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Applied Surface Science 397 (2017) 112–118

Contents lists available at ScienceDirect

Applied Surface Science

journa l h om epa ge: www.elsev ier .com/ locate /apsusc

ull Length Article

ne-dimensional Fe2O3/TiO2 photoelectrode and investigation of itshotoelectric properties in photoelectrochemical cell

i-Ming Song, Xin Zhou, Chunxue Yuan, Yu Zhang ∗, Qiang Tong, Ying Li, Luxia Cui,aliang Liu, Wei Zhang

iaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang10036, China

r t i c l e i n f o

rticle history:eceived 17 October 2016eceived in revised form8 November 2016ccepted 19 November 2016vailable online 19 November 2016

a b s t r a c t

We reported a novel Fe2O3/rutile TiO2 nanorod (NR) arrays with the heterogeneous structure for pho-toelectrochemical (PEC) cells, which were fabricated on fluorine-doped tin oxide glass (FTO) substratesthat serve as model architecture via a hydrothermal method. Fe2O3 was revealed as an inexpensive andeco-friendly semiconductor sensitizer to make TiO2 respond to visible light. By using this photoanode,the photoelectric conversion and water splitting properties of PEC cells based on the one-dimensional

eywords:e2O3/TiO2 photoelectrodehotoelectrochemical celleterogeneous structurehotocurrentand structure

(1D) Fe2O3/TiO2 heterostructures were investigated in detail under simulated sunlight. Meanwhile, theoptimization of photovoltaic performance was also achieved by regulating the amount of Fe2O3. The opencircuit voltage and short circuit current of the Fe2O3/TiO2 solar cell can reach 0.435 V and 1.840 mA/cm2,respectively. In addition, theoretical analysis of the photoelectric effect is preliminarily explored on thebasis of the flat band potential results.

© 2016 Elsevier B.V. All rights reserved.

. Introduction

Photoelectrochemical (PEC) cells have attracted increasingttention due to their promising applications for solar cells andater splitting [1–3]. The conventional PEC cell consists of a semi-

onductor photoanode, a redox electrolyte, and a counter electrode.he semiconductors such as TiO2, SrTiO3 and ZnO usually serves charge transport materials in photoanodes [4–6], due to theirong lifetime and large diffusion coefficient of the photogener-ted charge carriers, nevertheless, the visible light can not be usedufficiently in the photoanodes because of their wide band gap.herefore, materials with narrow band gap such as organic dye7,8], chalcogenide quantum dots (CdS [9–11], CuInS2 [12], Ag2S13] etc) have been used to sensitize these wide-band gap materi-ls. However, their poor stability and high costs greatly limit theirurther application. One method to solve these problems is directlysing narrow-band gap material. For example, Bian and co-workers

ave used graphitic carbon nitride as visible-light-driven photo-lectrode materials for PEC cells [14–17].

∗ Corresponding author.E-mail address: zhangy@lnu.edu.cn (Y. Zhang).

ttp://dx.doi.org/10.1016/j.apsusc.2016.11.143169-4332/© 2016 Elsevier B.V. All rights reserved.

�-Fe2O3, a common semiconductor with a narrow-band gap of2.1 eV, has demonstrated promising industrial applications becauseof its easy fabrication, good chemical resistance under causticoperating conditions, low cost and nontoxic nature [18–21]. Butsingle �-Fe2O3 photoanode has been limited due to the shortlifetime of photogenerated charge carriers, poor oxygen evo-lution reaction (OER) kinetics and short hole diffusion length[22–25]. Thus, semiconductor nanocomposites of �-Fe2O3 havebeen intensively investigated due to their good charge separa-tion based on the interfacial heterogeneous structure. Wang et al.demonstrated mesoporous Fe2O3/TiO2 heterostructured photo-catalyst with strong optical absorption and enhanced catalyticactivity. Fe2O3/TiO2 heterostructured microsphere demonstrateshighly visible light photoactivity because of their high electron-hole separation efficiency and mesoporous microsphere structure[26]. Zhang et al. prepared one-dimensional (1D) mesoporousFe2O3@TiO2 core-shell photocatalyst, which possesses the com-bined advantages, thus delivering clearly enhanced photocatalyticactivity for Rhodamine B under visible light irradiation and thedegradation of methyl orange under UV light irradiation [27]. Yao

et al. prepared Fe2O3-TiO2 core-shell nanorod arrays by using theglancing angle deposition technique and post-deposition anneal-ing, and showed higher catalytic efficiency for the degradation ofmethylene blue (MB) and greater efficiency for solar CO2 conver-

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X.-M. Song et al. / Applied Su

ion under visible light illumination when compared with purenatase TiO2 or �-Fe2O3 nanorod arrays [28]. Recently, Jing ando-workers confirmed that the promoted charge separation resultsrom the uncommon transfers of visible-excited high-energy elec-rons of Fe2O3 to rutile TiO2. Moreover, it is more favorable forhe uncommon electron transfers of �-Fe2O3 to rutile than tonatase, depending on the conduction band bottom level of TiO229]. Therefore, the high photocatalytic activities indicate stronghotogenerated charges separation exist in the Fe2O3-TiO2 het-rostructure. It is easily expected that Fe2O3 is a promising materialor sensitizer to form heterostructures with TiO2. However, previ-us studies have mainly focused on the photocatalytic activities ofe2O3/TiO2 composites for the degradation of organic dyes. As far ase know, there are few reports on Fe2O3 as an effective sensitizers

n PEC cells for photoelectric conversion and water splitting.In the present study, we designed a novel one-dimensional

e2O3/TiO2 photoanode for solar cells and PEC water splitting,hich was fabricated with Fe2O3 grown onto 1D TiO2 nanorods via

hydrothermal method. The photoanode presents some favorableharacteristics, which are easy fabrication, excellent light scatterffect, environmental friendliness and low cost [30]. The growthf Fe2O3 nanorods can be controlled by increasing the concentra-ions of FeCl3 and NaNO3. By hydrothermal method, Fe2O3 and TiO2an be combined to form a heterogeneous structure, endowed withhe advantages of its specific structural features, which can bet-er utilize visible light and improve the photoelectric conversionerformance of single TiO2 and Fe2O3.

. Experimental section

.1. Synthesis of ˛-Fe2O3 film

Fe2O3 photoanode was fabricated via a hydrothermal method. fluorine-doped tin oxide glass (FTO, Nippon Sheet Glass) of.0 × 2.5 cm was fully cleaned with deionized water, ethanol, ace-one and ethyl acetate. The FTO was put into a fresh aqueousolution of 0.03 M FeCl3 (99%, Aladdin) and 0.2 M NaNO3 (99%,inopharm Chemical Reagent Co., Ltd) in an autoclave with theingle conductive side facing the wall of the liner, then the auto-lave was placed in a regular laboratory oven and heated to 100 ◦Cor 12 h. After the reaction, the film formed on the FTO substratesas thoroughly rinsed with deionized water and annealed in air at

50 ◦C for 2 h at a ramp rate of 2 ◦C·min−1.

.2. Synthesis of pure TiO2 NR arrays

Pure TiO2 NR arrays were directly grown on FTO substrates20 ohm per square) via a hydrothermal method reported pre-iously. 15 mL of deionized water was mixed with 15 mL ofoncentrated hydrochloric acid (36–38%, Beijing Chemical Works).he mixture was stirred under ambient condition for 5 min. Then,.5 mL of tetrabutyl titanate (98+%, Aladdin) was added to the mix-ure and further stirred for 5 min. Then, 8 mL of the solution wasransferred to a Teflon-lined stainless steel autoclave (15 mL vol-me), where a cleaned FTO glass was placed in the Teflon reactorith the conductive side facing down. The hydrothermal synthesisas maintained at 150 ◦C for 20 h in a regular laboratory oven. After

he autoclave was cooled to room temperature, the FTO substrateith the TiO2 NR arrays were taken out, rinsed extensively witheionized water and allowed to dry in ambient air.

.3. Synthesis of Fe2O3/TiO2 nanocomposites

For the preparation of Fe2O3/TiO2 nanocomposites, an aqueousolution (10 mL) containing 0.03 M FeCl3 (99%, Aladdin) and 0.2 MaNO3 (99%, Sinopharm Chemical Reagent Co., Ltd) was sealed in a

cience 397 (2017) 112–118 113

15 mL Teflon-lined stainless steel autoclave. A FTO grown with TiO2was placed in the liner with the FTO side facing the wall of the liner.The liner was put into a self-sealing autoclave and heated at 100 ◦Cfor 12 h. After the reaction, the films formed on the FTO substrateswere thoroughly rinsed with deionized water and annealed in airat 550 ◦C for 2 h at a ramp rate of 2 ◦C · min−1. The amount of Fe2O3was regulated by increasing the concentrations of FeCl3 and NaNO3.2Fe2O3/TiO2 and 5Fe2O3/TiO2 mean 2 times and 5 times of initialconcentration of raw material, respectively.

2.4. Characterization

X-ray diffraction (XRD) patterns were characterized on a Bruker(Germany) D8 Advance diffractometer with Cu K� radiation in therange of 20◦−80◦ (2�). Field emission scanning electron microscopy(FESEM) images were determined by using a FESEM JSM-6700Fmicroscope. UV–vis diffuse reflectance spectroscopy (DRS) mea-surements were obtained on an UV–vis spectrometer (ShimadzuUV-2550) using BaSO4 as a reference standard. In photovoltaicmeasurements, the Fe2O3/TiO2 working electrodes together withplatinized conducting glasses serve as a prototype solar cell device.The current density-voltage (I–V) curves were recorded by an elec-trochemistry workgroup (CHI660E, Shanghai). A 500 W xenon lamp(CHFXQ500W, Beijing Trusttech Co. Ltd.) was used as the lightsource and a filter plate (simulated AM 1.5 sunlight, Beijing Trust-tech Co. Ltd.) was used to control the wavelength of light. Theoutput light intensity was about 100 mW/cm2, which was mea-sured with a radiometer (Photoelectronic Instrument Co., attachedto Beijing Normal University, China). The effective area of the solarcell is 0.25 cm2. The photocurrent density-time (I–t) curves werealso carried out using this photovoltaic measurement. The solarcells were directly tested in chopping mode, light on-off repeatedly.The photovoltage generated by the solar cells can result in strongphotocurrent and no applied bias was used. The flat band (FB)potentials of TiO2 and Fe2O3 were determined from Mott-Schottkyplots recorded by electrochemistry workgroup (CHI660E, Shang-hai). A three-electrode single compartment immersed in 0.5 MNa2SO4 solution was used for capacitance analysis. The as-preparedfilm on FTO was used as a working electrode while Ag/AgCl elec-trodes and platinum electrodes were used as reference electrodesand counter electrodes, respectively. The PEC water splitting mea-surements were recorded by electrochemistry workstation system(CHI660E, Shanghai) with a Xe lamp (CHFXM500, Beijing TrusttechCo. Ltd.) as light source under AM 1.5 optical filter (Beijing Trust-tech Co. Ltd.). A three-electrode configuration was used with thesamples on FTO as working electrode, Ag/AgCl reference electrodeand platinum counter electrode. The light intensity was calibratedto 100 mW/cm2.

3. Results and discussion

3.1. Structural studies

The XRD patterns of TiO2 NR arrays film, Fe2O3 film andFe2O3/TiO2 heterogeneous structure are depicted in Fig. 1. The crys-tal phase of the TiO2 NR arrays was a rutile phase with a tetragonalstructure (JCPDS 21–1276). The relatively high intensity of the (002)peak implies that the nanorods are well crystallized and orientedwith respect to the FTO substrate [31,32]. The data of Fe2O3 film canbe indexed to the characteristic peaks of �-Fe2O3 (JPCDS 86–0550),after subtracting the diffraction peaks originating from FTO. The

peak intensities of TiO2 in the composites are weak. This should becaused by the surface coating of the Fe2O3. Therefore �-Fe2O3 andTiO2 were successfully combined together, and the heterogeneousstructure was formed.

114 X.-M. Song et al. / Applied Surface S

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ig. 1. X-ray diffraction patterns of TiO2 NR arrays, Fe2O3 film and Fe2O3/TiO2 NRrrays films based on FTO glass.

Fig. 2 gives the FESEM images of TiO2 NR arrays, Fe2O3 film,e2O3/TiO2, 2Fe2O3/TiO2 and 5Fe2O3/TiO2 NR arrays, which wereynthesized by the procedures as Scheme 1. The insets in Fig. 2re the cross-sectional view of the samples. Fig. 2a shows typicalESEM images of the TiO2 NR arrays grown directly on the FTO sub-

trate. The nanorods containing many step edges are tetragonal inhape with an average diameter of 150–200 nm. The cross-sectionalmage indicates that the TiO2 nanorods grow perpendicularly to theTO substrate with a length of 3.5 �m [33]. As shown in Fig. 2b, sin-

ig. 2. FESEM images of top view and cross-sectional view (a) TiO2 NR arrays grown on a

rrays and (e) 5Fe2O3/TiO2 NR arrays, the scale bar in the insets is 2 �m.

Scheme 1. Proposed Growth Routes

cience 397 (2017) 112–118

gle Fe2O3 film has a dense surface layer with no special structure.The thickness of the film is about 800 nm. The FESEM images ofthe obtained Fe2O3/TiO2 heterogeneous structures with differentamounts of Fe2O3 are presented in Fig. 2c, d and e. In Fig. 2c, theaverage diameter of Fe2O3/TiO2 NR is 200–300 nm and the length isabout 4 �m, indicating Fe2O3 was coated on the outside of TiO2 NR,resulting in the larger average diameter. According to Fig. 2d, Fe2O3gradually filled in the gap of TiO2 NR arrays with the increasedamount of Fe2O3. When the amount of iron source continues toincrease, the thickness of the film reach 4.7 �m and Fe2O3 nanorodswere formed on the surface of TiO2 NR arrays as shown in Fig. 2e.This result is accordance with previous report that Fe2O3 nanorodscan be prepared with high concentration of iron source [34].

Fig. 3 shows UV–vis absorption reflectance spectroscopy of TiO2NR arrays, Fe2O3 film, Fe2O3/TiO2, 2Fe2O3/TiO2 and 5Fe2O3/TiO2NR arrays on FTO. It is known that absorption spectrum of a semi-conductor should be a wide band with a threshold based on itsband gap. According to the band gaps (Eg) of rutile TiO2 (3.0 eV), �-Fe2O3 (2.1 eV), the absorption threshold for TiO2 and Fe2O3 shouldbe about 413 nm and 590 nm, respectively. The thresholds of theabsorption spectrum of TiO2 (415 nm) and Fe2O3 (595 nm) in Fig. 3are really accordance with the band gap of rutile TiO2 and �-Fe2O3,respectively. In addition, the absorption threshold for Fe2O3/TiO2,2Fe2O3/TiO2 and 5Fe2O3/TiO2 NR arrays should be consistent withthat of Fe2O3 film, because Fe2O3 has relatively narrow band gapin the nanocomposites. So the absorption thresholds of the threenanocomposites are almost 590 nm (Fe2O3) as shown in the figure.

it is evident that a significant increase in the absorption intensityoccurred in three composites in the visible region. This result canalso be seen from the photos of the samples, where the colors of

FTO substrate, (b) a single Fe2O3 film, (c) Fe2O3/TiO2 NR arrays, (d) 2Fe2O3/TiO2 NR

of Fe2O3/TiO2 Nanorod Film.

X.-M. Song et al. / Applied Surface Science 397 (2017) 112–118 115

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ig. 3. UV–vis diffuse reflectance spectra of TiO2 NR arrays, Fe2O3 film, Fe2O3/TiO2,Fe2O3/TiO2 and 5Fe2O3/TiO2 NR arrays; the inset are the photos of five samples.

amples continue to dark with an increased amount of Fe2O3. It cane seen that the absorption intensity of TiO2 and three compositesre relatively large when compared with single Fe2O3 film in theange of 600–800 nm, Such enhanced absorbance is believed to theight scattering ability from the TiO2 NR arrays [35].

The Mott-Schottky equation was conducted to identify the flatand potential of the as-prepared TiO2 NR arrays and Fe2O3 film.ccording to the Mott-Schottky equation, a linear relationship of/C2 versus applied potential can be obtained, and the negativend positive slopes correspond to p- and n-type conductivities,espectively. The results in Fig. 4 panels show that the TiO2 ande2O3 are n-type semiconductors. As reported earlier, the flat bandotential represents the apparent Fermi level (EF) of a semicon-uctor in equilibrium with redox couple[36–38]. As the positionsf the conduction band edge (EC) of TiO2 and Fe2O3 were −4.21 eVnd −4.78 eV, respectively [39], their positions of the valance banddge (EV) can be concluded based on the Eg obtained from UV–vispectra, which are −7.23 eV and −6.88 eV. Therefore, the relativeositions of energy levels for two semiconductors were presented

n Fig. 5. We can propose the change of energy band structure ofhe two semiconductors before and after the contact as shown inig. 5 panels. The EF of TiO2 and Fe2O3 are −4.3 eV and −5.26 eV (vsacuum level), respectively. When TiO2 and Fe2O3 were brought inontact, the Fermi level should be at equilibrium conditions, a het-rogeneous structure can be formed after the contacting of the TiO2nd Fe2O3. The electrons in the VB of Fe2O3 would be excited intohe valence band edge CB when exposed to visible light. Then, thehotogenerated electrons were transferred from Fe2O3 to the CBf TiO2, leaving the photogenerated holes in the VB of Fe2O3. Thus,his heterogeneous structure will allow the separation of photoin-uced electrons and holes. This result is corresponding to previousesult obtained from Kelvin Probe technology [40].

.2. Photoelectrochemical performance

To further confirm the separation of photogenerated chargearriers in the samples, photocurrent experiment was carried outnder simulated sunlight and visible light (� > 400 nm) shown inigs. 6 and 7, respectively. Negative photocurrent represents thehotogenerated electrons transfer from TiO2/Fe2O3 film to FTO

lass, which is a typical characteristic of an n-type semiconductor41].

As shown in Fig. 6, the photocurrent density of single TiO2nd Fe2O3 electrodes are less than −0.5 mA/cm2, while the Fe2O3

Fig. 4. Variation of capacitance (C) with the applied potential in 0.5 M Na2SO4 solu-tion (pH = 6.45) presented in the Mott-Schottky relationship for TiO2 and Fe2O3 films.The capacitance was determined by electrochemical impedance spectroscopy.

sensitized TiO2 electrodes have photocurrent densities more than−1.5 mA/cm2, indicating the efficient generation and separation ofphotogenerated electrons and holes. In addition, it is clearly shownthat the photocurrent generated from Fe2O3/TiO2 is relatively highcompared with that from 2Fe2O3/TiO2 and 5Fe2O3/TiO2 electrodes.According to the result of FESEM, Fe2O3 gradually filled in the gapof TiO2 NR arrays with the increased amount of Fe2O3, which mayprevent the electrolyte from infiltrating to the inside of the film.So the charge transfer between electrolyte and film may be influ-enced in this case. According to Fig. 7, the photocurrent density ofa single TiO2 electrode is about −0.012 mA/cm2, which is less thansingle Fe2O3 and Fe2O3 sensitized TiO2 electrodes, indicating thatFe2O3 plays the role of absorbing visible light in the structure. Inaddition, it is clearly shown that the photocurrent generated from5Fe2O3/TiO2 is the highest compared with that from Fe2O3/TiO2and 2Fe2O3/TiO2 electrodes. Because more Fe2O3 can absorb morevisible light, which is beneficial to the generation of photogener-ated electrons and holes.

Current-voltage curves of TiO2, Fe2O3, Fe2O3/TiO2, 2Fe2O3/TiO2and 5Fe2O3/TiO2 solar cells, which were measured under illu-mination (simulated AM 1.5 sunlight) with a power density of

100 mW/cm2, as shown in Fig. 8, and the cell parameters of thesedevices are summarized in Table 1. The markedly enhanced deviceperformance of solar cells fabricated with Fe2O3/TiO2 NR arraysis clearly seen. The photovoltaic performance of a single Fe2O3

116 X.-M. Song et al. / Applied Surface Science 397 (2017) 112–118

Fig. 5. (a) Schematic energy-band diagram for isolated Fe2O3 and TiO2; (b) energy-band diagams for Fe2O3/TiO2 heterogeneous structure, and the separation of chargecarriers under irradiation.

Fig. 6. Photocurrent of TiO2, Fe2O3, Fe2O3/TiO2, 2Fe2O3/TiO2 and 5Fe2O3/TiO2 pho-toanodes under simulated AM 1.5 sunlight on/off cycles.

Fig. 7. Photocurrent of TiO2, Fe2O3, Fe2O3/TiO2, 2Fe2O3/TiO2 and 5Fe2O3/TiO2 pho-toanodes under visible light (� > 400 nm) on/off cycles.

Fig. 8. Current density-voltage curves of TiO2, Fe2O3, Fe2O3/TiO2, 2Fe2O3/TiO2 and5Fe2O3/TiO2 photoanodes under simulated AM 1.5 sunlight with a light intensity of100 mW/cm2.

Table 1Photovoltaic Parameters Obtained from the Current Density-Voltage Curves for theCells (This Data Is the Average of Tests Recorded on Three Different Devices) Basedon TiO2 Photoanode, Fe2O3 Photoanode and Fe2O3/TiO2 Photoanodes with differentamount of Fe2O3 under a Light Intensity of 100 mW/cm2.

sample Pmax(mW/cm2)

Jsc(mA/cm2)

Voc (V) FF � (%)

TiO2 0.1973 0.5260 0.497 0.7547 0.1973Fe2O3 0.0023 0.5320 0.024 0.5727 0.0023Fe2O3/TiO2 0.2086 1.8404 0.435 0.2606 0.2086

2Fe2O3/TiO2 0.1817 1.4912 0.424 0.2874 0.18175Fe2O3/TiO2 0.1548 1.6960 0.251 0.3636 0.1548

working electrode is relatively poor, which may be due to its weakelectron transporting ability. Obviously, those solar cells based onFe2O3/TiO2 films display excellent ability in converting the lightto electric current compared to single TiO2-based or Fe2O3-basedsolar cells. This may be attributed to sufficient light harvestingand charge separation by the heterogeneous structure and slowinterfacial electron recombination. As is revealed in Fig. 8, the

overall efficiency values of Fe2O3/TiO2 reach a maximum, withan increase of the amounts of Fe2O3, the overall efficiency valuesdecrease. There should be relatively little Fe2O3 covered the sur-

X.-M. Song et al. / Applied Surface S

Fig. 9. Photocurrent-potential (I–V) curves under chopped light collected for TiO2,F(t

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e2O3, Fe2O3/TiO2, 2Fe2O3/TiO2 and 5Fe2O3/TiO2 photoanodes in 1 M KOH solutionpH = 13.68). The frequency of chopped light is 0.25 Hz. The scan rate is 10 mV/s andhe intensity of the light is 100 mW/cm2.

ace of TiO2 film, which is beneficial to the electrolyte infiltratingnd the excited Fe2O3 can be easily reduced, resulting in relativelyigh photoelectric conversion efficiencies. On the other hand, lit-le Fe2O3 can reduce the charge diffusion path in Fe2O3 coating,nd photogenerated electrons can be directly injected to TiO2 NR42]. When illuminated with light intensity of 100 mW/cm2, theiO2-based solar cell sensitized by Fe2O3 can attain the highesthort-circuit current of 1.84 mA/cm2, open-circuit voltage of 0.44 V,ll factor FF of 0.26 and PCE of 0.2086%, which is more excellent thanhat found in the bare TiO2 NR arrays device. In addition, Fe2O3 hasts peculiar advantage in environmental friendliness, which makest a promising material for solar cells.

The PEC water oxidation experiment was carried out tourther investigate the photoelectric conversion ability of theamples. Fig. 9 shows the chopped light photocurrent-potentialurves of the samples in 1 M KOH solution under AM 1.5 tran-ient illumination. The photocurrent upon illuminating of thelectrodes indicates that photogenerated holes reaching the elec-rode/electrolyte interface contribute to the water oxidationeaction [34,43]. All the five samples exhibit the water split-ing capacities in the photoelectric chemical system. The order ofater oxidation onset potentials (vs Ag/AgCl) of the electrode is

he TiO2 ≈ Fe2O3/TiO2 ≈ 2Fe2O3/TiO2 < 5Fe2O3/TiO2 < Fe2O3. A neg-tive onset potential indicates small bias potential could realizeolar water splitting. This result may be attributed to the rela-ively low valence band of TiO2 and Fe2O3 [39,44], that is to say,he holes in the valence bands of TiO2 will be injected to the elec-rolyte more easily. The transient photocurrent peak upon turninghe light on/off represents the accumulation of holes at the Fe2O3-lectrolyte interface and the back reaction of electrons from theonduction band with the accumulated holes [45]. Photoelectrodeased on pure Fe2O3 shows obvious transient anodic and tran-ient anodic photocurrent, indicating accumulation of holes andhe back reaction of electrons from the conduction band withhe accumulated holes at the Fe2O3-electrolyte interface [30,41].hus the Single �-Fe2O3 photoanode has weaker water splittingapacity than Fe2O3/TiO2. It can be found the photocurrent densi-ies of Fe2O3/TiO2, 2Fe2O3/TiO2 and 5Fe2O3/TiO2 photoelectrodesre much higher than pure TiO2 and Fe2O3 photoelectrodes. The

elatively narrow band gap of Fe2O3 can enhance the light absorp-ion, resulting in much more photogenerated charge carriers. Thehotocurrent densities of Fe2O3/TiO2 are relatively high, which isonsistent with the I–V results discussed above.

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cience 397 (2017) 112–118 117

4. Conclusions

In this study, we reported a novel photoelectrode for PECcells fabricated with 1D Fe2O3/TiO2 via a facile hydrothermalmethod. The Mott-Schottky plots reveal the energy band positionsof the two semiconductors. Efficient separation of photogener-ated charge carriers can occur in the heterogeneous structure. 1DFe2O3/TiO2 semiconductor heterostructure has good visible-lightinduced photoelectric effect. On the basis of these photoanodes,the highest efficiency of TiO2-based solar cell sensitized by Fe2O3reached 0.2086%, with the short-circuit current of 1.84 mA/cm2 andopen-circuit voltage of 0.44 V, exhibiting excellent photoelectricproperty. The results of PEC water splitting indicate that the 1DFe2O3/TiO2 photoelectrode has relatively low onset potential andmuch higher photocurrent.

Acknowledgement

The authors are grateful to the National Natural Science Foun-dation of China (Nos. 21203082, 51273087).

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