High coverage hydrogen adsorption on the Fe3O4(110) surface

Exsolution of metal nanoparticles from perovskite-type oxides is a very promising approach to obtain catalysts with superior properties. One particularly interesting property of exsolution catalysts is the possibility of electrochemical switching between different activity states. In this work, synchrotron-based in-situ X-ray diffraction experiments on electrochemically polarized La0.6Sr0.4FeO3-δ thin film electrodes are performed, in order to simultaneously obtain insights into the phase composition and the catalytic activity of the electrode surface. This shows that reversible electrochemical switching between a high and low activity state is accompanied by a phase change of exsolved particles between metallic α-Fe and Fe-oxides. Reintegration of iron into the perovskite lattice is thus not required for obtaining a switchable catalyst, making this process especially interesting for intermediate temperature applications. These measurements also reveal how metallic particles on La0.6Sr0.4FeO3-δ electrodes affect the H2 oxidation and H2O splitting mechanism and why the particle size plays a minor role.

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“…and this step is rather fast 37,[42][43][44][45][46] . The atomic H ad,Fe very likely exchanges with H ad on LSF by surface diffusion.…”

Section: Resultsmentioning

confidence: 99%

Understanding electrochemical switchability of perovskite-type exsolution catalysts

et al. 2020

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“…For the most stable H 2 adsorption there is no correlation between the surface stability and the adsorption energy. For Fe 3 O 4 (110), the more stable A layer (0.947 J/m 2 ) has a homolytic dissociative adsorption energy of −1.73 eV and the less stable B layer (1.020 J/m 2 ) has a homolytic dissociative adsorption energy of −0.78 eV . For Fe 3 O 4 (111), the most stable Fe tet1 termination (0.944 J/m 2 ) has a homolytic dissociative adsorption energy of −1.62 eV and the second stable Fe oct2 termination (1.132J/m 2 ) has a heterolytic dissociative adsorption energy of −1.21 eV .…”

Section: Discussionmentioning

confidence: 99%

High-Coverage H₂ Adsorption on the Reconstructed Cu₂O(111) Surface

Zhang

Wang

et al. 2017

J. Phys. Chem. C

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The adsorption of H2 on the Cu2O(111) surface has been studied by spin-polarized density functional theory (DFT+U) calculations and atomic thermodynamics. It has been found that there exists reconstruction on a stoichiometric Cu2O(111) surface. The probability distribution of the reconstructed Cu2O(111) surfaces as a function of temperature has been analyzed using Boltzmann statistics. It has been found that the molecular H2 prefers to adsorption on the uncoordinated CuCUS atom at low coverages (1/4 or 1/2 monolayer), while totally dissociative H2 is preferred on the reconstructed Cu2O(111) surface at higher coverages (3/4 or 1 monolayer). For H2 splitting on the Cu2O(111) surface, homolytical dissociative adsorption on two surface-uncoordinated CuCUS atoms is preferred which is a new mechanism for H2 on metal oxides. More interesting is that the surface reconstruction will be recovered for eight hydrogen atoms binding on four uncoordinated CuCUS and four uncoordinated OCUS atoms at saturation coverage. It has been found that the adsorbed H atoms will put out the lattice oxygen to the surface at higher coverage (five and six H2), which agrees well with the experimental findings. The phase diagrams of H2 binding on ideal and reconstructed Cu2O(111) surfaces were plotted and analyzed. In addition, we compared and analyzed the adsorption mechanisms of H2 splitting on different metal oxides.

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“…Again, the DFT+U calculations were performed for the Fe oct -O and Fe oct -Fe tet -O bulk terminations (denoted A and B termination in ref. [403], respectively). H 2 O was found adsorb molecularly on the A termination at low coverage, and in a mixed mode at higher coverage, while dissociation to surface hydroxyls occurred on the B termination.…”

Section: H 2 O/fe 3 O 4 (110)mentioning

confidence: 91%

“…There has been one theoretical study of H 2 adsorption on Fe 3 O 4 (110) [403], albeit on bulk truncated surfaces inconsistent with experimental observation. Using GGA+U, Yu et al determined that H adsorbs preferentially at O atoms to form hydroxyl groups.…”

Section: H/fe 3 O 4 (110)mentioning

confidence: 98%

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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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High coverage hydrogen adsorption on the Fe3O4(110) surface

Cited by 18 publications

References 42 publications

Understanding electrochemical switchability of perovskite-type exsolution catalysts

Understanding electrochemical switchability of perovskite-type exsolution catalysts

High-Coverage H₂ Adsorption on the Reconstructed Cu₂O(111) Surface

Iron oxide surfaces

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High coverage hydrogen adsorption on the Fe3O4(110) surface

Cited by 18 publications

References 42 publications

Understanding electrochemical switchability of perovskite-type exsolution catalysts

Understanding electrochemical switchability of perovskite-type exsolution catalysts

High-Coverage H2 Adsorption on the Reconstructed Cu2O(111) Surface

Iron oxide surfaces

Contact Info

Product

Resources

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High-Coverage H₂ Adsorption on the Reconstructed Cu₂O(111) Surface