ChemInform Abstract: Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron(III) Oxide.

Tinnemans, A. H. A.; Koster, T.P.M.; Thewissen, D. H. M. W.; Mackor, A.; Schoonman, J.

doi:10.1002/chin.198630014

Cited by 5 publications

(6 citation statements)

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“…The admittance spectra can be adequatelyfitted to this equivalent circuit, with k, = 0.46 nSs", a = 0.91, RA = 8.4 kR, and RB = 0.74 MR. The full data analysis is reported in the next paper [48]. With regard to the electrode, the results using this equivalent circuit are in good agreement with the values obtained for the symmetrical cells above.…”

Section: Results and Discussion Electrical Propertiessupporting

confidence: 85%

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Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Tinnemans

Koster

Thewissen

et al. 1986

Ber Bunsenges Phys Chem

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Electrical Properties / Electrochemistry / Materials Properties / Photoelectrochemistry 1 Semiconductors Polycrystalline Mg-doped (0.1 -5 at.%) Fe203 photoelectrodes have been prepared by annealing at 1573 K followed by slow cooling in air to ambient temperature. These materials are essentially single-phase at Mg concentrations not exceeding 0.5 at. %. Disk-shaped (photo)-electrodes were prepared, and their electric and photoelectrochemical (PEC) properties were measured. The positive sign of the photovoltage and of the thermoelectric power 8, confirmed the materials to be p-type semiconducting. -Carrier concentrations calculated from 8, revealed each Mg2+ to introduce one electron-hole up to about 0.1 at.% Mg. The a.c. conductivities, showing conductivity activation enthalpies of about 0.5 eV in the temperature region 300-800 K, are affected by grain growth and porosity. -The currentvoltage characteristics in the dark and under illumination, the spectral response, and the flatband potential (Vh = +2.2 V vs. SCE pH = 10) have also been determined. -PEC photocurrents in the visible region correspond to very low (-0.lY0) monochromatic quantum efficiency which is due to the low electron-hole mobility. The electronic transition in the visible region is indirect, and evidence has been found for this transition to be Fe-Fe charge transfer. Surface pretreatment is found to have a major effect on the photoelectrochemical properties as deduced from current-voltage curves. The stability of the a-Fe203 electrode in alkaline solution is discussed. IntroductionThe cleavage of water into hydrogen and oxygen in a photoelectrochemical (PEC) cell using a semiconductor photoelectrode has been well established [l -41. Optimal solar energy conversion requires a chemically inert semiconducting electrode material which shows photoconductivity far into the visible, and operates with high energy-conversion efficiencies.Recently, we have studied impurity doping of the stable wide bandgap materials n-type Ti02 and SrTi03 in order to extend their photoresponse into the visible part of the solar spectrum [5, 61. It appeared that with transition metal ion dopants efficient power-conversion efficiencies could only be reached under near uv irradiation. Besides these titanates, the potential applicability of other oxides as photoelectrodes in PEC cells has been studied.The photoelectrochemical properties of iron oxide, a-Fe2O3, have attracted wide-spread attention [7 -301 due to its relatively low bandgap energy of about 2.2 eV [18,31] which is close to the ideal value for optical solar energy absorption, its stability against chemical, and photochemical corrosion [7-9, 16, 191, its vast abundance, and its low cost of preparation.Aliovalent doping is required to render a-Fe2O3 semiconducting [15 -181. However, the flat-band potential of n-type iron oxide lies far below the hydrogen reduction potential [20,27].Hence, a PEC cell with this electrode requires an external bias of about 0.6 eV. While photoassisted electrolysis of water has been dem...

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Section: Results and Discussion Electrical Propertiessupporting

confidence: 85%

“…The admittance spectra were fitted to the equivalent circuit shown in Fig. 4, and will be discussed in more detail elsewhere [48]. The capacitance data were used to construct Mott-Schottky plots.…”

Section: Current-voltage Characteristicsmentioning

confidence: 99%

Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Tinnemans

Koster

Thewissen

et al. 1986

Ber Bunsenges Phys Chem

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“…1−5 These impurities lead to perturbations in the electronic properties of the host material and favor intrinsic defects such as ion vacancies. 6−8 At various levels of dispersion, crystalline MgO particles with iron admixtures are used as pigments, 9 as components for magnetic devices and photovoltaics, 10 and as gas sensors. 11 Beyond dilute solutions in MgO (magnesiowustite), 12 at higher concentrations Fe ions give rise to the annealing-induced nucleation and growth of MgFe 2 O 4 nanoparticles.…”

Section: ■ Introductionmentioning

confidence: 99%

Stability and Local Environment of Iron in Vapor Phase Grown MgO Nanocrystals

et al. 2017

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Metallocene injection into a metal combustion flame has been used for trapping transition metal ions inside MgO nanocrystals. Vacuum annealing changes the properties of resulting nonequilibrium solids toward thermodynamic equilibrium and provides means to control impurity localization and, as a result, the nanomaterials’ functional properties. By combining structure characterization (X-ray diffraction and transmission electron microscopy) with X-ray absorption spectroscopy and Mössbauer measurements, we tracked valence state and local chemical environment changes of Fe3+ ions inside vapor phase synthesized MgO nanocrystals. At a concentration of (1.5 ± 0.2) at. % Fe about (1400 ± 200) Fe3+ ions are effectively diluted within 12 nm sized nanocubes, where they form complexes between Fe3+ ions and Mg2+ vacancies. Increase of the iron concentration produces additional effects: enhanced ion diffusion and particle coarsening at elevated temperatures, clustering of Fe3+–Mg2+ vacancy complexes and, after annealing to T = 1173 K, the nucleation of a magnesioferrite phase that can be detected by X-ray diffraction for 4 at. % samples. At 3 at. % Fe, corresponding impurity ions induce surface energy changes that have a substantial impact on particle shape. With regard to the functional properties associated with transition metal ions in insulating MgO host lattices, the here presented insights underline that annealing-induced reorganization of oxide nanoparticles provides important parameters to control distribution and localization of impurity ions.

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“…Strontium titanate, SrTiO 3 (STO), is an important material in the fields of electronics and catalysis. Owing to its large dielectric nonlinearity, temperature-dependent dielectric tunability, and low microwave losses, this material is an ideal candidate for microwave devices operating at cryogenic temperatures. , In addition, due to its simple structure and semiconducting character, STO has been employed as a model for mixed-metal oxide supports in catalytic reactions such as the partial and total oxidation of hydrocarbons, , photoassisted splitting of H 2 O − for H 2 generation, and reduction of CO 2 − for production of CH 4 and CH 3 OH. Electronic and catalytic applications require ceramic materials with controlled chemical composition, morphology, and atomic structure at both the bulk and surface levels.…”

Section: Introductionmentioning

confidence: 99%

Synthesis-Dependent Surface Acidity and Structure of SrTiO₃Nanoparticles

2010

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Chemisorption of pyridine and atmospheric CO 2 followed by means of visible Raman and DRIFT spectroscopy were employed to investigate the surface acidity and structure of as-prepared SrTiO 3 (STO) samples synthesized using three different approaches, solid-state reaction, molten salt, and sol-precipitation-hydrothermal treatment. Samples prepared via solid-state reaction consisted of irregularly shaped polycrystalline grains with a BET surface area of ∼2 m 2 /g, whereas those obtained via molten salt synthesis and sol-precipitation-hydrothermal treatment were single-crystalline nanocubes with the {100} faces primarily exposed and BET surface areas of ∼10 and 20 m 2 /g, respectively. Pyridine and atmospheric CO 2 chemisorption demonstrated that the differences in surface acidity between samples synthesized using different approaches are rather slight with a mixture of SrO-based and TiO-based terminations observed in all cases. In contrast, the typology of surface carbonate species arising from the reactive adsorption of atmospheric CO 2 varied significantly between samples, indicating the atomic structure of STO surfaces depends strongly on the synthetic method employed. The presence of coordinatively unsaturated Ti 4+ acid centers and highly nucleophilic O 2anions is particularly relevant in the perspective of employing morphology-controlled perovskite nanoparticles as supports in catalytic applications such as the oxidation of hydrocarbons.

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ChemInform Abstract: Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron(III) Oxide.

Abstract: Carrier concentrations calculated for sintered Mg‐doped (0.l ‐5 at.‐°/o) p‐ty‐ pe Fezo, photoelectrodes, reveal each Mg" to introduce one electron‐hole up to about 0.1 at.‐°/o Mg.

Cited by 5 publications

References 1 publication

Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Stability and Local Environment of Iron in Vapor Phase Grown MgO Nanocrystals

Synthesis-Dependent Surface Acidity and Structure of SrTiO₃Nanoparticles

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ChemInform Abstract: Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron(III) Oxide.

Abstract: Carrier concentrations calculated for sintered Mg‐doped (0.l ‐5 at.‐°/o) p‐ty‐ pe Fezo, photoelectrodes, reveal each Mg" to introduce one electron‐hole up to about 0.1 at.‐°/o Mg.

Cited by 5 publications

References 1 publication

Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide

Stability and Local Environment of Iron in Vapor Phase Grown MgO Nanocrystals

Synthesis-Dependent Surface Acidity and Structure of SrTiO3Nanoparticles

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Synthesis-Dependent Surface Acidity and Structure of SrTiO₃Nanoparticles