Electrochimica Acta 56 (2011) 4281–4286
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochromic properties of porous NiO thin film as a counter electrode for
NiO/WO complementary electrochromic window
3
a
a
a,∗
a
a
b
b
H. Huang , J. Tian , W.K. Zhang , Y.P. Gan , X.Y. Tao , X.H. Xia , J.P. Tu
a
College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014, China
Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 August 2010
Received in revised form 18 January 2011
Accepted 22 January 2011
Available online 28 January 2011
Highly porous nickel oxide (NiO) thin films were prepared on ITO glass by chemical bath deposition
CBD) method. SEM results show that the as-deposited NiO film is constructed by many interconnected
nanoflakes with a thickness of about 20 nm. The electrochromic properties of the NiO film were inves-
tigated in a nonaqueous LiClO4–PC electrolyte by means of optical transmittance, cyclic voltammetry
(
(CV) and electrochemical impedance spectroscopy (EIS) measurements. The NiO film exhibits a notice-
able electrochromic performance with a variation of transmittance up to 38.6% at 550 nm. The CV and
EIS measurements reveal that the NiO film has high electrochemical reaction activity and reversibility
due to its highly porous structure. The electrochromic (EC) window based on complementary WO3/NiO
structure shows an optical modulation of 83.7% at 550 nm, much higher than that of single WO3 film
(65.5% at 550 nm). The response time of the EC widow is found to be about 1.76 s for coloration and 1.54 s
for bleaching, respectively. These advantages such as large optical modulation, fast switch speed and
excellent cycle durability make it attractive for a practical application.
Keywords:
Nickel oxide
Electrochromism
Thin film
Electrochromic window
Lithium intercalation
©
2011 Elsevier Ltd. All rights reserved.
1
. Introduction
electrochromism and electrochemical performance of NiO films in
nonaqueous electrolyte solutions [15,16].
Electrochromic (EC) materials are able to change their optical
A high performance EC device should present high optical con-
trast, good optical memory and chemical stability to electrochromic
cycles. NiO films are being developed for application in dynamic
or “smart” windows that are at the forefront of emerging energy-
saving advances in building technologies [17]. NiO can be used as a
counter electrode to WO3 electrode in EC window, where the opti-
cal modulation increases because they are quite complementary
[18,19]. However, in the fabricating process of EC window, they are
chemically incompatible when NiO and WO3 have to be immersed
in acidic or alkaline aqueous electrolytes. The aqueous electrolyte
can be replaced by nonaqueous solvents such as propylene carbon-
ate (PC) and ␥-butyrolactone. It has been revealed that WO3 has
properties reversibly and persistently by an external voltage.
The transition metal oxide thin films, e.g. oxides of W, Ir, V, Ti
and Ni [1–4], are widely studied for their electrochromic behav-
ior. Among these materials, NiO is of considerable interest due
to high coloration efficiency (CE), good cyclic reversibility and
low material cost [5,6]. In the past years, many studies on the
electrochemical and electrochromic properties of NiO have been
conduced in aqueous electrolytes, where the optical modulation
depends on proton/electron transport [7–10]. Additionally, the
+
electrochromic effect during the injection/extraction of Li in/from
NiO films has been observed in water-free organic system [11–14].
Considering practical applications, high coloration efficiency
and long-term durability are required for NiO film. Therefore,
nonaqueous organic solvents are more suitable as the electrolyte
solution in comparison with aqueous electrolyte solution because
the nonaqueous electrolyte has a wider potential window for
electrochemical reactions. However, there are a few reports on the
a very reversible electrochromic behavior in the cited LiClO –PC
4
electrolyte [20–22]. The use of WO3 as the primary electrode in EC
window requires a counter electrode, which is reversible and elec-
trochromic in a complementary mode. The porous structure of NiO
film is believed to be helpful to the enhancement of electrochromic
performance. In our previous work, we found that the NiO film pre-
pared by chemical bath deposition (CBD) method had highly porous
structure and exhibited excellent EC properties in KOH electrolyte
[
23]. However, to the best of our knowledge, few investigations
ence, Zhejiang University of Technology, Zone 6, Chaohui, Hangzhou, Zhejiang
have been conducted in organic systems. In the present work, we
employed a simple CBD method to prepared highly porous NiO
film and investigated the EC properties of NiO films as the counter
3
10014, China. Tel.: +86 571 88320394; fax: +86 571 88320394.
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.01.078