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  • 1.
    Ghidiu, Michael
    et al.
    Drexel University, PA 19104 USA.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, PA 19104 USA.
    Kota, Sankalp
    Drexel University, PA 19104 USA.
    Bish, David
    Indiana University, IN 47405 USA.
    Gogotsi, Yury
    Drexel University, USA.
    Barsourm, Michel W.
    Drexel University, USA.
    Ion-Exchange and Cation Solvation Reactions in Ti3C2 MXene2016In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 28, no 10, p. 3507-3514Article in journal (Refereed)
    Abstract [en]

    Ti3C2 and other two-dimensional transition metal carbides known as MXenes are currently being explored for many applications involving intercalated ions, from electrochemical energy storage, to contaminant sorption from water, to selected ion sieving. We report here a systematic investigation of ion exchange in Ti3C2 MXene and its hydration/dehydration behavior. We have investigated the effects of the presence of LiCl during the chemical etching of the MAX phase Ti3AlC2 into MXene Ti3C2Tx (T stands for surface termination) and found that the resulting MXene has Li+ cations in the interlayer space. We successfully exchanged the Li+ cations with K+, Na+, Rb+, Mg2+, and Ca2+ (supported by X-ray photoelectron and energy-dispersive spectroscopy) and found that the exchanged material expands on the unit-cell level in response to changes in humidity, with the nature expansion dependent on the intercalated cation, similar to behavior of clay minerals; stepwise expansions of the basal spacing were observed, with changes consistent with the size of the H2O molecule. Thermogravimetric analysis of the dehydration behavior of these materials shows that the amounts of H2O contained at ambient humidity correlates simply with the hydration enthalpy of the intercalated cation, and that the diffusion of the exiting H2O proceeds with kinetics similar to clays. These results have implications for understanding, controlling, and exploiting structural changes and H2O sorption in MXene films and powders utilized in applications involving ions, such as electrochemical capacitors, sensors, reverse osmosis membranes, or contaminant sorbents.

  • 2.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.

    Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.

    MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.

    New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.

    In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.

    List of papers
    1. Room-Temperature Carbide-Derived Carbon Synthesis by Electrochemical Etching of MAX Phases
    Open this publication in new window or tab >>Room-Temperature Carbide-Derived Carbon Synthesis by Electrochemical Etching of MAX Phases
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    2014 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 126, no 19, p. 4977-4980Article in journal (Refereed) Published
    Abstract [en]

    Porous carbons are widely used in energy storage and gas separation applications, but their synthesis always involves high temperatures. Herein we electrochemically selectively extract, at ambient temperature, the metal atoms from the ternary layered carbides, Ti3AlC2, Ti2AlC and Ti3SiC2 (MAX phases). The result is a predominantly amorphous carbide-derived carbon, with a narrow distribution of micropores. The latter is produced by placing the carbides in HF, HCl or NaCl solutions and applying anodic potentials. The pores that form when Ti3AlC2 is etched in dilute HF are around 0.5 nm in diameter. This approach forgoes energy-intensive thermal treatments and presents a novel method for developing carbons with finely tuned pores for a variety of applications, such as supercapacitor, battery electrodes or CO2 capture.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2014
    Keywords
    Carbide; Cyclovoltammetrie; Elektrochemie; Kohlenstoff; Oxidationen
    National Category
    Chemical Sciences Physical Chemistry
    Identifiers
    urn:nbn:se:liu:diva-111125 (URN)10.1002/ange.201402513 (DOI)
    Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
    2. New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-Ion Batteries
    Open this publication in new window or tab >>New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-Ion Batteries
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    2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 43, p. 15966-15969Article in journal (Refereed) Published
    Abstract [en]

    New two-dimensional niobium and vanadium carbides have been synthesized by selective etching, at room temperature, of Al from Nb2AlC and V2AlC, respectively. These new matrials are promising electrode materials for Li-ion batteries, demonstrating good capability to handle high charge-discharge rates. Reversible capacities of 170 and 260 mA.h.g(-1) at 1 C, and 110 and 125 mA.h.g(-1) at 10 C were obtained for Nb2C and V2C-based electrodes, respectively.

    Place, publisher, year, edition, pages
    AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102084 (URN)10.1021/ja405735d (DOI)000326487800001 ()
    Note

    Funding Agencies|Office of Vehicle Technologies of the U.S. Department of Energy under the Batteries for Advanced Transportation Technologies (BATT) Program|DE-AC02-05CH112316951370|Knut and Alice Wallenberg Foundation||

    Available from: 2013-12-02 Created: 2013-11-29 Last updated: 2017-12-06
    3. Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
    Open this publication in new window or tab >>Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
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    2014 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 26, no 7, p. 2374-2381Article in journal (Refereed) Published
    Abstract [en]

    Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of similar to 1 x 1 cm(2) Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit similar to 90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to similar to 100 K. Below 100 K, the films resistivity increases with decreasing temperature and they exhibit negative magnetoresistance-both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.

    Place, publisher, year, edition, pages
    American Chemical Society, 2014
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-106852 (URN)10.1021/cm500641a (DOI)000334572300023 ()
    Available from: 2014-05-28 Created: 2014-05-23 Last updated: 2018-09-28Bibliographically approved
    4. X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
    Open this publication in new window or tab >>X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
    Show others...
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Herein, we report X-ray Photoelectron Spectroscopy (XPS) analysis for cold pressed exfoliated 2D nanocrystals of transition metal carbides, MXenes. MXenes are a recently discovered family of 2D materials produced by selective chemical etching of the A element from MAX phases which are ternary metal carbides and nitrides. The latter has the formula of Mn+1AXn, where M is an early transition metal, A is an A-group element, and X is C and/or N. This study is a comparison between two MXenes, Ti3C2Tx and Ti2CTx, where Tx stands for surface termination groups such as –O, –OH, and –F. Ti3C2Tx and Ti2CTx were prepared by immersion of Ti3AlC2 and Ti2AlC powders in 50% conc. HF. A thorough XPS analysis was performed through peak fitting of high resolution XPS spectra and valence band, VB, spectra analysis. The effect of Ar sputtering as well as the number of layers n was the primarily interest of this study. According to the peak fitting analysis, both phases contain the following species, Ti–C, C–C, Ti–F, Ti–O and Ti–OH resulting in the following chemical formulas: Ti3C2(OH)x(O)y(F)z and Ti2C(OH)x(O)y(F)z. Comparing the VB spectra with the DOS calculations show the valance band spectra is actually a mixture of MXene with various terminations of OH, O and F. Before Ar+ sputtering both phases show a large percentage of fluorinated-TiO2 which is due to MXene surface oxidation as well as CHx, C-O and COO groups arising from either surface contaminations or due to drying the etched powders in ethanol after washing the powder of the HF acid. According to the VB spectra, it is shown that the fluorinated TiO2 is actually a mixture of anatase and rutile. The number of layers, n, also plays a role; the lower n, the more the MXene is prone to oxidation.

    National Category
    Physical Chemistry Chemical Sciences
    Identifiers
    urn:nbn:se:liu:diva-111127 (URN)
    Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2018-06-04Bibliographically approved
  • 3.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Synthesis and transport properties of 2D transition metal carbides (MXenes)2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the isolation and characterization of graphene, there has been a growing interest in 2D materials owing to their unique properties compared to their 3D counterparts. Recently, a family of 2D materials of early transition metal carbides and nitrides, labelled MXenes, has been discovered (Ti2CTz, Ti3C2Tz, Mo2TiC2Tz, Ti3CNTz, Ta4C3Tz, Ti4N3Tz among many others), where T stands for surface-terminating groups (O, OH, and F). MXenes are mostly produced by selectively etching A layers (where A stands for group A elements, mostly groups 13 and 14) from the MAX phases. The latter are a family of layered ternary carbides and/or nitrides and have a general formula of Mn+1AXn (n = 1-3), where M is a transition metal and X is carbon and/or nitrogen. The produced MXenes have a conductive carbide core and a non-conductive O-, OH- and/or F-terminated surface, which allows them to work as electrodes for energy storage applications, such as Li-ion batteries and supercapacitors.

    Prior to this work, MXenes were produced in the form of flakes of lateral dimension of about 1 to 2 microns; such dimensions and form are not suitable for electronic characterization and applications. I have synthesized various MXenes (Ti3C2Tz, Ti2CTz and Nb2CTz) as epitaxial thin films, a more suitable form for electronic and photonic applications. These films were produced by HF, NH4HF2 or LiF + HCl etching of magnetron sputtered epitaxial Ti3AlC2, Ti2AlC, and Nb2AlC thin films. For transport properties of the Ti-based MXenes, Ti2CTz and Ti3C2Tz, changing n from 1 to 2 resulted in an increase in conductivity but had no effect on the transport mechanism (i.e. both Ti3C2Tx and Ti2CTx were metallic). In order to examine whether the electronic properties of MXenes differ when going from a few layers to a single flake, similar to graphene, the electrical characterization of a single Ti3C2Tz flake with a lateral size of about 10 μm was performed. These measurements, the first for MXene, demonstrated its metallic nature, along with determining the nature of the charge carriers and their mobility. This indicates that Ti3C2Tz is inherently of 2D nature independent of the number of stacked layers, unlike graphene, where the electronic properties change based on the number of stacked layers.

    Changing the transition metal from Ti to Nb, viz. comparing Ti2CTz and Nb2CTz thin films, the electronic properties and electronic conduction mechanism differ. Ti2CTz showed metallic-like behavior (resistivity increases with increasing temperature) unlike Nb2CTz where the conduction occurs via variable range hopping mechanism (VRH) - where resistivity decreases with increasing temperature.

    Furthermore, these studies show the synthesis of pure Mo2CTz in the form of single flakes and freestanding films made by filtering Mo2CTz colloidal suspensions. Electronic characterization of free-standing films made from delaminated Mo2CTz flakes was investigated, showing that a VRH mechanism prevails at low temperatures (7 to ≈ 60 K). Upon vacuum annealing, the room temperature, RT, conductivity of Mo2CTx increased by two orders of magnitude. The conduction mechanism was concluded to be VRH most likely dominated by hopping within each flake.

    Other Mo-based MXenes, Mo2TiC2Tz and Mo2Ti2C3Tz, showed VRH mechanism at low temperature. However, at higher temperatures up to RT, the transport mechanism was not clearly understood. Therefore, a part of this thesis was dedicated to further investigating the transport properties of Mo-based MXenes. This includes Mo2CTz, out-of-plane ordered Mo2TiC2Tz and Mo2Ti2C3Tz, and vacancy ordered Mo1.33CTz. Magneto-transport of free-standing thin films of the Mo-based MXenes were studied, showing that all Mo-based MXenes have two transport regimes: a VRH mechanism at lower temperatures and a thermally activated process at higher temperatures. All Mo-based MXenes except Mo1.33CTz show that the electrical transport is dominated by inter-flake transfer. As for Mo1.33CTz, the primary electrical transport mechanism is more likely to be intra-flake.

    The synthesis of vacancy ordered MXenes (Mo1.33CTz and W1.33CTz) raised the question of possible introduction of vacancies in all MXenes. Vacancy ordered MXenes are produced by selective etching of Al and (Sc or Y) atoms from the parent 3D MAX phases, such as (Mo2/3Sc1/3)2AlC, with in-plane chemical ordering of Mo and Sc. However, not all quaternary parent MAX phases form the in-plane chemical ordering of the two M metals; thus the synthesis of the vacancy-ordered MXenes is restricted to a very limited number of MAX phases. I present a new method to obtain MXene flakes with disordered vacancies that may be generalized to all quaternary MAX phases. As proof of concept, I chose Nb-C MXene, as this 2D material has shown promise in several applications, including energy storage, photothermal cell ablation and photocatalysts for hydrogen evolution. Starting from synthetizing (Nb2/3Sc1/3)2AlC quaternary solid solution and etching both the Sc and Al atoms resulted in Nb1.33C material with a large number of vacancies and vacancy clusters. This method may be applicable to other quaternary or higher MAX phases wherein one of the transition metals is more reactive than the other, and it could be of vital importance in applications such as catalysis and energy storage.  

    List of papers
    1. Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
    Open this publication in new window or tab >>Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films
    Show others...
    2014 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 26, no 7, p. 2374-2381Article in journal (Refereed) Published
    Abstract [en]

    Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of similar to 1 x 1 cm(2) Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit similar to 90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to similar to 100 K. Below 100 K, the films resistivity increases with decreasing temperature and they exhibit negative magnetoresistance-both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.

    Place, publisher, year, edition, pages
    American Chemical Society, 2014
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-106852 (URN)10.1021/cm500641a (DOI)000334572300023 ()
    Available from: 2014-05-28 Created: 2014-05-23 Last updated: 2018-09-28Bibliographically approved
    2. Electronic properties of freestanding Ti3C2Tx MXene monolayers
    Open this publication in new window or tab >>Electronic properties of freestanding Ti3C2Tx MXene monolayers
    2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 3, p. 033102-1-033102-4, article id 033102Article in journal (Refereed) Published
    Abstract [en]

    We report on the electrical characterization of single MXene Ti(3)C(2)Tx flakes ( where T is a surface termination) and demonstrate the metallic nature of their conductivities. We also show that the carrier density can be modulated by an external gate voltage. The density of free carriers is estimated to be 8 +/- 3 X 10(21) cm(-3) while their mobility is estimated to be 0.7 +/- 0.2 cm(2)/Vs. Electrical measurements, in the presence of a magnetic field, show a small, but clearly discernable, quadratic increase in conductance at 2.5 K. (C) 2016 AIP Publishing LLC.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2016
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-127457 (URN)10.1063/1.4939971 (DOI)000373055500039 ()
    Note

    Funding Agencies|Ceramics program of the Division of Materials Research of the National Science Foundation [DMR-1310245]

    Available from: 2016-04-30 Created: 2016-04-26 Last updated: 2018-09-28Bibliographically approved
    3. Synthesis and Characterization of 2D Molybdenum Carbide (MXene)
    Open this publication in new window or tab >>Synthesis and Characterization of 2D Molybdenum Carbide (MXene)
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    2016 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 26, no 18, p. 3118-3127Article in journal (Refereed) Published
    Abstract [en]

    Large scale synthesis and delamination of 2D Mo2CTx (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo2Ga2C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free-standing Mo2CTx films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor-like behavior of this MXene, in contrast to Ti3C2Tx which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 mu m thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm(-3) in a 1 M sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g(-1) are obtained. Free-standing Mo2CTx films, with approximate to 8 wt% carbon nanotubes, perform well when tested as an electrode material for Li-ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g(-1), respectively, are achieved for over 1000 cycles.

    Place, publisher, year, edition, pages
    WILEY-V C H VERLAG GMBH, 2016
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-130074 (URN)10.1002/adfm.201505328 (DOI)000377591500015 ()
    Note

    Funding Agencies|Swedish Research Council [621-2012-4430]; Swedish Foundation for Strategic Research through the Synergy Grant FUNCASE Functional Carbides for Advanced Surface Engineering; Laboratory Directed Research and Development Program of Oak Ridge National Laboratory; U.S. Army Research Office [W911NF-15-1-0133]

    Available from: 2016-07-06 Created: 2016-07-06 Last updated: 2018-09-28
    4. Variable range hopping and thermally activated transport in molybdenum-based MXenes
    Open this publication in new window or tab >>Variable range hopping and thermally activated transport in molybdenum-based MXenes
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    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 10, article id 104202Article in journal (Refereed) Published
    Abstract [en]

    The magnetotransport of freestanding, vacuum filtered, thin films of Mo2CTz, Mo1.33CTz, Mo2TiC2Tz, and Mo2Ti2C3Tz was measured in the 10-300-K temperature (T) range. Some of the films were annealed before measuring their transport properties. Analysis of the results suggest that-with the exception of the heavily defective Mo1.33CTz composition-in the 10- to 200-K temperature regime, variable range hopping between individual MXene sheets is the operative conduction mechanism. For Mo1.33CTz it is more likely that variable range hopping within individual flakes is rate limiting. At higher temperatures, a thermally activated process emerges in all cases. It follows that improved fabrication processes should lead to considerable improvements in the electrical transport of Mo-based MXenes.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-151642 (URN)10.1103/PhysRevB.98.104202 (DOI)000444204500005 ()
    Note

    Funding Agencies|Flag-ERA [JTC 2-17]; Knut and Alice Wallenberg (KAW) Foundation [2015.0043]; Stiftelsen fr Strategisk Forskning (SSF) Program [EM16-0004]; UGA Nanosciences Foundation, Grenoble, France

    Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2018-10-19
    5. Synthesis of Two-Dimensional Nb1.33C (MXene) with Randomly Distributed Vacancies by Etching of the Quaternary Solid Solution (Nb2/3Sc1/3)2AlC MAX Phase
    Open this publication in new window or tab >>Synthesis of Two-Dimensional Nb1.33C (MXene) with Randomly Distributed Vacancies by Etching of the Quaternary Solid Solution (Nb2/3Sc1/3)2AlC MAX Phase
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    2018 (English)In: ACS Applied Nano Materials, ISSN 2574-0970, Vol. 1, no 6, p. 2455-2460Article in journal (Refereed) Published
    Abstract [en]

    Introducing point defects in two-dimensional (2D) materials can alter or enhance their properties. Here, we demonstrate how etching a laminated (Nb2/3Sc1/3)2AlC MAX phase (solid solution) of both the Sc and Al atoms results in a 2D Nb1.33C material (MXene) with a large number of vacancies and vacancy clusters. This method is applicable to any quaternary, or higher, MAX phase, wherein one of the transition metals is more reactive than the other and could be of vital importance in applications such as catalysis and energy storage. We also report, for the first time, on the existence of solid solution (Nb2/3Sc1/3)3AlC2 and (Nb2/3Sc1/3)4AlC3 phases.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2018
    Keywords
    2D material; electronic properties; MXene; synthesis; transition-metal carbide
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-151667 (URN)10.1021/acsanm.8b00332 (DOI)
    Available from: 2018-09-28 Created: 2018-09-28 Last updated: 2018-10-19Bibliographically approved
  • 4.
    Halim, Joseph
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Science & Engineering and 3A.J. Drexel Nanotechnology Institute, Drexel University, Philadelphia, USA.
    Cook, Kevin M.
    University of Penn, PA 19104 USA Drexel University, PA 19104 USA .
    Näslund, Lars-Åke
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. University of Penn, PA 19104 USA .
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gogotsi, Yury
    University of Penn, PA 19104 USA Drexel University, PA 19104 USA .
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Barsoum, Michel W.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Department of Materials Science & Engineering, Drexel University, Philadelphia, USA.
    X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Herein, we report X-ray Photoelectron Spectroscopy (XPS) analysis for cold pressed exfoliated 2D nanocrystals of transition metal carbides, MXenes. MXenes are a recently discovered family of 2D materials produced by selective chemical etching of the A element from MAX phases which are ternary metal carbides and nitrides. The latter has the formula of Mn+1AXn, where M is an early transition metal, A is an A-group element, and X is C and/or N. This study is a comparison between two MXenes, Ti3C2Tx and Ti2CTx, where Tx stands for surface termination groups such as –O, –OH, and –F. Ti3C2Tx and Ti2CTx were prepared by immersion of Ti3AlC2 and Ti2AlC powders in 50% conc. HF. A thorough XPS analysis was performed through peak fitting of high resolution XPS spectra and valence band, VB, spectra analysis. The effect of Ar sputtering as well as the number of layers n was the primarily interest of this study. According to the peak fitting analysis, both phases contain the following species, Ti–C, C–C, Ti–F, Ti–O and Ti–OH resulting in the following chemical formulas: Ti3C2(OH)x(O)y(F)z and Ti2C(OH)x(O)y(F)z. Comparing the VB spectra with the DOS calculations show the valance band spectra is actually a mixture of MXene with various terminations of OH, O and F. Before Ar+ sputtering both phases show a large percentage of fluorinated-TiO2 which is due to MXene surface oxidation as well as CHx, C-O and COO groups arising from either surface contaminations or due to drying the etched powders in ethanol after washing the powder of the HF acid. According to the VB spectra, it is shown that the fluorinated TiO2 is actually a mixture of anatase and rutile. The number of layers, n, also plays a role; the lower n, the more the MXene is prone to oxidation.

  • 5.
    Halim, Joseph
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, PA 19104 USA.
    Kota, Sankalp
    Drexel University, PA 19104 USA.
    Lukatskaya, Maria R.
    Drexel University, PA 19104 USA; Drexel University, PA 19104 USA.
    Naguib, Michael
    Oak Ridge National Lab, TN 37381 USA.
    Zhao, Meng-Qiang
    Drexel University, PA 19104 USA; Drexel University, PA 19104 USA.
    Ju Moon, Eun
    Drexel University, PA 19104 USA.
    Pitock, Jeremy
    Drexel University, PA 19104 USA.
    Nanda, Jagjit
    Oak Ridge National Lab, TN 37381 USA.
    May, Steven J.
    Drexel University, PA 19104 USA.
    Gogotsi, Yury
    Drexel University, PA 19104 USA.
    Barsoum, Michel W.
    Drexel University, PA 19104 USA.
    Synthesis and Characterization of 2D Molybdenum Carbide (MXene)2016In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 26, no 18, p. 3118-3127Article in journal (Refereed)
    Abstract [en]

    Large scale synthesis and delamination of 2D Mo2CTx (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo2Ga2C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free-standing Mo2CTx films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor-like behavior of this MXene, in contrast to Ti3C2Tx which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 mu m thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm(-3) in a 1 M sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g(-1) are obtained. Free-standing Mo2CTx films, with approximate to 8 wt% carbon nanotubes, perform well when tested as an electrode material for Li-ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g(-1), respectively, are achieved for over 1000 cycles.

  • 6.
    Halim, Joseph
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Thörnberg, Jimmy
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    E. J., Moon
    Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States.
    M., Precner
    Institute of Electrical Engineering, Slovak Academy of Sciences, Bratislava 84104, Slovak Republic.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O. Å.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    M. W., Barsoum
    Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Synthesis of Two-Dimensional Nb1.33C (MXene) with Randomly Distributed Vacancies by Etching of the Quaternary Solid Solution (Nb2/3Sc1/3)2AlC MAX Phase2018In: ACS Applied Nano Materials, ISSN 2574-0970, Vol. 1, no 6, p. 2455-2460Article in journal (Refereed)
    Abstract [en]

    Introducing point defects in two-dimensional (2D) materials can alter or enhance their properties. Here, we demonstrate how etching a laminated (Nb2/3Sc1/3)2AlC MAX phase (solid solution) of both the Sc and Al atoms results in a 2D Nb1.33C material (MXene) with a large number of vacancies and vacancy clusters. This method is applicable to any quaternary, or higher, MAX phase, wherein one of the transition metals is more reactive than the other and could be of vital importance in applications such as catalysis and energy storage. We also report, for the first time, on the existence of solid solution (Nb2/3Sc1/3)3AlC2 and (Nb2/3Sc1/3)4AlC3 phases.

    The full text will be freely available from 2019-05-30 14:55
  • 7.
    Lukatskaya, Maria R.
    et al.
    Engineering Department, Drexel University, Philadelphia, USA.
    Halim, Joseph
    Engineering Department, Drexel University, Philadelphia, USA.
    Dyatkin, Boris
    Engineering Department, Drexel University, Philadelphia, USA.
    Naguib, Michael
    Engineering Department, Drexel University, Philadelphia, USA.
    Buranova, Yulia S.
    Engineering Department, Drexel University, Philadelphia, USA.
    Barsoum, Michel W.
    Engineering Department, Drexel University, Philadelphia, USA.
    Gogotsi, Yury
    Engineering Department, Drexel University, Philadelphia, USA.
    Room-Temperature Carbide-Derived Carbon Synthesis by Electrochemical Etching of MAX Phases2014In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 126, no 19, p. 4977-4980Article in journal (Refereed)
    Abstract [en]

    Porous carbons are widely used in energy storage and gas separation applications, but their synthesis always involves high temperatures. Herein we electrochemically selectively extract, at ambient temperature, the metal atoms from the ternary layered carbides, Ti3AlC2, Ti2AlC and Ti3SiC2 (MAX phases). The result is a predominantly amorphous carbide-derived carbon, with a narrow distribution of micropores. The latter is produced by placing the carbides in HF, HCl or NaCl solutions and applying anodic potentials. The pores that form when Ti3AlC2 is etched in dilute HF are around 0.5 nm in diameter. This approach forgoes energy-intensive thermal treatments and presents a novel method for developing carbons with finely tuned pores for a variety of applications, such as supercapacitor, battery electrodes or CO2 capture.

  • 8.
    Magnuson, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Näslund, Lars-Åke
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Chemical bonding in carbide MXene nanosheets2018In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, p. 27-32Article in journal (Refereed)
    Abstract [en]

    tThe chemical bonding in the carbide core and the surface chemistry in a new group of transition-metalcarbides Tin+1Cn-Tx(n = 1,2) called MXenes have been investigated by surface-sensitive valence bandX-ray photoelectron spectroscopy. Changes in band structures of stacked nano sheets of different thick-nesses are analyzed in connection to known hybridization regions of TiC and TiO2that affect elastic andtransport properties. By employing high excitation energy, the photoelectron cross-section for the C 2s– Ti 3d hybridization region at the bottom of the valence band is enhanced. As shown in this work, theO 2p and F 2p bands strongly depend both on the bond lengths to the surface groups and the adsorptionsites. The effect of surface oxidation and Ar+sputtering on the electronic structure is also discussed.

  • 9.
    Miranda, A.
    et al.
    University of Duisburg Essen, Germany.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, PA, USA.
    Barsoum, M. W.
    Drexel University, PA, USA.
    Lorke, A.
    University of Duisburg Essen, Germany.
    Electronic properties of freestanding Ti3C2Tx MXene monolayers2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 3, p. 033102-1-033102-4, article id 033102Article in journal (Refereed)
    Abstract [en]

    We report on the electrical characterization of single MXene Ti(3)C(2)Tx flakes ( where T is a surface termination) and demonstrate the metallic nature of their conductivities. We also show that the carrier density can be modulated by an external gate voltage. The density of free carriers is estimated to be 8 +/- 3 X 10(21) cm(-3) while their mobility is estimated to be 0.7 +/- 0.2 cm(2)/Vs. Electrical measurements, in the presence of a magnetic field, show a small, but clearly discernable, quadratic increase in conductance at 2.5 K. (C) 2016 AIP Publishing LLC.

  • 10.
    Palisaitis, Justinas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O. Å.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    On the Structural Stability of MXene and the Role of Transition Metal Adatoms2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 23, p. 10850-10855Article in journal (Refereed)
    Abstract [en]

    In the present communication, the atomic structure and coordination of surface adsorbed species on Nb2C MXene is investigated over time. In particular, the influence of the Nb adatoms on the structural stability and oxidation behavior of the MXene is addressed. This investigation is based on plan-view geometry observations of single Nb2C MXene sheets by a combination of atomic-resolution scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and STEM image simulations.

  • 11.
    Ren, Chang E.
    et al.
    Drexel University, USA.
    Zhao, Meng-Qiang
    Drexel University, USA.
    Makaryan, Taron
    Drexel University, USA.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, USA.
    Boota, Muhammad
    Drexel University, USA.
    Kota, Sankalp
    Drexel University, USA.
    Anasori, Babak
    Drexel University, USA.
    Barsoum, Michel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, USA.
    Gogotsi, Yury
    Drexel University, USA.
    Porous Two-Dimensional Transition Metal Carbide (MXene) Flakes for High-Performance Li-Ion Storage2016In: CHEMELECTROCHEM, ISSN 2196-0216, Vol. 3, no 5, p. 689-693Article in journal (Refereed)
    Abstract [en]

    Herein we develop a chemical etching method to produce porous two-dimensional (2D) Ti3C2Tx MXenes at room temperature in aqueous solutions. The as-produced porous Ti3C2Tx (p-Ti3C2Tx) have larger specific surface areas and more open structures than their pristine counterparts, and can be fabricated into flexible films with, or without, the addition of carbon nanotubes (CNTs). The as-fabricated p-Ti3C2Tx/CNT films showed significantly improved lithium ion storage capabilities compared to pristine Ti3C2Tx based films, with a very high capacity of approximate to 1250 mAhg(-1) at 0.1 C, excellent cycling stability, and good rate performance (330 mAhg(-1) at 10 C). Using the same chemical etching method, we also made porous Nb2CTx and V2CTx MXenes. Therefore, this study provides a simple, yet effective, procedure to introduce pores into MXenes and possibly other 2D sheets that in turn, can enhance their electrochemical properties.

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