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A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films
Solar Energy Materials & Solar Cells ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films Miao-Syuan Fan a, Sheng-Yuan Kao a, Ting-Hsiang Chang a, R. Vittal a, Kuo-Chuan Ho a,b,n a b
Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
art ic l e i nf o
a b s t r a c t
Article history: Received 31 December 2014 Received in revised form 6 June 2015 Accepted 8 June 2015
Prussian blue (PB) powder, which could be dispersed uniformly in water, was prepared through a simple process, and is designated as water dispersible Prussian blue (wPB). A PB thin film was spray-coated on an ITO substrate using the ink of this powder. Another PB thin film was prepared by the electrochemical deposition method (EDPB) for comparison. The properties of these two thin films were compared by using cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). A solid-state complementary electrochromic device (ECD) was fabricated based on a wPB thin film as the anodically coloring electrode and a poly(butyl viologen) (PBV) thin film as the cathodically coloring electrode. Succinonitrile (SN) with 0.1 M potassium bis(trifluoromethanesulfonyl) imide (KTFSI) and silicon dioxide (SiO2) nanoparticles was used as the solid electrolyte. The device could be switched reversibly between blue–violet and transparent upon application of 1.7 V and 1.0 V, and showed an initial transmittance change of 62.5% with a coloration efficiency of 157 cm2/C at 545 nm. The switching time required for both darkening and bleaching was about 10 s for a sample of 2.0 2.0 cm2. As for the electrochemical stability of the ECD, the transmittance change reached 58.4% at 545 nm after 1000 cycles, and the darkened state transmittance remained relatively constant after the same period. & 2015 Elsevier B.V. All rights reserved.
Keywords: Poly(butyl viologen) Potassium bis(trifluoromethanesulfonyl) imide Solid-state electrochromic device Succinonitrile Water dispersible Prussian blue
1. Introduction Because of global warming and energy crisis, energy conservation became a popularity topic. Electrochromic devices (ECD) are gaining importance, owing to their potential applications in energy-saving devices [1–3]. Electrochromism refers to reversible color changes of electrochromic materials involving electrochemical redox reactions. Electrochromism belongs to an important green environmental technology, because the transmittance of a window can be attenuated reversibly to provide indoor comfort [4–7]. The ECDs can be categorized into three types, solution type, hybrid type, and thin-film battery-like type. A complementary ECD is composed of an anodically and a cathodically coloring material. With rapid development of nanotechnology, recent research on Prussian blue (PB) electrochromism focuses on the ECD containing PB or its analogs utilizing nanoparticles [8–12]. PB is a famous elecrochromic material, and it has been extensively studied for many years; it has been proposed for use in n Corresponding author at: Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan. Tel.: þ 886 2 2366 0739; fax: þ886 2 2362 3040. E-mail address: [email protected] (K.-C. Ho).
various fields, e.g., electrocatalysis [13–15], fuel cells [16–18], electrochromic devices [19–22], hydrogen storage [23], and sensors [24,25]. PB has a face-centered cubic structure, in which alternating FeII and FeIII centers are bridged by cyanide ions in a FeII C≡N FeIII fashion; this situation leads to the formation of an infinite three dimensional network [26]. The preparation technique of PB plays a crucial role in its practical application. The film's uniformity over large areas is vital for hi-tech applications. Growing a uniform PB film on a transparent conducting electrode by means of an electrochemical process is not too easy. Poor stability of the deposition bath containing ferric cyanide and a metal salt is the major problem; the contents of the bath turn into a precipitate instantaneously during the mixing [27]. PB powder that could be dispersed uniformly in water was prepared through a simple process. The aqueous solution of the water dispersible Prussian blue (wPB) or the "ink" was sprayed on an ITO glass to make an electrode in a complementary ECD. Spray coating is efficient, suitable for large-area ECDs, and can be used for patterning. The thickness of the film could be controlled preciously using spray coating. The present technique of preparing wPB thus enables the fabrication of large-area ECDs, which can be used for energy-saving windows and sunglasses. In this study, we synthesized wPB nanoparticles through a surface modification process and dispersed them in water to
http://dx.doi.org/10.1016/j.solmat.2015.06.031 0927-0248/& 2015 Elsevier B.V. All rights reserved.
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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2
obtain an ink. This ink was spray-coated on an ITO glass to obtain a wPB film. PB film was also prepared by the electrochemical method and its electrochemical behavior was compared with that of the wPB film. A solid-state complementary ECD was fabricated based on the wPB and poly(butyl viologen) (PBV) thin films. Succinonitrile (SN), a plastic crystal, with 0.1 M potassium bis(trifluoromethanesulfonyl)imide (KTFSI) and 7 wt% of silicon dioxide (SiO2) nanoparticles was used as the solid-state electrolyte for the ECD. To eliminate the crystallization due to the presence of SN, 7 wt% of SiO2 was dispersed in the electrolyte. The amount of SiO2 was so small that it could not exert any influence on the contrast of the ECD. Indium-doped tin oxide (ITO) conducting glasses were used as the substrates for both electrodes of the ECD. The electrochromic behaviors of the thin films and the electrochromic performance of the device have been investigated.
wPB film could be controlled by the spraying process. The PB thin film was heated to 90 °C to evaporate the solvent. 2.4. Preparation of the electrodeposited Prussian blue (EDPB) film A cleaned ITO substrate (3.0 4.0 cm2) was used as the working electrode, and a Pt foil and Ag/AgCl were used as the counter and reference electrodes, respectively. The electrodeposited Prussian blue (EDPB) film was obtained on the ITO substrate, in an aqueous deposition bath of 10.0 mM FeCl3 6H2O, 10.0 mM K3Fe(CN)6, 0.1 M KCl, and 0.1 M HCl. For this, a constant cathodic current density of 0.04 mA/cm2 was applied to the electrode for 300 s. The as-deposited EDPB film was washed with DIW and dried with N2. 2.5. Electrolyte composition for the electrochromic device
2. Experimental 2.1. Materials All chemicals were used without further purification. Iron (III) nitrate nonahydrate (Fe(NO3)3 9H2O, 99.99%), sodium ferrocyanide decahydrate (Na4[Fe(CN)6] 10H2O, 499%), potassium bis (trifluoromethanesulfonyl)imide (KTFSI, 97%), potassium dihydrogen phosphate (KH2PO4, 499%), and potassium hydrogen phosphate (K2HPO4, 4 99%) were all purchased from Aldrich. Potassium ferrocyanide (K4Fe(CN)6, 99.99%) was obtained from Fisher Scientific. Succinonitrile (SN, 499.0%) was received from Acros Organics. Propylene carbonate (PC, 99.7%) was acquired from Alfa Aesar. Deionized water (DIW) with 18.2 MΩ cm of resistance was used. All experiments were performed at room temperature in air. ITO glasses of 3.0 4.0 cm2 were used as the substrates. The ITO glass was ultrasonically cleaned in an isopropyl alcohol for 10 min, and then in deionized water for 10 min. Finally, the ITO glass was dried under N2. After cleaning the ITO substrate, an epoxy tape (3 M Company, 60 μm thick) was attached to the ITO glass at the edges, intending to control the active area to be 2.0 2.0 cm2. A conducting copper tape (3 M Company, 3.0 0.5 cm2) was used as the bus bar at one side of the ITO glass. 2.2. Preparation of the PBV film The deposition bath of PBV contained 20.0 mM BVBr2, 10.0 mM KH2PO4, 90.0 mM K2HPO4, and 100.0 mM K4Fe(CN)6. The PBV thin film was deposited on an ITO substrate (Rsh ¼7 Ω/□) by anodic electropolymerization at 0.75 V (vs. Ag/AgCl) using the monomer bis(4-cyano-1-pyridino)butane dibromide (BVBr2) [28]. In our previous study [29], we have prepared a charge transfer complex using Fe(CN)64 and viologen monomer. The viologen monomers become radical cations at 0.75 V during the electropolymerization process. 2.3. Preparation of the wPB film An aqueous solution of Fe(NO3)3 9H2O was added to an aqueous solution of Na4[Fe(CN)6] 10H2O. The blue precipitate was vigorously shaken for 15 min, subsequently it was centrifuged and washed with DIW. Then aqueous Na4[Fe(CN)6] 10H2O was again added to the precipitate with vigorous stirring; the contents were vigorously stirred for one week. Finally, the solution was dried under reduced pressure to obtain the wPB nanoparticles. The wPB pigment was then dissolved in water to obtain its ink. This ink was sprayed on an ITO substrate (3.0 4.0 cm2) and the active area was controlled in 2.0 2.0 cm2. The thickness and active area of the
The solid electrolyte consisted of 0.1 M KTFSI salt, 7 wt% of silicon dioxide (SiO2) nanoparticles and SN. SN (melting temperature¼ 58 °C) is a plastic crystal which is solid state at room temperature. Before assembling the device, the solid electrolyte was heated to 90°C to bring it to the liquid state; this made the fabrication of the ECD easier. In order to decrease the crystallization of SN, 7 wt% of SiO2 nanoparticles was added to the matrix. Crystallization of an electrolyte is a bane to its ECD, because it could inhibit the migration of the ions through the electrolyte and could thereby decrease the stability of the device. Elimination of crystallization must be done in such a way that it would not adversely affect the performance of the device. SiO2 nanoparticles could disperse well in the electrolyte and eliminate its crystallization. 2.6. Assembly of the wPB-PBV electrochromic device Before assembling the device, the charge capacity of wPB film was optimized so that it matched well with that of PBV film and thereby could give the maximum transmittance to the complementary device. The heated SN was sandwiched between the PBV and wPB electrodes. The device was then cooled to room temperature so that the electrolyte became solid again. The thickness of the electrolyte was fixed to be 60 μm, by using an epoxy tape. The device was not subjected to either pre-darkening or pre-bleaching. The complementary ECD is designated as wPB/0.1 M KTFSIþ7 wt% SiO2 in SN/PBV. The electrochemical properties of the complementary ECD were studied using a potentiostat/galvanostat (Autolab, model PGSTAT30). The ECD was darkened or bleached by the application of 1.7 or 1.0 V, respectively. The voltage is the potential difference between the wPB electrode and the PBV electrode (wPB vs. PBV). The transmittances of both thin films and the corresponding ECD in the visible range were measured by an in-situ opto-electrochemical spectrophotometer (Ocean Optics, DH-2000-BAL). Another UV–vis-NIR spectrophotometer (V-670, Jasco), coupled with a 60 mm integrating sphere (ISN-723, Jasco), was used to measure the infrared reflective and transmittance spectra of the ECD.
3. Results and discussion 3.1. Characterization of wPB, EDPB, and PBV thin films 3.1.1. Particle size distribution Recent reports on wPB reveal that its particle size ranges from several nanometers to several hundreds of nanometers. The larger PB nanoparticles emerge from aggregation of nanoparticles. According to the literature, the insoluble PB nanoparticles could be
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
3
10
30
Current density (mA/cm )
25
PB/0.1 M KTFSI Scan rate: 0.1 V/s
2
Percentage of Intensity by number (%)
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20 15 10
5
0
-5 EDPB wPB
5 0
1
10
100
1000
-10 -0.8
10000
Particle size (nm) Fig. 1. The particle size distribution of PB which was dispersed in water. The mean particle size is about 10 nm.
well-dispersed in water via the modification of the ligands on PB crystal surfaces [30]. Fig. 1 shows that the wPB is well-distributed in DIW with the mean particle size being about 10 nm. The dispersion of PB nanoparticles in water is rather homogeneous. Because of small sizes of the particles, the corresponding film was uniform. If the precursors of Fe3 þ and [Fe(CN)6]4 are mixed quickly, there will be a rapid reaction for the reactants to yield PB particles. In this situation, the sizes of PB particles may be large and the distribution of particles may be inhomogeneous. We synthesized wPB nanoparticles through a surface modification process and dispersed them in water to obtain an ink. A nanoparticle possesses a surface charge that attracts the opposite charge near it to form a thin electric double layer surrounding it. The electric potential at the boundary of such an electric double layer in a colloidal dispersion is known as the zeta potential. The absolute value of the zeta potential could be predictive of the colloidal stability. A low absolute value of zeta potential was related to low stability of the aggregation, that is, the aggregation of the particles cannot be prevented due to lower electric potential in the interfacial layer. In general, an absolute value of zeta potential larger than 30 mV would lead to a stable suspension [31–33]. The zeta potential of the wPB particles was found to be 36.8 mV. This zeta potential indicates that the PB is well dispersed in the water. The ink was found to be very suitable for spray coating. The thickness of the wPB thin film could be controlled by spraying coating technique. These conditions are favorable to fabricate the proposed ECD with a maximum transmittance change. 3.1.2. Cyclic voltammetric (CV) analysis Two kinds of PB thin films were prepared; the one deposited by electrochemical technique is designated as EDPB film and the other obtained by spray coating is designated as wPB film, because it is dispersible in water. The two PB thin films were obtained in such a way that both of them showed a transmittance of 207 3% at 695 nm. The cyclic voltammograms of wPB and EDPB films for the 20th cycles are shown in Fig. 2. The electrolyte was 0.1 M KTFSI in PC. We restricted the potential window for the electrode only for the Prussian blue/Prussian white (PB/PW) couple, as the electrochromism occurs in this region. A platinum foil and a home-made Ag/Ag þ electrode were used as the working electrode and reference, respectively. The potential of the electrode was cycled between 0.6 and 0.5 V, at a scan rate 100 mV/s. Both thin films exhibit only one redox couple. The values of the anodic peak potential (Epa), cathodic peak potential (Epc), and difference between the anodic and cathodic peak potential (ΔEp) are listed in
-0.4 0.0 0.4 + Potential (V vs. Ag/Ag )
0.8
Fig. 2. Cyclic voltammagrams of wPB and EDPB films in 0.1 M KTFSI in PC, obtained between 1.6 and 0.5 V (vs. Ag/Ag þ ). Table 1 Potential parameters and charge transfer resistances of the films of wPB and EDPB.
wPB EDPB
Epa (V vs. Ag/Ag þ )
Epc (V vs. Ag/Ag þ )
ΔEp (V)
Rct (Ω cm2)
0.23 0.28
0.36 0.37
0.59 0.65
1.21 10.72
Table 1. A lower ΔEp indicates a higher kinetic ability for the PB redox reaction. As the ΔEp of the electrode with wPB (0.59 V) is smaller than that of the electrode with EDPB (0.65 V), the wPB electrode is considered to have a higher driving force for the redox reaction of PB/PW. The electrochemical redox reaction is as follows [34]:
Fe 4 [Fe (CN)6 ]3 + 4K + + 4e− ⇄ K 4 Fe 4 [Fe (CN)6 ]3 (PB)
(PW)
(1)
During the CV measurement, the wPB thin film exhibits reversible color change from blue (PB) to transparent (PW). Eq. (1) clearly indicates that the electrochromic reaction involves injection or extraction of cations. The CV of a PBV film is shown in Fig. S1. The electrolyte was 0.5 M KCl in DIW. We can observe three pairs of redox peaks of PBV, which is in accordance with previous literature [35]. The first set of cathodic peak at 1.07 V corresponds to the reduction of the purple radical cation (PBV þ ) to form yellow– brown di-reduced species (PBV0). The second set of cathodic peak at 0.61 V represents the reduction of the colorless cation (PBV2 þ ) to form the purple radical cation (PBV þ ). The third set of redox peaks at 0.18 and 0.24 V correspond to the redox reaction of Fe(CN)64 /Fe(CN)63 . 3.1.3. Morphologies of wPB and EDPB thin films Fig. 3a and b shows SEM images of the films of wPB and EDPB, respectively. Fig. 3a clearly shows that the wPB film is excellently uniform, and adheres well to the ITO substrate. No aggregated particles could be seen on the surface of the film. The image indicates a homogeneous dispersion of the wPB particles in water, which is in agreement with the corresponding zeta potential value. Fig. 3b displays the SEM image of the EDPB thin film. As can be seen in Fig. 3b, the EDPB film consists of agglomerations of nanoparticles and systematic cracks. The nanostructure of EDPB film is not suitable for electron hopping, and induces resistance within the film. The effects of the two preparation methods of PB film on its morphology are thus established. It could now be foreseen from the surface morphologies of the two kinds of PB films that the wPB film would exhibit a better or effective electrochromic switching response.
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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Fig. 3. SEM images of films of (a) wPB and (b) EDPB.
3.1.4. EIS analysis of wPB and EDPB films In order to further confirm the redox reactions of wPB and EDPB thin films, electrochemical impedance spectroscopy (EIS) was used. The EIS spectra of symmetric cells based on wPB and EDPB films are shown in Fig. 4. A symmetric cell is a cell with identical anode and cathode. The equivalent circuit is shown as an inset in the figure. The radii of the semicircles of the EIS spectra give the values of interfacial charge-transfer resistances (Rct) of the films. In the case of wPB, its spectrum is shown as an enlarged version in the same figure. The values of the charge transfer resistances (Rct) at the interface of wPB and EDPB/electrolyte are given in Table 1. The values of Rct for wPB and EDPB thin films are 1.21 and 10.72 Ω cm2, respectively. The Rct of wPB thin film is about one order smaller than that of the EDPB thin film. This lower interfacial charge-transfer resistance leads to much faster electrochemical kinetics at the interface of wPB film/electrolyte. Based on the results of cyclic voltammetry and electrochemical impedance spectroscopy, we have selected wPB as the thin film to combine with the conducting polymer, PBV, to fabricate the complementary ECD. 3.1.5. Absorbance spectra and transmittance The equilibrium absorbance spectra of the PBV film is shown in Fig. S2. When the potential was stepped from 0.5 to 1.2 V at an interval of 0.1 V, the highest absorbance appears at 550 nm. It is clear that the thin film presents violet color at 0.8 V. However, at more negative potentials, the absorbance decreases and the color of the film changes to yellow–brown, associated with the formation of PBV0. In order to obtain a high contrast for the ECD, this
20 Equivalent circuit model R R
-Z" (ohm)
15
CPE
10 EDPB wPB
5
0
5
10
15
20
25
30
35
Z' (ohm) Fig. 4. EIS spectra of symmetric cells based on wPB and EDPB films; inset shows the equivalent circuit model.
redox couple needs to be avoided. The inset in Fig. S2 shows photographs of the device at 0.8, 1.2 and 0.1 V, depicting the changed colors at these potentials. In addition, a series of absorbance spectra of the film of wPB was obtained as shown in Fig. S3. No absorbance characteristics can be seen at the applied potentials from 0.6 to 0.4 V. The absorbance increases, with the oxidation of the wPB, at the applied potential from 0.4 to 0.1 V. Thus, the wPB thin film switches its color from transparent to blue, as is shown in the inset of Fig. S3. The maximum absorbance peak appears at 690 nm. To confirm the above understandings on the electrochromic behaviors of films of wPB and PBV, the transmittance changes and response times of these films were experimentally determined at the specific absorption wavelengths of the films, as shown in Fig. S4. The response or switching time of the electrochromic film is defined as the time it takes for reaching 90% of the saturated ΔT. For the PBV, the initial transmittance change is about 70% at 550 nm. The bleaching and darkening times in aqueous electrolyte of 0.5 M KCl are 1.5 s and 3.2 s, respectively. On the other hand, the initial transmittance change of wPB is found to be about 58% at 690 nm. The switching times in nonaqueous electrolyte of 0.1 M KTFSI/PC for wPB are 9.5 s for bleaching and 8.3 s for darkening. 3.2. Characterization of the ECD containing wPB and PBV 3.2.1. Cyclic voltammetric analysis In this study, the complementary ECD was assembled with PBV as the cathodically coloring electrode and wPB as the anodically coloring electrode. Several literatures reported on the complementary ECDs with 4,4′-bipyridine derivatives [36–38]. These materials offer high transmittance change and PBV is one of such materials. The charge density to deposit PBV was fixed at 80 mC/cm2. As mentioned already in Section 2 that the charge capacity of wPB thin film was optimized so that it matched well with that of the PBV thin film and thereby could give the maximum transmittance to the complementary ECD. Fig. 5 shows cyclic voltammogram of the complementary ECD at the scan rate of 100 mV/s, which is slow enough to notice the color change. We can observe two redox centers for the complementary ECD. The peaks at 0.4 and 1.0 V represent the redox center for wPB. The peaks at 1.0 and 1.7 V correspond to the redox reaction of PBV by Eq. (2).
PBV 2 + (TFSI)2 + e− ⇄ [PBV +⋅TFSI−]+TFSI−
(2)
The overall redox reaction of the complementary ECD can be written as follows:
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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2.0
1.0 wPB/0.1 M KTFSI + 7 wt% SiO2 in SN/PBV
1.5
2
Scan rate: 0.1 V/s
η = 157 cm /C
0.8
1.0
Δ OD at 545 nm
2
Current density (mA/cm )
wPB/0.1 M KTFSI + 7 wt% SiO in SN/PBV
0.5 0.0 -0.5
1.0 V 0.9 V
0.6
1.2 ~ 1.6 V 1.1 V
0.8 V
0.2 0.7 V
0.0 -2
-1
0
1
2
3
Fig. 5. Cyclic voltammogram of the complementary ECD at the scan rate of 100 mV/s in a PC solution of 0.1 M KTFSI, obtained between 1.5 and 2.2 V (vs. Ag/Ag þ ).
4PBV 2 + (TFSI)2 + K 4 Fe 4 [Fe (CN)6 ]3 ⇄ 4 [PBV +⋅TFSI−] + Fe 4 [Fe (CN)6 ]3 + 4K + + 4TFSI−
-1.0 ~ 0.6 V
-1
Applied cell voltage (V)
(3)
Owing to the complementary reaction, the device shows a reversible CV from 1.0 to 1.7 V. The CV does not show any side reactions. Therefore the operating potential window was selected to be between 1.0 and 1.7 V for the ECD, considering both the stability of the device and the maximum optical attenuation. 3.2.2. Absorbance spectra and coloration efficiency of the ECD containing wPB and PBV Fig. 6 shows in-situ UV-absorption spectra of the complementary ECD obtained at different applied cell potentials. The potentials were stepped from 1.0 to 1.7 V at an interval of 0.1 V. Starting from 1.0 V, the absorption increases up to 1.7 V, upon coloration. In this range of applied potentials, the largest peak of absorbance can be seen at 545 nm, which exists over the visible wavelength region. This wavelength is sensitive to human eye. At 1.0 V, the device was in its bleached or transparent state. At 1.7 V the device assumed a blue violet color. The insets in Fig. 6 are the photographs of the device at 1.0 and 1.7 V, depicting the changed colors at these potentials. The high contrast in the colors can be seen in these photos. Fig. S5a and b shows the optical 1.5 wPB/0.1 M KTFSI + 7 wt% SiO2 in SN/PBV λmax= 545 nm
500
600 700 800 Wavelength (nm)
6
7
transmittance and reflectance spectra of the ECD at both bleached and darkened states, obtained by applying the cell potentials of 1.0 and 1.7 V, respectively. The maximum optical transmittance change occurred at 545 nm, which is consistent with the absorbance spectra. Fig. S6 shows the infrared reflective spectra of the device at the darkened and bleached states. It can be observed that the reflectance at the darkened state is much less than that at the bleached state. The maximum reflectance change of the device from 1000 to 2500 nm is about 14%. The decrements of the transmittance and reflectance of the ECD were caused by the higher absorbance in the darkened state [39–41], which is consistent with Fig. 6. Most of the reflectance may be attributed to the ITO substrate [42,43]. The coloration efficiency was calculated to be 157 cm2/C at 545 nm from Fig. 7, where the dotted straight line covers the optical density change (ΔOD) data from 1.0 to 1.7 V. 3.2.3. Transmittance attenuation and long-term stability of the ECD containing wPB and PBV Fig. 8 shows the transmittance change of the complementary ECD at 545 nm in response to the change of the potential between 1.0 and 1.7 V. The initial transmittances of the device at 545 nm are 73.1% at 1.0 V and 10.6% at 1.7 V. Similarly, the response time for switching the ECD is defined as the time required for reaching 90% of the limiting ΔT. The switching times for both bleaching and darkening processes were determined to be the same, being about 10 s. Since the complementary ECD shows response times very close to those of the wPB thin film in nonaqueous electrolyte
900
1000
Fig. 6. In–situ UV-absorption spectra of the complementary ECD obtained at different applied cell potentials. The potentials were stepped from 1.0 to 1.7 V at an interval of 0.1 V; the inset in Fig. 6 shows photographs of the device at 1.0 and 1.7 V, depicting the changed colors of the ECD at these potentials. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.)
Transmittance (%) at 545 nm
0.8 V
-1.0 ~ 0.7 V 0.0 400
1 2 3 4 5 2 Charge capacity (mC/cm )
wPB/0.1 M KTFSI + 7wt% SiO in SN/PBV
1.0
0.5
0
Fig. 7. The relationship between the optical density change (ΔOD) and the passed charge density for the complementary ECD at 545 nm.
1.7 V
Absorbance
1.7 V
0.4
-1.0 -1.5
5
80
λ
= 545 nm
-1.0 V
60
40
20 1.7 V
0
0
100
200
300
400
Time (s) Fig. 8. The transmittance change of the complementary ECD at 545 nm in response to the potential change between 1.0 and 1.7 V.
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Acknowledgment
Transmittance (%) at 545 nm
100 Bleached state Darkened state ΔT
80 60
We thank the financial support received from the Ministry of Science and Technology (MOST) of Taiwan (Project number: 1022221-E-002-185-MY2) and AUO Optronics Corp. The instrumentations used in this study were partially supported by the MOST of Taiwan.
40 Appendix A. Supplementary material
20 0
0
200
400 600 Cycle number
800
1000
Fig. 9. The long-term stability data of the ECD collected over 1000 cycles of uninterrupted operation. The device was tested under the applied cell voltages of 1.0 V for 15 s during bleaching and 1.7 V for 15 s during darkening.
(0.1 M KTFSI in PC), this implies that the electrochromic switching is not limited by the conductivity of the proposed solid electrolyte. This can be explained by the high ionic conductivity of the salt-SN electrolyte system [44–46]. Another device was prepared to study the long-term stability of the proposed ECD. The result is shown in Fig. 9. Initially the transmission change of the device at 545 nm is 62.0%; after the operation of the device for 1000 cycles, the transmittance change is about 58.4%. The bleached state transmittance reached 68.5% at 545 nm after 1000 cycles, and the darkened state transmittance remained relatively constant after the same period.
4. Conclusions Prussian blue (PB) powder that could be dispersed uniformly in water was prepared through a simple process. Dynamic light scattering analysis reveals that the wPB powder is well-distributed in water and the mean particle size is about 10 nm. PB thin film was also prepared by an electrochemical method. Cyclic voltammetric analysis, scanning electron microscopy images, and electrochemical impedance spectra of these films indicated that wPB film would show a higher kinetic ability, and thereby a better electrochromic behavior. A solid-state complementary electrochromic device (ECD) was assembled based on the configuration of wPB/0.1 M KTFSI þ7 wt% SiO2 in SN/PBV. Owing to the complementary reaction, the device showed a reversible CV from 1.0 to 1.7 V. The device showed a high contrast from blue violet to transparent. The largest absorbance peak of the ECD was found to be at 545 nm. The transmission change (ΔT) and coloration efficiency of the proposed ECD were found to be about 62.5% and 157 cm2/C at 545 nm, respectively. The switching times for both bleaching and darkening were calculated to be the same, being about 10 s for a sample of 2.0 2.0 cm2. As for the long-term stability, the initial transmittance of the ECD at 545 nm is 72.2% at 1.0 V and 10.2% at 1.7 V. The bleached state transmittance at 545 nm decayed to 68.5% after operating the device continuously for 1000 cycles, while the darkened state transmittance remained nearly constant. The large contrast of the device and its reversible color change render the proposed device attractive for further research.
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.solmat.2015.06. 031.
References [1] T. Deutschmann, E. Oesterschulze, Micro-structured electrochromic device based on poly(3,4-ethylenedioxythiophene), J. Micromech. Microeng. 23 (2013) 065032. [2] U. Abaci, H.Y. Guney, U. Kadiroglu, Morphological and electrochemical properties of PPy, PAni bilayer films and enhanced stability of their electrochromic device (PPy/PAni-PEDOT, PAni/PPy-PEDOT), Electrochim. Acta 96 (2013) 214–224. [3] S. Sun, X. Chang, T. Liu, Y. Lu, Y. Wang, Solvothermal synthesis of tungsten oxide mesocrystals and their electrochromic performance, Mater. Lett. 105 (2013) 54–57. [4] R.R. Kharade, S.S. Mali, S.P. Patil, K.R. Patil, M.G. Gang, P.S. Patil, J.H. Kim, P.N. Bhosale, Enhanced electrochromic coloration in Ag nanoparticle decorated WO3 thin films, Electrochim. Acta 102 (2013) 358–368. [5] S. Stojkovikj, M. Najdoski, V. Koleva, S. Demiri, Preparation of electrochromic thin films by transformation of maganese (II) carbonate, J. Phys. Chem. Solids 74 (2013) 1433–1438. [6] E.N. Esmer, S. Tarkuc, Y.A. Udum, L. Toppare, Near infrared electrochromic polymer based on phenazine moieties, Mater. Chem. Phys. 131 (2001) 519–524. [7] A. Lakshmi, A.R. J, G. Gopu, P. Arumugam, C. Vedhi, Electrochemical, electrochromic behaviour and effects of supporting electrolyte on nano-thin film of poly(3,4-ethylenedioxythiophene), Electrochim. Acta 92 (2013) 452–459. [8] P.C. Pandey, A.K. Pandey, Novel synthesis of Prussian blue nanoparticles and nanocomposite sol: electro-analytical application in hydrogen peroxide sensing, Electrochim. Acta 87 (2013) 1–8. [9] N.L. Torad, M. Hu, M. Imura, M. Naito, Y. Yamauchi, Large Cs adsorption capability of nanostructured Prussian blue particles with high accessible surface areas, J. Mater. Chem. 22 (2012) 18261–18267. [10] H. Ming, N.L.K. Torad, Y.D. Chiang, K.C.W. Wu, Y. Yamauchi, , Size- and shapecontrolled synthesis of Prussian blue nanoparticles by a polyvinylpyrrolidoneassisted crystallization process, CrystEngComm 14 (2012) 3387–3396. [11] Z. Jia, Synthesis of Prussian blue nanocrystals with metal complexes as precursors: quantitative calculations of species distribution and its effects on particles size, Colloid Surf. A-Physicochem. Eng. Asp. 389 (2011) 144–148. [12] M. Presle, J. Lemainque, J.M. Guigner, E. Larquet, I. Maurin, J.P. Boilot, T. Gacoin, Controlled growth of core@shell heterostructures based on Prussian blue analogues, New J. Chem. 35 (2011) 1296–1301. [13] L. Xu, G. Zhang, J. Chen, Y. Zhou, G. Yuan, F. Yang, Spontaneous redox synthesis of Prussian blue/graphene nanocomposite as a non-precious metal catalyst for efficient four-electron oxygen reduction in acidic medium, J. Power Sources 240 (2013) 101–108. [14] P. Yu, J. Yan, H. Zhao, L. Su, J. Zhang, L. Mao, Rational functionalization of carbon nanotube/ionic liquid bucky gel with dual tailor-made electrocatalysts for four-electron reduction of oxygen, J. Phys. Chem. C 112 (2008) 2177–2182. [15] Y. Ma, Y. Du, W. Ye, B. Su, M. Yang, C. Wang, Electrocatalytic oxidation of ethanol on platinum electrode decorated with Nd–Fe–Mo hybrid-metallic cyano-bridged mixing coordination polymer in weak acidic medium, Int. J. Electrochem. Sci. 7 (2012) 2654–2679. [16] L. Fu, S.J. You, G.Q. Zang, F.L. Yang, X.H. Fang, Z. Gong, PB/PANI-modified electrode used as a novel oxygen reduction cathode in microbial fuel cell, Biosens. Bioelectron. 26 (2011) 1975–1979. [17] D.M.F. Santos, P.G. Saturnino, R.F.M. Lobo, C.A.C. Sequeira, Direct borohydride/ peroxide fuel cells using Prussian blue cathodes, J. Power Sources 208 (2012) 131–137. [18] G. Selvarani, S.K. Prashant, A.K. Sahu, P. Sridhar, S. Pitchumani, A.K. Shukla, A direct borohydride fuel cell employing Prussian blue as mediated electrotransfer hydrogen peroxide reduction catalyst, J. Power Sources 178 (2008) 86–91. [19] Z. Jiao, J.L. Song, X.W. Sun, X.W. Liu, J.M. Wang, L. Ke, H.V. Demir, A fastswitching light-writable and electric-erasable negative photoelectrochromic cell based on Prussian blue films, Sol. Energy Mater. Sol. Cells 98 (2012)
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
M.-S. Fan et al. / Solar Energy Materials & Solar Cells ∎ (∎∎∎∎) ∎∎∎–∎∎∎ 154–160. [20] B. Seelandt, M. Wark, Electrodeposited Prussian blue in mesoporous TiO2 as electrochromic hybrid material, Microporous Mesoporous Mater. 164 (2012) 67–70. [21] Y. Rong, S. Kim, F. Su, D. Myers, M. Taya, New effective process to fabricate fast switching and high contrast electrochromic device based on viologen and Prussian blue/antimoy tin oxide nano-composites with dark colored state, Electrochim. Acta 56 (2011) 6230–6236. [22] R.J. Mortimer, T.S. Varley, In situ spectroelectrochemistry and colour measurement of a complementary electrochromic device based on surface-confined Prussian blue and aqueous solution-phase methyl viologen, Sol. Energy Mater. Sol. Cells 99 (2012) 213–220. [23] B. Zamora, A.A.A. Hajjaj, A.A. Shah, Kinetic and thermodynamic studies of hydrogen adsorption on titanate nanotubes decorated with a Prussian blue analogue, Int. J. Hydrog. Energy 38 (2013) 6406–6416. [24] Z. Chu, L. Shi, Y. Liu, W. Jin, N. Xu, In-situ growth of micro-cubic Prussian blue-TiO2 composite film as a highly sensitive H2O2 sensor by aerosol codeposition approach, Biosens. Bioelectron. 47 (2013) 329–334. [25] H. Byrd, B.E. Chapman, C.L. Talley, Prussian blue coated electrode as a sensor for electroinactive cations in aqueous solutions, J. Chem. Educ. 90 (2013) 775–777. [26] J. Keggin, F. Miles, Structures and formulas of the Prussian blues and related compounds, Nature 137 (1936) 577–578. [27] L.C. Chen, K.S. Tseng, K.C. Ho, Enhanced electrodeposition of indium hexacyanoferrate thin films through improved plating solution stability, J. Solid State Electrochem. 7 (2002) 1–5. [28] Y.C. Hsu, K.C. Ho, Anionic effect on the intercalation and spectral properties of poly(butyl viologen) films, J. New Mater. Electrochem. Syst. 8 (2005) 49–57. [29] Y.C. Hsu, V.S. Vasantha, P.Y. Chen, K.C. Ho, A new stable Fe(CN)63 /4 immobilized poly(butylviologen)-modified electrode for dopamine determination, Sens. Actuat. B-Chem. 137 (2009) 313–319. [30] A. Gotoh, H. Uchida, M. Ishizaki, T. Satoh, S. Kaga, S. Okamoto, M. Ohta, M. Sakamoto, T. Kawamoto, H. Tanaka, M. Tokumoto, S. Hara, H. Shiozaki, M. Yamada, M. Miyake, M. Kurihara, Simple synthesis of three primary colour nanoparticle inks of Prussian blue and its analogues, Nanotechnology 18 (2007) 345609. [31] D.H. Everett, Basic Principles of Colloid Science, Royal Society of Chemistry, London, 1988. [32] D. Li, M.B. Müller, S. Gilje, R.B. Kaner, G.G. Wallace, Processable aqueous dispersions of graphene nanosheets, Nat. Nanotechnol. 3 (2008) 101–105. [33] C. Saldíasa, L. Velásquez, C. Quezada, A. Leiva, Physicochemical assessment of Dextran-g-Poly(ɛ-caprolactone) micellar nanoaggregates as drug nanocarriers, Carbohydr. Polym. 117 (2015) 458–467.
7
[34] H. Shiozaki, T. Kawamoto, H. Tanaka, S. Hara, M. Tokumoto, A. Gotoh, T. Satoh, M. Ishizaki, M. Kurihara, Masatomi Sakamoto, Electrochromic thin film fabricated using a water-dispersible ink of Prussian blue nanoparticles, Jpn. J. Appl. Phys. 47 (2008) 1242–1244. [35] Y.C. Hsu, K.C. Ho, The anionic effect on the intercalation and spectral properties of poly(butyl viologen) films, J. New Mater. Electrochem. Syst. 8 (2005) 49–57. [36] G. Wang, X. Fu, J. Huang, C. Wu, L. Wu, Q. Du, Synthesis of a new star-shaped 4,4′-bipyridine derivative and its multicolor solid electrochromic devices, Org. Electron. 12 (2011) 1216–1222. [37] B. Gadgil, P. Damlin, T. Aaritalo, J. Kankare, C. Kvarnstrom, Electrosynthesis and characterization of viologen cross linked thiophene copolymer, Electrochim. Acta 97 (2013) 378–385. [38] C.F. Lin, C.Y. Hsu, H.C. Lo, C.L. Lin, L.C. Chen, K.C. Ho, , A complementary electrochromic system based on a Prussian blue thin film and a heptyl viologen solution, Sol. Energy Mater. Sol. Cells 95 (2011) 3074–3080. [39] W. Estrada, A.M. Andersson, C.G. Granqvist, Infrared reflectance spectroscopy of electrochromic NiOxHy films made by reactive dc sputtering, J. Mater. Res. 6 (1991) 1715–1719. [40] R. Sydam, M. Deepa, A new organo–inorganic hybrid of poly(cyclotriphosphazene-4,4′-bipyridinium)chloride with a large electrochromic contrast, J. Mater. Chem. C 1 (2013) 7930–7940. [41] A.A. Argun, J.R. Reynolds, Line patterning for flexible and laterally configured electrochromic devices, J. Mater. Chem. 15 (2005) 1793–1800. [42] H.L. Hartnagel, A.L. Dawar, A.K. Jain, Semiconducting Transparent Thin Films, Taylor & Francis, England, 1995. [43] N.M. Khusayfan, M.M. El-Nahass, Study of structure and electro-optical characteristics of indium tin oxide thin films, Adv. Condens. Matter Phys. 2013 (2013) 408182. [44] R.K. Gupta, H.M. Kim, H.W. Rhee, Poly(ethylene oxide): succinonitrile-a polymeric matrix for fast-ion conducting redox-couple solid electrolytes, J. Phys. D: Appl. Phys. 44 (2011) 205106. [45] S. Das, S.J. Prathapa, P.V. Menezes, T.N. Guru Row, A.J. Bhattacharyya, Study of ion transport in lithium perchlorate-succinonitrile plastic crystalline electrolyte via ionic conductivity and in situ cryo-crystallography, J. Phys. Chem. B 113 (2009) 5025–5031. [46] L.Z. Fan, X.L. Wang, F. Long, X. Wang, Enhanced ionic conductivities in composite polymer electrolytes by using succinonitrile as a plasticizer, Solid State Ion. 179 (2008) 1772–1775.
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A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films Miao-Syuan Fan a, Sheng-Yuan Kao a, Ting-Hsiang Chang a, R. Vittal a, Kuo-Chuan Ho a,b,n a b
Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
art ic l e i nf o
a b s t r a c t
Article history: Received 31 December 2014 Received in revised form 6 June 2015 Accepted 8 June 2015
Prussian blue (PB) powder, which could be dispersed uniformly in water, was prepared through a simple process, and is designated as water dispersible Prussian blue (wPB). A PB thin film was spray-coated on an ITO substrate using the ink of this powder. Another PB thin film was prepared by the electrochemical deposition method (EDPB) for comparison. The properties of these two thin films were compared by using cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). A solid-state complementary electrochromic device (ECD) was fabricated based on a wPB thin film as the anodically coloring electrode and a poly(butyl viologen) (PBV) thin film as the cathodically coloring electrode. Succinonitrile (SN) with 0.1 M potassium bis(trifluoromethanesulfonyl) imide (KTFSI) and silicon dioxide (SiO2) nanoparticles was used as the solid electrolyte. The device could be switched reversibly between blue–violet and transparent upon application of 1.7 V and 1.0 V, and showed an initial transmittance change of 62.5% with a coloration efficiency of 157 cm2/C at 545 nm. The switching time required for both darkening and bleaching was about 10 s for a sample of 2.0 2.0 cm2. As for the electrochemical stability of the ECD, the transmittance change reached 58.4% at 545 nm after 1000 cycles, and the darkened state transmittance remained relatively constant after the same period. & 2015 Elsevier B.V. All rights reserved.
Keywords: Poly(butyl viologen) Potassium bis(trifluoromethanesulfonyl) imide Solid-state electrochromic device Succinonitrile Water dispersible Prussian blue
1. Introduction Because of global warming and energy crisis, energy conservation became a popularity topic. Electrochromic devices (ECD) are gaining importance, owing to their potential applications in energy-saving devices [1–3]. Electrochromism refers to reversible color changes of electrochromic materials involving electrochemical redox reactions. Electrochromism belongs to an important green environmental technology, because the transmittance of a window can be attenuated reversibly to provide indoor comfort [4–7]. The ECDs can be categorized into three types, solution type, hybrid type, and thin-film battery-like type. A complementary ECD is composed of an anodically and a cathodically coloring material. With rapid development of nanotechnology, recent research on Prussian blue (PB) electrochromism focuses on the ECD containing PB or its analogs utilizing nanoparticles [8–12]. PB is a famous elecrochromic material, and it has been extensively studied for many years; it has been proposed for use in n Corresponding author at: Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan. Tel.: þ 886 2 2366 0739; fax: þ886 2 2362 3040. E-mail address: [email protected] (K.-C. Ho).
various fields, e.g., electrocatalysis [13–15], fuel cells [16–18], electrochromic devices [19–22], hydrogen storage [23], and sensors [24,25]. PB has a face-centered cubic structure, in which alternating FeII and FeIII centers are bridged by cyanide ions in a FeII C≡N FeIII fashion; this situation leads to the formation of an infinite three dimensional network [26]. The preparation technique of PB plays a crucial role in its practical application. The film's uniformity over large areas is vital for hi-tech applications. Growing a uniform PB film on a transparent conducting electrode by means of an electrochemical process is not too easy. Poor stability of the deposition bath containing ferric cyanide and a metal salt is the major problem; the contents of the bath turn into a precipitate instantaneously during the mixing [27]. PB powder that could be dispersed uniformly in water was prepared through a simple process. The aqueous solution of the water dispersible Prussian blue (wPB) or the "ink" was sprayed on an ITO glass to make an electrode in a complementary ECD. Spray coating is efficient, suitable for large-area ECDs, and can be used for patterning. The thickness of the film could be controlled preciously using spray coating. The present technique of preparing wPB thus enables the fabrication of large-area ECDs, which can be used for energy-saving windows and sunglasses. In this study, we synthesized wPB nanoparticles through a surface modification process and dispersed them in water to
http://dx.doi.org/10.1016/j.solmat.2015.06.031 0927-0248/& 2015 Elsevier B.V. All rights reserved.
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
M.-S. Fan et al. / Solar Energy Materials & Solar Cells ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
obtain an ink. This ink was spray-coated on an ITO glass to obtain a wPB film. PB film was also prepared by the electrochemical method and its electrochemical behavior was compared with that of the wPB film. A solid-state complementary ECD was fabricated based on the wPB and poly(butyl viologen) (PBV) thin films. Succinonitrile (SN), a plastic crystal, with 0.1 M potassium bis(trifluoromethanesulfonyl)imide (KTFSI) and 7 wt% of silicon dioxide (SiO2) nanoparticles was used as the solid-state electrolyte for the ECD. To eliminate the crystallization due to the presence of SN, 7 wt% of SiO2 was dispersed in the electrolyte. The amount of SiO2 was so small that it could not exert any influence on the contrast of the ECD. Indium-doped tin oxide (ITO) conducting glasses were used as the substrates for both electrodes of the ECD. The electrochromic behaviors of the thin films and the electrochromic performance of the device have been investigated.
wPB film could be controlled by the spraying process. The PB thin film was heated to 90 °C to evaporate the solvent. 2.4. Preparation of the electrodeposited Prussian blue (EDPB) film A cleaned ITO substrate (3.0 4.0 cm2) was used as the working electrode, and a Pt foil and Ag/AgCl were used as the counter and reference electrodes, respectively. The electrodeposited Prussian blue (EDPB) film was obtained on the ITO substrate, in an aqueous deposition bath of 10.0 mM FeCl3 6H2O, 10.0 mM K3Fe(CN)6, 0.1 M KCl, and 0.1 M HCl. For this, a constant cathodic current density of 0.04 mA/cm2 was applied to the electrode for 300 s. The as-deposited EDPB film was washed with DIW and dried with N2. 2.5. Electrolyte composition for the electrochromic device
2. Experimental 2.1. Materials All chemicals were used without further purification. Iron (III) nitrate nonahydrate (Fe(NO3)3 9H2O, 99.99%), sodium ferrocyanide decahydrate (Na4[Fe(CN)6] 10H2O, 499%), potassium bis (trifluoromethanesulfonyl)imide (KTFSI, 97%), potassium dihydrogen phosphate (KH2PO4, 499%), and potassium hydrogen phosphate (K2HPO4, 4 99%) were all purchased from Aldrich. Potassium ferrocyanide (K4Fe(CN)6, 99.99%) was obtained from Fisher Scientific. Succinonitrile (SN, 499.0%) was received from Acros Organics. Propylene carbonate (PC, 99.7%) was acquired from Alfa Aesar. Deionized water (DIW) with 18.2 MΩ cm of resistance was used. All experiments were performed at room temperature in air. ITO glasses of 3.0 4.0 cm2 were used as the substrates. The ITO glass was ultrasonically cleaned in an isopropyl alcohol for 10 min, and then in deionized water for 10 min. Finally, the ITO glass was dried under N2. After cleaning the ITO substrate, an epoxy tape (3 M Company, 60 μm thick) was attached to the ITO glass at the edges, intending to control the active area to be 2.0 2.0 cm2. A conducting copper tape (3 M Company, 3.0 0.5 cm2) was used as the bus bar at one side of the ITO glass. 2.2. Preparation of the PBV film The deposition bath of PBV contained 20.0 mM BVBr2, 10.0 mM KH2PO4, 90.0 mM K2HPO4, and 100.0 mM K4Fe(CN)6. The PBV thin film was deposited on an ITO substrate (Rsh ¼7 Ω/□) by anodic electropolymerization at 0.75 V (vs. Ag/AgCl) using the monomer bis(4-cyano-1-pyridino)butane dibromide (BVBr2) [28]. In our previous study [29], we have prepared a charge transfer complex using Fe(CN)64 and viologen monomer. The viologen monomers become radical cations at 0.75 V during the electropolymerization process. 2.3. Preparation of the wPB film An aqueous solution of Fe(NO3)3 9H2O was added to an aqueous solution of Na4[Fe(CN)6] 10H2O. The blue precipitate was vigorously shaken for 15 min, subsequently it was centrifuged and washed with DIW. Then aqueous Na4[Fe(CN)6] 10H2O was again added to the precipitate with vigorous stirring; the contents were vigorously stirred for one week. Finally, the solution was dried under reduced pressure to obtain the wPB nanoparticles. The wPB pigment was then dissolved in water to obtain its ink. This ink was sprayed on an ITO substrate (3.0 4.0 cm2) and the active area was controlled in 2.0 2.0 cm2. The thickness and active area of the
The solid electrolyte consisted of 0.1 M KTFSI salt, 7 wt% of silicon dioxide (SiO2) nanoparticles and SN. SN (melting temperature¼ 58 °C) is a plastic crystal which is solid state at room temperature. Before assembling the device, the solid electrolyte was heated to 90°C to bring it to the liquid state; this made the fabrication of the ECD easier. In order to decrease the crystallization of SN, 7 wt% of SiO2 nanoparticles was added to the matrix. Crystallization of an electrolyte is a bane to its ECD, because it could inhibit the migration of the ions through the electrolyte and could thereby decrease the stability of the device. Elimination of crystallization must be done in such a way that it would not adversely affect the performance of the device. SiO2 nanoparticles could disperse well in the electrolyte and eliminate its crystallization. 2.6. Assembly of the wPB-PBV electrochromic device Before assembling the device, the charge capacity of wPB film was optimized so that it matched well with that of PBV film and thereby could give the maximum transmittance to the complementary device. The heated SN was sandwiched between the PBV and wPB electrodes. The device was then cooled to room temperature so that the electrolyte became solid again. The thickness of the electrolyte was fixed to be 60 μm, by using an epoxy tape. The device was not subjected to either pre-darkening or pre-bleaching. The complementary ECD is designated as wPB/0.1 M KTFSIþ7 wt% SiO2 in SN/PBV. The electrochemical properties of the complementary ECD were studied using a potentiostat/galvanostat (Autolab, model PGSTAT30). The ECD was darkened or bleached by the application of 1.7 or 1.0 V, respectively. The voltage is the potential difference between the wPB electrode and the PBV electrode (wPB vs. PBV). The transmittances of both thin films and the corresponding ECD in the visible range were measured by an in-situ opto-electrochemical spectrophotometer (Ocean Optics, DH-2000-BAL). Another UV–vis-NIR spectrophotometer (V-670, Jasco), coupled with a 60 mm integrating sphere (ISN-723, Jasco), was used to measure the infrared reflective and transmittance spectra of the ECD.
3. Results and discussion 3.1. Characterization of wPB, EDPB, and PBV thin films 3.1.1. Particle size distribution Recent reports on wPB reveal that its particle size ranges from several nanometers to several hundreds of nanometers. The larger PB nanoparticles emerge from aggregation of nanoparticles. According to the literature, the insoluble PB nanoparticles could be
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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Current density (mA/cm )
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PB/0.1 M KTFSI Scan rate: 0.1 V/s
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M.-S. Fan et al. / Solar Energy Materials & Solar Cells ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Particle size (nm) Fig. 1. The particle size distribution of PB which was dispersed in water. The mean particle size is about 10 nm.
well-dispersed in water via the modification of the ligands on PB crystal surfaces [30]. Fig. 1 shows that the wPB is well-distributed in DIW with the mean particle size being about 10 nm. The dispersion of PB nanoparticles in water is rather homogeneous. Because of small sizes of the particles, the corresponding film was uniform. If the precursors of Fe3 þ and [Fe(CN)6]4 are mixed quickly, there will be a rapid reaction for the reactants to yield PB particles. In this situation, the sizes of PB particles may be large and the distribution of particles may be inhomogeneous. We synthesized wPB nanoparticles through a surface modification process and dispersed them in water to obtain an ink. A nanoparticle possesses a surface charge that attracts the opposite charge near it to form a thin electric double layer surrounding it. The electric potential at the boundary of such an electric double layer in a colloidal dispersion is known as the zeta potential. The absolute value of the zeta potential could be predictive of the colloidal stability. A low absolute value of zeta potential was related to low stability of the aggregation, that is, the aggregation of the particles cannot be prevented due to lower electric potential in the interfacial layer. In general, an absolute value of zeta potential larger than 30 mV would lead to a stable suspension [31–33]. The zeta potential of the wPB particles was found to be 36.8 mV. This zeta potential indicates that the PB is well dispersed in the water. The ink was found to be very suitable for spray coating. The thickness of the wPB thin film could be controlled by spraying coating technique. These conditions are favorable to fabricate the proposed ECD with a maximum transmittance change. 3.1.2. Cyclic voltammetric (CV) analysis Two kinds of PB thin films were prepared; the one deposited by electrochemical technique is designated as EDPB film and the other obtained by spray coating is designated as wPB film, because it is dispersible in water. The two PB thin films were obtained in such a way that both of them showed a transmittance of 207 3% at 695 nm. The cyclic voltammograms of wPB and EDPB films for the 20th cycles are shown in Fig. 2. The electrolyte was 0.1 M KTFSI in PC. We restricted the potential window for the electrode only for the Prussian blue/Prussian white (PB/PW) couple, as the electrochromism occurs in this region. A platinum foil and a home-made Ag/Ag þ electrode were used as the working electrode and reference, respectively. The potential of the electrode was cycled between 0.6 and 0.5 V, at a scan rate 100 mV/s. Both thin films exhibit only one redox couple. The values of the anodic peak potential (Epa), cathodic peak potential (Epc), and difference between the anodic and cathodic peak potential (ΔEp) are listed in
-0.4 0.0 0.4 + Potential (V vs. Ag/Ag )
0.8
Fig. 2. Cyclic voltammagrams of wPB and EDPB films in 0.1 M KTFSI in PC, obtained between 1.6 and 0.5 V (vs. Ag/Ag þ ). Table 1 Potential parameters and charge transfer resistances of the films of wPB and EDPB.
wPB EDPB
Epa (V vs. Ag/Ag þ )
Epc (V vs. Ag/Ag þ )
ΔEp (V)
Rct (Ω cm2)
0.23 0.28
0.36 0.37
0.59 0.65
1.21 10.72
Table 1. A lower ΔEp indicates a higher kinetic ability for the PB redox reaction. As the ΔEp of the electrode with wPB (0.59 V) is smaller than that of the electrode with EDPB (0.65 V), the wPB electrode is considered to have a higher driving force for the redox reaction of PB/PW. The electrochemical redox reaction is as follows [34]:
Fe 4 [Fe (CN)6 ]3 + 4K + + 4e− ⇄ K 4 Fe 4 [Fe (CN)6 ]3 (PB)
(PW)
(1)
During the CV measurement, the wPB thin film exhibits reversible color change from blue (PB) to transparent (PW). Eq. (1) clearly indicates that the electrochromic reaction involves injection or extraction of cations. The CV of a PBV film is shown in Fig. S1. The electrolyte was 0.5 M KCl in DIW. We can observe three pairs of redox peaks of PBV, which is in accordance with previous literature [35]. The first set of cathodic peak at 1.07 V corresponds to the reduction of the purple radical cation (PBV þ ) to form yellow– brown di-reduced species (PBV0). The second set of cathodic peak at 0.61 V represents the reduction of the colorless cation (PBV2 þ ) to form the purple radical cation (PBV þ ). The third set of redox peaks at 0.18 and 0.24 V correspond to the redox reaction of Fe(CN)64 /Fe(CN)63 . 3.1.3. Morphologies of wPB and EDPB thin films Fig. 3a and b shows SEM images of the films of wPB and EDPB, respectively. Fig. 3a clearly shows that the wPB film is excellently uniform, and adheres well to the ITO substrate. No aggregated particles could be seen on the surface of the film. The image indicates a homogeneous dispersion of the wPB particles in water, which is in agreement with the corresponding zeta potential value. Fig. 3b displays the SEM image of the EDPB thin film. As can be seen in Fig. 3b, the EDPB film consists of agglomerations of nanoparticles and systematic cracks. The nanostructure of EDPB film is not suitable for electron hopping, and induces resistance within the film. The effects of the two preparation methods of PB film on its morphology are thus established. It could now be foreseen from the surface morphologies of the two kinds of PB films that the wPB film would exhibit a better or effective electrochromic switching response.
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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4
Fig. 3. SEM images of films of (a) wPB and (b) EDPB.
3.1.4. EIS analysis of wPB and EDPB films In order to further confirm the redox reactions of wPB and EDPB thin films, electrochemical impedance spectroscopy (EIS) was used. The EIS spectra of symmetric cells based on wPB and EDPB films are shown in Fig. 4. A symmetric cell is a cell with identical anode and cathode. The equivalent circuit is shown as an inset in the figure. The radii of the semicircles of the EIS spectra give the values of interfacial charge-transfer resistances (Rct) of the films. In the case of wPB, its spectrum is shown as an enlarged version in the same figure. The values of the charge transfer resistances (Rct) at the interface of wPB and EDPB/electrolyte are given in Table 1. The values of Rct for wPB and EDPB thin films are 1.21 and 10.72 Ω cm2, respectively. The Rct of wPB thin film is about one order smaller than that of the EDPB thin film. This lower interfacial charge-transfer resistance leads to much faster electrochemical kinetics at the interface of wPB film/electrolyte. Based on the results of cyclic voltammetry and electrochemical impedance spectroscopy, we have selected wPB as the thin film to combine with the conducting polymer, PBV, to fabricate the complementary ECD. 3.1.5. Absorbance spectra and transmittance The equilibrium absorbance spectra of the PBV film is shown in Fig. S2. When the potential was stepped from 0.5 to 1.2 V at an interval of 0.1 V, the highest absorbance appears at 550 nm. It is clear that the thin film presents violet color at 0.8 V. However, at more negative potentials, the absorbance decreases and the color of the film changes to yellow–brown, associated with the formation of PBV0. In order to obtain a high contrast for the ECD, this
20 Equivalent circuit model R R
-Z" (ohm)
15
CPE
10 EDPB wPB
5
0
5
10
15
20
25
30
35
Z' (ohm) Fig. 4. EIS spectra of symmetric cells based on wPB and EDPB films; inset shows the equivalent circuit model.
redox couple needs to be avoided. The inset in Fig. S2 shows photographs of the device at 0.8, 1.2 and 0.1 V, depicting the changed colors at these potentials. In addition, a series of absorbance spectra of the film of wPB was obtained as shown in Fig. S3. No absorbance characteristics can be seen at the applied potentials from 0.6 to 0.4 V. The absorbance increases, with the oxidation of the wPB, at the applied potential from 0.4 to 0.1 V. Thus, the wPB thin film switches its color from transparent to blue, as is shown in the inset of Fig. S3. The maximum absorbance peak appears at 690 nm. To confirm the above understandings on the electrochromic behaviors of films of wPB and PBV, the transmittance changes and response times of these films were experimentally determined at the specific absorption wavelengths of the films, as shown in Fig. S4. The response or switching time of the electrochromic film is defined as the time it takes for reaching 90% of the saturated ΔT. For the PBV, the initial transmittance change is about 70% at 550 nm. The bleaching and darkening times in aqueous electrolyte of 0.5 M KCl are 1.5 s and 3.2 s, respectively. On the other hand, the initial transmittance change of wPB is found to be about 58% at 690 nm. The switching times in nonaqueous electrolyte of 0.1 M KTFSI/PC for wPB are 9.5 s for bleaching and 8.3 s for darkening. 3.2. Characterization of the ECD containing wPB and PBV 3.2.1. Cyclic voltammetric analysis In this study, the complementary ECD was assembled with PBV as the cathodically coloring electrode and wPB as the anodically coloring electrode. Several literatures reported on the complementary ECDs with 4,4′-bipyridine derivatives [36–38]. These materials offer high transmittance change and PBV is one of such materials. The charge density to deposit PBV was fixed at 80 mC/cm2. As mentioned already in Section 2 that the charge capacity of wPB thin film was optimized so that it matched well with that of the PBV thin film and thereby could give the maximum transmittance to the complementary ECD. Fig. 5 shows cyclic voltammogram of the complementary ECD at the scan rate of 100 mV/s, which is slow enough to notice the color change. We can observe two redox centers for the complementary ECD. The peaks at 0.4 and 1.0 V represent the redox center for wPB. The peaks at 1.0 and 1.7 V correspond to the redox reaction of PBV by Eq. (2).
PBV 2 + (TFSI)2 + e− ⇄ [PBV +⋅TFSI−]+TFSI−
(2)
The overall redox reaction of the complementary ECD can be written as follows:
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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2.0
1.0 wPB/0.1 M KTFSI + 7 wt% SiO2 in SN/PBV
1.5
2
Scan rate: 0.1 V/s
η = 157 cm /C
0.8
1.0
Δ OD at 545 nm
2
Current density (mA/cm )
wPB/0.1 M KTFSI + 7 wt% SiO in SN/PBV
0.5 0.0 -0.5
1.0 V 0.9 V
0.6
1.2 ~ 1.6 V 1.1 V
0.8 V
0.2 0.7 V
0.0 -2
-1
0
1
2
3
Fig. 5. Cyclic voltammogram of the complementary ECD at the scan rate of 100 mV/s in a PC solution of 0.1 M KTFSI, obtained between 1.5 and 2.2 V (vs. Ag/Ag þ ).
4PBV 2 + (TFSI)2 + K 4 Fe 4 [Fe (CN)6 ]3 ⇄ 4 [PBV +⋅TFSI−] + Fe 4 [Fe (CN)6 ]3 + 4K + + 4TFSI−
-1.0 ~ 0.6 V
-1
Applied cell voltage (V)
(3)
Owing to the complementary reaction, the device shows a reversible CV from 1.0 to 1.7 V. The CV does not show any side reactions. Therefore the operating potential window was selected to be between 1.0 and 1.7 V for the ECD, considering both the stability of the device and the maximum optical attenuation. 3.2.2. Absorbance spectra and coloration efficiency of the ECD containing wPB and PBV Fig. 6 shows in-situ UV-absorption spectra of the complementary ECD obtained at different applied cell potentials. The potentials were stepped from 1.0 to 1.7 V at an interval of 0.1 V. Starting from 1.0 V, the absorption increases up to 1.7 V, upon coloration. In this range of applied potentials, the largest peak of absorbance can be seen at 545 nm, which exists over the visible wavelength region. This wavelength is sensitive to human eye. At 1.0 V, the device was in its bleached or transparent state. At 1.7 V the device assumed a blue violet color. The insets in Fig. 6 are the photographs of the device at 1.0 and 1.7 V, depicting the changed colors at these potentials. The high contrast in the colors can be seen in these photos. Fig. S5a and b shows the optical 1.5 wPB/0.1 M KTFSI + 7 wt% SiO2 in SN/PBV λmax= 545 nm
500
600 700 800 Wavelength (nm)
6
7
transmittance and reflectance spectra of the ECD at both bleached and darkened states, obtained by applying the cell potentials of 1.0 and 1.7 V, respectively. The maximum optical transmittance change occurred at 545 nm, which is consistent with the absorbance spectra. Fig. S6 shows the infrared reflective spectra of the device at the darkened and bleached states. It can be observed that the reflectance at the darkened state is much less than that at the bleached state. The maximum reflectance change of the device from 1000 to 2500 nm is about 14%. The decrements of the transmittance and reflectance of the ECD were caused by the higher absorbance in the darkened state [39–41], which is consistent with Fig. 6. Most of the reflectance may be attributed to the ITO substrate [42,43]. The coloration efficiency was calculated to be 157 cm2/C at 545 nm from Fig. 7, where the dotted straight line covers the optical density change (ΔOD) data from 1.0 to 1.7 V. 3.2.3. Transmittance attenuation and long-term stability of the ECD containing wPB and PBV Fig. 8 shows the transmittance change of the complementary ECD at 545 nm in response to the change of the potential between 1.0 and 1.7 V. The initial transmittances of the device at 545 nm are 73.1% at 1.0 V and 10.6% at 1.7 V. Similarly, the response time for switching the ECD is defined as the time required for reaching 90% of the limiting ΔT. The switching times for both bleaching and darkening processes were determined to be the same, being about 10 s. Since the complementary ECD shows response times very close to those of the wPB thin film in nonaqueous electrolyte
900
1000
Fig. 6. In–situ UV-absorption spectra of the complementary ECD obtained at different applied cell potentials. The potentials were stepped from 1.0 to 1.7 V at an interval of 0.1 V; the inset in Fig. 6 shows photographs of the device at 1.0 and 1.7 V, depicting the changed colors of the ECD at these potentials. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.)
Transmittance (%) at 545 nm
0.8 V
-1.0 ~ 0.7 V 0.0 400
1 2 3 4 5 2 Charge capacity (mC/cm )
wPB/0.1 M KTFSI + 7wt% SiO in SN/PBV
1.0
0.5
0
Fig. 7. The relationship between the optical density change (ΔOD) and the passed charge density for the complementary ECD at 545 nm.
1.7 V
Absorbance
1.7 V
0.4
-1.0 -1.5
5
80
λ
= 545 nm
-1.0 V
60
40
20 1.7 V
0
0
100
200
300
400
Time (s) Fig. 8. The transmittance change of the complementary ECD at 545 nm in response to the potential change between 1.0 and 1.7 V.
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
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6
Acknowledgment
Transmittance (%) at 545 nm
100 Bleached state Darkened state ΔT
80 60
We thank the financial support received from the Ministry of Science and Technology (MOST) of Taiwan (Project number: 1022221-E-002-185-MY2) and AUO Optronics Corp. The instrumentations used in this study were partially supported by the MOST of Taiwan.
40 Appendix A. Supplementary material
20 0
0
200
400 600 Cycle number
800
1000
Fig. 9. The long-term stability data of the ECD collected over 1000 cycles of uninterrupted operation. The device was tested under the applied cell voltages of 1.0 V for 15 s during bleaching and 1.7 V for 15 s during darkening.
(0.1 M KTFSI in PC), this implies that the electrochromic switching is not limited by the conductivity of the proposed solid electrolyte. This can be explained by the high ionic conductivity of the salt-SN electrolyte system [44–46]. Another device was prepared to study the long-term stability of the proposed ECD. The result is shown in Fig. 9. Initially the transmission change of the device at 545 nm is 62.0%; after the operation of the device for 1000 cycles, the transmittance change is about 58.4%. The bleached state transmittance reached 68.5% at 545 nm after 1000 cycles, and the darkened state transmittance remained relatively constant after the same period.
4. Conclusions Prussian blue (PB) powder that could be dispersed uniformly in water was prepared through a simple process. Dynamic light scattering analysis reveals that the wPB powder is well-distributed in water and the mean particle size is about 10 nm. PB thin film was also prepared by an electrochemical method. Cyclic voltammetric analysis, scanning electron microscopy images, and electrochemical impedance spectra of these films indicated that wPB film would show a higher kinetic ability, and thereby a better electrochromic behavior. A solid-state complementary electrochromic device (ECD) was assembled based on the configuration of wPB/0.1 M KTFSI þ7 wt% SiO2 in SN/PBV. Owing to the complementary reaction, the device showed a reversible CV from 1.0 to 1.7 V. The device showed a high contrast from blue violet to transparent. The largest absorbance peak of the ECD was found to be at 545 nm. The transmission change (ΔT) and coloration efficiency of the proposed ECD were found to be about 62.5% and 157 cm2/C at 545 nm, respectively. The switching times for both bleaching and darkening were calculated to be the same, being about 10 s for a sample of 2.0 2.0 cm2. As for the long-term stability, the initial transmittance of the ECD at 545 nm is 72.2% at 1.0 V and 10.2% at 1.7 V. The bleached state transmittance at 545 nm decayed to 68.5% after operating the device continuously for 1000 cycles, while the darkened state transmittance remained nearly constant. The large contrast of the device and its reversible color change render the proposed device attractive for further research.
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.solmat.2015.06. 031.
References [1] T. Deutschmann, E. Oesterschulze, Micro-structured electrochromic device based on poly(3,4-ethylenedioxythiophene), J. Micromech. Microeng. 23 (2013) 065032. [2] U. Abaci, H.Y. Guney, U. Kadiroglu, Morphological and electrochemical properties of PPy, PAni bilayer films and enhanced stability of their electrochromic device (PPy/PAni-PEDOT, PAni/PPy-PEDOT), Electrochim. Acta 96 (2013) 214–224. [3] S. Sun, X. Chang, T. Liu, Y. Lu, Y. Wang, Solvothermal synthesis of tungsten oxide mesocrystals and their electrochromic performance, Mater. Lett. 105 (2013) 54–57. [4] R.R. Kharade, S.S. Mali, S.P. Patil, K.R. Patil, M.G. Gang, P.S. Patil, J.H. Kim, P.N. Bhosale, Enhanced electrochromic coloration in Ag nanoparticle decorated WO3 thin films, Electrochim. Acta 102 (2013) 358–368. [5] S. Stojkovikj, M. Najdoski, V. Koleva, S. Demiri, Preparation of electrochromic thin films by transformation of maganese (II) carbonate, J. Phys. Chem. Solids 74 (2013) 1433–1438. [6] E.N. Esmer, S. Tarkuc, Y.A. Udum, L. Toppare, Near infrared electrochromic polymer based on phenazine moieties, Mater. Chem. Phys. 131 (2001) 519–524. [7] A. Lakshmi, A.R. J, G. Gopu, P. Arumugam, C. Vedhi, Electrochemical, electrochromic behaviour and effects of supporting electrolyte on nano-thin film of poly(3,4-ethylenedioxythiophene), Electrochim. Acta 92 (2013) 452–459. [8] P.C. Pandey, A.K. Pandey, Novel synthesis of Prussian blue nanoparticles and nanocomposite sol: electro-analytical application in hydrogen peroxide sensing, Electrochim. Acta 87 (2013) 1–8. [9] N.L. Torad, M. Hu, M. Imura, M. Naito, Y. Yamauchi, Large Cs adsorption capability of nanostructured Prussian blue particles with high accessible surface areas, J. Mater. Chem. 22 (2012) 18261–18267. [10] H. Ming, N.L.K. Torad, Y.D. Chiang, K.C.W. Wu, Y. Yamauchi, , Size- and shapecontrolled synthesis of Prussian blue nanoparticles by a polyvinylpyrrolidoneassisted crystallization process, CrystEngComm 14 (2012) 3387–3396. [11] Z. Jia, Synthesis of Prussian blue nanocrystals with metal complexes as precursors: quantitative calculations of species distribution and its effects on particles size, Colloid Surf. A-Physicochem. Eng. Asp. 389 (2011) 144–148. [12] M. Presle, J. Lemainque, J.M. Guigner, E. Larquet, I. Maurin, J.P. Boilot, T. Gacoin, Controlled growth of core@shell heterostructures based on Prussian blue analogues, New J. Chem. 35 (2011) 1296–1301. [13] L. Xu, G. Zhang, J. Chen, Y. Zhou, G. Yuan, F. Yang, Spontaneous redox synthesis of Prussian blue/graphene nanocomposite as a non-precious metal catalyst for efficient four-electron oxygen reduction in acidic medium, J. Power Sources 240 (2013) 101–108. [14] P. Yu, J. Yan, H. Zhao, L. Su, J. Zhang, L. Mao, Rational functionalization of carbon nanotube/ionic liquid bucky gel with dual tailor-made electrocatalysts for four-electron reduction of oxygen, J. Phys. Chem. C 112 (2008) 2177–2182. [15] Y. Ma, Y. Du, W. Ye, B. Su, M. Yang, C. Wang, Electrocatalytic oxidation of ethanol on platinum electrode decorated with Nd–Fe–Mo hybrid-metallic cyano-bridged mixing coordination polymer in weak acidic medium, Int. J. Electrochem. Sci. 7 (2012) 2654–2679. [16] L. Fu, S.J. You, G.Q. Zang, F.L. Yang, X.H. Fang, Z. Gong, PB/PANI-modified electrode used as a novel oxygen reduction cathode in microbial fuel cell, Biosens. Bioelectron. 26 (2011) 1975–1979. [17] D.M.F. Santos, P.G. Saturnino, R.F.M. Lobo, C.A.C. Sequeira, Direct borohydride/ peroxide fuel cells using Prussian blue cathodes, J. Power Sources 208 (2012) 131–137. [18] G. Selvarani, S.K. Prashant, A.K. Sahu, P. Sridhar, S. Pitchumani, A.K. Shukla, A direct borohydride fuel cell employing Prussian blue as mediated electrotransfer hydrogen peroxide reduction catalyst, J. Power Sources 178 (2008) 86–91. [19] Z. Jiao, J.L. Song, X.W. Sun, X.W. Liu, J.M. Wang, L. Ke, H.V. Demir, A fastswitching light-writable and electric-erasable negative photoelectrochromic cell based on Prussian blue films, Sol. Energy Mater. Sol. Cells 98 (2012)
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i
M.-S. Fan et al. / Solar Energy Materials & Solar Cells ∎ (∎∎∎∎) ∎∎∎–∎∎∎ 154–160. [20] B. Seelandt, M. Wark, Electrodeposited Prussian blue in mesoporous TiO2 as electrochromic hybrid material, Microporous Mesoporous Mater. 164 (2012) 67–70. [21] Y. Rong, S. Kim, F. Su, D. Myers, M. Taya, New effective process to fabricate fast switching and high contrast electrochromic device based on viologen and Prussian blue/antimoy tin oxide nano-composites with dark colored state, Electrochim. Acta 56 (2011) 6230–6236. [22] R.J. Mortimer, T.S. Varley, In situ spectroelectrochemistry and colour measurement of a complementary electrochromic device based on surface-confined Prussian blue and aqueous solution-phase methyl viologen, Sol. Energy Mater. Sol. Cells 99 (2012) 213–220. [23] B. Zamora, A.A.A. Hajjaj, A.A. Shah, Kinetic and thermodynamic studies of hydrogen adsorption on titanate nanotubes decorated with a Prussian blue analogue, Int. J. Hydrog. Energy 38 (2013) 6406–6416. [24] Z. Chu, L. Shi, Y. Liu, W. Jin, N. Xu, In-situ growth of micro-cubic Prussian blue-TiO2 composite film as a highly sensitive H2O2 sensor by aerosol codeposition approach, Biosens. Bioelectron. 47 (2013) 329–334. [25] H. Byrd, B.E. Chapman, C.L. Talley, Prussian blue coated electrode as a sensor for electroinactive cations in aqueous solutions, J. Chem. Educ. 90 (2013) 775–777. [26] J. Keggin, F. Miles, Structures and formulas of the Prussian blues and related compounds, Nature 137 (1936) 577–578. [27] L.C. Chen, K.S. Tseng, K.C. Ho, Enhanced electrodeposition of indium hexacyanoferrate thin films through improved plating solution stability, J. Solid State Electrochem. 7 (2002) 1–5. [28] Y.C. Hsu, K.C. Ho, Anionic effect on the intercalation and spectral properties of poly(butyl viologen) films, J. New Mater. Electrochem. Syst. 8 (2005) 49–57. [29] Y.C. Hsu, V.S. Vasantha, P.Y. Chen, K.C. Ho, A new stable Fe(CN)63 /4 immobilized poly(butylviologen)-modified electrode for dopamine determination, Sens. Actuat. B-Chem. 137 (2009) 313–319. [30] A. Gotoh, H. Uchida, M. Ishizaki, T. Satoh, S. Kaga, S. Okamoto, M. Ohta, M. Sakamoto, T. Kawamoto, H. Tanaka, M. Tokumoto, S. Hara, H. Shiozaki, M. Yamada, M. Miyake, M. Kurihara, Simple synthesis of three primary colour nanoparticle inks of Prussian blue and its analogues, Nanotechnology 18 (2007) 345609. [31] D.H. Everett, Basic Principles of Colloid Science, Royal Society of Chemistry, London, 1988. [32] D. Li, M.B. Müller, S. Gilje, R.B. Kaner, G.G. Wallace, Processable aqueous dispersions of graphene nanosheets, Nat. Nanotechnol. 3 (2008) 101–105. [33] C. Saldíasa, L. Velásquez, C. Quezada, A. Leiva, Physicochemical assessment of Dextran-g-Poly(ɛ-caprolactone) micellar nanoaggregates as drug nanocarriers, Carbohydr. Polym. 117 (2015) 458–467.
7
[34] H. Shiozaki, T. Kawamoto, H. Tanaka, S. Hara, M. Tokumoto, A. Gotoh, T. Satoh, M. Ishizaki, M. Kurihara, Masatomi Sakamoto, Electrochromic thin film fabricated using a water-dispersible ink of Prussian blue nanoparticles, Jpn. J. Appl. Phys. 47 (2008) 1242–1244. [35] Y.C. Hsu, K.C. Ho, The anionic effect on the intercalation and spectral properties of poly(butyl viologen) films, J. New Mater. Electrochem. Syst. 8 (2005) 49–57. [36] G. Wang, X. Fu, J. Huang, C. Wu, L. Wu, Q. Du, Synthesis of a new star-shaped 4,4′-bipyridine derivative and its multicolor solid electrochromic devices, Org. Electron. 12 (2011) 1216–1222. [37] B. Gadgil, P. Damlin, T. Aaritalo, J. Kankare, C. Kvarnstrom, Electrosynthesis and characterization of viologen cross linked thiophene copolymer, Electrochim. Acta 97 (2013) 378–385. [38] C.F. Lin, C.Y. Hsu, H.C. Lo, C.L. Lin, L.C. Chen, K.C. Ho, , A complementary electrochromic system based on a Prussian blue thin film and a heptyl viologen solution, Sol. Energy Mater. Sol. Cells 95 (2011) 3074–3080. [39] W. Estrada, A.M. Andersson, C.G. Granqvist, Infrared reflectance spectroscopy of electrochromic NiOxHy films made by reactive dc sputtering, J. Mater. Res. 6 (1991) 1715–1719. [40] R. Sydam, M. Deepa, A new organo–inorganic hybrid of poly(cyclotriphosphazene-4,4′-bipyridinium)chloride with a large electrochromic contrast, J. Mater. Chem. C 1 (2013) 7930–7940. [41] A.A. Argun, J.R. Reynolds, Line patterning for flexible and laterally configured electrochromic devices, J. Mater. Chem. 15 (2005) 1793–1800. [42] H.L. Hartnagel, A.L. Dawar, A.K. Jain, Semiconducting Transparent Thin Films, Taylor & Francis, England, 1995. [43] N.M. Khusayfan, M.M. El-Nahass, Study of structure and electro-optical characteristics of indium tin oxide thin films, Adv. Condens. Matter Phys. 2013 (2013) 408182. [44] R.K. Gupta, H.M. Kim, H.W. Rhee, Poly(ethylene oxide): succinonitrile-a polymeric matrix for fast-ion conducting redox-couple solid electrolytes, J. Phys. D: Appl. Phys. 44 (2011) 205106. [45] S. Das, S.J. Prathapa, P.V. Menezes, T.N. Guru Row, A.J. Bhattacharyya, Study of ion transport in lithium perchlorate-succinonitrile plastic crystalline electrolyte via ionic conductivity and in situ cryo-crystallography, J. Phys. Chem. B 113 (2009) 5025–5031. [46] L.Z. Fan, X.L. Wang, F. Long, X. Wang, Enhanced ionic conductivities in composite polymer electrolytes by using succinonitrile as a plasticizer, Solid State Ion. 179 (2008) 1772–1775.
Please cite this article as: M.-S. Fan, et al., A high contrast solid-state electrochromic device based on nano-structural Prussian blue and poly(butyl viologen) thin films, Solar Energy Materials and Solar Cells (2015), http://dx.doi.org/10.1016/j.solmat.2015.06.031i