WO3 and W2N nanowire arrays for photoelectrochemical hydrogen production

Chakrapani, Vidhya; Thangala, Jyothish; Sunkara, Mahendra K.

doi:10.1016/j.ijhydene.2009.09.031

Cited by 216 publications

(151 citation statements)

References 32 publications

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“…Tungsten trioxide, WO 3 , an earth-abundant, oxidatively stable semiconductor, is one such material that could fulfill the role of photoanode. [14][15][16][17][18][19][20][21][22][23][24] In most deposition methods, the presence of oxygen vacancies serve as shallow electron donors and naturally dope the WO 3 n-type. 25 Its band gap of 2.6 eV is higher than ideal for the large band gap absorber in a tandem cell.…”

Section: Introductionmentioning

confidence: 99%

“…30,31 Even in acidic conditions, some photocorrosion of WO 3 has been observed due to the formation of peroxo-species as intermediates during water oxidation. [22][23][24]32 Although peroxide formation and the oxidation of most acid counterion species are reactions that are thermodynamically less feasible than water oxidation, the kinetics of these reactions are often more favorable than oxygen evolution. 14 The photogenerated minority-carrier holes in the valence band of WO 3 have a potential of B2.97 V vs. NHE at pH 0.…”

Section: Introductionmentioning

confidence: 99%

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Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Spurgeon

Velázquez

McDowell

2014

Phys. Chem. Chem. Phys.

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WO 3 is a promising candidate for a photoanode material in an acidic electrolyte, in which it is more stable than most metal oxides, but kinetic limitations combined with the large driving force available in the WO 3 valence band for water oxidation make competing reactions such as the oxidation of the acid counterion a more favorable reaction. The incorporation of an oxygen evolving catalyst (OEC) on the WO 3 surface can improve the kinetics for water oxidation and increase the branching ratio for O 2 production. Ir-based OECs were attached to WO 3 photoanodes by a variety of methods including sintering from metal salts, sputtering, drop-casting of particles, and electrodeposition to analyze how attachment strategies can affect photoelectrochemical oxygen production at WO 3 photoanodes in 1 M H 2 SO 4 . High surface coverage of catalyst on the semiconductor was necessary to ensure that most minority-carrier holes contributed to water oxidation through an active catalyst site rather than a sidereaction through the WO 3 /electrolyte interface. Sputtering of IrO 2 layers on WO 3 did not detrimentally affect the energy-conversion behavior of the photoanode and improved the O 2 yield at 1.2 V vs. RHE from B0% for bare WO 3 to 50-70% for a thin, optically transparent catalyst layer to nearly 100% for thick, opaque catalyst layers. Measurements with a fast one-electron redox couple indicated ohmic behavior at the IrO 2 /WO 3 junction, which provided a shunt pathway for electrocatalytic IrO 2 behavior with the WO 3 photoanode under reverse bias. Although other OECs were tested, only IrO 2 displayed extended stability under the anodic operating conditions in acid as determined by XPS.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Spurgeon

Velázquez

McDowell

2014

Phys. Chem. Chem. Phys.

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“…Nanowires with a range of vanadium-to-oxygen ratio were prepared with high purity without the introduction of extraneous reducing agents by simply tuning the filament power and partial pressure of oxygen and water vapor in the chamber, as was shown in our recent work for other oxides. 32,33 Figure 1C shows the scanning electron micrograph (SEM) of as-synthesized oxide grown on fluorinated tin oxide (FTO) substrates. From the image, the as-synthesized deposits are seen to be vertically-aligned, single crystalline nanowires with diameters in the range of 60-80 nm and length extending to 1-2 microns.…”

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confidence: 99%

Defect-induced Burstein-Moss shift in reduced V2O5 nanostructures

et al. 2016

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The main effects of oxygen vacancy defects on the electronic and optical properties of V 2 O 5 nanowires were studied through in-situ Raman, photoluminescence, absorption, and photoemission spectroscopy. Both thermal reduction and electrochemical reduction via lithium insertion leads to the creation of oxygen vacancy defects in the crystal that gives rise to new electronic mid-gap defect states at energy 0.75 eV below the conduction band edge. The defect formation results in delocalization and injection of excess electrons into the conduction band, as opposed to localized electron injection as previously suggested. Contrary to what is seen in most oxides, the presence of vacancy defects leads to band filling and an increase in the optical band gap of V 2 O 5 from 1.95 eV to 2.45 eV, which is attributed to the Burstein-Moss effect. Other observed changes in the optical properties are correlated to the changes in the electronic structure of the oxide as result of defect formation. Further, in-situ Raman measurements during the electrochemical reduction at room temperature show that the oxygen atom that is most readily reduced is the three-fold coordinated oxygen (O3). Reduction of V 2 O 5 through the formation of oxygen vacancy, V O , defects have been studied both by theoretical and experimental studies. 10,11,12,13,14,15 In this work, we address some of the key unanswered questions regarding the correlation between optical properties and electronic structure of The rise of absorbance in the NIR spectral range in reduced oxide is a result of optical excitation of V O defect related mid-gap states. In addition, using in-situ Raman measurements during reduction process, we show that the oxygen atom that most readily participates during electrochemical reduction at room-temperature and gets reduced is the three-fold coordinated oxygen (O3).Vacancies in vanadium oxide have been probed using a variety of spectroscopic techniques, such as scanning tunneling microscopy, 9,26,27 electron energy loss spectroscopy, 28,29 electron paramagnetic resonance studies, 16,12,23 X-ray absorption measurements, 30 and X-ray photoemission spectroscopy (XPS). 15,17 However, most of these techniques either require ultrahigh vacuum (UHV) or controlled environment for operation that makes it difficult to adapt it to 6 in-situ catalytic studies. Here, we use near-infrared photoluminescence (NIR-PL) and Raman spectroscopy that allows for study of vacancy defects and their interaction with redox species under in-operando electrochemical conditions at room temperature, as shown in our recent study. 31 The spectral range of various types of electronic transitions in V 2 O 5 is shown in Fig.1A.Representative PL spectra of stoichiometric and non-stoichiometric V 2 O 5 are shown in Fig.1B.The optical gap of nominally undoped V 2 O 5 is in the range of 1.9-2.5 eV and hence emission spectrum lies in the ultraviolet-to-visible part of the spectral range. In most TMOs, deviation from stoichiometry is a result of the presence of high density ...

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“…For example, vertically aligned nanowires are highly desirable for many solar cell applications for fast and direct electron transport to the back contact. 24 The high diffusion coefficient of ions such as Li along certain crystallographic directions means nanostructured platelets are highly efficient for Li ion transport in battery applications. 26 In this regard, HWCVD is well suited for tuning the morphology of metal oxide nanostructures.…”

Section: A Control Of the Morphologymentioning

confidence: 99%

“…Previous studies have shown that the hot wire CVD (HWCVD) technique, which consists of reacting oxygen with a hot filament of the respective transition metal, can successfully be used for synthesis of various metal oxides. [22][23][24] The main advantages of this technique are the ability to grow relatively pure films without the use of extraneous solvents and counter ions and the ease with which single crystalline nanostructures can be deposited over a large surface area.…”

Section: Introductionmentioning

confidence: 99%

Modulation of stoichiometry, morphology and composition of transition metal oxide nanostructures through hot wire chemical vapor deposition

et al. 2015

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A hot wire chemical vapor deposition technique is described for synthesis of 1D nanostructures of a controlled morphology, stoichiometry, and composition. The synthesis involves the evaporation and condensation of metal oxide vapor through the reaction of oxygen with the hot filaments of respective transition metals. The stoichiometry and morphology of MoO 3 and WO 3 were modulated by varying the filament temperature and partial pressure of oxygen in the growth chamber. Based on the results under different conditions, a morphological phase diagram, and a growth model based on the extent of gas phase supersaturation were developed to understand the growth mechanism. Further, ternary transition metal oxide, NiMoO 4, was synthesized as a proof-of-concept for tuning the composition of deposition through simultaneous evaporation of two metal oxides.

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WO3 and W2N nanowire arrays for photoelectrochemical hydrogen production

Cited by 216 publications

References 32 publications

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Defect-induced Burstein-Moss shift in reduced V2O5 nanostructures

Modulation of stoichiometry, morphology and composition of transition metal oxide nanostructures through hot wire chemical vapor deposition

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