Environmentally dependent stability of low-index hematite surfaces

Guo, Haibo; Barnard, Amanda S.

doi:10.1016/j.jcis.2012.07.011

Cited by 24 publications

(32 citation statements)

References 93 publications

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“…On the contrary, calculations at zero bias predict a hydroxylated surface. 12,21,23,31,32 In fact, to the best of our knowledge all experimental studies investigating in detail the hydroxylation state of the surface are conducted in contact with water vapour and not in liquid water. 12,14,33 While in all these cases a hydroxylated surface was found, our calculations imply that the surface would lose protons when put in liquid water under illumination.…”

Section: Surface Free Energymentioning

confidence: 99%

Photo-driven oxidation of water on α-Fe2O3 surfaces: An ab initio study

Nguyen

Seriani

Piccinin

et al. 2014

The Journal of Chemical Physics

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Adopting the theoretical scheme developed by the Nørskov group [see, for example, Nørskov et al., J. Phys. Chem. B 108, 17886 (2004)], we conducted a density functional theory study of photo-driven oxidation processes of water on various terminations of the clean hematite (α-Fe2O3) (0001) surface, explicitly taking into account the strong correlation among the 3d states of iron through the Hubbard U parameter. Six best-known terminations, namely, Fe−Fe−O3− (we call S1), O−Fe−Fe−(S2), O2−Fe−Fe−(S3), O3−Fe−Fe− (S4), Fe−O3−Fe− (S5), and O−Fe−O3−(S6), are first exposed to water, the stability of resulting surfaces is investigated under photoelectrochemical conditions by considering different chemical reactions (and their reaction free energies) that lead to surfaces covered by O atoms or/and OH groups. Assuming that the water splitting reaction is driven by the redox potential for photogenerated holes with respect to the normal hydrogen electrode, UVB, at voltage larger than UVB, most 3-oxygen terminated substrates are stable. These results thus suggest that the surface, hydroxylated in the dark, should release protons under illumination. Considering the surface free energy of all the possible terminations shows that O3–S5 and O3–S1 are the most thermodynamically stable. While water oxidation process on the former requires an overpotential of 1.22 V, only 0.84 V is needed on the latter.

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Section: Surface Free Energymentioning

confidence: 99%

Photo-driven oxidation of water on α-Fe2O3 surfaces: An ab initio study

Nguyen

Seriani

Piccinin

et al. 2014

The Journal of Chemical Physics

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“…It was reported that O-terminated surfaces had unfavorable energies compared to those of Fe-terminated surfaces, 40 while other studies showed that the oxygen-balanced terminations (in which the coe±cients of O 2 , NO 2 were zero) had lower surface energies than those that were oxygen-unbalanced (in which NO 2 was either positive or negative), 24 because the terminations of di®erent surfaces were oxygen atom terminated or ferric terminated depending on the surface energy. Therefore, to investigate the di®erences between these possible terminations, slab models of H(001), H(101) and H(104) with di®erent terminations are presented in Figs.…”

Section: Surface Terminationsmentioning

confidence: 99%

“…To avoid the interactions among large-size molecules, we used 1 Â 2 Â 2 super cells of H (001) These models contained all of the typical features of H(001), H(101), and H(104) that are commonly used in past studies. 24 The surface sizes of H(001), H(101), and H(104) were 10.07 Å Â 10.07 Å, The structures were optimized with the BroydenFletcher-Goldfarb-Shanno (BFGS) method, and the convergence criteria for the geometric optimization and energy calculation were set as follows: (a) an energy tolerance of the 1 Â 10 À5 eV/atom; (b) a self-consistent¯eld tolerance of the 1 Â 10 À6 eV/ atom; (c) a maximum force tolerance of 0.03 eV/Å; and (d) a maximum displacement tolerance of 1:0 Â 10 À3 Å. The selection of these parameters was determined by performing tests on the stability of the structure and relative energies as the accuracy of the parameters increased.…”

Section: Computational Detailsmentioning

confidence: 99%

“…In addition to (001), researchers found that the (101) and (104) surfaces were also morphologically signi¯cant. 24 Therefore, we investigated and compared Hematite (001) crystal faces, Hematite (101) crystal faces and Hematite (104) crystal faces (H(001), H(101) and H(104)) to determine the origins of the preferred orientation of the Hematite nano rings. The as-synthesized iron oxide nanostructures were characterized by a¯eld emission scanning electron microscopy (SEM), a transmission electron microscopy (TEM) and a high-resolution TEM (HRTEM).…”

Section: Introductionmentioning

confidence: 99%

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The Synthesis and Mechanism of (001)-Orientated Hematite Nano Rings: A Combined Theoretical and Experimental Investigation

Liu

Gong

et al. 2017

NANO

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In this study, we synthesized Hematite nano rings using hydrothermal treatment. The experimental results demonstrated that the (001)-orientated Hematite nano rings were produced in all of the obtained products. To determine the formation mechanism of the (001) orientation, the lowest three index crystal faces of Hematite, Hematite (001), Hematite (101), and Hematite (104), were investigated with the Cambridge Sequential Total Energy Package (CASTEP) within the Materials Studio software environment (MS5.5) using the density functional theory (DFT). Our theoretical results showed that Hematite (001), the Hematite crystal with the lowest surface energy, had the greatest Hematite nano ring growth. In addition, we present the growth process of the Hematite nano rings based on our experimental and theoretical results.

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“…31 Single crystals of hematite with nearly 100% exposed [012] facets show improved photocatalytic properties over nanoplates with dominant [001] facets. 32 Fe2O3 with high-index facets shows a noticeable catalytic activity. However, differing from catalytic reaction course, Fe2O3 is gradually reduced and structurally destroyed during CLC process.…”

Section: Introductionmentioning

confidence: 99%

Reaction Activity and Deep Reduction Reaction Mechanism of a High Index Iron Oxide Surface in Chemical Looping Combustion

Wu¹,

Lin²,

Long³

et al. 2015

Acta Physico-Chimica Sinica

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The possibility of morphological control of iron oxide as an oxygen carrier for chemical looping combustion was investigated using density functional theory and experiment. First, we calculated the reactivity of Fe2O3 with high-index facets [104] and low-index facets [001], as well as the deep reduction reaction mechanism of these two facets. Surface reaction results show that the activity of Fe2O3[104] for oxidizing CO is greater than that of Fe2O3[001]. Fe2O3[104] was reduced into iron oxide at lower oxidation state or into iron, which could then be regenerated after being oxidized by O2. The deep reduction reaction mechanism between oxygen carrier and CO shows that Fe2O3[104] can be completely reduced into Fe, and Fe2O3[104] exhibits high oxygen transfer ability. However, Fe2O3[001] can only be reduced to a limited extent, with a high energy barrier preventing further reduction, while it also exhibits limited oxygen transfer capacity. Results of experiments further verify the high reactivity and stability of Fe2O3[104].

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Environmentally dependent stability of low-index hematite surfaces

Cited by 24 publications

References 93 publications

Photo-driven oxidation of water on α-Fe2O3 surfaces: An ab initio study

Photo-driven oxidation of water on α-Fe2O3 surfaces: An ab initio study

The Synthesis and Mechanism of (001)-Orientated Hematite Nano Rings: A Combined Theoretical and Experimental Investigation

Reaction Activity and Deep Reduction Reaction Mechanism of a High Index Iron Oxide Surface in Chemical Looping Combustion

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