Structure of the NiFe2O4(001) surface in contact with gaseous O2 and water vapor

Shi, Xiang; Li, Yefei; Bernasek, S. L.; Selloni, Annabella

doi:10.1016/j.susc.2015.03.012

Cited by 32 publications

(23 citation statements)

References 26 publications

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“…The Coulomb repulsions of 3d states of Ni and Fe were taken into account as the reference. 52 Spin polarization and magnetic properties were considered as well. 53 We used the most preferable surface (111) of nickel ferrite spinel, which has been reported by previous theoretical studies.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature

et al. 2016

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H2 selective catalytic reduction (H2-SCR) has been proposed as a promising technology for controlling NOx emission because hydrogen is clean and does not emit greenhouse gases. We demonstrate that Pt doped into a nickel ferrite spinel structure can afford a high catalytic activity of H2-SCR. A superior NO conversion of 96% can be achieved by employing a novel NiFe1.95Pt0.05O4 spinel-type catalyst at 60 °C. This novel catalyst is different from traditional H2-SCR catalysts, which focus on the role of metallic Pt species and neglect the effect of oxidized Pt states in the reduction of NO. The obtained Raman and XPS spectra indicate that Pt in the spinel lattice has different valence states with Pt(2+) occupying the tetrahedral sites and Pt(4+) residing in the octahedral ones. These oxidation states of Pt enhance the back-donation process, and the lack of filling electrons of the 5d band causes Pt to more readily hybridize with the 5σ orbital of the NO molecule, especially for octahedral Pt(4+), which enhances the NO chemisorption on the Pt sites. We also performed DFT calculations to confirm the enhancement of adsorption of NO onto Pt sites when doped into the Ni-Fe spinel structure. The prepared Pt/Ni-Fe catalysts indicate that increasing the dispersity of Pt on the surfaces of the individual Ni-Fe spinel-type catalysts can efficiently promote the H2-SCR activity. Our demonstration provides new insight into designing advanced catalysts for H2-SCR.

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Section: ■ Results and Discussionmentioning

confidence: 99%

“…We chose a plane-wave energy cutoff of 400 eV with the residual force components on each atom lower than ∼0.05 eV Å –1 atom –1 . The Coulomb repulsions of 3d states of Ni and Fe were taken into account as the reference . Spin polarization and magnetic properties were considered as well …”

Section: Experimental Sectionmentioning

confidence: 99%

Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature

et al. 2016

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“…The structure, electronic properties, and energetics of the NiFe 2 O 4 ð001Þ surface and its interaction with water both in the absence and in the presence of surface oxygen vacancies have been studied using DFT+U. 122 It was shown that water adsorbs dissociatively on the surface oxygen vacancies leading to the formation of surface hydroxyls. Furthermore, it was found that at high temperature, water desorbs leaving a surface containing oxygen vacancies.…”

Section: Surfaces and Adsorptionmentioning

confidence: 99%

Photoelectrochemical and theoretical investigations of spinel type ferrites (M_xFe_3−xO₄) for water splitting: a mini-review

et al. 2016

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Solar-assisted water splitting using photoelectrochemical cells (PECs) is one of the promising pathways for the production of hydrogen for renewable energy storage. The nature of the semiconductor material is the primary factor that controls the overall energy conversion efficiency. Finding semiconductor materials with appropriate semiconducting properties (stability, efficient charge separation and transport, abundant, visible light absorption) is still a challenge for developing materials for solar water splitting. Owing to the suitable bandgap for visible light harvesting and the abundance of iron-based oxide semiconductors, they are promising candidates for PECs and have received much research attention. Spinel ferrites are subclasses of iron oxides derived from the classical magnetite (Fe II Fe III 2 O 4) in which the Fe II is replaced by one (some cases two) additional divalent metals. They are generally denoted as M x Fe 3−x O 4 (M ¼ Ca, Mg, Zn, Co, Ni, Mn, and so on) and mostly crystallize in spinel or inverse spinel structures. In this mini review, we present the current state of research in spinel ferrites as photoelectrode materials for PECs application. Strategies to improve energy conversion efficiency (nanostructuring, surface modification, and heterostructuring) will be presented. Furthermore, theoretical findings related to the electronic structure, bandgap, and magnetic properties will be presented and compared with experimental results. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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“…Surfaces with V O s are favoured, and these react with water to create adsorbed hydroxyls in a humid atmosphere. Reprinted from ref [533],. with permission from Elsevier.…”

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confidence: 99%

Iron oxide surfaces

Parkinson

2016

Surface Science Reports

501

463

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The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), hematite (α-Fe 2 O 3 ), and wüstite (Fe 1-x O) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe 3 O 4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment, and because it is an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed.The best understood iron oxide surface at present is probably Fe 3 O 4 (100); the structure is known with a high degree of precision and the major defects and properties are well characterised. A major factor in this is that a termination at the Fe oct -O plane can be reproducibly prepared by a variety of methods, as long as the surface is annealed in 10 Such straightforward preparation of a monophase termination is generally not the case for other iron oxide surfaces. All available evidence suggests the oft-studied (√2×√2)R45° reconstruction results from a rearrangement of the cation lattice in the outermost unit cell in which two octahedral cations are replaced by one tetrahedral interstitial, a motif conceptually similar to well-known Koch-Cohen defects in Fe (0001) is the most studied hematite surface, but 2 difficulties preparing stoichiometric surfaces under UHV conditions have hampered a definitive determination of the structure. There is evidence for at least three terminations: a bulk-like termination at the oxygen plane, a termination with half of the cation layer, and a termination with ferryl groups. When the surface is reduced the so-called "bi-phase" structure is formed, which eventually transforms to a Fe 3 O 4 (111)-like termination. The structure of the bi-phase surface is controversial; a largely accepted model of coexisting Fe 1-x O and α-Fe 2 O 3 (0001) islands was recently challenged and a new structure based on a thin film of Fe 3 O 4 (111) on α-Fe 2 O 3 (0001) was proposed. The merits of the compet...

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Structure of the NiFe2O4(001) surface in contact with gaseous O2 and water vapor

Cited by 32 publications

References 26 publications

Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature

Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature

Photoelectrochemical and theoretical investigations of spinel type ferrites (M_xFe_3−xO₄) for water splitting: a mini-review

Iron oxide surfaces

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Structure of the NiFe2O4(001) surface in contact with gaseous O2 and water vapor

Cited by 32 publications

References 26 publications

Pt-Doped NiFe2O4 Spinel as a Highly Efficient Catalyst for H2 Selective Catalytic Reduction of NO at Room Temperature

Pt-Doped NiFe2O4 Spinel as a Highly Efficient Catalyst for H2 Selective Catalytic Reduction of NO at Room Temperature

Photoelectrochemical and theoretical investigations of spinel type ferrites (MxFe3−xO4) for water splitting: a mini-review

Iron oxide surfaces

Contact Info

Product

Resources

About

Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature

Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature

Photoelectrochemical and theoretical investigations of spinel type ferrites (M_xFe_3−xO₄) for water splitting: a mini-review