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1.	Anasori, Babak, et al. (author) Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes) 2015 In: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 9:10, s. 9507-9516 Journal article (peer-reviewed)abstract The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), MM-2 C-2 and MM-2 C-2(3), where M and M are two different early transition metals. In these solids, M layers sandwich M" carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties.
2.	Byeon, Ayeong, et al. (author) Two-Dimensional Titanium Carbide MXene As a Cathode Material for Hybrid Magnesium/Lithium-Ion Batteries 2017 In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 9:5, s. 4296-4300 Journal article (peer-reviewed)abstract As an alternative to pure lithium-ion, Lit, systems, a hybrid magnesium, Mg2+, and Li+ battery can potentially combine the high capacity, high voltage, and fast Li+ intercalation of Li-ion battery cathodes and the high capacity, low cost, and dendrite-free Mg metal anodes. Herein, we report on the use of two-dimensional titanium carbide, Ti3C2Tx (MXene), as a cathode in hybrid Mg2+/Li+ batteries, coupled with a Mg metal anode. Free-standing and flexible Ti3C2Tx/carbon nanotube composite "paper" delivered-,100 mAh at 0.1 C and similar to 50 mAh g(-1) at 10 C. At 1 C the capacity was maintained for amp;gt;500 cycles at 80 mAh g(-1). The Mo2CTx MXene also demonstrated good performance as a cathode material in this hybrid battery. Considering the variety of available MXenes, this work opens the door for exploring a new large family of 2D materials with high electrical conductivity and large intercalation capacity as cathodes for hybrid Mg2+/Li+ batteries.
3.	Ding, Haoming, et al. (author) Chemical scissor-mediated structural editing of layered transition metal carbides 2023 In: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 379:6637, s. 1130-1135 Journal article (peer-reviewed)abstract Intercalated layered materials offer distinctive properties and serve as precursors for important two-dimensional (2D) materials. However, intercalation of non-van der Waals structures, which can expand the family of 2D materials, is difficult. We report a structural editing protocol for layered carbides (MAX phases) and their 2D derivatives (MXenes). Gap-opening and species-intercalating stages were respectively mediated by chemical scissors and intercalants, which created a large family of MAX phases with unconventional elements and structures, as well as MXenes with versatile terminals. The removal of terminals in MXenes with metal scissors and then the stitching of 2D carbide nanosheets with atom intercalation leads to the reconstruction of MAX phases and a family of metal-intercalated 2D carbides, both of which may drive advances in fields ranging from energy to printed electronics.
4.	Downes, Marley, et al. (author) M5X4: A Family of MXenes 2023 In: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 17:17, s. 17158-17168 Journal article (peer-reviewed)abstract MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes make up the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4T x . Only one M5X4 MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two M(5)AX(4) mixed transition metal MAX phases, Ti2.5Ta2.5AlC4 and Ti2.675Nb2.325AlC4, and their successful topochemical transformation into Ti2.5Ta2.5C4T x and Ti2.675Nb2.325C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M(5)AX(4) MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, leading to more exciting applications for MXenes.
5.	Etman, Ahmed S., 1986- (author) Aqueous Exfoliation of Transition Metal Oxides for Energy Storage and Photocatalysis Applications : Vanadium Oxide and Molybdenum Oxide Nanosheets 2019 Doctoral thesis (other academic/artistic)abstract Two-dimensional (2D) transition metal oxides (TMOs) are a category of materials which have unique physical and chemical properties compared to their bulk counterparts. However, the synthesis of 2D TMOs commonly includes the use of environmental threats such as organic solvents. In this thesis, we developed environmentally friendly strategies to fabricate TMO nanosheets from the commercially available bulk oxides. In particular, hydrated vanadium pentoxide (V2O5∙nH2O) nanosheets and oxygen deficient molybdenum trioxide (MoO3-x) nanosheets were prepared. The V2O5∙nH2O nanosheets were drop-cast onto multi-walled carbon nanotube (MWCNT) paper and applied as a free-standing electrode (FSE) for a lithium battery. The accessible capacity of the FSE was dependent on the electrode thickness; the thickest electrode delivered the lowest accessible capacity. Alternatively, a composite material of V2O5∙nH2O nanosheets with 10% MWCNT (VOx-CNT composite) was prepared and two types of electrodes, FSE and conventionally cast electrode (CCE), were employed as cathode materials for lithium batteries. A detailed comparison between these electrodes was presented. In addition, the VOx-CNT composite was applied as a negative electrode for a sodium-ion battery and showed a reversible capacity of about 140 mAh g-1. On the other hand, the MoO3-x nanosheets were employed as binder-free electrodes for supercapacitor application in an acidified Na2SO4 electrolyte. Furthermore, the MoO3-x nanosheets were used as photocatalysts for organic dye degradation. The simple eco-friendly synthesis methods coupled with the potential application of the TMO nanosheets reflect the significance of this thesis in both the synthesis and the energy-related applications of 2D materials.
6.	Ghidiu, Michael, et al. (author) Ion-Exchange and Cation Solvation Reactions in Ti3C2 MXene 2016 In: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 28:10, s. 3507-3514 Journal article (peer-reviewed)abstract 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.
7.	Goyenola, Cecilia, 1983- (author) Nanostructured carbon-based thin films : prediction and design 2015 Doctoral thesis (other academic/artistic)abstract Carbon-based thin films are a vast group of materials of great technological importance. Thanks to the different bonding options for carbon, a large variety of structures (from amorphous to nanostructured) can be achieved in the process of film synthesis. The structural diversity increases even more if carbon is combined with relatively small quantities of atoms of other elements. This results in a set of materials with many different interesting properties for a wide range of technological applications.This doctoral thesis is about nanostructured carbon-based thin films. In particular, the focus is set on theoretical modeling, prediction of structural features and design of sulfo carbide (CSx) and carbon fluoride (CFx) thin films.The theoretical approach follows the synthetic growth concept (SGC) which is based on the density functional theory. The SGC departure point is the fact that the nanostructured films of interest can be modeled as assemblies of low dimensional units (e.g., finite graphene-like model systems), similarly to modeling graphite as stacks of graphene sheets. Moreover, the SGC includes a description of the groups of atoms that act as building blocks (i.e., precursors) during film deposition, as well as their interaction with the growing film.This thesis consists of two main parts:Prediction: In this work, I show that nanostructured CSx thin films can be expected for sulfur contents up to 20 atomic % with structural characteristics that go from graphite-like to fullerene-like (FL). In the case of CFx thin films, a diversity of structures are predicted depending on the fluorine concentration. Short range ordered structures, such as FL structure, can be expected for low concentrations (up to 5 atomic %). For increasing fluorine concentration, diamond-like and polymeric structures should predominate. As a special case, I also studied the ternary system CSxFy. The calculations show that CSxFy thin films with nanostructured features should be possible to synthesize at low sulfur and fluorine concentrations and the structural characteristics can be described and explained in terms of the binaries CSx and CFx.Design: The carbon-based thin films predicted in this thesis were synthesized by magnetron sputtering. The results from my calculations regarding structure and composition, and analysis of precursors (availability and role during deposition process) were successfully combined with the experimental techniques in the quest of obtaining films with desired structural features and understanding their properties.
8.	Halim, Joseph, et al. (author) Synthesis and Characterization of 2D Molybdenum Carbide (MXene) 2016 In: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 26:18, s. 3118-3127 Journal article (peer-reviewed)abstract 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.
9.	Halim, Joseph, 1985- (author) Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes) 2014 Licentiate thesis (other academic/artistic)abstract 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.
10.	Halim, Joseph, et al. (author) Transparent Conductive Two-Dimensional Titanium Carbide Epitaxial Thin Films 2014 In: Chemistry of Materials. - : American Chemical Society. - 0897-4756 .- 1520-5002. ; 26:7, s. 2374-2381 Journal article (peer-reviewed)abstract 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.
11.	Halim, Joseph, et al. (author) X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes) 2014 Other publication (other academic/artistic)abstract 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.
12.	Halim, Joseph, 1985-, et al. (author) X-ray photoelectron spectroscopy of select multi-layered transition metal carbides (MXenes) 2016 In: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 362, s. 406-417 Journal article (peer-reviewed)abstract In this work, a detailed high resolution X-ray photoelectron spectroscopy (XPS) analysis is presented for select MXenes a recently discovered family of two-dimensional (2D) carbides and carbonitrides. Given their 2D nature, understanding their surface chemistry is paramount. Herein we identify and quantify the surface groups present before, and after, sputter-cleaning as well as freshly prepared vs. aged multi layered cold pressed discs. The nominal compositions of the MXenes studied here are Ti-3 C2Tx,Ti3CNTx, Nb2CTx and Nb4C3Tx where T represents surface groups that this work attempts to quantify. In all the cases, the presence of three surface terminations, O, OH and F, in addition to OH-terminations relatively strongly bonded to H2O molecules, was confirmed. From XPS peak fits, it was possible to establish the average sum of the negative charges of the terminations for the aforementioned MXenes. Based on this work, it is now possible to quantify the nature of the surface terminations. This information can, in turn, be used to better design and tailor these novel 2D materials for various applications. Published by Elsevier B.V.
13.	Kumar, Divyaratan, 1995- (author) Water-in-polymer Salt Electrolyte (WIPSE) for Sustainable Lignin Batteries 2023 Doctoral thesis (other academic/artistic)abstract Organic electrolytes are widely used in energy storage technologies, but they are known to have safety, cost, and eco friendliness concerns. Water based electrolytes do not have those issues but are limited by their narrow range potential range of operation to 1.2V. Above that voltage, significant side reactions lead to gas evolution, side reaction and high selfdischarge rate in organic batteries. Because of their superior ionic conductivities, which are critical for reducing device resistance and improving power; as well as their cost-effective ness and non-flammability, researchers have had a second look at water-based electrolyte and found out that super concentrated aqueous solutions behave differently, and their electrochemical stability window can be widened.In this thesis, polyacrylate (PAAK) based "water in polymer salt" electrolyte (WIPSE) has been identified as a promising solution for large-scale energy storage devices. This new family of "water in salt" electrolytes offers a broad electrochemical stability window of up to 3V, a high ionic conductivity (100 mS/cm) and is non-flammable, making it ideal for high power electrochemical storage devices. However, little is known about the matter transport in PAAK based WIPSE and in "water in salt" electrolytes in general. Therefore, this thesis also aims to investigate the properties of PAAK using spectroscopic techniques such as Raman spectroscopy and diffusion NMR to understand the behavior of water and the mechanism of ionic transport in relation to water and polymer chain dynamics. Since the electrolyte only transports cations, it is suitable for use in "cation rocking chair" batteries that utilize two types of polymeric quinones, lignin, and polyimide redox polymers, as positive and negative electrodes, respectively. The electrochemically active redox polymers with K+ ions at neutral pH are ions at neutral pH are advantageous for avoiding corrosion in metal collectors. Further for understanding the fundamental of self-discharge mechanism, the impact of some critical chemical and physical parameters on performance of lignin-based batteries have been investigated.The final chapter of the thesis introduces a novel approach to address the challenges associated with Zn-ion batteries by utilizing the "water-inpolymer salt" electrolyte concept modified by salt additives. The goal is to enable the use of lignin-carbon (L-C) electrodes in a Zinc battery. Lignin, carbon and zinc are among the most affordable, environmentally friendly and sustainable options for energy storage for energy storage. By incorporating WIPSE electrolytes these batteries can offer additional benefits, such as improved safety and the prevention of dendrite formation. Our findings demonstrate that acrylate groups in the electrolyte stabilize the flux on the zinc electrode surface, promoting parallel deposition and significantly reducing dendritic formation through vertical growth. The assembled Zn-lignin battery delivers a maximum energy of 23 Wh/kg and a maximum power of 610 W/kg, with an exceptional 82% retention after 8000 cycles. With the reduced expected environmental impact of green and the cost- effectiveness of these polymer electrolytes, the resulting battery shows great promise in the battery market. Its emergence has opened a new avenue in the pursuit of safe and efficient batteries, which has been a major area of focus within the energy storage industry.
14.	Li, Lengwan, et al. (author) Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation 2023 In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:45 Journal article (peer-reviewed)abstract A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high-aspect-ratio 1D flexible nanocellulose fibrils, and 2D Ti3C2Tx MXene is presented. The self-assembly process results in a stratified structure with the nanoparticles aligned in-plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm−1 and the in-plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano- and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out-of-plane swelling, reaching 85% strain.
15.	Lukatskaya, Maria R., et al. (author) Room-Temperature Carbide-Derived Carbon Synthesis by Electrochemical Etching of MAX Phases 2014 In: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 126:19, s. 4977-4980 Journal article (peer-reviewed)abstract 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.
16.	Melianas, Armantas, et al. (author) High-Speed Ionic Synaptic Memory Based on 2D Titanium Carbide MXene 2022 In: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 32:12, s. 2109970- Journal article (peer-reviewed)abstract Synaptic devices with linear high-speed switching can accelerate learning in artificial neural networks (ANNs) embodied in hardware. Conventional resistive memories however suffer from high write noise and asymmetric conductance tuning, preventing parallel programming of ANN arrays. Electrochemical random-access memories (ECRAMs), where resistive switching occurs by ion insertion into a redox-active channel, aim to address these challenges due to their linear switching and low noise. ECRAMs using 2D materials and metal oxides however suffer from slow ion kinetics, whereas organic ECRAMs enable high-speed operation but face challenges toward on-chip integration due to poor temperature stability of polymers. Here, ECRAMs using 2D titanium carbide (Ti3C2Tx) MXene that combine the high speed of organics and the integration compatibility of inorganic materials in a single high-performance device are demonstrated. These ECRAMs combine the speed, linearity, write noise, switching energy, and endurance metrics essential for parallel acceleration of ANNs, and importantly, they are stable after heat treatment needed for back-end-of-line integration with Si electronics. The high speed and performance of these ECRAMs introduces MXenes, a large family of 2D carbides and nitrides with more than 30 stoichiometric compositions synthesized to date, as promising candidates for devices operating at the nexus of electrochemistry and electronics.
17.	Naguib, Michael, et al. (author) New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-Ion Batteries 2013 In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA. - 0002-7863 .- 1520-5126. ; 135:43, s. 15966-15969 Journal article (peer-reviewed)abstract 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.
18.	Naguib, Michael, et al. (author) On the Topotactic Transformation of Ti2AlC into a Ti-C-O-F Cubic Phase by Heating in Molten Lithium Fluoride in Air 2011 In: Journal of The American Ceramic Society. - : Wiley-Blackwell. - 0002-7820 .- 1551-2916. ; 94:12, s. 4556-4561 Journal article (peer-reviewed)abstract Herein we report on the formation of a TiCOF phase via the topotactic transformation of Ti2AlC by immersion in molten lithium fluoride, LiF, at 900 degrees C in air for 2 h. The Al diffuses out of the structure and reacts with LiF to form Li3AlF6. X-ray diffraction, Raman spectroscopy, optical, scanning and transmission electron microscopy, with energy-dispersive spectroscopy, showed the selective etching of Al from the structure and the formation of a cubic, rock-salt, TiCOF phase. The transformation is topotaxial, involves de-twinning of the hexagonal Ti2AlC structure and results in domains that are of the order of 10 nm. The reaction rate is significantly higher when the reaction is carried out in air than when it is carried out in vacuum.
19.	Naguib, Michael, et al. (author) Synthesis of a new nanocrystalline titanium aluminum fluoride phase by reaction of Ti(2)AlC with hydrofluoric acid 2011 In: RSC ADVANCES. - : RSC Publishing. - 2046-2069. ; 1:8, s. 1493-1499 Journal article (peer-reviewed)abstract A new nanocrystalline phase of titanium aluminum fluoride, with a stoichiometry of Ti(2)AlF(9)-exact stoichiometry measured herein is Ti(2.1)Al(0.9)F(9),-was synthesized by the fluorination of Ti(2)AlC in anhydrous hydrofluoric acid at 55 degrees C for 2 h. The results from X-ray diffraction, scanning and high-resolution transmission electron microscopy and selected area diffraction, together with crystal structure solution via simulated annealing, confirmed the formation of a nanocrystalline material with a trigonal structure belonging to the R3 space group. The structure can also be viewed as being comprised of corner-sharing octahedra that are arranged in a distorted simple cubic arrangement. Thermogravimetric analysis, in argon, indicates that this phase is stable up to approximate to 850 degrees C. Density functional theory calculations estimate the band gap to be approximate to 5 eV and the bulk modulus to be approximate to 109 GPa.
20.	Naguib, Michael, et al. (author) Two-Dimensional Nanocrystals Produced by Exfoliation of Ti(3)AlC(2) 2011 In: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 23:37, s. 4248-4253 Journal article (peer-reviewed)abstract n/a
21.	Naguib, Michael, et al. (author) Two-Dimensional Transition Metal Carbides 2012 In: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 6:2, s. 1322-1331 Journal article (peer-reviewed)abstract Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (andgt;60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti2AlC, Ta4AlC3, (Ti-0.5,Nb-0.5)(2)AlC, (V-0.5,Cr-0.5)(3)AlC2, and Ti3AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the "A" group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.
22.	Navarro Suárez, Adriana, 1983, et al. (author) Development of asymmetric supercapacitors with titanium carbide-reduced graphene oxide couples as electrodes 2018 In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 259, s. 752-761 Journal article (peer-reviewed)abstract Two-dimensional (2D) nanomaterials have attracted significant interest for supercapacitor applications due to their high surface to volume ratio. Layered 2D materials have the ability to intercalate ions and thus can provide intercalation pseudocapacitance. Properties such as achieving fast ion diffusion kinetics and maximizing the exposure of the electrolyte to the surface of the active material are critical for optimizing the performance of active materials for electrochemical capacitors (i.e. Supercapacitors). In this study, two 2D materials, titanium carbide (Ti 3 C 2 T x ) and reduced graphene oxide (rGO), were used as electrode materials for asymmetric supercapacitors, with the resulting devices achieving high capacitance values and excellent capacitance retention in both aqueous and organic electrolytes. This work demonstrates that Ti 3 C 2 T x is a promising electrode material for flexible and high-performance energy storage devices.
23.	Ren, Chang E., et al. (author) Porous Two-Dimensional Transition Metal Carbide (MXene) Flakes for High-Performance Li-Ion Storage 2016 In: ChemElectroChem. - : WILEY-V C H VERLAG GMBH. - 2196-0216. ; 3:5, s. 689-693 Journal article (peer-reviewed)abstract 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.
24.	Vahid Mohammadi, Armin, et al. (author) The world of two-dimensional carbides and nitrides (MXenes) 2021 In: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 372:6547 Research review (peer-reviewed)abstract A decade after the first report, the family of two-dimensional (2D) carbides and nitrides (MXenes) includes structures with three, five, seven, or nine layers of atoms in an ordered or solid solution form. Dozens of MXene compositions have been produced, resulting in MXenes with mixed surface terminations. MXenes have shown useful and tunable electronic, optical, mechanical, and electrochemical properties, leading to applications ranging from optoelectronics, electromagnetic interference shielding, and wireless antennas to energy storage, catalysis, sensing, and medicine. Here we present a forward-looking review of the field of MXenes. We discuss the challenges to be addressed and outline research directions that will deepen the fundamental understanding of the properties of MXenes and enable their hybridization with other 2D materials in various emerging technologies.
25.	Volkov, Anton, 1989- (author) Ionic and electronic transport in electrochemical and polymer based systems 2017 Doctoral thesis (other academic/artistic)abstract Electrochemical systems, which rely on coupled phenomena of the chemical change and electricity, have been utilized for development an interface between biological systems and conventional electronics. The development and detailed understanding of the operation mechanism of such interfaces have a great importance to many fields within life science and conventional electronics. Conducting polymer materials are extensively used as a building block in various applications due to their ability to transduce chemical signal to electrical one and vice versa. The mechanism of the coupling between the mass and charge transfer in electrochemical systems, and particularly in conductive polymer based system, is highly complex and depends on various physical and chemical properties of the materials composing the system of interest.The aims of this thesis have been to study electrochemical systems including conductive polymer based systems and provide knowledge for future development of the devices, which can operate with both chemical and electrical signals. Within the thesis, we studied the operation mechanism of ion bipolar junction transistor (IBJT), which have been previously utilized to modulate delivery of charged molecules. We analysed the different operation modes of IBJT and transition between them on the basis of detailed concentration and potential profiles provided by the model.We also performed investigation of capacitive charging in conductive PEDOT:PSS polymer electrode. We demonstrated that capacitive charging of PEDOT:PSS electrode at the cyclic voltammetry, can be understood within a modified Nernst-Planck-Poisson formalism for two phase system in terms of the coupled ion-electron diffusion and migration without invoking the assumption of any redox reactions.Further, we studied electronic structure and optical properties of a self-doped p-type conducting polymer, which can polymerize itself along the stem of the plants. We performed ab initio calculations for this system in undoped, polaron and bipolaron electronic states. Comparison with experimental data confirmed the formation of undoped or bipolaron states in polymer film depending on applied biases.Finally, we performed simulation of the reduction-oxidation reaction at microband array electrodes. We showed that faradaic current density at microband array electrodes increases due to non-linear mass transport on the microscale compared to the corresponding macroscale systems. The studied microband array electrode was used for developing a laccase-based microband biosensor. The biosensor revealed improved analytical performance, and was utilized for in situ phenol detection.
26.	Yang, Jian, et al. (author) Two-Dimensional Nb-Based M4C3 Solid Solutions (MXenes) 2016 In: Journal of The American Ceramic Society. - : WILEY-BLACKWELL. - 0002-7820 .- 1551-2916. ; 99:2, s. 660-666 Journal article (peer-reviewed)abstract Herein, two new two-dimensional Nb4C3-based solid solutions (MXenes), (Nb-0.8,Ti-0.2)(4)C3Tx and (Nb-0.8,Zr-0.2)(4)C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb-0.8,Ti-0.2)(4)AlC3 and (Nb-0.8,Zr-0.2)(4)AlC3. This is the first report on a Zr-containing MXene. Intercalation of Li ions into these two compositions, and Nb4C3Tx was studied to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb4C3Tx, but were not present in Nb2CTx. After 20 cycles at a rate of C/4, the specific capacities of (Nb-0.8,Ti-0.2)(4)C3Tx and (Nb-0.8,Zr-0.2)(4)C3Tx were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb4C3Tx.

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