoparticles.
Electrochromism, a reversible color change of materials through a
supply of voltage, can be applied for diverse purposes e.g. in
display devices, mirrors, smart windows and military camouflage.1
Especially, electrochromic mirrors and windows have been
commercialized in devices of cars and airplanes.1 In addition
to the color diversity and memory effect, the response time of
materials is an important factor in device applications. For
example, while display devices require a fast response time, a
relatively slow response time is acceptable in smart windows or
military camouflage.1,2 Thus, information on the response
time of materials in certain systems will be valuable.
Our research group has continued the development of new
organic and inorganic electrochromic systems for smart window
and display applications.11 In this work, we report the electro-
chromic performance of the electrochemically deposited PB nano-
particles on transparent graphene film. Especially, considering the
slow electron transfer behavior of high-quality graphene as
recently reported by Banks et al.,6 the response times of
graphene-based electrochromic systems were compared with
those of the commercial indium tin oxide (ITO) electrode.
A transparent and high-quality graphene film with 1 cm2
area was prepared by a CVD method based on the literature
method.5 Raman spectroscopy showed that the prepared
materials mainly consisted of single-layered graphene, which
matches well with a reported result (Fig. 1c and S1 in ESIw).5
The aqueous precursor solution containing 5.0 mM FeCl3,
5.0 mM K3Fe(CN)6, 0.10 M KCl and 0.10 M HCl was
prepared and then PB nanoparticles were electrodeposited on
the graphene film with 0.9 cm2 area through cyclic voltammetry.
Fig. 1a shows the scanning electron microscopy (SEM) image of
the PB nanoparticles on graphene that were prepared by 40 scans
between +0.30 and +0.80 V with a scan rate of 100 mV sÀ1
(Fig. 1d). As shown in the photograph in Fig. 1e, the transparent
graphene film was coated with blue-colored materials. The
average size of the PB particles was measured as 45 Æ 6 nm
(Fig. 1b). The UV-visible absorption spectroscopy showed the
maximum absorption peak at 720 nm (Fig. 1e).
Recently, graphene has emerged as a new conductive platform
for diverse electronic devices.3 The quality of graphene has been
gradually increased by advances in synthetic methods. A large
amount of graphene can be prepared by the reduction of
graphene oxide in solution by the Hummers method.4 However,
the remaining oxygen contents often limit the electrochemical
properties. Recently, a chemical vapor deposition (CVD) method
using a copper catalyst afforded high-quality graphene films.5
However, more explorations are definitely required to ensure the
real merits of this new material. For example, a slow electron
transfer in high-quality graphene has been recently reported by
Banks et al., and thus its application as electrode materials for
sensor devices has been questioned.6 However, carbon-based
electrode materials have been believed to show unique physical
properties such as flexibility,7 which facilitates further exploration
of graphene-based devices. Moreover, as far as we are aware, no
study has investigated the electrochromic performance on graphene.
Prussian Blue (PB), FeIII4[FeII(CN)6]3, is an interesting
material in terms of its electrochemical and magnetic properties.8
In addition, it has been used as a pigment8a due to its intense
The amount of loaded PB nanoparticles was controlled to
prepare seven materials by changing the scan-cycle number
from 10 (P-10) to 20 (P-20), 30 (P-30), 40 (P-40), 60 (P-60), 80
(P-80) and 100 (P-100). The absorbance in UV-vis absorption
spectroscopy gradually increased with increasing scan-cycle
numbers (Fig. 2a). SEM analysis revealed that the size of the
PB nanoparticles and the thickness of the materials increased
gradually (Fig. 2b and S4 and S5 in the ESIw).
a Department of Chemistry and Department of Energy Science,
Sungkyunkwan University, Suwon 440-746, Korea.
E-mail: sson@skku.edu; Fax: +82-031-290-4572;
Tel: +82-031-299-5932
b Samsung Advanced Institute of Technology (SAIT), Suwon 440-600,
Korea
w Electronic supplementary information (ESI) available: Experimental
details, characterization of graphene and PB materials on ITO
electrodes. See DOI: 10.1039/c2cc30161j
c
3884 Chem. Commun., 2012, 48, 3884–3886
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Fig. 1 (a) SEM image, (b) size distribution diagram of PB nano-
particles (P-40, 420 nm thickness) on graphene, (c) SEM image and
photograph of graphene on glass, (d) cyclic voltammograms of
electrodeposition process and (e) UV-vis absorption spectroscopy
and photograph of P-40.
The electrochromic performance of the PB nanoparticles on
graphene was studied in aqueous 0.10 M KCl electrolyte
solution by cyclic voltammetry, chronoamperometry and
UV-vis absorption spectroscopy. The cyclic voltammetry of
the PB nanoparticles on graphene showed the reversible
reduction peaks at +0.15 V (vs. Ag/Ag+) with color change
from blue to colorless (Fig. 3). Depending on the amount
of materials, the difference between the oxidative wave and
the reductive wave increased, indicating the slower electron
transfer in the thicker materials.
Fig. 2 (a) Absorbance at 720 nm depending on scan-cycle number,
(b) size distribution and (c) SEM images of PB nanoparticles on
graphene.
As described in the introduction part, the response time is a
very important factor in practical applications of electrochromic
systems. The response time was defined as the time required to
reach 90% of the maximum absorbance change. Usually,
inorganic polymeric materials showed a relatively slow response
time due to the low conductivity and the resultant slow electron
transfer. The response times of PB materials in the literature
were reported in range of 5–10 s and were dependent on the
structure and thickness of the PB films.12 To improve the
response time, organic polymer electrolyte–PB composites were
fabricated.13 In the present work, we studied the response time
of the PB nanoparticles on graphene using chronoamperometry
by applying À0.30 V (for bleaching) and +0.60 V (for coloring).
Fig. 4 and Table 1 summarize the results.
Fig. 3 (a) Electrochromic properties of P-40 and (b) representative
cyclic voltammograms of P-20, P-40 and P-80.
space among the materials which allowed the electrolyte to
penetrate through the films. In comparison, P-60, P-80 and
P-100 showed the relatively compact characteristic of materials
and a deficient space between the PB materials. Thus, the sharp
increase of the response times in P-60, P-80 and P-100 was
attributed to the compact structure and thick thickness of film.
The response times of the PB nanoparticles on graphene
were compared with those on the commercial ITO electrode.
Because the electron transfer in graphene was considered to
occur mainly through a peripheral edge,14 a high quality
graphene with a large basal and low edge plane showed a
slow electron transfer.6 The CVD method using a copper
As the thickness (Fig. 2 and S4 in the ESIw) and intensity
change of the PB on graphene increased, the response times
gradually increased (Table 1). The observed response times
revealed that the re-coloring process is generally faster than
the beaching one. From P-60 through P-80 to P-100, the
response times sharply increased from 13.4 through 25.3 to
38.0 s (in the bleaching process). According to the SEM studies,
the PB films on graphene in P-10, P-20, P-30 and P-40 had a
c
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Notes and references
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Fig. 4 Absorbance changes at 720 nm of PB nanoparticles on graphene
with À0.30 V and +0.60 V (vs. Ag/Ag+) respectively. The transmittance
changes of P-10, P-20, P-30, P-40, P-60, P-80, and P-100 at 720 nm were
7%, 18%, 31%, 50%, 59%, 71% and 80% respectively.
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Table 1 Response times of PB nanoparticles on graphenea
Observed response times/s
Intensity change
Materials
Bleachingb
Coloringc
DT (%)
P-10
P-20
P-30
P-40
P-60
P-80
P-100
4.2 (2.8)
7.5 (4.1)
8.9 (4.3)
9.7 (4.7)
13.4 (6.7)
25.3 (12.2)
38.0 (19.4)
3.3 (2.4)
5.8 (3.3)
6.1 (3.8)
7.2 (4.0)
8.9 (6.1)
17.1 (10.9)
28.6 (18.6)
7
18
31
50
59
71
80
a
The absorbance changes at 720 nm were measured using 0.10 M KCl
as the electrolyte solution. The values in parentheses correspond to the
response times for PB materials with the same intensity changes on the
commercial ITO electrode (refer to the ESI). À0.30 V (vs. Ag/Ag+
)
b
was applied. +0.60 V (vs. Ag/Ag+) was applied.
c
catalyst was known to produce a high quality graphene with
single or a few layers. The PB materials on the commercial
ITO electrode with nearly the same UV-vis absorbance at
720 nm were systematically prepared by controlling the cycles
of cyclic voltammetry in electrodeposition (Fig. S2 and S3 in
the ESIw). As summarized in Table 1, the response times of the
PB materials on graphene are about half as fast as those on the
ITO electrode. As mentioned above, although the response
times were quite dependent on the materials themselves, the
properties of electrode materials are also critical in this study
and therefore are considered in practical applications. The
results suggest that PB materials on transparent graphene film
are a promising candidate system for smart (flexible) window
devices.
This work was supported by grants NRF-2011-0031392
(Priority Research Centers Program) and R31-2008-10029
(WCU program) through the National Research Foundation
of Korea funded by the Ministry of Education, Science and
Technology.
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c
3886 Chem. Commun., 2012, 48, 3884–3886
This journal is The Royal Society of Chemistry 2012