Diffusion Controlled and Transient Photocurrents of Photo‐Oxidation Reactions at Polycrystalline α ‐ Fe2 O 3

Anderman, M.; Kennedy, John H.

doi:10.1149/1.2115533

Cited by 36 publications

(26 citation statements)

References 7 publications

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“…It has been reported that the conduction band of iron oxide by Mott-Schottky measurements is slightly above [30,31] and below [32,33] the H + /H 2 half-cell potential. The former claims were later confirmed by the report of Somorjai and Damme [21] who measured the flat-band potential of iron oxide varying between À0.9 and À1.1 V (vs. SCE) at pH 13.…”

Section: Discussionmentioning

confidence: 99%

Photoreduction of CO2 in an optical-fiber photoreactor: Effects of metals addition and catalyst carrier

Nguyen

2008

Applied Catalysis A: General

139

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Section: Discussionmentioning

confidence: 99%

Photoreduction of CO2 in an optical-fiber photoreactor: Effects of metals addition and catalyst carrier

Nguyen

2008

Applied Catalysis A: General

139

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“…This situation is a result of the relatively new use of semiconductor electrodes in electrochemical systems (13)(14)(15)(16), the kinetic complexity of photoelectrochemical current flow, and the diversity of properties found for different semiconducting materials (8) and for different crystals of the same semiconducting material. that control the rates of electrochemical reactions at metals (e.g., diffusion of solution species, reorganization energies, and double-layer effects) (1)(2)(3)(4)(5), the rates of photoelectrochemical reactions are affected by processes that occur within the electrode (e.g., carrier diffusion and recombination) and by the dependence of these processes on light intensity and photon energy (6)(7)(8)(9)(10)(11)(12). **Electrochemical Society Active Member.…”

mentioning

confidence: 99%

A Comparison of Photochemical Properties of Amorphous and Polycrystalline Fe2 O 3

Benko¹,

Longo²,

Koffyberg³

1985

J. Electrochem. Soc.

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A comparison is made of the photoelectrochemica] properties of Fe,.,,6Sn0.00~O:~ in two forms: as polycrystalline sintered compacts and as amorphous thin films prepared by RF sputtering. There is no essential difference in optical bandgaps, Mott-Schottky intercepts, band-edge positions, and optical absorption spectra. For the photo-oxidation of water, the difference between instantaneous and steady-state photocurrents is much larger for the amorphous than for crystalline form, which indicates a difference in the density and/or effectiveness of surface states. This difference between instantaneous and steady-state currents disappears, for both amorphous and crystalline Fe~O3, on adding the S 2-/S. '2-redox couple to the solution. The dark current of the amorphous form is larger, and its quantum efficiency in the ultraviolet is smaller.Ferric oxide has been studied extensively as a photoanode; its relatively small bandgap, good chemical stability, and easy preparation makes it an interesting material for application in liquid-junction solar cells. However, its properties as a photoanode for water oxidation are apparently far from simple: on exposure to light, the photocurrents show strong transient excursions, and they do not set in at the flatband potential. Moreover, the Mott-Schottky plots are often found to be curved, and dependent on the measuring frequency as well. These deviations from simple behavior have been reported for Fe20:~ in the form of single crystals (1, 2), polycrystalline ceramics (3-5), and flame-oxidized iron (6, 7). The extent to which these complexities occur seems to depend sensitively on the sample preparation conditions; this points towards an important role for defect states, either in the bulk or at the surface.In this paper, we report a comparison of the photoelectrochemical behavior of polycrystalline and amorphous Fe20:~. Our basic result is that the absence of long-range order in amorphous Fe20:~ has no influence on those properties which are normally associated with the crystalline electronic band structure. Only those parameters which control the kinetics of the forward and backreactions of the photo-oxidation of water (without added redox couples) differ significantly between the amorphous and crystalline forms.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-04-05 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-04-05 to IPABSTRACT Electron-transfer processes at highly doped p-InP electrodes were investigated by monitoring the cyclic voltammetric dark currents of a series of metallocenes in acetonitrile solutions. The formal reduction potentials of the metallocenes span the bandgap of InP, allowing a comparison of the cyclic voltammetric response as a function of the formal reduction potential and the energetic condition of the electrode surface. Since th...

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“…For example, the results given in Table I indicate that n = 2 fits the data reasonably well, and would be consistent with oxidation of S(III) in $2042-to S(IV) in SO~ 2-. [2] during analysis. Another alternative is seen in Eq.…”

Section: Resultsmentioning

confidence: 99%

Photoelectrochemical Oxidation of Inorganic Anions at Polycrystalline α ‐ Fe2 O 3 Photoanodes

Salama

Kennedy

1989

J. Electrochem. Soc.

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The photo-oxidation of sulfite, arsenite, nitrite, and dithionite ions was observed at pH 12 using Fe202 and TiO2 semiconductor electrodes. In all cases the n-value was 2 for the photo-oxidation process. Sulfite and dithionite ions competed well against hydroxide ion for photogenerated holes, or, alternatively, for hydroxyl radicals produced in the primary oxidation step. These ions were all less effective at TiO2 electrodes, where 02 formation was more favored.Previous photoelectrochemical studies (1, 2) have shown that oxidation of halide ions competes with oxidation of water at a-Fe20~ photoanodes. Iodide ion was especially effective with >90% of the current resulting in iodine formation at pH 9 in solutions containing >0.2M KI (1). Very little effort has been spent studying photo-oxidation of other inorganic anions. Here, we report the oxidation of SO32-, AsO2-, NO2-, and $2042-at ~-Fe203 and at TiO2 electrodes. ExperimentalReagent grade Na2SO3, Na2S204, NaNO2, NaAsO2, and Na2SO4 were used as received. Electrodes were prepared with high purity Fe203 (Alfa Products) and SiC powder as a dopant. Electrodes were prepared by mixing the ~-Fe203 powder and 1 atom percent (a/o) SiC powder dopant in acetone as described previously (3). The mixture was stirred for 3h, allowing the acetone to evaporate. The mixed powder was ground for 15 min and then 300 mg samples were pressed into pellets at -40 kpsi. The pellets were sintered at 1350~ for 16-17h. Pellets had an area of 0.385 cm 2. Electrical contacts were formed by sputtering gold onto the back surface, then attaching a copper wire to the gold-covered surface using silver epoxy. The back surface was isolated with 3-5 mil epoxy resin. TiO2 electrodes were supplied by Furuuchi Chemical Company, Japan.Sulfite analysis was carried out iodometrically by adding the sample to 0.1M HC1 containing excess iodine. The excess iodine was titrated with standard sodium thiosulfate. Sulfate analysis was accomplished by precipitation of BaSO4 from a hot, acidified (pH = 1) sample solution and collected on a paper filter. The precipitate was dissolved in hot ammoniacal standard EDTA solution. The pH of the solution was adjusted to pH = 10 with NH4OH buffer, and the excess EDTA was titrated with a standard Mg(II) solution (4). Arsenite analysis was accomplished by adding the sample to a slightly acidic (NaHCO3 added if solution acidic) excess iodine solution. The excess iodine solution was titrated with standard sodium arsenite solution.Nitrite analysis was carried out by adding the solution to acidic (0.4M H2SO4) KMnO4 solution. The excess KMnO4 was titrated with a standard Fe(II) solution. KMnO4 oxidizes NO2-to NO3-under these conditions. Dithionite ($2042-) analysis was accomplished by adding excess iodine to the slightly acidified solution and titrating the excess iodine with standard sodium thiosulfate. Dithionite first decomposes (5) according to Eq. [1] and the products are oxidized by iodine according to Eq. [2]

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Diffusion Controlled and Transient Photocurrents of Photo‐Oxidation Reactions at Polycrystalline α ‐ Fe2 O 3

Cited by 36 publications

References 7 publications

Photoreduction of CO2 in an optical-fiber photoreactor: Effects of metals addition and catalyst carrier

Photoreduction of CO2 in an optical-fiber photoreactor: Effects of metals addition and catalyst carrier

A Comparison of Photochemical Properties of Amorphous and Polycrystalline Fe2 O 3

Photoelectrochemical Oxidation of Inorganic Anions at Polycrystalline α ‐ Fe2 O 3 Photoanodes

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