The Anodic Oxidation of Hydrogen on Platinized Tungsten Oxides

Hobbs, B. S.; Tseung, A. C. C.

doi:10.1149/1.2404265

Cited by 56 publications

(18 citation statements)

References 15 publications

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“…In both the cubic and hexagonal systems, the hydrogenintercalated bronze energy is positive and large, indicating that the hydrogen bronzes are not stable. In the experimental system the hydrogen bronzes are easily oxidised as the protons are highly mobile [31,35]. This result also relates to hydrogen being the only intercalate that does not ionise in the bronze structures, as evidenced by the charge density plots earlier.…”

Section: Energies Of Formationmentioning

confidence: 62%

Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

Ingham

Hendy

Chong³

et al. 2005

Phys. Rev. B

115

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Tungsten trioxide adopts a variety of structures which can be intercalated with charged species to alter the electronic properties, thus forming 'tungsten bronzes'. Similar optical effects are observed upon removing oxygen from WO3, although the electronic properties are slightly different. Here we present a computational study of cubic and hexagonal alkali bronzes and examine the effects on cell size and band structure as the size of the intercalated ion is increased. With the exception of hydrogen (which is predicted to be unstable as an intercalate), the behaviour of the bronzes are relatively consistent. NaWO3 is the most stable of the cubic systems, although in the hexagonal system the larger ions are more stable. The band structures are identical, with the intercalated atom donating its single electron to the tungsten 5d valence band. Next, this was extended to a study of fractional doping in the NaxWO3 system (0 ≤ x ≤ 1). A linear variation in cell parameter, and a systematic change in the position of the Fermi level up into the valence band was observed with increasing x. In the underdoped WO3−x system however, the Fermi level undergoes a sudden jump into the conduction band at around x = 0.2. Lastly, three compounds of a layered WO4 · α,ω-diaminoalkane hybrid series were studied and found to be insulating, with features in the band structure similar to those of the parent WO3 compound which relate well to experimental UVvisible spectroscopy results.

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Section: Energies Of Formationmentioning

confidence: 62%

Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

Ingham

Hendy

Chong³

et al. 2005

Phys. Rev. B

115

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“…It is necessary therefore to consider the provision of a replenishment pathway, together with a means of preventing the diffusion of the dissolved ions to the counter electrode. WO 3 has been widely used as a component in anode [19][20][21][22] and cathode 6-11 catalysts in acid media. However, it is slightly soluble in acidic media.…”

mentioning

confidence: 99%

Oxygen Reduction on Teflon Bonded Pt/WO[sub 3]/C Electrode in Sulfuric Acid

Sun¹,

Chiu²,

Tseung³

2001

Electrochem. Solid-State Lett.

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Highly dispersed Pt/WO 3 /C was prepared by freeze-drying followed by hydrogen reduction. The catalyst particle size was examined by transmission electron microscopy and X-ray diffraction line broadening technique as well as electrochemical Pt surface area measurement by H 2 and CO stripping. Oxygen reduction on Teflon bonded Pt/WO 3 /C electrode was investigated under O 2 and air in 0.5 M H 2 SO 4 at 25 and 70°C. Pt/WO 3 /C was more active for oxygen reduction in sulfuric acid than Pt/C catalyst. The dissolved tungsten compounds ͑peroxy-tungstate͒ from the WO 3 in the electrode participate in the oxygen reduction as a homogeneous catalyst for the decomposition of H 2 O 2 , leading to significantly higher activity of the Pt/WO 3 /C for oxygen reduction. By coating the electrode with a thin layer Nafion dispersion, continual loss of WO 3 by dissolution and diffusion to the bulk electrolyte is avoided.There is a need to improve the performance of oxygen electrode in acid media for fuel cell applications. 1,2 Pt is the most favored catalyst for this because most of the other metals are corroded in acid media. Attempts to improve the performance of the Pt catalyst have involved alloying it with transition metals 3-12 and mixing it with acid resistant oxides such as WO 3 . 13-16 Although all of these efforts resulted in improved performance, the mechanism of the improvement is not clear. Furthermore, it has been observed that such alloys are invariably corroded, releasing transition metal ions into the electrolyte. 6-11 Recent work in our group has confirmed the pivotal role of homogeneous catalysis 17,18 in the improvement of oxygen reduction on Pt in acid media, via the formation of transition metal-peroxy compounds and their subsequent decomposition at Pt surface. Typically, dissolved W or Fe ͑10-100 ppm͒ 17,18 in sulfuric acid increased the current density of oxygen reduction by 70% at 0.6 V vs. SHE, 70°C. However, the long-term performance is not satisfactory because the dissolved ions will be plated out at the counter electrode. It is necessary therefore to consider the provision of a replenishment pathway, together with a means of preventing the diffusion of the dissolved ions to the counter electrode. WO 3 has been widely used as a component in anode [19][20][21][22] and cathode 6-11 catalysts in acid media. However, it is slightly soluble in acidic media. 23 It would be useful to consider WO 3 as a reservoir for the supply of dissolved tungsten species and to use Nafion coating to prevent the diffusion of dissolved W species to the counter electrode. In order to see the effect of WO 3 , it is necessary to compare the performance of Pt/C and Pt/WO 3 /C electrode, taking into account the Pt loading and specific surface area of the Pt in the two different electrodes. ExperimentalPreparation of Pt/WO 3 /C catalyst.-Pt/WO 3 supported catalyst was prepared by freeze-drying. 24 Vulcan XC-72 carbon ͑Cabot͒ support was treated in a stream of N 2 at 900°C for 3 h to remove any surface contaminant. After treatment, the ...

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“…Bearing in mind that adsorption does not occur on pure WO3, but only on samples containing palladium, it can be assumed that the adsorption process takes effect through the "hydrogen spillover" mechanism, meaning that atomic hydrogen is produced on dispersed palladium, which spills over to WO3 forming, by adsorption, the hydrogen bronze, as the published data [6][7][8][9]11] show for this and similar cases. Maximum values derived were -AH = 200Jg 1.…”

Section: Pd/wo3-h2 Systemmentioning

confidence: 99%

Kinetic-thermal processes of hydrogen sorption on Pd/WO3 and Pd/MoO3 bronze

Šušić

Solonin

1989

J Mater Sci

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Kinetic-thermal investigations of the hydrogen sorption process in the temperature range from ambient to 720 K on powder samples of Pd/WO3 and Pd/MoO 3 show that it takes place according to the "hydrogen spillover" mechanism, during which the corresponding hydrogen bronzes are formed. Hydrogen sorption changes the structure of the Pd/WO3 bronze, while it breaks the structure of the Pd/MoO3 bronze producing the amorphous state on heating to 570 K. The hydrogen bronze Pd/HxWO 3, heated in oxygen, decomposes at around 830 K, resuming the original form of the yellow Pd/WO3 bronze. A repeated cyclic heating of Pd/HxMOO 3 bronze in hydrogen and oxygen in turn (thermogravimetric analysis and differential scanning calorimetry methods) shows that the sorbed hydrogen reacts violently with oxygen and to form water. In the opposite way, hydrogen sorption on the sample after heating in oxygen also proceeds violently, producing hydrogen bronze after the initial formation of water with oxygen. When heated in oxygen after hydrogen up to 720 K, the sample is oxidized to the maximum extent, returning to the original grey colour and the crystal state. Further heating in hydrogen produces a hydrogen bronze of dark blue colour, while the structure is decomposed. The kinetic processes were investigated and kinetic and thermal parameters were determined. The change in structure is also demonstrated by X-ray diffractometry and electron microscopy.

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The Anodic Oxidation of Hydrogen on Platinized Tungsten Oxides

Cited by 56 publications

References 15 publications

Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

Oxygen Reduction on Teflon Bonded Pt/WO[sub 3]/C Electrode in Sulfuric Acid

Kinetic-thermal processes of hydrogen sorption on Pd/WO3 and Pd/MoO3 bronze

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