W‐Based Atomic Laminates and Their 2D Derivative W<sub>1.33</sub>C MXene with Vacancy Ordering

Meshkian, Rahele; Dahlqvist, Martin; Lu, Jun; Wickman, Björn; Halim, Joseph; Thörnberg, Jimmy; Tao, Quanzheng; Li, Shixuan; Intikhab, Saad; Snyder, Joshua; Barsoum, Michel W.; Yildizhan, Melike; Pališaitis, Justinas; Hultman, Lars; Persson, Per; Rosén, Johanna

doi:10.1002/adma.201706409

Cited by 282 publications

(217 citation statements)

References 43 publications

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“…are estimated to be around 0.156, 0.172, 0.177, 0.162, and 0.185 eV/Å 2 , respectively. Since all obtained exfoliation energies are less than 0.205 eV/Å 2 , we predict, according to our previous analysis [70], that the above iMAX phases can be exfoliated into 2D iMXenes, as indeed observed in experiments [54,56,71].…”

Section: A Imax Phasessupporting

confidence: 79%

“…In fact, currently, (Mo 2/3 Sc 1/3 ) 2 AlC and (Mo 2/3 Y 1/3 ) 2 AlC have been exfoliated to Mo 1.33 C experimentally [54,71]. Likewise, (W 2/3 Sc 1/3 ) 2 AlC and (W 2/3 Y 1/3 ) 2 AlC have been exfoliated to W 1.33 C experimentally [56].…”

Section: A Imax Phasesmentioning

confidence: 98%

“…One of the unique structural characteristics of MAX phases is that they can be formed in various solid solutions with pure or mixtures of M, A, and X elements [41][42][43][44][45][46][47][48][49][50][51]. In addition to traditional M n+1 AX n MAX phases, several sets of crystalline ordered double transition metal MAX phases, M ′ 2 M ′′ AX 2 , M ′ 2 M ′′ 2 AX 3 [52,53], and (M ′ 2/3 M ′′ 1/3 ) 2 AX [54][55][56], have been discovered recently. In M ′ 2 M ′′ AX 2 and M ′ 2 M ′′ 2 AX 3 , the layers are occupied purely with an M ′ , M ′′ , A, or X element.…”

Section: Introductionmentioning

confidence: 99%

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Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials

Khazaei

Wang

Sevik

et al. 2018

Phys. Rev. Materials

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Recently, a group of MAX phases, (Mo 2/3 Y 1/3 )2AlC, (Mo 2/3 Sc 1/3 )2AlC, (W 2/3 Sc 1/3 )2AlC, (W 2/3 Y 1/3 )2AlC, and (V 2/3 Zr 1/3 )2AlC, with in-plane ordered double transition metals, named iMAX phases, have been synthesized. Experimentally, some of these MAX phases can be chemically exfoliated into two-dimensional (2D) single-or multilayered transition metal carbides, so-called MXenes. Accordingly, the 2D nanostructures derived from iMAX phases are named iMXenes. Here, we investigate the structural stabilities and electronic structures of the experimentally discovered iMAX phases and their possible iMXene derivatives. We show that the iMAX phases and their pristine, F, or OH-terminated iMXenes are metallic. However, upon O termination, (Mo 2/3 Y 1/3 )2C, (Mo 2/3 Sc 1/3 )2C, (W 2/3 Y 1/3 )2C, and (W 2/3 Sc 1/3 )2C iMXenes turn into semiconductors. The semiconducting iMXenes may find applications in piezoelectricity owing to the absence of centrosymmetry. Our calculations reveal that the semiconducting iMXenes possess giant piezoelectric coefficients as large as 45×10 −10 C/m.

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Section: A Imax Phasessupporting

confidence: 79%

Section: A Imax Phasesmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials

Khazaei

Wang

Sevik

et al. 2018

Phys. Rev. Materials

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“…The structure is inherited from the parent MAX phase (hexagonal, space group P6 3 /mmc ), but compositional tuning displays an extraordinary toolbox for property tuning through MXenes based on single M and X elements, as well as alloys on both M and X . In addition, there are reports on MXenes forming out‐of‐plane and in‐plane double‐M elemental ordering, as well as vacancy‐ordered structures . Manipulation of the surface terminations constitutes the final and most powerful variable for property tuning .…”

mentioning

confidence: 99%

2D Transition Metal Carbides (MXenes) for Carbon Capture

et al. 2018

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charge storage, [7,8] electromagnetic interference shielding, [9] filtering, [10] and a range of additional applications. [7] MXenes constitute a large and growing family of 2D materials [11,12] that are obtained from the laminated M n+1 AX n (MAX) phases (M is a transition metal, A is a group A element-mostly groups 13 and 14-and X is C and/or N) [13] by chemical etching of the atomically thin A element layers that separate sheets of M n+1 X n . As the A element is removed, the MXene surfaces are immediately functionalized by surface terminating species, T x . [6,14] Hence, the proper MXene formula is M n+1 X n T x . Accordingly, the MXene properties can be tuned through structure, intrinsic composition, and surface terminations. The structure is inherited from the parent MAX phase (hexagonal, space group P6 3 /mmc), but compositional tuning displays an extraordinary toolbox for property tuning through MXenes based on single M and X elements, as well as alloys on both M and X. [12,15] In addition, there are reports on MXenes forming out-of-plane [16] and in-plane [17] double-M elemental ordering, as well as vacancy-ordered structures. [18,19] Manipulation of the surface terminations constitutes the final and most powerful variable for property tuning. [20] Despite several theoretical investigations, [21][22][23] noninherent terminations have remained experimentally unexplored. Currently, the MXene preparation dictates that T x is inherent to the etchant and predominantly a combination of O and F, where OH has also been considered as a minor [24] or even negligible contribution. [25] In the area of carbon capture (CC), MXenes are predicted to be highly efficient for capturing CO 2 , enabling capture of 2-8 mol CO 2 kg −1 . [20,21] However, the MXene surfaces were assumed to be termination free, an experimentally unrealistic starting point, given the current wet-chemical preparation routes for MXenes. To unlock the MXene potential for noninherent terminations or adsorption of other molecules, such as CO 2 , we have subjected the archetype Ti 3 C 2 T x MXene to a novel approach. Using in situ environmental transmission electron microscopy (ETEM), single Ti 3 C 2 T x sheets were subjected to an initial high-temperature treatment to desorb F, [25] and a subsequent H 2 exposure to remove the persistent O from the surfaces. The thereafter termination-depleted MXene was subsequently exposed to CO 2 gas, resulting in the first MXene to be terminated by a noninherent molecule. Additionally, termination-depleted MXene surfaces were exposed to N 2 gas after which no N adsorption was observed, Global warming caused by burning of fossil fuels is indisputably one of mankind's greatest challenges in the 21st century. To reduce the everincreasing CO 2 emissions released into the atmosphere, dry solid adsorbents with large surface-to-volume ratio such as carbonaceous materials, zeolites, and metal-organic frameworks have emerged as promising material candidates for capturing CO 2 . However, challenges remain because of limited CO...

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“…Among these materials, 2D TMCs possess excellent electrical conductivity, electrochemical activity, high surface area, and strong chemical resilience . These make them particularly desirable for various clean energy applications such as energy storage and catalysis .…”

Section: Summary Of Catalyst Activity Of Different Carbides For Her Imentioning

confidence: 99%

Self‐Assembly of Large‐Area 2D Polycrystalline Transition Metal Carbides for Hydrogen Electrocatalysis

et al. 2018

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hydrogen evolution using sustainably produced electricity has promised a carbonfree production of a chemical fuel. [5] However, most commercial hydrogen is still produced via steam reforming of methane because there are few scalable base-metal replacements for platinum at the scales required for electrocatalysis. [6] Dimensional reduction of 3D materials to 0D, 1D, or 2D nanostructures (thickness vs lateral size < 1%), [7,8] has attracted interest for discovering intriguing new catalytic properties. Notably, including 2D nanostructures comprised of metals, [9] transition metal dichalcogenides, [10][11][12] transition metal oxides, [13,14] and 2D transition metal carbides (TMCs) [15] have been explored for enhanced catalytic performance, and advances in this area have led to reliable and cost-effective fabrication methods ideal for base-metal hydrogen evolution catalysts.Among these materials, 2D TMCs possess excellent electrical conductivity, electrochemical activity, high surface area, and strong chemical resilience. [16] These make them particularly desirable for various clean energy applications such as energy storage [17][18][19] and catalysis. [7,15] The most widely applied method toward 2D TMCs requires a selective etching process from their Low-dimensional (0/1/2 dimension) transition metal carbides (TMCs) possess intriguing electrical, mechanical, and electrochemical properties, and they serve as convenient supports for transition metal catalysts. Large-area single-crystalline 2D TMC sheets are generally prepared by exfoliating MXene sheets from MAX phases. Here, a versatile bottom-up method is reported for preparing ultrathin TMC sheets (≈10 nm in thickness and >100 μm in lateral size) with metal nanoparticle decoration. A gelatin hydrogel is employed as a scaffold to coordinate metal ions (Mo 5+ , W 6+ , Co 2+ ), resulting in ultrathin-film morphologies of diverse TMC sheets. Carbonization of the scaffold at 600 °C presents a facile route to the corresponding MoC x , WC x , CoC x , and to metal-rich hybrids (Mo 2−x W x C and W/Mo 2 C-Co). Among these materials, the Mo 2 C-Co hybrid provides excellent hydrogen evolution reaction (HER) efficiency (Tafel slope of 39 mV dec −1 and 48 mV j = 10 mA cm −2 in overpotential in 0.5 m H 2 SO 4 ). Such performance makes Mo 2 C-Co a viable noble-metal-free catalyst for the HER, and is competitive with the standard platinum on carbon support. This template-assisted, self-assembling, scalable, and low-cost manufacturing process presents a new tactic to construct low-dimensional TMCs with applications in various cleanenergy-related fields. Hydrogen ElectrocatalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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W‐Based Atomic Laminates and Their 2D Derivative W_1.33C MXene with Vacancy Ordering

Cited by 282 publications

References 43 publications

Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials

Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials

2D Transition Metal Carbides (MXenes) for Carbon Capture

Self‐Assembly of Large‐Area 2D Polycrystalline Transition Metal Carbides for Hydrogen Electrocatalysis

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W‐Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering

Cited by 282 publications

References 43 publications

Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials

Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials

2D Transition Metal Carbides (MXenes) for Carbon Capture

Self‐Assembly of Large‐Area 2D Polycrystalline Transition Metal Carbides for Hydrogen Electrocatalysis

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Product

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W‐Based Atomic Laminates and Their 2D Derivative W_1.33C MXene with Vacancy Ordering