Polytypism in Sulfate-Intercalated Layered Double Hydroxides of Zn and M(III) (M = Al, Cr): Observation of Cation Ordering in the Metal Hydroxide Layers

Radha, Santosh Kumar; Kamath, P. Vishnu

doi:10.1021/ic3023198

Cited by 20 publications

(46 citation statements)

References 32 publications

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“…The structure refined (space group P-3, a = b = 5.414 Å, c = 11.07 Å) 8 not have hexagonal symmetry any more, with three nonbonded in-plane HO---OH distances. The position of the hydroxyl ions cannot be described by the symbols A, B, and C, which is used to describe a close packing of atoms.…”

Section: ■ Results and Discussionmentioning

confidence: 98%

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Layered Double Hydroxides: Proposal of a One-Layer Cation-Ordered Structure Model of Monoclinic Symmetry

2015

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Layered double hydroxides are obtained by partial isomorphous substitution of divalent metal ions by trivalent metal ions in the structure of mineral brucite, Mg(OH)2. The widely reported three-layer polytype of rhombohedral symmetry, designated as polytype 3R1, is actually a one-layer polytype of monoclinic symmetry (space group C2/m, a = 5.401 Å, b = 9.355 Å, c = 11.02 Å, β = 98.89°). This structure has a cation-ordered metal hydroxide layer defined by a supercell a = √3 × a0; b = 3 × a0 (a0 = cell parameter of the cation-disordered rhombohedral cell). Successive layers are translated by (1/3, 0, 1) relative to one another. When successive metal hydroxide layers are translated by (2/3, 0, 1) relative to one another, the resultant crystal, also of monoclinic symmetry, generates a powder pattern corresponding to the polytype hitherto designated as 3R2. This structure model not only removes all the anomalies intrinsic to the widely accepted cation-disordered structure but also abides by Pauling's rule that forbids trivalent cations from occupying neighboring sites and suggests that it is unnecessary to invoke rhombohedral symmetry when the metal hydroxide layer is cation ordered. These results have profound implications for the correct description of polytypism in this family of layered compounds.

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Section: ■ Results and Discussionmentioning

confidence: 98%

“…8 There are, in our opinion, three ways in which the hexagonal LDH crystal could distort to monoclinic symmetry. Although these factors are interrelated, each can be examined in turn to arrive at the major causative factor.…”

Section: ■ Structure Refinementmentioning

confidence: 99%

Layered Double Hydroxides: Proposal of a One-Layer Cation-Ordered Structure Model of Monoclinic Symmetry

2015

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“…All of the three LDHs crystallize in hexagonal symmetry (space group P 3; a obs = 5.35–5.41 Å, c obs = 11.05–11.15 Å; obs: observed) . These structures were used as input for the SIESTA program.…”

Section: Resultsmentioning

confidence: 99%

“…All of the three LDHs crystallize in hexagonal symmetry (space group P3; a obs = 5.35-5.41 Å, c obs = 11.05-11.15 Å; obs: observed). [17][18][19] These structures were used as input for the SIESTA program. The experimental structures were obtained from X-ray diffraction data and do not include proton positions.…”

Section: Computation Of the Structure By Energy Minimizationmentioning

confidence: 99%

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Electronic‐Structure Calculations of Cation‐Ordered II‐III Layered Double Hydroxides: Origin of the Distortion of the Metal‐Coordination Symmetry

2017

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Cation ordering brings down the crystal symmetry and introduces distortion into the coordination polyhedra around the divalent cations. In particular, edge sharing of the differently sized [M(OH)6] polyhedra causes a non‐uniform distension of the array of hydroxy ions. The question arises as to whether this distortion has its origin in the Jahn–Teller distortion of metal coordination or a 2D “Peierls”‐type distortion of the array of hydroxy ions. To address this question, DFT calculations were performed on the sulfate‐intercalated [Cu–Cr], [Zn–Cr], and [Zn–Al] layered double hydroxides (LDHs). An analysis of the density of states shows that the distortion of the Cu2+ coordination polyhedron is due to the Jahn–Teller effect, whereas the Zn2+ coordination polyhedron in [Zn–Al] LDH likely suffers a “Peierls”‐type distortion. In the [Zn–Cr] LDH, electronic‐structure calculations do not predict any distortion in the metal coordination, which is in agreement with experimental results that show only a slight departure from ideal symmetry.

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Highly Active Trimetallic NiFeCr Layered Double Hydroxide Electrocatalysts for Oxygen Evolution Reaction

Yang

Dang

Shearer

et al. 2018

Advanced Energy Materials

534

294

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rechargeable metal-air batteries. [1,2] This reaction demands efficient electrocatalysts that can accelerate the reaction rate, lower the overpotential, and remain stable over time. Currently, noble-metal-based compounds such as IrO 2 and RuO 2 provide good OER performance under alkaline conditions, but their large-scale application is restricted by their scarcity and high cost. [3] Accordingly, much research effort has been devoted to the development of high-performance earth-abundant OER electrocatalysts based on transition-metal elements, usually in the form of metal oxides or metal (oxy)hydroxides, that are inexpensive and stable upon prolonged exposure under oxidizing conditions. [4][5][6][7] In addition to the synergistic effects of transition metals and electrical conductivity, the intrinsic activities of these transition metal oxide or (oxy)hydroxide OER catalysts are closely connected to the number of 3d electrons of the metals; the surface transition-metal ions exhibited e g orbitals which could bond with surfaceanion adsorbates and then influence the binding of oxygenic intermediates. [8,9] The binding strength of these intermediates is thought to dictate catalytic activity. [10] Identifying the relationship between OER activity and the catalyst electronic structure can provide a simple rationale for gaining mechanistic insights and finding new design strategies for the earth-abundant OER catalysts.Among various transition metal-based OER catalysts, metal layered double hydroxides (LDHs) and oxyhydroxides have attracted much attention because of their abundance in the earth's crust and their considerable catalytic activity. [5,6,[11][12][13][14][15][16][17][18][19][20][21] NiFe LDH and more generally NiFe (oxy)hydroxides have emerged as the most active OER catalyst compared to other bimetallic earth-abundant LDHs under basic conditions, [6,15,17,22] and several studies have been directed at understanding the role of Fe in increasing the OER intrinsic activity of NiFe-containing (oxy) hydroxide materials. [23] Boettcher and co-workers demonstrated that Fe incorporation into NiOOH lattice enhances the electronic conductivity in the film and Fe exerts a partial-chargetransfer activation effect on Ni centers throughout the catalyst film, but the enhanced catalytic efficiency cannot be completely explained. [17] To better understand the role of Fe, they further studied other incorporated metal cations (Mn, Ti, Ce, Fe, and La) in NiO x H y , finding that only Fe permanently increases the OER The development of efficient and robust earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is an ongoing challenge. Here, a novel and stable trimetallic NiFeCr layered double hydroxide (LDH) electrocatalyst for improving OER kinetics is rationally designed and synthesized. Electrochemical testing of a series of trimetallic NiFeCr LDH materials at similar catalyst loading and electrochemical surface area shows that the molar ratio Ni:Fe:Cr = 6:2:1 exhibits the best intrinsic OER catalytic activity ...

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Polytypism in Sulfate-Intercalated Layered Double Hydroxides of Zn and M(III) (M = Al, Cr): Observation of Cation Ordering in the Metal Hydroxide Layers

Cited by 20 publications

References 32 publications

Layered Double Hydroxides: Proposal of a One-Layer Cation-Ordered Structure Model of Monoclinic Symmetry

Layered Double Hydroxides: Proposal of a One-Layer Cation-Ordered Structure Model of Monoclinic Symmetry

Electronic‐Structure Calculations of Cation‐Ordered II‐III Layered Double Hydroxides: Origin of the Distortion of the Metal‐Coordination Symmetry

Highly Active Trimetallic NiFeCr Layered Double Hydroxide Electrocatalysts for Oxygen Evolution Reaction

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