Three-dimensional nanoporous TiO2 network films with excellent electrochemical capacitance performance

Article abstract of DOI:10.1016/j.jallcom.2014.01.213

The three-dimensional (3D) nanoporous hydrogenated TiO₂ (denoted as H-TiO₂) network film on titanium substrate was fabricated by a novel and controllable method. The fabrication process involved dealloying, alkaline reflux and hydrogenation. The dealloying produced the 3D nanoporous titanium film with open pores and interconnected nanoflakes nearly perpendicular to the substrate. The oxidation of the 2D titanium nanoflakes in the alkaline reflux resulted in the formation of the TiO₂ nanotubes with an inner diameter of 5-10 nm and a length larger than 1.5 μm. The 3D nanoporous TiO₂ network film was formed by the self assembly of these long and thin TiO₂ nanotubes. Hydrogenation induced the formation of oxygen vacancies and more hydroxyl groups on the H-TiO₂ surface. The 3D nanoporous H-TiO₂ network film presented a capacitance of 1.05 mF cm^-2 at the scanning rate of 100 mV s^{- 1}. Furthermore, the H-TiO₂ network film electrode also showed remarkable rate capability as well as excellent electrochemical cycling stability with a capacitance reduction of less than 7% after 1000 charge-discharge cycles at the current density of 100 μA cm^{- 2}. The prominent electrochemical capacitance properties of the 3D H-TiO₂ network film electrode could be attributed to its unique structural characteristics.

Full text of DOI:10.1016/j.jallcom.2014.01.213

Journal of Alloys and Compounds 597 (2014) 1–7
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Three-dimensional nanoporous TiO2 network films with excellent
electrochemical capacitance performance
⇑
Huan Zhou, Yuan Zhong, Zhishun He, Liying Zhang, Jianming Wang , Jianqing Zhang, Chu-nan Cao
Department of Chemistry, Zhejiang University, Hangzhou 310027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The three-dimensional (3D) nanoporous hydrogenated TiO2 (denoted as H-TiO2) network film on
titanium substrate was fabricated by a novel and controllable method. The fabrication process involved
dealloying, alkaline reflux and hydrogenation. The dealloying produced the 3D nanoporous titanium film
with open pores and interconnected nanoflakes nearly perpendicular to the substrate. The oxidation of
the 2D titanium nanoflakes in the alkaline reflux resulted in the formation of the TiO2 nanotubes with
Received 29 December 2013
Received in revised form 28 January 2014
Accepted 28 January 2014
Available online 6 February 2014
an inner diameter of 5–10 nm and a length larger than 1.5 lm. The 3D nanoporous TiO2 network film
Keywords:
was formed by the self assembly of these long and thin TiO2 nanotubes. Hydrogenation induced the for-
mation of oxygen vacancies and more hydroxyl groups on the H-TiO2 surface. The 3D nanoporous H-TiO2
network film presented a capacitance of 1.05 mF cmꢀ2 at the scanning rate of 100 mV sꢀ1. Furthermore,
the H-TiO2 network film electrode also showed remarkable rate capability as well as excellent electro-
chemical cycling stability with a capacitance reduction of less than 7% after 1000 charge–discharge cycles
Titanium dioxide
Nanoporous structure
Hydrogenation
Supercapacitor
Dealloying
at the current density of 100
H-TiO2 network film electrode could be attributed to its unique structural characteristics.
Ó 2014 Elsevier B.V. All rights reserved.
l
A cmꢀ2. The prominent electrochemical capacitance properties of the 3D
1. Introduction
materials, and these studies have resulted in significant enhance-
ment of capacitance storage. In all these cases, the controllable
synthesis of 3D nanostructures plays an important role to achieve
the application targets of advanced materials.
Electrochemical capacitors (ECs), also called supercapacitors or
ultracapacitors, are regarded as promising power sources for
hybrid electric vehicles and portable electronic devices due to their
long cycle life and great power densities [1–6]. In general, based on
their charging mechanisms, ECs fall into two categories, electro-
chemical double layer capacitor (EDLC) and pseudocapacitors.
The former is based on the separation of charges at the interface
between the electrode and electrolyte. The latter utilizes the fast
faradic process involving reversible redox reactions [3].
Over the past decade, numerous substances have been explored
as possible supercapacitor electrode materials such as carboneous
materials [7], conducting polymers [8], hybrid composites and
transition metal oxides [9]. In recent years, more attention has
been devoted to synthesis of nanoporous materials. Many investi-
gations have demonstrated that the hierarchical structures with
highly porous characteristics may improve the performances of
materials [10–15]. To date, numerous 3D porous structured mate-
rials, such as VO2 [16], MnO2 [17], Co3O4 [18], Nb2O5 [19] and
Ni(OH)2 [20], have been intensively explored as supercapacitor
Titanium dioxide has been considered as a promising electrode
material for supercapacitors because of its low cost, natural
abundance, high chemical stability and environmental friendliness
[21–23]. In general, TiO2 contributes a very low non-faradic capac-
itance (10–40 l
F cmꢀ2) in the charge–discharge process [24–26]. It
is widely believed that the low electrochemical capacitance results
from the low specific surface area and high electric resistance of
TiO2. Various synthetic strategies [27–33] have been probed to
improve the electrochemical capacitance of TiO2. Ramadoss et al.
[27] prepared vertically aligned TiO2 nanorod arrays on fluorine
doped tin oxide substrate using a hydrothermal method, and
the as-prepared electrode exhibited a maximum specific capaci-
tance of 85
retention ratio of 80% after 1000 cycles. Salari et al. [28,33] found
that the specific capacitance value (911
F cmꢀ2) of the TiO2 nano-
tube array heat-treated under argon atmosphere was much higher
than that (30
F cmꢀ2) of the corresponding TiO2 sample heat-
l
F cmꢀ2 at a scan rate of 5 mV sꢀ1 and a capacitance
l
l
treated under air atmosphere. Recently, it was demonstrated that
the donor densities and electrochemical activity of TiO2 nanostruc-
tures can be significantly improved by the thermal treatment in
⇑
Corresponding author. Tel.: +86 571 87951513; fax: +86 571 87951895.
E-mail address: wjm@zju.edu.cn (J. Wang).
http://dx.doi.org/10.1016/j.jallcom.2014.01.213
0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

2
H. Zhou et al. / Journal of Alloys and Compounds 597 (2014) 1–7
Fig. 1. Schematic illustration for the fabrication process of three-dimensional (3D) nanoporous H-TiO2 network film.
hydrogen atmosphere [34–36]. Although the above investigations
have been conducted, the controllable fabrication of 3D nanopor-
ous TiO2 films with prominent electrochemical capacitance proper-
ties still remains a great challenge.
In this investigation, we report a novel strategy for the fabrica-
tion of a 3D nanoporous hydrogenated TiO2 network film on tita-
nium substrate, as illustrated in Fig. 1. Attractively, it is found
that the 3D nanoporous network consists of thin TiO2 nanotubes.
The fabrication mainly includes dealloying, alkali reflux and
annealing in hydrogen-containing atmosphere (hydrogenation). It
is demonstrated that the as-prepared 3D nanoporous TiO2 network
film exhibits large specific capacitance, excellent rate capability
and high electrochemical-cycling stability. The reasons that the
3D nanoporous TiO2 network film shows prominent electrochemi-
cal capacitance performance are discussed in detail.
2. Experimental
Fig. 2. XRD patterns of the annealed alloy film (a), dealloying film (b) and final
product films annealed in air (c) and the hydrogen-containing argon (d). Symbols A
and R represent anatase and rutile phases (JCPDS card no. 71-1166 and 89-6975),
respectively.
2.1. Electrode preparation
The porous Ti film was first fabricated by a dealloying method. A zinc film was
prepared by a cathodic electrodeposition in the electrolyte solution containing
0.6 M ZnSO4, 0.1 M (NH4)2SO4 and 10 mM sodium dodecyl sulfate (SDS) at room
temperature. A titanium foil (99.5%, 1.0 cm ꢁ 2.0 cm ꢁ 0.25 mm, Alfa Aesar) was
assembled as the working electrode. Prior to deposition, the titanium foil was pol-
ished with 2000# grit waterproof abrasive paper, and ultrasonically cleaned in ace-
tone and deionized water for 10 min, respectively. The deposition was conducted in
a two-electrode cell with a platinum counter electrode at a constant current density
of 10 mA cmꢀ2 for 30 min. After rinsed extensively with deionized water and dried
in a nitrogen stream, the titanium foil with the electrodeposited zinc layer was an-
nealed at 150 °C for 2 h in an Ar-filled tube furnace. The selective dissolution of zinc
from the annealed film was carried out in 1 M KOH solution at 60 °C for 10 h. The
obtained porous Ti film was refluxed in a three-necked flask with 6 M KOH solution
at 110 °C for 12 h. After the refluxing, the sample was washed in deionized water
and immersed in 0.5 M hydrochloric acid for 12 h. After rinsed with deionized
I ꢂ
Dt
V ꢂ S
C0 ¼
ð2Þ
D
where S (cm2) is the geometric area of the working electrode,
tential scan rate,
current on CV curves, I (A) is the applied current, and
v
(mV sꢀ1) is the po-
V (V) is the sweep potential window, I(V) (A) is the voltammetric
D
Dt (s) is the discharge time.
3. Results and discussion
Fig. 2 illustrates the XRD patterns of various films. As shown in
Fig. 2a, the annealed alloy film consists of a mass of zinc (JCPDS
card no. 65-3358) and a small quantity of titanium (JCPDS card
no. 44-1294). The mutual diffusion of Zn and Ti during the heat
treatment results in the formation of Zn–Ti alloy surface film,
which is similar to the formation process of Zn–Ni alloy film
[37]. The XRD pattern of the dealloying film in Fig. 2b shows that
the XRD peaks of zinc disappear and the XRD peaks of Ti appear,
indicating that the porous Ti film is obtained through the selective
etching of zinc from the annealed film in the alkaline solution [37].
The EDX result in Fig. 3 reveals that a large amount of Ti and a
small quantity of oxygen exist in the dealloying film, suggesting
that titanium is covered with a thin oxide layer. As shown in
water and dried in
a nitrogen stream, the resulting sample was annealed at
630 °C in air and the 20% hydrogen-containing argon for 2 h, respectively. In the fol-
lowing discussions, the samples annealed in air and the 20% hydrogen-containing
argon were designated as air-TiO2 and H-TiO2, respectively.
2.2. Physical characterization
The X-ray diffraction (XRD) patterns of film electrodes were recorded using a
Rigaku D/Max 2550 X-ray diffractometer with Cu
Ka radiation at 40 kV and
300 mA. The X-ray photoelectron spectroscopy (XPS) analysis of film electrodes
was performed by a PHI 5000C X-ray physical electronics photoelectron spectrom-
eter with Mg Ka radiation at 15 kV and 500 W. The morphologies and microstruc-
tures of various film electrodes were observed with scanning electron microscopy
(SEM, SIRION-100, FEI Co. Ltd.) and transmission electron microscopy (TEM/HRTEM,
JEM-2010, JEOL), respectively. The surface composition of the Ti film was analyzed
by energy dispersive X-ray (EDX) spectroscopy (GENE IS 4000).
2.3. Electrochemical measurements
Electrochemical measurements were performed at room temperature in a typ-
ical three-electrode glass cell with a platinum counter electrode and a Ag/AgCl ref-
erence electrode. Various film electrodes were used as the working electrode. 0.5 M
Na2SO4 aqueous solution was employed as electrolyte. Cyclic voltammetry (CV) was
measured at various scan rates using a potentiostat (CHI 660C). Electrochemical
impedance spectroscopy (EIS) measurements were carried out by an electrochem-
ical analyzer (Parstat 2273), with the frequency range of 100 kHz to 0.01 Hz and a.c.
signal amplitude of 5 mV. Galvanostatic charge/discharge tests were performed at
various current densities by a potentiostat (Arbin BT-2000, USA).
The average specific capacitance (C, F cmꢀ2) from the CV curves is calculated
according to the following integral equation (1). The average specific capacitance
(C0, F cmꢀ2) from the charge/discharge curves can be calculated in terms of Eq.
(2) [28].
Z
1
C ¼
I
dV
ð1Þ
ðVÞ
v
ꢂ DV ꢂ S
Fig. 3. EDX analysis of the dealloying film.

H. Zhou et al. / Journal of Alloys and Compounds 597 (2014) 1–7
3
Fig. 2c and d, the final product films annealed in both air and the
Table 1
hydrogen-containing argon are composed of anatase and rutile
phases of TiO2. That is, the hydrogenation treatment does not alter
the phase structure of TiO2. The transformation from metallic Ti to
Ti (IV) generally results from the oxidation of oxygen during the
refluxing treatment. In energy storage applications such as batter-
ies and supercapacitors, it has been demonstrated that the elctro-
chemical properties of titania particles mostly depend on the
particle size rather than the phases, and no significant differences
are found beween rutile and anatase [23,38].
The effect of hydrogenation on the chemical composition and
oxidation state of the TiO2 film was obtained from XPS measure-
ments. Fig. 4a shows the XPS spectra of Ti 2p signal for H-TiO2
and air-TiO2 samples. The two peaks at 465.1 and 458.9 eV can
be attributed to the characteristic Ti 2p1/2 and Ti 2p3/2 peaks
[34,35], respectively. Compared to those of air-TiO2, the peaks of
H-TiO2 show a shift towards the lower binding energy. This indi-
cates that the Ti atoms in two samples have different chemical
environments, suggesting the existence of Ti3+ (oxygen vacancies)
inside H-TiO2 [36]. Fig. 4b and c compare the O 1s core level XPS
spectra of air-TiO2 and H-TiO2 samples. The XPS peaks at 529.8
and 531.3 eV are the typical peaks of Ti–O–Ti and Ti–OH species
[34–36], respectively. Deconvolution and curve fitting of the O 1s
2p spectra were performed by CasaXPS software, and the corre-
sponding data are given in Table 1. It can be seen that the content
of Ti–OH species in the H-TiO2 sample is substantially higher than
that in air-TiO2 sample, indicating that the H-TiO2 surfaces are
functionalized by hydroxyl groups.
XPS data for O 1s.
Sample
Binding energy
Area
(%)
Binding energy
(eV)
Area
(%)
Ti–OH%
(eV)
H-TiO2
Air-TiO2
529.31
529.31
70.42
84.63
531.59
531.92
29.58
15.38
29.58
15.37
structure with open pores and interconnected nanoflakes that are
nearly perpendicular to the substrate. In the dealloying proecess
of the annealed Ti–Zn film in the alkaline solution, the more active
zinc atoms are selectively dissolved, and the more noble titanium
atoms are chemically driven to aggregate into two-dimentional
(2D) nanoflakes by a phase separation process [37,39]. As illus-
trated by the top-view SEM images in Fig. 5c and d, the as-prepared
H-TiO2 film exhibits a 3D nanoporous network structure. The TEM
images in Fig. 6a–c clearly show that the 3D nanoporous network
film consists of many long TiO2 nanotubes with an inner diameter
of 5–10 nm and a wall thickness of 2–4 nm. The selected area elec-
tron diffraction (SAED) pattern in Fig. 6d shows the five sets of
obvious diffraction rings that can be indexed as the A(101),
R(110), A(112), A(200) and R(211) planes of TiO2 from the inner
to the outer, confirming that the as-prepared film is composed of
anatase (A) and rutile (R) phases. As illustrated by the cross-sec-
tional SEM image of H-TiO2 film in the inset of Fig. 5c, the oriented
TiO2 nanotubes perpendicularly grow on Ti substrate, and the
thickness of the H-TiO2 film is about 1.5 lm. These long and thin
TiO2 nanotubes are prone to bend and enlace with each other, thus
the top-view SEM images of as-prepared H-TiO2 film exhibit a
Fig. 5a and b shows the SEM images of the porous Ti film ob-
tained by the dealloying. The Ti film exhibits a 3D nanoporous
Fig. 4. XPS spectra of Ti 2p peaks (a) and O 1s peaks for Air-TiO2 (b) and H-TiO2 (c).

4
H. Zhou et al. / Journal of Alloys and Compounds 597 (2014) 1–7
Fig. 5. SEM images of the porous Ti film obtained by dealloying (a, b) and H-TiO2 film (c, d). The inset in c shows the cross-sectional SEM image of H-TiO2 film.
Fig. 6. TEM images (a–c) and SAED pattern (d) of H-TiO2 network film. Symbols A and R in d represent anatase and rutile phases, respectively.

H. Zhou et al. / Journal of Alloys and Compounds 597 (2014) 1–7
5
nanoporous network structure. That is, the as-prepared 3D nano-
porous H-TiO2 network film is formed by the interconnected TiO2
nanotubes perpendicularly growing on Ti substrate. It should be
pointed out that the transformation from the 2D titanium
nanoflakes to the titania nanotubes could result from the oxidation
of oxygen and a wrapping process during the alkali refluxing treat-
ment [40,41]. The corresponding rolling-up mechanism involves
the wrapping of multilayered nanosheets into nanotubes, where
the driving force for the curving of multilayered nanosheets may
be the mechanical stress induced during the oxidation/peeling of
nanosheets [42].
reported for TiO2 electrodes [22–33,38]. Although our H-TiO2
network film shows slightly lower areal capacitance value than
the anodized TiO2 nanotube array calcined in pure hydrogen gas
[43], it is fabricated by a novel and controllable method, and its
thermal treatment is conducted in the less hydrogen atmosphere.
It is noted in Fig. 7c that the areal capacitance of the 3D H-TiO2 net-
work film drops from 1.21 to 0.70 mF cmꢀ2 when the scanning rate
increases from 2 to 1000 mV sꢀ1, with a capacitance retention ratio
of 58.0%. In comparison, the air-TiO2 network film shows a capac-
itance retention ratio of 28.6%. This suggests that the 3D H-TiO2
network film has an enhanced rate capability.
Fig. 7a shows the cyclic voltammetric (CV) curves of the 3D
nanoporous TiO2 network films in 0.5 M Na2SO4 aqueous solution
at the scan rate of 100 mV sꢀ1. The two CV curves exhibit nearly
symmetrical rectangular shapes, indicative of electrical double-
layer capacitance behavior. In comparison to the 3D air-TiO2 net-
work film, the 3D H-TiO2 network film shows substantially larger
capacitive current densities, suggesting its higher electrochemical
activity. As illustrated in Fig. 7b, all the CV curves of the 3D
H-TiO2 network film at various scan rates exhibit quasi-rectangular
shapes, and no significant change in the CV shapes appears as the
scan rate increases from 2 to 1000 mV sꢀ1. This indicates the good
capacitive behavior and high-rate capability of the 3D H-TiO2 net-
work film. Fig. 7c shows the calculated areal capacitances of the 3D
nanoporous TiO2 network films as a function of scanning rate. The
areal capacitances of the 3D H-TiO2 network film are much larger
than the corresponding values of the 3D air-TiO2 network film.
For example, the 3D H-TiO2 network film displays a capacitance
of 1.05 mF cmꢀ2 at the scanning rate of 100 mV sꢀ1, which is a
14-fold enhancement compared to the air-TiO2 film
(0.07 mF cmꢀ2). The areal capacitance of the H-TiO2 network film
is also substantially higher than those capacitance values recently
The electrochemical properties of the 3D nanoporous H-TiO2
network film were further investigated by galvanostatic charge/
discharge measurements. Fig. 8a exhibits the charge/discharge
curves of different TiO2 film electrodes at the current density of
100 l
A cmꢀ2. Compared with those of the pristine-TiO2 and air-
TiO2 film electrodes, the charge/discharge curves of the H-TiO2 film
electrode are substantially prolonged, revealing an enhanced
capacitive behavior. The areal capacitance of the H-TiO2 film elec-
trode is calculated to be 0.89 mF cmꢀ2, which is significantly larger
than the corresponding values of the pristine-TiO2 (0.06 mF cmꢀ2),
air-TiO2 (0.12 mF cmꢀ2) and the previously reported TiO2 elec-
trodes [22–33]. Fig. 8b shows the charge/discharge curves of the
H-TiO2 network film electrode at the current densities ranging
from 100–1000 l
A cmꢀ2. It can be seen that the charge curves
are clearly symmetrical to their corresponding discharge counter-
parts, and the charge/discharge potentials linearly vary with time.
This shows the non-faradaic capacitance behavior and good rate
capability of the 3D H-TiO2 network film, which is in good agree-
ment with the CV results. Fig. 8c presents the cycle performance
of the pristine-TiO2, Air-TiO2 and H-TiO2 network film electrodes
at the current density of 100 l
A cmꢀ2. The H-TiO2 network film
Fig. 7. (a) CV curves of the H-TiO2 and air-TiO2 network films obtained at a scanning rate of 100 mV sꢀ1. (b) CV curves collected for the H-TiO2 network film at various scan
rates. (c) Areal capacitance of H-TiO2 and air-TiO2 network films measured as a function of scan rate.

6
H. Zhou et al. / Journal of Alloys and Compounds 597 (2014) 1–7
Fig. 8. (a) Galvanostatic charge–discharge curves of pristine-TiO2, air-TiO2 and H-TiO2 network films collected at a current density of 100
discharge curves of H-TiO2 network film collected at current densities of 100–1000
A cmꢀ2. (c) Cycle performance of pristine-TiO2, air-TiO2 and H-TiO2 network films at a
current density of 100
A cmꢀ2. (d) Nyquist plots for air-TiO2 and H-TiO2 film electrodes at open circuit state and the corresponding equivalent circuit in the inset.
l
A cmꢀ2. (b) Galvanostatic charge–
l
l
electrode exhibits only 6.2% deterioration of the initial capacitance
after 1000 cycles. While the capacitance losses of the pristine-TiO2
and Air-TiO2 film electrodes after 1000 cycles are 35.96% and
21.63%, respectively. This demonstrates the enhanced electro-
chemical cycling performance of the H-TiO2 network film
electrode.
Table 2
Parameter values obtained by the simulation of the Nyquist plots in Fig. 8d.
Sample Rs
(X
cm2) Rc
(
X
cm2) CPE1 (
l
F cm–2
)
n1
0.87 465.9
0.78 60.96
CPE2 (
l
F cm–2
)
n2
H-TiO2 3.32
Air-TiO2 4.97
101.30
231.60
31.60
13.38
0.76
0.72
The EIS measurements were performed to evaluate the effects
of hydrogenation on the electrochemical kinetics of the 3D TiO2
network films. Fig. 8d shows the Nyquist plots for the electrodes
at open circuit state. The Nyquist plots of the two samples display
a similar shape. Considering that no evidence of any faradaic reac-
tion is observed in both the CV and charge/discharge curves, it is
reasonable to conclude that the depressed semicircle in the high-
frequency region can be attributed to the contact resistance (Rc)
and capacitance (CPE1) between the TiO2 nanotubes and titanium
substrate [44]. In the low-frequency region, the imaginary part of
the impedance is much larger than the corresponding real part,
which is a characteristic of the capacitive behavior [45,46]. The
loop in the low-frequency region is related to the double-layer
capacitance (CPE2). The equivalent circuit of the EIS is shown in
the inset of Fig. 8d, where Rs is the bulk solution resistance [44–
47]. It can be seen from the simulation results in Table 2 that the
H-TiO2 network film shows a much lower contact resistance (Rc)
and a much larger double-layer capacitance (CPE2) value com-
pared to the air-TiO2 network film. This implies that the electrical
conductivity and double-layer capacitance of the 3D TiO2 network
film are effectively improved by the hydrogenation treatment.
The excellent electrochemical capacitance properties of the as-
prepared 3D nanoporous H-TiO2 network film electrode can be
attributed to its unique structure characteristics. The hierarchically
nanoporous architecture assembled from long and thin TiO2 nano-
tubes not only provides easy access of the surfaces to liquid elec-
trolyte but also offers more active sites for the charge separation,
manifesting the larger specific capacitance. Hydrogenation leads
to the occurrence of Ti3+ (oxygen vacancies) in H-TiO2 phase and
the formation of more hydroxyl groups on the surface of H-TiO2
nanotubes, which improves electrical conductivity and increases
the active sites for the adsorption/desorption of ions [36]. This is
largely responsible for the excellent capacitance performance of
the H-TiO2 network film electrode, especially at a high current rate.
The titania nanotubes are in-situ formed by using the 2D titanium
nanoflakes as precursor, thus they have the robust adhesion on the
substrate, which could play an important role in ensuring the en-
hanced rate capability and excellent electrochemical cycling stabil-
ity of the H-TiO2 network film electrode. Different from the TiO2
nanotube arrays in the previous investigations [28,29,31,33], the
3D H-TiO2 network film in this work is composed of the intercon-
nected long and thin TiO2 nanotubes perpendicularly growing on Ti
substrate, thereby facilitating the transport of electrons. This has
certain contribution to the enhanced capacitance performance of
the H-TiO2 network film electrode.
4. Conclusions
The 3D nanoporous hydrogenated TiO2 network film on tita-
nium substrate has been successfully fabricated by the novel

H. Zhou et al. / Journal of Alloys and Compounds 597 (2014) 1–7
7
[15] C. Wang, D.L. Wang, C.S. Dai, J. Electrochem. Soc. 155 (2008) A390–A394.
[16] L.Y. Liang, H.M. Liu, W.S. Yang, J. Alloys Comp. 559 (2013) 167–173.
[17] Z.X. Song, W. Liu, M. Zhao, Y.J. Zhang, G.C. Liu, C. Yu, J.S. Qiu, J. Alloys Comp.
560 (2013) 151–155.
[18] M.X. Liao, Y.F. Liu, Z.H. Hu, Q. Yu, J. Alloys Comp. 562 (2013) 106–110.
[19] K. Brezesinski, J. Wang, J. Haetge, C. Reitz, S.O. Steinmueller, S.H. Tolbert, B.M.
Smarsly, B. Dunn, T. Brezesinski, J. Am. Chem. Soc. 132 (2010) 6982–6990.
[20] D.S. Kong, J.M. Wang, H.B. Shao, J.Q. Zhang, C.N. Cao, J. Alloys Comp. 509 (2011)
5611–5616.
[21] J.M. Macak, F. Schmidt-Stein, P. Schmuki, Electrochem. Commun. 9 (2007)
1783–1787.
[22] F. Fabregat-Santiago, H. Randriamahazaka, H. Randriamahazaka, A. Zaban, J.
Garcia-Canadas, G. Garcia-Belmonte, J. Bisquert, Phys. Chem. Chem. Phys. 8
(2006) 1827–1833.
[23] D. Dambournet, I. Belharouak, K. Amine, Chem. Mater. 22 (2010) 1173–1179.
[24] Y.B. Xie, L.M. Zhou, C.J. Huang, H.T. Huang, J. Lu, Electrochim. Acta 53 (2008)
3643–3649.
[25] T. Brezesinski, J. Wang, S.H. Tolbert, B. Dunn, J. Sol–Gel. Sci. Technol. 57 (2011)
330–335.
strategy involving dealloying, alkali reflux and hydrogenation. The
3D H-TiO2 network film consists of the interconnected long and
thin TiO2 nanotubes resulting from the oxidation of the 2D tita-
nium nanoflakes obtained by the dealloying. Hydrogenation results
in the formation of oxygen vacancies in H-TiO2 phase and more hy-
droxyl groups on the surface of H-TiO2 nanotubes, which increases
the electrical conductivity and the active sites for the adsorption/
desorption of ions. The 3D nanoporous H-TiO2 network film exhib-
its the substantially large specific capacitance, enhanced rate
capability and excellent electrochemical cycling performance. This
results from the hierarchically nanoporous network architecture,
the formation of oxygen vacancies and more hydroxyl groups,
and the robust adhesion on titanium substrate. These attractive
results are important for both developing the novel fabrication
strategy of the 3D nanostructured film and promoting the promis-
ing applications of TiO2 materials in some energy storage and con-
version systems such as supercapacitors and Li-ion batteries.
[26] B.E. Conway, W.G. Pell, J. Solid State Electrochem. 7 (2003) 637–644.
[27] A. Ramadoss, S.J. Kim, J. Alloys Comp. 561 (2013) 262–267.
[28] M. Salari, K. Konstantinov, H.K. Liu, J. Mater. Chem. 21 (2011) 5128–5133.
[29] Z. Endut, M. Hamdi, W.J. Basirun, Appl. Surf. Sci. 280 (2013) 962–964.
[30] Z.Y. Zhang, F. Xiao, Y.L. Guo, S. Wang, Y.Q. Liu, ACS Appl. Mater. Inter. 5 (2013)
2227–2233.
Acknowledgements
[31] M.S. Kim, T.W. Lee, J.H. Parka, J. Electrochem. Soc. 156 (2009) A584–A588.
[32] J. Wang, J. Polleux, J. Lim, B. Dunn, J. Phys. Chem. C 111 (2007) 14925–14931.
[33] M. Salari, S.H. Aboutalebi, K. Konstantinov, H.K. Liu, Phys. Chem. Chem. Phys.
13 (2011) 5038–5041.
[34] X.B. Chen, L. Liu, P.Y. Yu, S.S. Mao, Science 331 (2011) 746–750.
[35] M.S. Lazarus, T.K. Sham, Chem. Phys. Lett. 92 (1982) 670–674.
[36] A. Naldoni, M. Allieta, S. Santangelo, M. Marelli, F. Fabbri, S. Cappelli, C.L.
Bianchi, R. Psaro, V.D. Santo, J. Am. Chem. Soc. 134 (2012) 7600–7603.
[37] J. Cai, J. Xu, J.M. Wang, L.Y. Zhang, H. Zhou, Y. Zhong, D. Chen, H.Q. Fan, H.B.
Shao, J.Q. Zhang, C.N. Cao, Int. J. Hydrogen Energy 38 (2013) 934–941.
[38] M. Koelsch, S. Cassaignon, C.T.T. Minh, J.F. Guillemoles, J.P. Jolivet, Thin Solid
Films 451 (2004) 86–92.
[39] J. Erlebacher, M.J. Aziz, A. Karma, N. Dimitrov, K. Sieradzki, Nature 410 (2001)
450–453.
[40] D.V. Bavykin, V.N. Parmon, A.A. Lapkin, F.C. Walsh, J. Mater. Chem. 14 (2004)
3370–3377.
[41] A. Kukovecz, N. Hodos, E. Horvath, G. Radnoczi, Z. Konya, I. Kiricsi, J. Phys.
Chem. B 109 (2005) 17781–17783.
[42] D. Wu, J. Liu, X.N. Zhao, A.D. Li, Y.F. Chen, N.B. Ming, Chem. Mater. 18 (2006)
547–553.
[43] X.H. Lu, G.M. Wang, T. Zhai, M.H. Yu, J.Y. Gan, Y.X. Tong, Y. Li, Nano Lett. 12
(2012) 1690–1696.
[44] H.H. Lee, K.Y. Lee, J.Y. Lee, J. Alloys Comp. 260 (1997) 201–207.
[45] Y. Liu, R. Zhao, M. Ghaffari, J.H. Lin, S. Liu, H. Cebeci, R.G. Villoria, R. Montazami,
D. Wang, B.L. Wardle, J.R. Heflin, Q.M. Zhang, Sens. Actuat. A-Phys. 181 (2012)
70–76.
[46] X.M. Liu, L. Juan, L. Zhan, L. Tang, Y.L. Wang, W.M. Qiao, X.Y. Liang, L.C. Ling, J.
Electroanal. Chem. 642 (2010) 75–81.
[47] F. Gobal, M. Faraji, Electrochim. Acta 100 (2013) 133–139.
This work was supported by the National Natural Science Foun-
dation of China (Nos. 51174176, 51271168 and J1210042) and the
Specialized Research Fund for the Doctoral Program of Higher
Education of China (Grant No. 20120101110045).
References
[1] J. Miller, P. Simon, Science 321 (2008) 651–652.
[2] P. Simon, Y. Gogotsi, Nat. Mater. 7 (2008) 845–854.
[3] G.P. Wang, L. Zhang, J.J. Zhang, Chem. Soc. Rev. 41 (2012) 797–828.
[4] R.R. Salunkhe, K. Jang, H. Yu, S. Yu, T. Ganesh, S.H. Han, H. Ahn, J. Alloys Comp.
509 (2011) 6677–6682.
[5] L.Y. Niu, Z.P. Li, J.F. Sun, Z.J. Fan, Y. Xu, P.W. Gong, S.R. Yang, J.Q. Wang, J. Alloys
Comp. 575 (2013) 152–157.
[6] K.V. Gurav, U.M. Patil, S.W. Shin, G.L. Agawane, M.P. Suryawanshi, S.M. Pawar,
P.S. Patil, C.D. Lokhande, J.H. Kim, J. Alloys Comp. 573 (2013) 27–31.
[7] Y. Chen, X. Zhang, D.C. Zhang, P. Yu, Y.W. Ma, Carbon 49 (2011) 573–580.
[8] D.P. Dubal, S.V. Patil, A.D. Jagadale, C.D. Lokhande, J. Alloys Comp. 509 (2011)
8183–8188.
[9] S. Chen, J.W. Zhu, X.D. Wu, Q.F. Han, X. Wang, ACS Nano 4 (2010) 2822–2830.
[10] Y.H. Xu, J.C. Guo, C.S. Wang, J. Mater. Chem. 22 (2012) 9562–9567.
[11] L.Y. Zhang, Y. Zhong, Z.S. He, J.M. Wang, J. Xu, J. Cai, N. Zhang, H. Zhou, H.Q. Fan,
H.B. Shao, J.Q. Zhang, C.N. Cao, J. Mater. Chem. A 1 (2013) 4277–4285.
[12] D.W. Kim, K.Y. Rhee, S.J. Park, J. Alloys Comp. 530 (2012) 6–10.
[13] L.Y. Zhang, L. Xu, J.M. Wang, H.B. Shao, Y.Q. Fan, J.Q. Zhang, J. Phys. Chem. C 115
(2011) 18027–18034.
[14] P. Acevedo-Pena, L. Lartundo-Rojas, I. Gonzalez, J. Electrochem. Soc. 160 (2013)
C291–C297.