- Nano Express
- Open Access
Unique and facile solvothermal synthesis of mesoporous WO3 using a solid precursor and a surfactant template as a photoanode for visible-light-driven water oxidation
© Li et al.; licensee Springer. 2014
Received: 16 July 2014
Accepted: 11 September 2014
Published: 2 October 2014
Mesoporous tungsten trioxide (WO3) was prepared from tungstic acid (H2WO4) as a tungsten precursor with dodecylamine (DDA) as a template to guide porosity of the nanostructure by a solvothermal technique. The WO3 sample (denoted as WO3-DDA) prepared with DDA was moulded on an electrode to yield efficient performance for visible-light-driven photoelectrochemical (PEC) water oxidation. Powder X-ray diffraction (XRD) data of the WO3-DDA sample calcined at 400°C indicate a crystalline framework of the mesoporous structure with disordered arrangement of pores. N2 physisorption studies show a Brunauer-Emmett-Teller (BET) surface area up to 57 m2 g-1 together with type IV isotherms and uniform distribution of a nanoscale pore size in the mesopore region. Scanning electron microscopy (SEM) images exhibit well-connected tiny spherical WO3 particles with a diameter of ca. 5 to 20 nm composing the mesoporous network. The WO3-DDA electrode generated photoanodic current density of 1.1 mA cm-2 at 1.0 V versus Ag/AgCl under visible light irradiation, which is about three times higher than that of the untemplated WO3. O2 (1.49 μmol; Faraday efficiency, 65.2%) was evolved during the 1-h photoelectrolysis for the WO3-DDA electrode under the conditions employed. The mesoporous electrode turned out to work more efficiently for visible-light-driven water oxidation relative to the untemplated WO3 electrode.
The recent advances in nanostructured materials have expanded their potential applications in much-desired materials for efficient solar energy conversion[1–6]. Photoelectrochemical (PEC) water splitting into oxygen and hydrogen is an attractive but challenging way for the conversion of solar energy, following the pioneer work on a TiO2 photoanode for water splitting by Honda and Fujishima. Unfortunately, owing to its wide electronic bandgap (3.0 to 3.2 eV), TiO2 absorbs only an ultraviolet fraction of a solar spectrum (which accounts for just 4% of solar irradiation), being consequently responsible for low efficiency in utilization of solar light[2, 7, 9]. For solar water splitting, intensive researches have been focused on nanostructured materials with narrow bandgaps including WO3[3, 4, 10–19]. WO3, an n-type semiconductor, has attracted immense attention as a photoanode material for water oxidation in PEC cells because of its visible light response (bandgap, Eg = 2.6 to 2.8 eV), a valence band edge position thermodynamically possible for water oxidation (about 3 V versus the normal hydrogen electrode), and good photochemical stability under the acidic conditions[3, 10–12, 20–24].
Porous material design, which has been developed employing template-directed approaches using small organic compounds, supramolecular assembly, and polymer beads, is of great importance in many research fields because of the high porosity, large area per unit volume, and favorable design of a porous structure[25, 28, 29]. So far, several efforts in nanostructural and porosity controls of WO3 have been provided to increase the contact area between an electrode and an electrolyte solution and to make electron transport in WO3 films more efficient, enhancing performance of PEC water oxidation at WO3 electrodes[3, 11, 30–33]. For example, Santato et al. have reported that crystalline WO3 photoanodes with interconnected nanoparticulate structures improved photoelectrochemical properties[30–32]. Berger et al. have demonstrated that random porous layers of WO3 produced significantly higher photocurrent efficiency than a compact layer. Our group recently demonstrated a crystalline small mesoporous network of a WO3 photoanode for high improvement in performance of PEC water oxidation.
Numerous methods have been employed to control the dimension, morphology, and crystal structure of WO3, e.g., vacuum evaporation, chemical vapor deposition[35, 36], sol–gel precipitation[22, 30–32], hydrothermal/solvothermal[37–40], surfactant/hard template techniques[3, 41, 42], and so on. Among the abundant methods, hydrothermal/solvothermal techniques can provide a cost-effective and one-step route synthesis of WO3[37–40]. Although the surfactant template techniques require a liquid tungsten precursor to utilize interaction with a surfactant in principle, we have focused on the interaction between a solid tungsten precursor and a surfactant under solvothermal conditions to yield mesoporous WO3. Herein, we report the unique and facile synthesis of mesoporous WO3 utilizing solid H2WO4 as a tungsten precursor with an organic amphiphilic molecule, dodecylamine (DDA), as a surfactant template for porosity of the nanostructure. The mesoporous WO3 exhibited high surface area and improved the performance of PEC water oxidation compared to the corresponding materials prepared without a template.
Tungstic acid (H2WO4) was purchased from Kanto Chemical Co., Inc. (Chuo-ku, Tokyo, Japan). DDA was obtained from Sigma-Aldrich (St. Louis, MO, USA). Polyethylene glycol (PEG, molecular weight = 2,000) was obtained from Wako Chemical Co. (Osaka, Japan). Marpolose (60MP-50) was purchased from Matsumoto Yushi-Seiyaku Co. (Osaka, Japan). An indium tin oxide (ITO)-coated glass substrate was obtained from Asahi Glass Co. (Tokyo, Japan). Millipore water (Merck Ltd., Tokyo, Japan) was used for all the experiments. All other chemicals unless mentioned otherwise were of analytical grade and used as received.
Synthesis of mesoporous WO3
In a typical synthesis, 1.7 g of DDA (9.0 mmol) was dissolved in 15 mL ethanol under stirring at room temperature. Tungstic acid (0.9 g; 3.6 mmol) was added to the DDA solution with stirring for 30 min to yield a suspension. It was transferred to a Teflon-lined stainless steel autoclave and then placed in an oil bath at 150°C for 24 h. After the autoclave was cooled down to room temperature, the solid product was recovered by centrifugation, then washed repeatedly by ethanol and air-dried. The solid product was calcined at 400°C with a rate of 1°C min-1 and then maintained at 400°C for 1 h in flowing N2, followed by changing to O2 flow (at 400°C) for 2 h to result in a WO3 sample (denoted as WO3-DDA). A control sample (denoted as WO3-bulk) was prepared in the same manner except for the addition of DDA.
Preparation of electrodes
The WO3 film-coated ITO electrodes (ITO/WO3) were prepared employing a doctor-blade technique. Before coating, ITO glass substrates (1.0 cm-2 area) were cleaned up by a UV-ozone treatment (photo surface processor PL16-110, Sen Lights Co., Osaka, Japan) for 15 min. In a typical procedure, WO3 powder (200 mg), PEG (100 mg), and Marpolose (20 mg) were mixed in 300 μL of water. The mixture suspension was stirred for approximately 2 to 4 h until a smooth paste was formed. The resulting paste was squeezed over an ITO glass substrate by a doctor-blade coater and dried at 80°C for 15 min. After repeating the procedure for two times, the electrodes were calcined at 400°C and maintained at 400°C in flowing N2 for 1 h, followed by changing to O2 flow (at 400°C) for 2 h.
Characterization of the morphological features and the crystalline phase was conducted by field-emission scanning electron microscopy (FESEM; JSM-6500 F, JEOL Ltd., Akishima, Tokyo, Japan) and powder X-ray diffraction (XRD; MiniFlexII, Rigaku Corporation, Tokyo, Japan) using monochromated Cu Kα (λ = 1.54 Å) radiation. Nitrogen adsorption-desorption isotherms were measured using a BELSORP-miniII (BEL Japan, Inc., Osaka, Japan) at 77 K. Prior to gas adsorption, samples were degassed in vacuum for 4 h at 150°C. The Brunauer-Emmett-Teller (BET) method was utilized to calculate the surface areas. The pore size distributions were obtained from analysis of the adsorption branches of the isotherms by the Barrett-Joyner-Halenda (BJH) method. Fourier transform infrared spectra were recorded on a Jasco FT/IR-4200 spectrophotometer (Jasco Inc., Tokyo, Japan).
Photoelectrochemical measurement was carried out in a two-compartment photoelectrochemical cell separated by a Nafion membrane using an electrochemical analyzer (HZ-3000, Hokuto Denko Co. Ltd., Tokyo, Japan). A three-electrode system has been employed by using ITO/WO3 and Ag/AgCl electrodes in one compartment as the working and reference electrodes, respectively, and a Pt wire in the other compartment as the counter electrode. An aqueous 0.1 M phosphate solution was used as an electrolyte in both compartments of the cell, which was saturated with Ar gas prior to the measurement. The cyclic voltammogram (CV) was recorded at a scan rate of 50 mV s-1 at 25°C. Light (λ > 390 nm) was irradiated from the backside of the working electrode using a 500-W xenon lamp (Optical ModuleX; Ushio Inc., Tokyo, Japan) with a UV-cut filter (L39) and liquid filter (0.2 M CuSO4) for cutting of heat ray. The output of light intensity was calibrated as 100 mW cm-2 using a spectroradiometer (USR-40; Ushio Inc., Tokyo, Japan). Photoelectrocatalysis was conducted under the potentiostatic conditions of 0.5 V versus Ag/AgCl at 25°C under illumination of light (λ > 390 nm, 100 mW cm-2) for 1 h. The amounts of H2 and O2 evolved were determined from the analysis of the gas phase (headspace volume: 87.3 mL) of counter and working electrode compartments, respectively, using gas chromatography (GC-8A with a TCD detector and molecular sieve 5A column and Ar carrier gas; Shimadzu Corporation, Kyoto, Japan).
Results and discussion
Physicochemical properties of WO 3 samples
Calcination temperature (°C)
Surface area (m2 g-1)
Pore volume (cm3 g-1)
Pore size (nm)
Summary of photoelectrocatalytic water oxidation at different ITO/WO 3 photoanodes calcined at 500°C in 0.1 M phosphate solution
This work was partially supported by the JST PRESTO program and Grant-in-Aid for Scientific Research (B) from the Ministry of Education, Culture, Sports, Science and Technology (No. 24350028). DC thanks JSPS for providing postdoctoral fellowship.
- Kamat PV, Tvrdy K, Baker DR, Radich JG: Beyond photovoltaics: semiconductor nanoarchitectures for liquid-junction solar cells. Chem Rev 2010, 110: 6664. 10.1021/cr100243pView ArticleGoogle Scholar
- Kudo A, Miseki Y: Heterogeneous photocatalyst materials for water splitting. Chem Soc Rev 2009, 38: 253. 10.1039/b800489gView ArticleGoogle Scholar
- Chandra D, Saito K, Yui T, Yagi M: Crystallization of tungsten trioxide having small mesopores: highly efficient photoanode for visible-light-driven water oxidation. Angew Chem Int Ed 2013, 52: 12606. 10.1002/anie.201306004View ArticleGoogle Scholar
- Kim HG, Borse PH, Jang JS, Ahn CW, Jeong ED, Lee JS: Engineered nanorod perovskite film photocatalysts to harvest visible light. Adv Mater 2011, 23: 2088. 10.1002/adma.201004171View ArticleGoogle Scholar
- Zukalová M, Zukal A, Kavan L, Nazeeruddin MK, Liska P, Grätzel M: Organized mesoporous TiO2 films exhibiting greatly enhanced performance in dye-sensitized solar cells. Nano Lett 2005, 5: 1789. 10.1021/nl051401lView ArticleGoogle Scholar
- Kim J, Koh JK, Kim B, Kim JH, Kim E: Nanopatterning of mesoporous inorganic oxide films for efficient light harvesting of dye-sensitized solar cells. Angew Chem Int Ed 2012, 51: 6864. 10.1002/anie.201202428View ArticleGoogle Scholar
- Gratzel M: Photoelectrochemical cells. Nature 2001, 414: 338. 10.1038/35104607View ArticleGoogle Scholar
- Fujishima A, Honda K: TiO2 photoelectrochemistry and photcatalysis. Nature 1972, 238: 37. 10.1038/238037a0View ArticleGoogle Scholar
- Aprile C, Corma A, Garcia H: Enhancement of the photocatalytic activity of TiO2 through spatial structuring and particle size control: from subnanometric to submillimetric length scale. Phys Chem Chem Phys 2008, 10: 769. 10.1039/b712168gView ArticleGoogle Scholar
- Ng KH, Minggu LJ, Kassim MB: Gallium-doped tungsten trioxide thin film photelectrodes for photoelectrochemical water splitting. Int J Hydrogen Energy 2013, 38: 9585. 10.1016/j.ijhydene.2013.02.144View ArticleGoogle Scholar
- Kim JK, Shin K, Cho SM, Lee T-W, Park JH: Synthesis of transparent mesoporous tungsten trioxide films with enhanced photoelectrochemical response: application to unassisted solar water splitting. Energy Environ Sci 2011, 4: 1465. 10.1039/c0ee00469cView ArticleGoogle Scholar
- Chatchai P, Murakami Y, Kishioka S-y, Nosaka AY, Nosaka Y: Efficient photocatalytic activity of water oxidation over WO3/BiVO4 composite under visible light irradiation. Electrochim Acta 2009, 54: 1147. 10.1016/j.electacta.2008.08.058View ArticleGoogle Scholar
- Hisatomi T, Dotan H, Stefik M, Sivula K, Rothschild A, Grätzel M, Mathews N: Enhancement in the performance of ultrathin hematite photoanode for water splitting by an oxide underlayer. Adv Mater 2012, 24: 2699. 10.1002/adma.201104868View ArticleGoogle Scholar
- Satsangi VR, Kumari S, Singh AP, Shrivastav R, Dass S: Nanostructured hematite for photoelectrochemical generation of hydrogen. Int J Hydrogen Energy 2008, 33: 312. 10.1016/j.ijhydene.2007.07.034View ArticleGoogle Scholar
- Rahman G, Joo O-S: Photoelectrochemical water splitting at nanostructured α-Fe2O3 electrodes. Int J Hydrogen Energy 2012, 37: 13989. 10.1016/j.ijhydene.2012.07.037View ArticleGoogle Scholar
- Li Y, Takata T, Cha D, Takanabe K, Minegishi T, Kubota J, Domen K: Vertically aligned Ta3N5 nanorod arrays for solar-driven photoelectrochemical water splitting. Adv Mater 2013, 25: 125. 10.1002/adma.201202582View ArticleGoogle Scholar
- Maeda K, Higashi M, Lu D, Abe R, Domen K: Efficient nonsacrificial water splitting through two-step photoexcitation by visible light using a modified oxynitride as a hydrogen evolution photocatalyst. J Am Chem Soc 2010, 132: 5858. 10.1021/ja1009025View ArticleGoogle Scholar
- Maeda K, Domen K: Water oxidation using a particulate BaZrO3-BaTaO2N solid-solution photocatalyst that operates under a wide range of visible light. Angew Chem Int Ed 2012, 51: 9865. 10.1002/anie.201204635View ArticleGoogle Scholar
- Abe T, Nagai K, Kabutomori S, Kaneko M, Tajiri A, Norimatsu T: An organic photoelectrode working in the water phase: visible-light-induced dioxygen evolution by a perylene derivative/cobalt phthalocyanine bilayer. Angew Chem Int Ed 2006, 45: 2778. 10.1002/anie.200504454View ArticleGoogle Scholar
- Yang B, Zhang Y, Drabarek E, Barnes PRF, Luca V: Enhanced photoelectrochemical activity of sol–gel tungsten trioxide films through textural control. Chem Mater 2007, 19: 5664. 10.1021/cm071603dView ArticleGoogle Scholar
- Seabold JA, Choi K-S: Effect of a cobalt-based oxygen evolution catalyst on the stability and the selectivity of photo-oxidation reactions of a WO3 photoanode. Chem Mater 2011, 23: 1105. 10.1021/cm1019469View ArticleGoogle Scholar
- Yagi M, Maruyama S, Sone K, Nagai K, Norimatsu T: Preparation and photoelectrocatalytic activity of a nano-structured WO3 platelet film. J Solid State Chem 2008, 181: 175. 10.1016/j.jssc.2007.11.018View ArticleGoogle Scholar
- Miseki Y, Kusama H, Sugihara H, Sayama K: WO3 photocatalyst showing efficient solar energy conversion for O2 production and Fe (III) ion reduction under visible light. J Phys Chem Lett 2010, 1: 1196. 10.1021/jz100233wView ArticleGoogle Scholar
- Miseki Y, Fujiyoshi S, Gunji T, Sayama K: Photocatalytic water splitting under visible light utilizing I3-/I- and IO3-/I- redox mediators by Z-scheme system using surface treated PtO x /WO3 as O2 evolution photocatalyst. Catal Sci Tech 2013, 3: 1750. 10.1039/c3cy00055aView ArticleGoogle Scholar
- Corma A: From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem Rev 1997, 97: 2373. 10.1021/cr960406nView ArticleGoogle Scholar
- Kresge CT, Leonowicz ME, Roth WJ, Vartuli JC, Beck JS: Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism. Nature 1992, 359: 710. 10.1038/359710a0View ArticleGoogle Scholar
- Chandra D, Bekki M, Nakamura M, Sonezaki S, Ohji T, Kato K, Kimura T: Dye-sensitized biosystem sensing using macroporous semiconducting metal oxide films. J Mater Chem 2011, 21: 5738. 10.1039/c0jm04347hView ArticleGoogle Scholar
- Davis ME: Ordered porous materials for emerging applications. Nature 2002, 417: 813. 10.1038/nature00785View ArticleGoogle Scholar
- Sanchez C, Boissière C, Grosso D, Laberty C, Nicole L: Design, synthesis, and properties of inorganic and hybrid thin films having periodically organized nanoporosity. Chem Mater 2008, 20: 682. 10.1021/cm702100tView ArticleGoogle Scholar
- Santato C, Ulmann M, Augustynski J: Photoelectrochemical properties of nanostructured tungsten trioxide films. J Phys Chem B 2001, 105: 936. 10.1021/jp002232qView ArticleGoogle Scholar
- Santato C, Ulmann M, Augustynski J: Enhanced visible light conversion efficiency using nanocrystalline WO3 films. Adv Mater 2001, 13: 511. 10.1002/1521-4095(200104)13:7<511::AID-ADMA511>3.0.CO;2-WView ArticleGoogle Scholar
- Santato C, Odziemkowski M, Ulmann M, Augustynski J: Crystallographically oriented mesoporous WO3 films: synthesis, characterization, and application. J Am Chem Soc 2001, 123: 10639. 10.1021/ja011315xView ArticleGoogle Scholar
- Berger S, Tsuchiya H, Ghicov A, Schmuki P: High photocurrent conversion efficiency in self-organized porous WO3. Appl Phys Lett 2006, 88: 203119. 10.1063/1.2206696View ArticleGoogle Scholar
- Colton RJ, Guzman AM, Rabalais JW: Electrochromism in some thin-film transition-metal oxides characterized by x-ray electron spectroscopy. J Appl Phys 1978, 49: 409. 10.1063/1.324349View ArticleGoogle Scholar
- Yous B, Robin S, Donnadieu A, Dufour G, Maillot C, Roulet H, Senemaud C: Chemical vapor deposition of tungsten oxides: A comparative study by X-ray photoelectron spectroscopy, X-ray diffraction and reflection high energy electron diffraction. Mater Res Bull 1984, 19: 1349. 10.1016/0025-5408(84)90199-5View ArticleGoogle Scholar
- Sivakumar R, Moses Ezhil Raj A, Subramanian B, Jayachandran M, Trivedi DC, Sanjeeviraja C: Preparation and characterization of spray deposited n-type WO3 thin films for electrochromic devices. Mater Res Bull 2004, 39: 1479. 10.1016/j.materresbull.2004.04.023View ArticleGoogle Scholar
- Saha D, Jensen KMØ, Tyrsted C, Bøjesen ED, Mamakhel AH, Dippel A-C, Christensen M, Iversen BB: In situ total X-ray scattering study of WO3 nanoparticle formation under hydrothermal conditions. Angew Chem Int Ed 2014, 53: 3667. 10.1002/anie.201311254View ArticleGoogle Scholar
- Wang N, Wang D, Li M, Shi J, Li C: Photoelectrochemical water oxidation on photoanodes fabricated with hexagonal nanoflower and nanoblock WO3. Nanoscale 2014, 6: 2061. 10.1039/c3nr05601eView ArticleGoogle Scholar
- Zeng W, Li Y, Zhang H: Hierarchical WO3 porous microspheres and their sensing properties. J Mater Sci: Mater Electron 2014, 25: 1512. 10.1007/s10854-014-1761-1Google Scholar
- Katsumata H, Inoue K, Suzuki T, Kaneco S: Facile synthesis of WO3 nanorod thin film on W substrate with enhance photocatalytic performance. Catal Lett 2014, 144: 837. 10.1007/s10562-014-1194-8View ArticleGoogle Scholar
- Brezesinski T, Fattakhova Rohlfing D, Sallard S, Antonietti M, Smarsly BM: Highly crystalline WO3 thin films with ordered 3D mesoporosity and improved electrochromic performance. Small 2006, 2: 1203. 10.1002/smll.200600176View ArticleGoogle Scholar
- Sadakane M, Sasaki K, Kunioku H, Ohtani B, Ueda W, Abe R: Preparation of nano-structured crystalline tungsten(vi) oxide and enhanced photocatalytic activity for decomposition of organic compounds under visible light irradiation. Chem Commun 2008, 6552.Google Scholar
- Chandra D, Yokoi T, Tatsumi T, Bhaumik A: Highly luminescent organic–inorganic hybrid mesoporous silicas containing tunable chemosensor inside the pore wall. Chem Mater 2007, 19: 5347. 10.1021/cm701918tView ArticleGoogle Scholar
- Grosman A, Ortega C: Capillary condensation in porous materials. Hysteresis and interaction mechanism without pore blocking/percolation process. Langmuir 2008, 24: 3977. 10.1021/la703978vView ArticleGoogle Scholar
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