This document describes a study on the effects of platinum (Pt) doping on the photoelectrochemical performance of nanostructured alpha-iron oxide (α-Fe2O3) thin films deposited via electrodeposition. Un-doped and Pt-doped α-Fe2O3 thin films were characterized using various techniques. The results showed that Pt doping increased the density of small nanoparticles in the films and enhanced the photocurrent density for water splitting by up to a factor of 1.4 compared to un-doped films. The highest photocurrent density of 0.56 mA/cm2 was achieved for a 3% Pt-doped film. Electrochemical impedance analysis also revealed that Pt d

1. Electrodeposited nanostructured a-Fe2O3 thin films for solar water splitting:
Influence of Pt doping on photoelectrochemical performance
Gul Rahman a,b
, Oh-Shim Joo a,*
a
Clean Energy Research Center, Korea Institute of Science and Technology (KIST), Seongbuk-gu, Seoul 130-650, Republic of Korea
b
School of Science, University of Science and Technology, 52 Eoeun dong, Yuseong-gu, Daejeon 305-333, Republic of Korea
h i g h l i g h t s
Un-doped and Pt doped a-Fe2O3 thin films were synthesized by simple electrodeposition.
The surface morphology of a-Fe2O3 thin films changed with Pt % in the film.
A high photocurrent for water splitting was observed on Pt doped films.
Pt doping also enhanced the catalytic activity of a-Fe2O3 thin films for water oxidation.
a r t i c l e i n f o
Article history:
Received 19 April 2012
Received in revised form
26 February 2013
Accepted 15 March 2013
Keywords:
Semiconductors
Electrochemical techniques
Nanostructures
Thin films
Electrochemical properties
a b s t r a c t
Electrochemically deposited a-Fe2O3 thin films, whose composition was tuned by Pt doping, were
investigated as photoanode for photoelectrochemical water splitting. Morphological and structural
characteristics of the nanostructured a-Fe2O3 thin films were studied by scanning electron microscopy
and X-ray diffraction techniques. The films were characterized by Raman spectroscopy and X-ray
photoelectron spectroscopy to determine the effect of Pt doping on the a-Fe2O3 structure. The photo-
electrochemical performance of the films was examined by linear sweep voltammetry and electro-
chemical impedance spectroscopy. Results of these studies showed that Pt doping increased the density
of small-sized nanoparticles in a-Fe2O3 thin films. The Pt doped films exhibited higher photo-
electrochemical activity by a factor of 1.4 over un-doped a-Fe2O3 films. The highest photocurrent density
of 0.56 mA cmÀ2
was registered for 3% pt doped film at 0.4 V versus Ag/AgCl in 1 M NaOH electrolyte and
under standard illumination conditions (AM 1.5 G, 100 mW cmÀ2
). This high photoactivity can be
attributed to the high active surface area and increased donor density caused by Pt doping in the film.
Electrochemical impedance analysis also revealed significantly low charge transfer resistance of Pt doped
films, indicating its superior electrocatalytic activity for water splitting reaction compared to un-doped
a-Fe2O3 thin films.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
In the search of new sources to cope with energy crisis related to
fossil fuels, efficient storage of solar energy in the form of hydrogen
using cost effective and stable semiconductor material, has been a
subject of interest since 1972 [1]. Metal oxide semiconductors such
as TiO2, WO3, ZnO, BiVO4, and a-Fe2O3 have been investigated
extensively for photoelectrochemical (PEC) water splitting [2e10].
Among them, a-Fe2O3 is a promising material for water oxidation
with suitable bandgap (Eg w 2.1 eV), stability in aqueous solution,
ample abundance, non-toxic and environmentally friendly [9,11e
13]. However, the practical use of this material is limited by
several problems such as low electron mobility (w10À2
cm2
VÀ1
sÀ1
)
[14,15], short hole-diffusion length (w2e4 nm) [16], low absorption
coefficient due to the indirect bandgap and short life time of charge
carriers (w10 ps) [17]. Also, the conduction band edge of hematite
does not straddle the reversible hydrogen potential and require high
overpotential (external bias) for water reduction [18].
More challenges with the use of a-Fe2O3 photoelectrode for
efficient water splitting are its slow water oxidation kinetics and
poor charge transport properties [12,13,19]. Significant improve-
ments have been achieved by many research groups to elevate the
slow rate of water oxidation by applying water oxidation catalysts
such as oxides of Ru, Ir, and cobalt [20e22]. For instance, the surface
* Corresponding author. Tel.: þ82 2 958 5215; fax: þ82 2 958 5807.
E-mail addresses: joocat61@gmail.com, joocat@kist.re.kr (O.-S. Joo).
Contents lists available at SciVerse ScienceDirect
Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
0254-0584/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.matchemphys.2013.03.042
Materials Chemistry and Physics 140 (2013) 316e322

2. modification of a-Fe2O3 with IrO2 was reported to remarkably in-
crease the rate of oxygen evolution reaction and overall water
splitting efficiency [21]. The poor charge transport properties of a-
Fe2O3 can be enhanced by improving the quality of nanostructures
(crystallinity, crystallographic orientation) and by changing the
composition of film by doping. Several research groups have
focused their research on hematite thin films to improve the low
electronic conductivity by tuning the composition (e.g., doping)
[23]. Both metals and non-metals have been utilized as dopants to
enhance the carrier density and hence the conductivity of a-Fe2O3
[18,23,24].
Nanostructured hematites have been synthesized by several
techniques, including hydrothermal synthesis [13,25], spray py-
rolysis [11,26], colloidal and magnetite colloidal solution ap-
proaches [27], atomic layer deposition (ALD) [28], atmospheric
pressure chemical vapor deposition (APCVD) [29], and electro-
chemical methods [30]. Hematite films prepared by APCVD, ALD
and magnetite colloidal solution methods have shown particularly
promising results. However, these approaches require a special
instrument configuration or the use of toxic organic solvents and
metaleorganic precursors.
In this study, we demonstrated the use of cathodic electrode-
position to synthesize Pt doped nanostructured a-Fe2O3 thin films.
This method is cost-effective and safe, and it can be performed with
a simple apparatus. The size, film thickness, and morphology of the
a-Fe2O3 nanoparticles can be tailored by simply tuning the depo-
sition conditions. McFarland co-workers have extensively utilized
electrodeposition technique to synthesize doped a-Fe2O3 films and
studied the effect of doping on the photoactivity and overall PEC
performance of a-Fe2O3 [8,30]. In their particular studies of Pt
doped a-Fe2O3 films [30], no evidence of enhanced electrocatalytic
activity was observed due to the dopant. Herein, we found that Pt
doping not only elevate the photoactivity of a-Fe2O3 by improving
the charge transport properties, but also significantly decreases the
charge transfer resistance of the film for water oxidation and hence,
improve its electrocatalytic activity. A thorough investigation of the
physical and photoelectrochemical properties of un-doped and Pt
doped electrochemically deposited a-Fe2O3 thin films is presented
in this study.
2. Experimental
2.1. Synthesis of a-Fe2O3 thin films
Nanostructured a-Fe2O3 thin films were obtained after anneal-
ing of the electrochemically deposited iron films on a fluorine-
doped tin oxide (FTO, TEC 8, Pilkington glass) glass substrate. The
electrodeposition bath consisted of an aqueous solution of 10 mM
iron(II) sulfate heptahydrate (FeSO4$7H2O, Samchun, 98e102%). For
Pt doped films, H2PtCl6. 5.7(H2O) was added into deposition bath
ranging from 1 to 5 wt. % of Pt/(Pt þ Fe). For the electrodeposition of
the hematite films, a typical three-electrode electrochemical cell
was used that comprised the FTO substrate (1 cm  1.5 cm), plat-
inum (2 cm  2 cm) and Ag/AgCl/NaCl (3 M) as the working,
counter and reference electrodes, respectively. The FTO substrate
was ultrasonically pre-cleaned by sequential rinses with acetone,
distilled water and isopropanol. The cell was connected to a
potentiostat (IviumStat technologies, Netherlands) that was used
for iron oxide film preparation and other electrochemical mea-
surements. Iron films were deposited on the FTO substrate from an
iron precursor solution by applying a constant potential of À1.0 V
(versus Ag/AgCl electrode) for 10 min. After each deposition, the
film was thoroughly rinsed with de-ionized water and then dried
with a gentle stream of argon. To obtain crystalline nanostructures,
the as-deposited films were annealed at 700 C (reached at a rate of
2 C minÀ1
) for 2 h in air to obtain highly activated a-Fe2O3
nanostructures.
2.2. Structural and morphological characterization
Scanning electron microscopy images were collected with a field
emission scanning electron microscope (NOVA NanoSEM200- FEI
Company). The crystalline phases were identified by XRD (XRD-6000,
Shimadzu, Japan) with Ka radiations (l ¼ 1.542 A). Diffraction pat-
terns were recorded from 20 to 80 2q with a sampling pitch of 0.020.
The phase analysis was additionally performed using Raman
Microscope (Nicolet ALMEGA XR Dispersive Raman). The laser
beam (l ¼ 633 nm) was focused on the sample by a lens to produce
a spot. The spectra were measured from 100 to 2000 cmÀ1
in 10 s
acquisition times.
2.3. X-ray photoelectron spectroscopy (XPS)
XPS spectra of the film were acquired with PHI 5000 VersaProbe
(Ulvac-PHI) under high vacuum condition (6.8 Â 10À8
pa), using a
monochromatic Al Ka X-ray source (1486.6 eV). The data were
collected from a spot size of 100 mm  100 mm. Carbon 1s peak
(284.6 eV) was used for internal calibration.
2.4. Photoelectrochemical characterization
The photoelectrochemical characterization of the a-Fe2O3 was
performed using an IviumStat potentiostat with a three-electrode
configuration: a working electrode (the hematite film), a
platinum-wire counter electrode and an Ag/AgCl (in 3 M NaCl)
reference electrode. A copper wire was soldered on the exposed
portion of the FTO substrate (to establish a connection), and an
epoxy resin was used to seal all exposed portions of the FTO except
for the well-defined working area of the hematite electrodes. For
photocurrent measurements, the electrodes were immersed in a
solution of 1 M NaOH (pH 13.6). The hematite electrode was
scanned from À400 to 700 mV (versus Ag/AgCl electrode) at a rate
of 50 mV sÀ1
. The samples were illuminated from the front side
with simulated sunlight from a 150 W short-arc xenon lamp
(Portable solar simulator, PEC-L01) equipped with an air mass filter
(A.M. 1.5 G) with a corrected intensity of 1 sun (100 mW cmÀ2
) at
the sample surface. The electrolyte was purged with nitrogen gas
before the experiments to prevent any possible reaction with dis-
solved oxygen at the counter electrode.
2.5. Electrochemical impedance spectroscopy (EIS)
Electrochemical impedance spectroscopy (EIS) was performed
in 1 M NaOH using an IviumStat with a three-electrode configu-
ration. A sinusoidal perturbation with an amplitude of 10 mV and
frequencies ranging from 100 kHz to 10 Hz was superimposed on a
bias voltage ranging from À200 to 400 mV (versus Ag/AgCl elec-
trode). EIS was performed in the dark, and a Nyquist plot was
constructed to simulate the equivalent circuit to obtain the space
charge layer capacitance of the a-Fe2O3 thin films.
3. Results and discussions
3.1. SEM analysis
Top-view scanning electron microscopy images of the un-doped
and different wt.% Pt doped a-Fe2O3 thin films are shown in panel
aee of Fig. 1. The un-doped film (image a) shows vertically grown
segregated islands of nanostructures made up of small nano-
particles. These islands are separated by empty channels. Inset to
G. Rahman, O.-S. Joo / Materials Chemistry and Physics 140 (2013) 316e322 317

3. image (a) shows the cross sectional SEM image of the un-doped
film whose thickness was estimated w250 nm. The morphology
of 1 and 2% Pt doped films did not show significant variation as
compared to un-doped a-Fe2O3 film. However, further increase in
Pt amount changed the surface morphology of Fe2O3 deposits.
Image (d) shows the surface morphology of 3% Pt doped film in
which the particles are regularly distributed with average diameter
of w100 nm. The segregated islands consisted of small-sized
nanoparticles seems to be separated from each other. The film
appeared more dense and uniform than that of un-doped film. A
similar but less prominent effect was observed in 5% Pt doped film
as shown by image (e). These results predict that Pt doping controls
the growth mechanism during cathodic electrodeposition of a-
Fe2O3 thin films and affects the size and overall morphology of
nanostructures.
3.2. Structural and chemical analysis
The XRD patterns of high temperature annealed un-doped and
Pt doped a-Fe2O3 thin films are presented in Fig. 2. Results show the
presence of two representative peaks of a-Fe2O3 for (104) and (110)
planes respectively (consistent with the powder standards (PDF #
01-089-0599)). The intensities of these peaks indicate the presence
of well-crystalline hematite phase. The intensity of (104) peak
which is slightly larger than (110) peak, indicate that the most
conductive plane (001) of the a-Fe2O3 is not aligned vertically to
FTO substrate [27]. When Pt was introduced in the film, no signif-
icant change was observed in the position and intensity of a-Fe2O3
representative peaks. However, a detectable peak broadening was
seen in 5% Pt doped film. As shown in SEM image, 5% doped film
contained small-sized nanoparticles on its surface. The observed
Fig. 1. SEM images of un-doped and Pt doped a-Fe2O3 films; (a) un-doped film, (b) 1% Pt, (c) 2% Pt, (d) 3% Pt, and (e) 5% Pt.
G. Rahman, O.-S. Joo / Materials Chemistry and Physics 140 (2013) 316e322318

4. peak broadening could therefore be related to these small nano-
particles caused by Pt doping in a-Fe2O3 thin films.
To investigate the effect of Pt doping on the crystal phases of a-
Fe2O3 thin films, the samples were analyzed by Raman spectros-
copy. Fig. 3 shows the Raman spectra of the un-doped and Pt-doped
a-Fe2O3 thin films. The spectra exhibited typical bands of a-Fe2O3
phase, showing peaks at 224, 243, 292, 409, 495, and 610 cmÀ1
and
matched well with the reported Raman data for hematite [31]. The
band around 660 cmÀ1
was observed in all samples, which was
attributed to presence of Fe3O4 or disorder phase within the Fe2O3
crystal lattice [32]. The intensity of this peak was observed to in-
crease with Pt concentration which could be attributed to the
change in the surface structure and grain boundary disorder of a-
Fe2O3 as previously described [31]. This result agrees well with the
Pt and Ti doped hematite thin films [30,33].
The chemical composition of the un-doped and Pt-doped a-
Fe2O3 films was investigated using X-ray photoelectron
spectroscopy (XPS). The Fe 2p spectra (Fig. 4(A)) of un-doped and
5 wt.% Pt-doped films exhibited the typical 2p1/2 and 2p3/2 peaks of
Fe3þ
at w724.4 and 710.8 eV, respectively [34]. A characteristic
satellite peak was also observed at 718.8 eV, suggesting the a-Fe2O3
phase in both un-doped and Pt-doped films. Fig. 4(B) depicts the Pt
4f spectra obtained from the a-Fe2O3 films with 0 and 5 wt.% Pt. The
result revealed that Pt is in the form of Ptþ4
and not Pt0
as evi-
denced by the Pt 4f5/2 and 4f7/2 peaks at w78.0 and w74.0 eV [35].
The surface concentration of Pt calculated from XPS analysis
(Fig. 4(C)) was 0.04, 0.08, 0.11, and 0.29% for 1, 2, 3, and 5 wt. % Pt in
film deposition solution, respectively. The doped Pt concentration
is substantially smaller than in deposition solution which suggests
that a small amount of Pt is introduced in the lattice of a-Fe2O3. In
general, the Mþ4
substitution in hematite cause the reduction of
Feþ3
to Feþ2
due to the extra electron on dopant. However, no Feþ2
peaks were observed in the Fe 2p spectra of Pt doped films. This
may be because of the quite low amount of Pt in the films or high
oxidizing annealing conditions employed in our experiment.
3.3. Photoelectrochemical performance
The PEC performance of the a-Fe2O3 photoanode films was
studied in a 1 M NaOH solution using a three-electrode electro-
chemical cell connected to a potentiostat and a solar simulator. The
potentials were measured relative to the Ag/AgCl (3 M NaCl) elec-
trode. Fig. 5(A) depicts the currentepotential (IeV) curves of un-
doped and Pt doped a-Fe2O3 films in 1 M NaOH solution in the
dark and under illumination. In case of un-doped film, photocur-
rent onset at wÀ0.1 V and increased with applied potential until
w0.3 V. However, little change was observed above 0.3 V and the
current attained the shape of plateau that can be attributed to the
electron transport limitations in a-Fe2O3 thin films. Pt doped films
showed higher photoactivity than un-doped film. For instance, the
photocurrent density of un-doped film was 0.39 mA cmÀ2
at 0.4 V,
and 0.56 mA cmÀ2
for 3% Pt doped sample. This increase in
photocurrent is attributed to the increased Pt % as well as to greater
surface area of doped films. Positive shift of photocurrent onset
potential was observed for doped films from wÀ0.1 to 0.08 V
versus Ag/AgCl, compared to un-doped film. This positive shift in-
dicates the water oxidation kinetics is limited due to the increased
surface states as a result of increased surface area of Pt doped films.
The shift can be overcome by coupling Pt doped films with oxygen
evolving catalysts. Similar effect of dopant on the photocurrent
onset potential has been observed for other a-Fe2O3 films [11,25].
Another important observation was the change of dark current
with Pt doping of a-Fe2O3 thin films. Fig. 5(B) illustrates the
extended form of dark curves of un-doped and Pt doped films. The
onset potential of dark current decreases significantly with Pt
doping which indicate that the overpotential required for water
oxidation is reduced on Pt doped films. A maximum of w100 mV
reduction of overpotential was observed on 5% Pt doped film over
un-doped film. Such a reduction in overpotential of water oxidation
means that the Pt doped film surface became more catalytic for
oxygen evolution than the un-doped a-Fe2O3 film surface. This
could be related to the high active surface area of Pt doped films
which contain small-sized nanoparticles as compared to the un-
doped film (shown by SEM analysis).
3.4. EIS analysis
To obtain a better understanding of the charge transport prop-
erties of un-doped and Pt doped films, electrochemical impedance
measurements were performed. According to the depletion layer
model, the semiconductor space charge layer capacitance (C)
Fig. 3. Raman spectra of un-doped and Pt-doped a-Fe2O3 films; (a) un-doped film, (b)
1% Pt, (c) 2% Pt, (d) 3% Pt, and (e) 5% Pt.
Fig. 2. XRD patterns of un-doped and Pt doped a-Fe2O3 films; (a) un-doped film, (b) 1%
Pt, (c) 2% Pt, (d) 3% Pt, and (e) 5% Pt. The representative peaks of a-Fe2O3 are designated
by asterisk (*).
G. Rahman, O.-S. Joo / Materials Chemistry and Physics 140 (2013) 316e322 319

5. depends on the applied potential (V) and is given by the Motte
Schottky equation:
1=C2
¼
2=εrεoeND
V À Vfb À kBT=e
;
where εr is the dielectric constant of the semiconductor (εr ¼ 80
for hematite), εo is the vacuum permittivity, e is the charge of the
electron, ND is the donor density, Vfb is the flat band potential, kB
is the Boltzmann constant and T is the absolute temperature. The
MotteSchottky plots were generated from the capacitance values
measured at 10 kHz in the dark as shown by Fig. 6. The positive
slopes of the plot indicate the presence of a characteristic n-type
semiconductor and that electrons are the majority charge carriers
[23]. From the slopes of MotteSchottky plots, donor density was
calculated while the flat band potential was estimated from the
intercept of potential axis. These values are tabulated in Table 1.
The values of flat band potential of Pt doped films are more
positive compared to un-doped film and are in the range reported
for a-Fe2O3 [36]. Overall, these values are more cathodic than the
photocurrent onset potentials shown in Fig. 5(A). This difference
in flat band potentials and photocurrent onset potentials is
mainly attributed to a high electronehole recombination as a
result of surface states [33]. From the slope of MotteSchottky
plots, a donor density of 7.9 Â 1018
cmÀ3
was calculated for un-
doped film which is increased up to 9.8 Â 1018
cmÀ3
for 5% Pt
doped film. These results provide direct evidence to support that
the Pt doping serve as electron donor and the donor density
increased with Pt doping in a-Fe2O3 due to the substitution of
Feþ3
by Ptþ4
in the hematite lattice. The increased donor density
causes shrinking of the space-charge layer width and,
consequently, strengthen the electric field near the film electro-
lyte interface. The separation and transport of electrons and holes
are thus enhanced, thereby improving the photoelectrochemical
performance of the film. To investigate it further, the Debye
length of un-doped and Pt doped films was calculated using the
formula:
LD ¼
εoεrkBT=2e2
ND
1=2
where LD is the Debye length, εr is the dielectric constant of the
semiconductor, εo is the vacuum permittivity, e is the charge of the
electron, ND is the donor density, kB is the Boltzmann constant and T
is the absolute temperature. According to the Schottky barrier
model, the transit time through the depletion layer is proportional
to the square of the Debye length [37]. As can be seen in Table 1, a
higher Pt concentration corresponds to a shorter Debye length,
which would decrease the transit time and be helpful for electrone
hole separation, thus a higher photocurrent can be expected [38].
However, we noted that increasing the Pt concentration more than
3% did not improve the photocurrent significantly. This could be
attributed to the fact that a narrower depletion layer is deleterious
for suppressing the recombination rate. These observations
together suggest that the strategy of doping hematite should be
to include appropriate amount of dopant in the structure to
balance the competing effects between charge separation and
recombination.
Furthermore, the water oxidation kinetics at the a-Fe2O3 film/
electrolyte interface was investigated by constructing Nyquist plots
of the photoanodes at 0.75 V in the dark. The Nyquist plots of un-
doped and Pt doped a-Fe2O3 thin films and fitted curves are
Fig. 4. X-ray photoelectron spectra of: (A) Fe 2p and (B) Pt 4f recorded from un-doped and 5% Pt-doped a-Fe2O3 films (C). Atomic % of Pt in the deposited film measured by XPS
analysis.
G. Rahman, O.-S. Joo / Materials Chemistry and Physics 140 (2013) 316e322320

6. shown in Fig. 7. The symbols represent the experimental results,
and the solid lines are the fitting results of the calculated data. Inset
to the figure shows the corresponding equivalent circuit and the
fitting results are summarized in Table 2. For all films, semi-circle
shaped Nyquist plots were obtained. The equivalent circuit repre-
sents solution resistance (Rs), a-Fe2O3 film/electrolyte interface
resistance (Rct) and its corresponding capacitive counterpart
(CPEct). The lower resistance and higher constant phase element
values represent better charge transport at a-Fe2O3 film/electrolyte
interface. According to the fitting results in Table 2, Pt doping
causes great difference in charge transfer resistance of a-Fe2O3
films. Un-doped film showed high charge transfer resistance to
water oxidation reaction but as the Pt % increased in the film, a
significant decline was observed. The lowest Rct observed was
43.85 U for 5% Pt doped film which is w4.2 fold smaller than un-
doped film (Rct ¼ 183.7 U). Such a lower charge transfer resis-
tance is attributed to the high active surface area of Pt doped films
Fig. 5. (A) Current vs. potential curves of un-doped and Pt doped a-Fe2O3 films; (a) un-
doped film, (b) 1% Pt, (c) 2% Pt, (d) 3% Pt, and (e) 5% Pt. The photocurrent was measured
under standard illumination conditions (AM 1.5 G 100 mW cmÀ2
). (B) Extended form
of dark currents of (A).
Fig. 6. MotteSchottky plots of un-doped and Pt doped a-Fe2O3 films analyzed in the
dark; (a) un-doped film, (b) 1% Pt, (c) 2% Pt, (d) 3% Pt, and (e) 5% Pt. The electro-
chemical impedance analysis was performed in 1 M NaOH, and the MotteSchottky
analysis was performed at 10 kHz.
Table 1
Various parameters obtained from MotteSchottky plots of un-doped and Pt doped
a-Fe2O3 films analyzed in the dark.
Electrode Donor density
(ND)/E18.cmÀ3
Flat band
potential (Vfb)/V
Debye
length LD/nm
Un-doped 7.9 À0.66 2.67
1% Pt 3.9 À0.46 3.80
2% Pt 8.7 À0.55 2.55
3% Pt 9.2 À0.47 2.48
5% Pt 9.8 À0.56 2.40
Fig. 7. Nyquist plots un-doped and Pt doped a-Fe2O3 films showing the imaginary
versus the real component of the impedance at À0.75 vs Ag/AgCl and the fitted plots
obtained in the dark.
Table 2
Equivalent circuit parameters obtained from fitting of Nyquist plots of un-doped and
Pt doped a-Fe2O3 films.
Electrode RS/U Rct/U CPEct/F
Un-doped 30.41 183.7 4.218E-5
1% Pt 27.3 151.1 4.247E-5
2% Pt 26.32 122.0 3.760E-5
3% Pt 31.56 66.96 7.030E-5
5% Pt 25.3 43.85 3.405E-6
G. Rahman, O.-S. Joo / Materials Chemistry and Physics 140 (2013) 316e322 321

7. that catalyze water oxidation effectively. The value of constant
phase element also increased significantly for 3 and 5% doped film,
indicating yet again the better electrocatalytic activity of Pt doped
a-Fe2O3 films over un-doped film.
4. Conclusions
In summary, a-Fe2O3 thin films were prepared and doped with
Pt using cathodic electrodeposition. SEM analysis showed that Pt
doping changed the surface morphology of a-Fe2O3 films by
reducing the size and increasing the particle density. These small-
sized nanoparticles exhibited high photocurrent and overall PEC
performance. Electrochemical impedance spectroscopy revealed
that Pt doped films have higher donor density than that of un-
doped film which is responsible for high photoactivity. Moreover,
a significantly low charge transfer resistance was observed for
water oxidation on Pt doped a-Fe2O3 films, indicating its potential
for photoelectrochemical applications.
Acknowledgments
The authors gratefully acknowledge financial support from the
Ministry of Science and Technology of Korea that supported the
research at the Hydrogen R D Center, which is a 21st Century
Frontier R D program. The authors also acknowledge the research
program of the Korea Institute of Science and Technology (KIST).
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