| 1. |
- Badr, Hussein O., et al.
(författare)
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Bottom-up, scalable synthesis of anatase nanofilament-based two-dimensional titanium carbo-oxide flakes
- 2022
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Ingår i: Materials Today. - : ELSEVIER SCI LTD. - 1369-7021 .- 1873-4103. ; 54
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) materials offer advantages that their 3D counterparts do not. The conventional method for the bulk synthesis of 2D materials has predominantly been through etching layered solids. Herein, we convert - through a bottom-up approach - 10 binary and ternary titanium carbides, nitrides, borides, phosphides, and silicides into 2D flakes by immersing them in a tetramethylammonium hydroxide solution at temperatures in the 25-85 degrees C range. Based on X-ray diffraction, density functional theory, X-ray photoelectron, electron energy loss, Raman, X-ray absorption near edge structure spectroscopies, transmission and scanning electron microscope images and selected area diffraction, we conclude that the resulting flakes are carbon containing anatase-based layers that are, in turn, comprised of approximate to 6 x 10 angstrom(2) nanofilaments in cross-section some of which are few microns long. Electrodes made from some of these films performed well in lithium-ion and lithium-sulphur systems. These materials also reduce the viability of cancer cells thus showing potential in biomedical applications. Synthesizing 2D materials, at near ambient conditions, with non-layered, inexpensive, green precursors (e.g., TiC) is paradigm shifting and will undoubtedly open new and exciting avenues of research and applications.
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| 2. |
- Dahlqvist, Martin, et al.
(författare)
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MAX phases – Past, present, and future
- 2023
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Ingår i: Materials Today. - : Elsevier B.V.. - 1369-7021 .- 1873-4103.
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Tidskriftsartikel (refereegranskat)abstract
- The MAX phases are a class of nanolaminated materials composed of an early transition-metal (M), an A-group element (A) and C, N, B and/or P (X). Progress in MAX phase research in recent years has increased their number from the original 50 or so, to more than 300 phases. Since half of the 342 MAX phases have been discovered after 2018, an overview of the progress made in the field is timely. Currently, 28 M elements, 28 A elements, and 6 X elements have been incorporated in the MAX phases, alloys included. We further categorize MAX phases based on the synthesis route used to make them; if made via a one-step approach in bottom-up synthesis or formed through elemental replacement reactions in top-down synthesis. This classification is also correlated to theoretical phase stability predictions, that in turn, can be used to identify novel synthesizable MAX phase compositions as well as to suggest suitable synthesis routes. Furthermore, using phase stability predictions we identify 182 new theoretically stable MAX phases awaiting experimental confirmation. Notably, as MAX phases are precursors for MXenes, the dramatically increased interest in the latter for a large host of potential applications renders the former even more valuable. © 2023 The Author(s)
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| 3. |
- ElMeligy, Tarek Aly, et al.
(författare)
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Synthesis, characterization, properties, first principles calculations, and X-ray photoelectron spectroscopy of bulk Mn5SiB2 and Fe5SiB2 ternary borides
- 2021
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Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 888
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we synthesize fully dense, bulk, predominantly single-phase, polycrystalline samples of the layered ternary transition metal borides Mn5SiB2 and Fe5SiB2 by reactively hot-pressing Mn, Fe, FeB, Si, and B powders. The atomic structures were imaged using high-resolution scanning transmission electron mi-croscopy and revealed high-crystal quality. Elongated striped defects, confined below the nanometer in width, were observed. Selected area electron diffraction further accentuates the high-crystal quality by discrete spots of pattern, that is expected from a tetragonal crystal structure along the [001] zone axis. With Vickers hardness values of 12.1 +/- 0.4 GPa, and 12.7 +/- 0.1 GPa, for Mn5SiB2 and Fe5SiB2 respectively, these borides are relatively soft. The room temperature electrical resistivities were 1.5 +/- 0.1 and 1.2 +/- 0.1 mu Omega m, for Mn5SiB2 and Fe5SiB2, respectively. The binding energies of the Mn, Fe and Si measured by X-ray photoelectron spectroscopy bolster the idea that the bonds are quite metallic in character. Density functional theory (DFT) calculations confirm that the ground states of both compounds are ferromagnetic as observed experimentally. We also use DFT to predict the elastic and electronic properties. In both compounds, the density of states at the Fermi level are dominated by the d-orbitals of the transition metals. Neither material was readily machinable with conventional tooling, but is so with sharp cobalt steel bits or electro-discharge machining (EDM). (C) 2021 Elsevier B.V. All rights reserved.
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| 4. |
- Halim, Joseph, et al.
(författare)
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Tailored synthesis approach of (Mo2/3Y1/3)(2)AlC i-MAX and its two-dimensional derivative Mo1.33CTz MXene: enhancing the yield, quality, and performance in supercapacitor applications
- 2021
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 13:1, s. 311-319
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Tidskriftsartikel (refereegranskat)abstract
- A vacancy-ordered MXene, Mo1.33CTz, obtained from the selective etching of Al and Sc from the parent i-MAX phase (Mo2/3Sc1/3)(2)AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (Mo2/3Y1/3)(2)AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY2.3 alloy instead of elemental Al and Y for the synthesis of (Mo2/3Y1/3)(2)AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, Mo3Al2C. Furthermore, through a modified etching procedure, we obtain a Mo1.33CTz MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm(-3)) and gravimetric (436 F g(-1)) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the Mo1.33CTz MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.
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| 5. |
- Hanner, Luke A., et al.
(författare)
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Synthesis, characterization and first principle modelling of the MAB phase solid solutions: (Mn1-xCrx)(2)AlB2 and (Mn1-xCrx)(3)AlB4
- 2021
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 9:2, s. 112-118
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Tidskriftsartikel (refereegranskat)abstract
- The MAB phases are a family of layered ternary transition metal borides, with atomically laminated crystal structures comprised of transition metal boride (M-B) layers interleaved by single, or double, Al (A) layers. Herein, density functional theory is implemented to evaluate the thermodynamic stability of disordered (Mn1-xCrx)(2)AlB2, and disordered and ordered (Mn1-xCrx)(3)AlB4 quaternaries. The (Mn1-xCrx)(2)AlB2 solid solutions were synthesized over the entire range of substitution. A (Mn1-xCrx)(3)AlB4 solid solution was produced, on the base of Cr3AlB4, to form (Mn0.33Cr0.66)(3)AlB4. Powder X-ray diffraction shows lattice parameter shifts and unit cell expansions indicative of successful solid solution formations.
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| 6. |
- Hu, Yong-Jie, et al.
(författare)
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Structural and electronic properties of two-dimensional titanium carbo-oxides
- 2023
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Ingår i: 2D Materials. - : IOP Publishing Ltd. - 2053-1583. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- This work was inspired by new experimental findings where we discovered a two-dimensional (2D) material comprised of titanium-oxide-based one-dimensional (1D) sub-nanometer filaments. Preliminary results suggest that the 2D material contains considerable amounts of carbon, C, in addition to titanium, Ti, and oxygen, O. The aim of this study is to investigate the low-energy, stable atomic forms of 2D titanium carbo-oxides as a function of C content. Via a combination of first-principles calculations and an effective structure sampling scheme, the stable configurations of C-substitutions are comprehensively searched by templating different 2D TiO2 polymorphs and considering a two O to one C replacement scheme. Among the searched stable configurations, a structure where the (101) planes of anatase bound the top and bottom surfaces with a chemical formula of TiC1/4O3/2 was of particularly low energy. Furthermore, the variations in the electronic band structure and chemical bonding environments caused by the high-content C substitution are investigated via additional calculations using a hybrid exchange-correlation functional.
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| 7. |
- Nikolaevsky, Mark, et al.
(författare)
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Possible monoclinic distortion of Mo2GaC under high pressure
- 2020
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 127:14
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present high-pressure diffraction results of the Mo-based M-n (+) (1)AX(n) phase, Mo2GaC. A diamond anvil cell was used to compress the material up to 30 GPa, and x-ray diffraction was used to determine the structure and unit cell parameters as a function of pressure. Somewhat surprisingly, we find that, at 295 +/- 25 GPa, the bulk modulus of Mo2GaC is the highest reported of all the MAX phases measured to date. The c/a ratio increases with increasing pressure. At above 15 GPa, a splitting in the (1 0 0) reflection occurs. This result, coupled with new density functional theory calculations, suggests that a second order phase transition to possibly a mixture of hexagonal and monoclinic structures may explain this splitting. Such experimentally and theoretically supported phase transitions were not predicted in previously published calculations.
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| 8. |
- Yang, Li, et al.
(författare)
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A Highly Reversible Aqueous Ammonium-Ion Battery based on alpha-MoO3/Ti3C2Tz Anodes and (NH4)(x)MnO2/CNTs Cathodes
- 2023
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Ingår i: Batteries & Supercaps. - : WILEY-V C H VERLAG GMBH. - 2566-6223. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous ammonium-ion batteries (AAIBs) are appealing due to their relatively low cost and good rate performance. In general, AAIBs are environmentally friendlier than their non-aqueous counterparts. However, it is still a challenge to achieve highly reversible AAIBs with decent voltages and energy/power densities. Herein, we report on a full-cell configuration using alpha-MoO3/Ti3C2Tz films as anodes, and (NH4)(x)MnO2/CNTs films as cathodes in a 1 M ammonium acetate (NH4Ac) electrolyte. At 2 V, the operating cell voltage, OCV, is one of the highest reported for AAIBs. A maximum energy density of similar to 32 Wh kg(-1) (similar to 54 Wh L-1) at 0.2 A g(-1) and a maximum power density of similar to 10 kW kg(-1) (similar to 17 kW L-1) at 10 A g(-1) are attained. When the full cells are cycled 2,000 times at 1 A g(-1) they retain similar to 73 % of their initial capacity. When cycling at 10 A g(-1), similar to 96 % of capacity is retained after 43,500 cycles. After 10 h, self-discharge reduces the OCV to similar to 72 % of its original value. This work provides a roadmap for developing high performance AAIBs with high voltages and high energy/power densities. Before this is possible it is imperative that the self-discharge rate be substantially reduced.
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| 9. |
- Zheng, Wei, et al.
(författare)
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Aqueous Electrolytes, MXene-Based Supercapacitors and Their Self-Discharge
- 2022
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Ingår i: Advanced Energy and Sustainability Research. - : Wiley. - 2699-9412. ; 3:2
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Tidskriftsartikel (refereegranskat)abstract
- Significant efforts have been dedicated to developing Ti3C2Tz-based MXene aqueous supercapacitors (SCs) with improved energy and power densities. Notably less research has been devoted to an equally important characteristic of aqueous SCs, viz. self-discharge (SD). The SD rates are rarely reported despite their crucial importance from a practical point of view. Herein, the SD rates in four different aqueous electrolytes: H2SO4, KOH, LiCl, and LiBr in Ti3C2Tz-based aqueous SCs are compared. For the latter two, the SD rates vary as a function of salt concentration in the electrolytes with higher LiCl or LiBr concentrations having the lowest SD rates, viz. 78.3% and 81.5% in 14m LiCl and LiBr, respectively, after 10h. Further, the influence of dissolved oxygen and the purities of the starting powders are examined, and it is concluded that parasitic reactions, including oxygen, are responsible for the SD.
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| 10. |
- Zheng, Wei, et al.
(författare)
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Boosting the volumetric capacitance of MoO3-x free-standing films with Ti3C2 MXene
- 2021
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 370
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Tidskriftsartikel (refereegranskat)abstract
- The high theoretical capacitance of molybdenum trioxide (MoO3) renders it an attractive supercapacitor electrode material. However, its low electronic conductivity restricts charge transfer and slows its reaction kinetics. Herein, we vacuum filtered porous, free-standing, flexible and highly conductive films comprised of oxygen vacancy-rich MoO3-x nanobelts and delaminated Ti3C2 MXene in a mass ratio of 80:20, respectively. When tested as supercapacitor electrodes, in a 5 M LiCl electrolyte, volumetric capacitances of 631 F cm−3 at 1 A g−1, and 474 F cm−3 at 10 A g−1 were obtained. To increase the energy density, asymmetric supercapacitors, wherein the anodes were MoO3-based and the cathodes were nitrogen-doped activated carbon were assembled and tested. The resulting volumetric energy density was 48.6 Wh L−1. After 20,000 continuous charge/discharge cycles at 20 A g−1, 96.3 % of the initial charge remained. These values are outstanding for free-standing supercapacitor electrodes, especially in aqueous electrolytes.
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