Additive treatment effect of TiO2 as supports for Pt-based electrocatalysts on oxygen reduction reaction activity

Article abstract of DOI:10.1016/j.electacta.2010.01.055

In this study, we investigated the additive treatment effect of TiO₂ as alternative support materials to common carbon black for Pt-based electrocatalysts on electrocatalytic activity for oxygen reduction reaction (ORR). The shape of TiO₂ was varied by hydrothermal treatment with various additives, such as urea, thiourea, and hydrofluoric acid. From the results of transmission electron microscopy (TEM) images and ultraviolet-visible spectroscopy (UV-vis) spectra, it was identified that the morphology of hydrofluoric acid (HF)-treated TiO₂ was changed into a round shape having lower aspect ratio than other samples, and its band gap was decreased. Notably, the electronic state of HF-treated TiO₂ support was changed into highly reduced (electron rich) state which led to the increase of ORR activity, compared to other samples treated with different additives or before treatment. The electrocatalytic characteristics changes after treatment with various additives were investigated by using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), cyclic voltammograms (CV), and rotating disk electrode (RDE) techniques. Crown Copyright

Full text of DOI:10.1016/j.electacta.2010.01.055

Electrochimica Acta 55 (2010) 3628–3633
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Additive treatment effect of TiO as supports for Pt-based electrocatalysts on
2
oxygen reduction reaction activity
∗
Dae-Suk Kim, Essam F. Abo Zeid, Yong-Tae Kim
School of Mechanical Engineering, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 September 2009
Received in revised form
In this study, we investigated the additive treatment effect of TiO2 as alternative support materials to
common carbon black for Pt-based electrocatalysts on electrocatalytic activity for oxygen reduction reac-
tion (ORR). The shape of TiO2 was varied by hydrothermal treatment with various additives, such as urea,
thiourea, and hydrofluoric acid. From the results of transmission electron microscopy (TEM) images and
ultraviolet–visible spectroscopy (UV–vis) spectra, it was identified that the morphology of hydrofluoric
acid (HF)-treated TiO2 was changed into a round shape having lower aspect ratio than other samples, and
its band gap was decreased. Notably, the electronic state of HF-treated TiO2 support was changed into
highly reduced (electron rich) state which led to the increase of ORR activity, compared to other sam-
ples treated with different additives or before treatment. The electrocatalytic characteristics changes
after treatment with various additives were investigated by using X-ray diffraction (XRD), X-ray photoe-
mission spectroscopy (XPS), cyclic voltammograms (CV), and rotating disk electrode (RDE) techniques.
2
8 December 2009
Accepted 14 January 2010
Available online 25 January 2010
Keywords:
Polymer electrolyte membrane fuel cell
(
PEMFC)
Cathode electrocatalyst
Oxygen reduction reaction
Oxide support
TiO2
Crown Copyright © 2010 Published by Elsevier Ltd. All rights reserved.
1
. Introduction
The polymer electrolyte membrane fuel cell (PEMFC) has been
of electrocatalysts and reported that oxide supports showed better
corrosion resistance and lower degradation of active surface area
[8–15]. Among the many possible oxides, a considerable attention
recognizedas themost suitable powersource toreplace the internal
combustion engine for transportation applications due to its eco-
friendly system and high power density [1]. However, the reliability
of PEMFC must be improved before commercialization of fuel cell
electric vehicles (FCEV) becomes practical. Approximately 5500 h
of fuel cell operation is required for a FCEV, and the oxygen reduc-
tion reaction (ORR) activity of the cathode electrocatalyst strongly
affects PEMFC performance and long-term stability [2]. Carbon
materials are usually employed as the supports for platinum or
platinum alloy-based electrocatalysts because it has high-surface
area and good electronic conductivity [3–6]. A main drawback is,
however, carbon corrosion at the cathode site in which the elec-
trode potential and pH are relatively high. As carbon is eroded
away, noble metal nanoparticles can be lost from the electrode
or lumped into larger particles. This may cause the deterioration
of both catalytic activity and stability; alternative carbon supports
which have high durability are therefore required for practical fuel
cell operation [7].
has been paid to TiO materials for durable supports with its suit-
2
able characteristics in PEMFC operation condition, such as low cost,
commercial availability, stability in water, and the facility to control
size and structure [16–21].
Unfortunately, TiO materials are semiconductors having wide
2
band gaps of 3.0 eV for rutile and 3.2 eV for anatase structure
[22–24], the improvement of electronic conductivity is therefore
required to apply them to actual electrocatalyst supports.
In this paper, we demonstrated a unique method to change the
electronic characteristics of TiO2 supports based on a hydrother-
mal treatment with various additives which gave rise to a drastic
change of their morphology. The change of electrocatalytic activity
were finally investigated by using ultraviolet–visible spectroscopy
(UV–vis), transmission electron microscopy (TEM), X-ray diffrac-
tion (XRD), X-ray photoemission spectroscopy (XPS), and cyclic
voltammograms (CV) with rotating disk electrode (RDE).
2. Experimental
In recent, the studies on oxide supports as alternative materials
to carbon supports have been carried out to enhance the durability
2.1. Catalysts synthesis
Four kinds of additive-treated TiO2 support samples were
∗ Corresponding author. Tel.: +82 51 510 1012; fax: +82 51 514 0685.
E-mail address: yongtae@pusan.ac.kr (Y.-T. Kim).
obtained via the hydrothermal reaction with various additives. At
first, rutile TiO2 (2 g, Aldrich) was mixed in 90 ml of deionized
0
013-4686/$ – see front matter. Crown Copyright © 2010 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.01.055

D.-S. Kim et al. / Electrochimica Acta 55 (2010) 3628–3633
3629
(
DI) water with sonication. Followed by the dissolution of TiO ,
ethanol were used as the sample beam data. The spectra were taken
from 200 nm to 1000 nm at room temperature.
2
◦
the hydrothermal reaction was conducted at 200 C with rotation
at 150 rpm for 24 h, with urea (0.86 g, Kanto Chemical), thiourea
(
or without any additives. After the reaction, the precipitate was
filtered and washed with DI water and ethanol several times,
and then, samples were dried at 70 C. The non-additive-treated
TiO2 is referred to as TiO2 (non), and additive-treated TiO2 in
urea, thiourea, and hydrofluoric acid (HF) is as TiO2 (urea), TiO2
(
X-ray photoemission spectroscopy (XPS, ESCALAB250) spectra
were obtained to confirm the electronic state of Pt and Ti as well
as elemental. The X-ray source was Al K␣ with energy of 1486.6 eV
operating at 15 kV and 150 W, and the spot size was 500 ␮m. The
resulting binding energies were calibrated to the C1s (284.6 eV)
peak.
0.95 g, Kanto Chemical), and hydrofluoric acid (0.747 ml, J.T. Baker)
◦
X-ray diffraction (XRD, Philips Panalytical) measurements of the
Pt/TiO2 electrocatalysts were carried out using Cu K␣ radiation
(ꢀ = 1.5406 Å). The XRD spectra were obtained using high resolution
thiourea), and TiO (HF), respectively.
2
Pt electrocatalysts supported on additive-treated TiO supports
2
◦
were prepared with the borohydride reduction method. Additive-
in the step-scanning mode with a counting time of 50 s per 0.05 .
◦
treated TiO2 supports and H PtCl ·6H O (support weight 20 wt.%
Scans were recorded in the 2ꢁ range of 10–95 . Scherrer’s equation
2
6
2
of Pt) were dissolved in DI water with sonication. To reduce the
Pt precursor, NaBH4 dissolved in DI water was rapidly dropped
into the solution with vigorous stirring for 12 h. The precipitate
was filtered and washed several times with DI water and ethanol.
After evaporation and drying, Pt electrocatalysts supported on the
additive-treated TiO2 were obtained, which were referred to in
was used to estimate the particle size from the XRD results. For
this purpose, the (1 1 1) peak of the Pt face-centered cubic (FCC)
◦
structure on 2ꢁ = 40 was selected.
2.3. Electrochemical measurements
this paper as Pt/TiO (non), Pt/TiO (urea), Pt/TiO (thiourea), and
2
2
2
All electrochemical measurements were performed in a three-
Pt/TiO (HF).
2
electrode electrochemical cell on a potentiostat (Biologic VSP) at
room temperature. A thin-layer rotating disk electrode (5 mm in
diameter) was used as a working electrode, which was polished
with Al O slurries and washed in DI water with sonication before
2.2. Catalyst characterization
2
3
The morphology of electrocatalyst samples was observed by
the experiments. Well dispersed Pt/TiO (2.5 mg) and carbon black
2
using transmission electron microscopy (TEM, JEOL JEM-2011).
Specimens for TEM observation were prepared by placing a drop
of the particle-dispersed ethanol solution onto a copper grid; then,
the TEM was operated at an accelerating voltage of 200 keV. All
images were taken by a charge-coupled device (CCD) camera.
(1.5 mg, Alfa Aesar) as conductors by an ultrasonicator in DI water
were deposited onto a glassy carbon electrode by dropping 20 ␮l of
electrocatalysts ink with a micropipette, resulting in Pt loading in
25.48 ␮g/cm2
. Uniform and thin Pt/TiO + carbon black elec-
electrode
2
trocatalyst layer on the glassy carbon electrode were obtained by
mild evaporation and drying at room temperature. Nafion solution
(0.025 wt.%, 20 ␮l) was dropped onto the electrocatalysts coated
The absorbance spectra of TiO were recorded on a double beam
2
UV–vis spectrophotometer (Scinco SD-1000). Ethanol was used as
the reference beam data, and various TiO2 samples dispersed in
◦
electrode and dried in a vacuum oven at 70 C for 30 min. Finally, we
Fig. 1. Representative TEM images of Pt nanoparticles on (a) TiO2 (non), (b) TiO2 (urea), (c) TiO2 (thiourea), and (d) TiO2 (HF).

3
630
D.-S. Kim et al. / Electrochimica Acta 55 (2010) 3628–3633
Fig. 2. UV–visible diffuse reflectance spectrum of the various TiO2 samples.
Fig. 3. Plot of determining band gap energy of the various TiO2 samples. The insert
is a plot of ln(˛hꢂ) vs. ln(hꢂ − Eg).
could obtain the electrode coated with uniform and thin electocagt-
alysts layer for thin film rotating disk electrode (TF-RDE) technique.
A platinum wire and a silver chloride electrode (Ag/AgCl sat 3.5 M
KCl) were used as a counter and a reference electrode, respectively.
band gap Eg by extrapolating the straight line to the hꢂ axis inter-
cept [27–30]. Using this method, the value of n for the oxide was
approximately 4 based on the inset of Fig. 3, hence, all the TiO2
supports treated with various additives are the indirect band gap
semiconductors. As can be seen in Fig. 3, the calculated band gaps
for TiO (non), TiO (urea), TiO (thiourea), and TiO (HF) were 2.87,
Cyclic voltammetry (CV) measurements were performed in O -free
2
0
.1 M HClO electrolyte obtained by purging high-purity N gas for
4
2
3
0 min. The electrodes were cycled in the potential range between
0.195 and 1.005 V versus Ag/AgCl at a scan rate of 20 mV/s after
2
2
2
2
−
2
.85, 2.71, and 2.07 eV, respectively.
Consequently, the optical absorption edges of the additive-
electrochemical cleaning with a quick scan (scan rate: 200 mV/s)
for 50 cycles. After CV measurements, oxygen reduction reaction
treated TiO2 samples were shifted to the lower energy region
(
ORR) was subsequently performed in the same potential range in
compared to the non-additive TiO . Notably, it was revealed that HF
2
oxygen-saturated 0.1 M HClO4 by purging pure O2 gas at rotating
speeds of 100, 400, 900, 1600, and 2500 rpm with a scan rate of
was the best additive for the shape change into lower aspect ratio,
which resulted in the band gap decrease. This result is remark-
ably consistent with previous studies. Wautelet and co-workers
reported that the energy band gap of a TiO2 semiconductor was
affected by the nano-structure of shape and size [31], and this shape
change is a key factor in changing the electronic structure of TiO2
supports. The hydrofluoric acid treatment can be therefore another
5
mV/s. All of the current densities were normalized to the geo-
metric area of the rotating disk electrode.
3
. Results and discussion
Fig. 1 shows the TEM images of Pt-based electrocatalysts sup-
effective method to decrease the band gap of TiO semiconductor.
2
ported on the additive-treated TiO supports. TiO (non) supports
2
2
The electronic state of the additive-treated TiO2 supports for
Pt-based electrocatalysts were investigated by X-ray photoelectron
spectroscopy (XPS). Fig. 4 shows the Pt4f peak (a) and the Ti2p peak
(b) of the additive-treated TiO2 supports for the Pt-based electro-
catalysts. The obtained binding energies were calibrated to the C1s
(284.6 eV) peak. Through the survey scan, TiO2 samples were not
doped by various additives. It is believed that doping was not taken
have a nano-stick shape, and the supported Pt nanoparticles were
aggregated. In Fig. 1(b and c), the shape of TiO2 (urea) and TiO2
(
thiourea) was similar to TiO (non), but the Pt nanoparticles were
2
more dispersed than on the TiO (non) sample. An interesting point
2
shown in Fig. 1(d) is that TiO (HF) has more round shapes and Pt
2
nanoparticles were more uniformly dispersed with a smaller parti-
cle size than any other samples. Beranek et al. reported that florine
because complete TiO rutile power was used instead of a Ti precur-
2
−
(
F ) contained substance affected the morphology and character-
sor in the sample preparation. The Pt4f peak showed similar results
for all samples, which indicated that there was no remarkable dif-
ference in electronic state of Pt supported on additive-treated TiO2.
istics of TiO2 [25,26]. Hence, the HF was identified as the most
efficient additive to change the shape of TiO in hydrothermal treat-
2
ment.
However, for the Pt/TiO (HF) sample, the Ti2p peak shifted to the
2
The absorbance spectra of TiO were recorded on a double beam
2
lower binding energy which corresponded to the electron reach
state shown in Fig. 4b. This implies that Ti ion in TiO2 (HF) is in
more electron rich phase which can be the origin of the band gap
decrease. Table 1 shows the curve fitting results of XPS Ti2p3/2 and
UV–vis spectrophotometer to measure the band gap of additive-
treated TiO . The UV–visible diffuse reflectance spectrum of the
2
various TiO samples is shown in Fig. 2. The optical absorption near
2
the band edge energy follows the relation
Ti2p1/2 core peaks for various Pt/TiO samples. It was clearly shown
2
hꢂ = A × (hꢂ − Eg)n/2,
that all the additive-treated TiO2 samples had a small shoulder
at lower binding energy than main peak corresponding to more
˛
(1)
reduced Ti2+ or Ti state as well as a dominant Ti peak. Espe-
3+
4+
where ˛, v, A, and Eg are the absorption coefficient, light frequency,
proportionality constant, and band gap, respectively. In Eq. (1), n
determines the characteristic of a semiconductor. n = 1 for a direct
band gap semiconductor and n = 4 for an indirect band gap semi-
conductor. The values of n and Eg were determined by the following
steps: first, we plotted ln(˛hꢂ) vs. ln(hꢂ − Eg) using an approximate
value of Eg, and then determined the value of n from the slope of
the straight line. Second, we plotted (˛hꢂ)2 vs. hꢂ and determined
2+
3+
cially, Pt/TiO (HF) has the highest relative intensity of Ti or Ti
2
state, which can act as a electron donor and thereby improve the
electronic characteristics on the surface of TiO supports.
2
Fig. 5 shows the XRD analysis of the various Pt/TiO2 catalysts.
All the diffraction peaks show (1 1 1), (2 0 0), (2 2 0), and (3 1 1) of
the FCC crystal lattice of platinum. The average particle size of the
Pt catalyst supported on the additive-treated TiO2 was calculated
/n

D.-S. Kim et al. / Electrochimica Acta 55 (2010) 3628–3633
3631
Fig. 5. X-ray diffraction patterns of the various Pt/TiO2 catalysts. (*) Represents XRD
patterns of the TiO2 rutile nanosized support.
Table 2
Average particle size of catalysts from XRD data of Fig. 5.
Surface area (m2
g
−1
)
Catalyst
Average particle size (nm)
Pt/TiO2 (non)
Pt/TiO2 (urea)
Pt/TiO2 (thiourea)
Pt/TiO2 (HF)
6.05
4.52
4.17
3.64
46.3
62.0
67.2
77.0
◦
peak of 40 of Pt (1 1 1) was only calculated using the Lorentzian.
The surface area (SA) platinum of the catalyst can be calculated,
assuming homogeneously distributed and spherical particles, by
the following equation:
4
ꢃr2
6 × 000
SA =
=
(3)
ꢄ × (4/3)ꢃr3
ꢄd
2
−1
The surface area of platinum (m g ) can be calculated from
the surface area of a spherical particle (4ꢃr ) over the mass of a
2
Fig. 4. XPS spectra for (a) Pt4f peak and (b) Ti2p peak of the various Pt/TiO2 samples.
The insert is a plot of XPS spectrum of the Ti2p photoemission from Pt/TiO2 (HF).
3
spherical particle (ꢄ × 4/3ꢃr ). d (d = 2r) is the average particle size
of the platinum from the Eq. (2) and ꢄ is the density of Pt particles
−
3
using Scherrer’s equation from the full-width half-maximum of the
Pt (1 1 1) peak:
(21.4 g cm ) [32,33]. Table 2 shows the average particle size of
Pt and the surface area of Pt. It was identified through the XRD
data that the platinum nanoparticles of the additive-treated TiO2
samples were smaller, and the surface area was higher, than Pt/TiO2
kꢀ
d(Å ) =
(2)
ˇ cos ꢁ
(
non) samples. Notably, Pt/TiO (HF) had the smallest size of Pt and
2
where d is the average particle size (Å), k is the shape-sensitive coef-
ficient (0.9), ꢀ is the wavelength of radiation used (1.54056 Å), ˇ is
the full-width half-maximum (in rad) of the peak, and ꢁ is the angle
at the position of peak maximum (in rad). All the diffraction peaks
the largest surface area among the additive treated samples.
Cyclic voltammograms were employed to obtain the electro-
chemical surface area (ECSA) of Pt/TiO2 electrocatalysts. Fig. 6
shows CV obtained in N -saturated 0.1 M HClO4 at a scan rate of
2
◦
◦
overlapped between 40 of Pt (1 1 1) and 41 of TiO2 (1 1 1). The
Table 1
Distribution of Ti species and relative intensities in Pt/TiO2 samples.
Sample
Assigned
Binding
Relative
chemical state
energy (eV)
intensity (%)
Pt/TiO2 (non)
Ti(IV)
Ti(III)
Ti(II)
458.22
456.3
–
36.4
30.2
–
Pt/TiO2 (urea)
Pt/TiO2 (thiourea)
Pt/TiO2 (HF)
Ti(IV)
Ti(III)
Ti(II)
458.3
457.17
454.36
33.1
15.8
17.7
Ti(IV)
Ti(III)
Ti(II)
458.18
456.71
454.38
41.9
12.5
12.3
Ti(IV)
Ti(III)
Ti(II)
458.06
456.48
454.38
32.5
23.5
10.7
Fig. 6. Cyclic voltammograms of the various Pt/TiO2 + carbon black electrocatalyst
in N2-saturated 0.1 M HClO4 solution at a scan rate of 20 mV/s.

3
632
D.-S. Kim et al. / Electrochimica Acta 55 (2010) 3628–3633
ꢀ
ꢀꢀ
Fig. 8. Polarization curves of Pt/TiO2 (HF) + carbon black electrocatalysts in oxygen-
saturated 0.1 M HClO4 solution at various rotating speeds from 100 to 2500 rpm
with a scan rate of 5 mV/s.
Fig. 7. Cyclic voltammograms of the Pt/TiO2 (urea) + carbon black. Q and Q repre-
sent the amount of charge exchanged during the electro-adsorption and desorption
of H2 on Pt sites. The gray-filled rectangular area is an estimate of the charge con-
tribution from Pt double-layer charging and the capacitance of the support.
The measured electrode current densities at different constant
potentials were applied to the Koutecky–Levich plot. Fig. 9(b) rep-
2
0 mV/s for the different additives used in the Pt/TiO samples. In
2
−
1
resents the inverse current (j ) as a function of the inverse of
this study, we used carbon black as conductor materials because,
although the band gap of TiO was decreased by shape change, the
−
1/2
the square root of the rotation rate (ω
); i.e., the so-called
2
Koutecky–Levich plot [36]:
electronic conductivity was still insufficient to apply to electrocat-
alyst supports. The columbic charge for hydrogen desorption (QH)
was used to calculate the active surface of the electrode. Among
the samples, the CV of Pt/TiO2 (urea) + carbon black are represen-
tatively shown in Fig. 7. The value of QH was calculated by taking
the mean value between the amounts of charge exchanged dur-
1
J
1
JK
1
1
JK
1
=
+ J
=
+
(5)
Bω1/2
diff
ꢀ
ꢀꢀ
ing the electro-adsorption (Q ) and desorption (Q ) of H on the
2
platinum sites [34]. The gray-filled rectangular area, which is an
estimate of the charge contribution from Pt double-layer charging
and the capacitance of the support, was evaluated for every sample,
as shown in Fig. 7.
ꢀ
ꢀꢀ
The charges of Q , Q , QH and ECSA are summarized in Table 3.
The ECSA was calculated as follows [33]:
QH
ECSA =
(4)
[
Pt] × 0.21
where [Pt] is the platinum loading (25.48 ␮g cm−2) in the electrode,
−
2
QH is the charge for the hydrogen desorption (mC cm ), and 0.21
−
mC cm ) is the charge required to oxidize a monolayer of H on
2
2
(
platinum [35]. Additive-treated TiO2 samples, especially Pt/TiO2
HF), showed the better ECSA because of the high dispersion of Pt
(
particles compared to Pt/TiO (non), as can be also identified in TEM
2
images (Fig. 1).
To estimate the electrocatalytic activity for ORR, TF-RDE tech-
nique was adopted. Fig. 8 shows polarization curves of Pt/TiO2
(
HF) + carbon black electrocatalysts in oxygen-saturated 0.1 M
HClO4 solution at various rotating speeds from 100 to 2500 rpm
with a scan rate of 5 mV/s. As can be seen in Fig. 9(a), Pt/TiO (HF)
2
demonstrated the best ORR activity, while other samples showed
insufficient performance to apply them to cathode electrocatalysts.
This is because only HF treated TiO2 supports have an improved
electronic characteristics on the surface due to the narrowed band
gap. It is interesting to note that the order of ORR activity in
various samples is in accordance with the band gap narrowing,
in the following sequence: Pt/TiO2 (non) + carbon black < Pt/TiO2
(
(
urea) + carbon black < Pt/TiO2 (thiourea) + carbon black < Pt/TiO2
HF) + carbon black. Therefore, the most important factor to decide
Fig. 9. ORR (a) of the various Pt/TiO2 + carbon black electrocatalysts in oxygen-
saturated 0.1 M HClO4 solution at a rotating speed of 1600 rpm and scan rate of
the ORR activity for electrocatalysts supported on oxide semicon-
ductor materials is the surface electronic characteristics of supports
which is determined by the band gap.
5
mV/s. Koutecky–Levich plots (b) for ORR on the various Pt/TiO2 + carbon black
electrocatalysts at 0.4 V.

D.-S. Kim et al. / Electrochimica Acta 55 (2010) 3628–3633
3633
Table 3
Hydrogen adsorption and desorption charges, mean values, and electrochemical active surface (EAS) for different additives used.
ꢀ
−2
ꢀꢀ
−2
−2
−1
EAS (m2
g )
−1
Catalyst
Q (mC cm
)
Q
(mC cm
)
QH (mC cm
)
QH/[Pt] (mC mg
)
Pt/TiO2 (non)
Pt/TiO2 (urea)
Pt/TiO2 (thiourea)
Pt/TiO2 (HF)
5.292
12.70
8.076
17.06
1.609
5.357
2.695
9.720
3.451
9.029
5.386
13.39
135.4
354.4
211.4
525.5
664.8
1686
1007
2502
in which
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Pt/TiO2 (HF) with carbon black were found to be 2.73, 3.04, 3.24,
and 3.33 respectively. We can therefore conclude that the addi-
tive treatment of TiO , especially HF-treatment, leads to more facile
[
[
2
kinetics closed to the four electron ORR pathway by decreasing the
band gap and the higher ECSA of Pt nanoparticles. The absolute
value of transferred electron, namely, ORR kinetics is however still
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2
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4
. Conclusions
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Although the oxide materials are considered as alternative sup-
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intrinsic semiconductor properties are the hurdle to apply them
to actual electrocatalyst supports. To solve this problem, we intro-
duced a unique method to decrease band gap by shape control
using hydrothermal treatment with various additives. The additive-
treated TiO2 supports affected the size and the dispersion of Pt
particles, and changed the surface area, which could be identified by
TEM, XRD, and CV. Pt electrocatalysts supported on HF-treated TiO2
exhibited the highly enhanced ORR activity compared to the other
samples because of the narrowed band gap based on the existence
of Ti2+ and Ti which act as a donor. The HF treatment is there-
fore one of promising approach which enables us to employ TiO2
as electrocatalyst supports by improving electronic characteristics.
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Acknowledgment
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This work was supported by the Korea Research Foundation
Grant (KRF-2008-331-D00094) funded by the Korean Government
[
(
MOEHRD) and the second phase of the Brain Korea 21 Program in
008.
2