| 1. |
- Qin, Leiqiang, 1987-, et al.
(författare)
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Flexible Solid-State Asymmetric Supercapacitors with Enhanced Performance Enabled by Free-Standing MXene-Biopolymer Nanocomposites and Hierarchical Graphene-RuOx Paper Electrodes
- 2020
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Ingår i: Batteries & Supercaps. - : WILEY-V C H VERLAG GMBH. - 2566-6223. ; 3:7, s. 604-610
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) transition metal carbides and carbonitrides, called MXenes, with metallic conductivity and hydrophilic surfaces, show great promise as electrode materials for supercapacitors. A major drawback of 2D nanomaterials is the re-stacking of the nanosheets, which prevents full utilization of surface area and blocks the access of the electrolyte. In this study, a free-standing nanocomposite paper electrode is realized by combining Mo1.33C MXene and positively charged biopolymer lignin (the second most abundant biopolymer in nature, L-DEA). The self-assembled layered architecture with alternating polymer and MXene flakes increases the interlayer space to promote ion transport, and with combining charge storage capability of the lignin derivative and MXene in an interpenetrating MXene/L-DEA nanocomposite, which offers an impressive capacitance of 503.7 F g(-1). Moreover, we demonstrate flexible solid-state asymmetric supercapacitors (ASCs) using Mo1.33C@L-DEA as the negative electrode and electrochemically exfoliated graphene with ruthenium oxide (EG@RuOx) as the positive electrode. This asymmetric device operates at a voltage window of 1.35 V, which is about two times wider than that of a symmetric Mo1.33C@L-DEA based supercapacitor. Finally, the ASCs can deliver an energy density of 51.9 Wh kg(-1) at a power density of 338.5 W kg(-1), with 86 % capacitance retention after 10000 charge-discharge cycles.
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| 2. |
- Qin, Leiqiang, et al.
(författare)
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High-Performance Ultrathin Flexible Solid-State Supercapacitors Based on Solution Processable Mo1.33C MXene and PEDOT:PSS
- 2018
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 28:2
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Tidskriftsartikel (refereegranskat)abstract
- MXenes, a young family of 2D transition metal carbides/nitrides, show great potential in electrochemical energy storage applications. Herein, a high performance ultrathin flexible solid-state supercapacitor is demonstrated based on a Mo1.33C MXene with vacancy ordering in an aligned layer structure MXene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film posttreated with concentrated H2SO4. The flexible solid-state supercapacitor delivers a maximum capacitance of 568 F cm(-3), an ultrahigh energy density of 33.2 mWh cm(-3) and a power density of 19 470 mW cm(-3). The Mo1.33C MXene/PEDOT:PSS composite film shows a reduction in resistance upon H2SO4 treatment, a higher capacitance (1310 F cm(-3)) and improved rate capabilities than both pristine Mo1.33C MXene and the nontreated Mo1.33C/PEDOT:PSS composite films. The enhanced capacitance and stability are attributed to the synergistic effect of increased interlayer spacing between Mo1.33C MXene layers due to insertion of conductive PEDOT, and surface redox processes of the PEDOT and the MXene.
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| 3. |
- Rosén, Johanna, 1975-, et al.
(författare)
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In- and Out-of-Plane Ordered MAX Phases and Their MXene Derivatives
- 2019
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Ingår i: 2D Metal Carbides and Nitrides (MXenes). - Cham : Springer. - 9783030190262 - 9783030190255 - 9783030190286 ; , s. 37-52
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Bokkapitel (refereegranskat)abstract
- The family of MXenes has expanded since the discovery of chemical order in parent quaternary MAX phases, displaying either out-of-plane (o-MAX) or in-plane (i-MAX) order upon alloying. Through selective chemical etching of these materials, corresponding MXenes can be derived, with out-of-plane and in-plane ordering of elements, as well as with ordering of vacancies. Both o-MAX and i-MAX phases have increased the number of metals that can be incorporated in these laminated carbides and nitrides. Examples of realized MXenes with out-of-plane order are Mo2Ti2C3 and Mo2ScC2, and for in-plane ordering of vacancies, there are Mo1.33C and W1.33C. Their versatile chemistry shows a high promise for a range of applications, including energy storage and catalysis
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| 4. |
- Tao, Quanzheng, 1989-
(författare)
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Single crystal growth and structural characterization of thetheoretically predicted nanolaminate M2Al2C3 where M=Sc and Er
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Tidskriftsartikel (refereegranskat)abstract
- Nanolaminated materials including magnetic elements are of interest for commonly observed non-trivial magnetic characteristics and as potential precursors for 2D materials. Here, we explore the previously unknown layered phase M2Al2C3 where M = Sc and Er. Sc2Al2C3 was synthesized as single crystals of ~mm2 size, and its structure was determined by single crystal X-ray diffraction and scanning transmission electron microscopy. Evaluation of phase stability and possible vacancy formation based on first principles calculations confirm the attained phase, and suggest full occupancy on both the Al and C sites. Potential realization of the hypothetical phase Y2Al2C3 is also proposed. Furthermore, we also demonstrate that Er2Al2C3 can be synthesized in powder form, providing experimental evidence for stoichiometries based on rare earth (RE) elements, which in turn suggests possible incorporation of other lanthanides.
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| 5. |
- Tao, Quanzheng, 1989-
(författare)
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Synthesis and characterization of two- and three-dimensional nanolaminated carbides
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused towards the synthesis and characterization of novel nanolaminated materials in primarily bulk (powder) form. Of particular interest is magnetic materials, or laminates that can be used as precursor for two-dimensional (2D) materials. 2D materials typically display a large surface-to-volume ratio, and as such they are very promising for applications within energy storage and catalysis. A more recently discovered family of 2D transition metal carbides/nitrides, called MXenes, are currently attracting a lot of attention. MXenes are produced by selective etching of parent 3D nanolaminates, so called MAX phases, facilitating removal of selected atomic layers, and formation of 2D sheets.In my work on new nanolaminates as precursors for 2D materials, I have synthesized (Mo2/3Sc1/3)2AlC and have studied its crystal structure. It was found that Mo and Sc are chemically ordered in the metal layers, with the in-plane ordering motivating the notation i-MAX for this new type of MAX phase alloy. By selective etching of Sc and Al, we thereafter produced a 2D materials with ordered vacancies, Mo1.33C, and studied the electrochemical properties. It was found that the material displayed a high capacitance, ~1200 F cm-3, which is 65% higher that the counterpart without vacancies, Mo2C.I also synthesized a previously not known out-of-plane ordered Mo2ScAlC2 MAX phase. By selective etching of Al, we produced a 2D material, Mo2ScC2, which is correspondingly ordered in the out-of-plane direction. Another related laminated material was also discovered and synthesized, Sc2Al2C3, and its crystal structure was determined. The material is potentially useful for conversion into a 2D material. I have also shown that Sc2Al2C3 is an example of a series of materials with the same crystal structure, with Sc replaced by other metals.Magnetic materials are used in many applications, such as for data storage devices. In particular, layered magnetic materials are of interest due to their anisotropic structure and potential formation of interesting magnetic characteristics. I have been synthesizing and characterizing magnetic nanolaminates, starting with the (V,Mn)3GaC2 MAX phase in the form of an epitaxial thin film. Analysis of the magnetic behavior showed a ferromagnetic response above room temperature I thereafter showed that our previously discovered family of i-MAX phases could be expanded with a subclass of ordered nanolaminates based on rare earth (RE) elements, of the general formula (Mo2/3RE1/3)2AlC , where RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. I studied their crystal structure by scanning transmission microscopy (STEM), X-ray diffraction (XRD), and neutron diffraction. We found that these phases can crystalize in three different structures, of space group C2/m, C2/c, and Cmcm, respectively. The magnetic behavior was studied and the magnetic structure of two materials could be determined. We suggest that the complex behavior identified is due to competing magnetic interaction and frustration.I also synthesized another rare earth-based nanolaminate, Mo4Ce4Al7C3. The crystal structure was investigated by single crystal X-ray diffraction and STEM. Magnetization analysis reveal a ferromagnetic ground state below 10.5 K. X-ray absorption near-edge structure provide evidence that Ce is in a mixed-valence state. X-ray magnetic circular dichroism shows that only one of the two Ce sites are magnetic.
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