12 research outputs found
Chemistry of two-dimensional transition metal carbides (MXenes)
With consumer trends pushing toward smaller, faster, more flexible, multitasking devices, researchers striving to meet these needs have targeted two-dimensional (2D) materials – and graphene in particular – as holding the most promise for use in advanced applications. But in 2011, a significant interest has been triggered by a newly discovered family of novel 2D materials – layered transitional metal carbides and carbonitrides, named MXenes. Those compounds were of general formula Mn+1XnTx, where M stands for metal atom, X is C and/or N, n = 1, 2 or 3, and Tx represents surface groups. Being initially suggested as a material for electrical energy storage systems, MXenes’ properties and their potential applications have not been explored. This work is the first complete study of MXenes’ chemistry that sheds light on the chemical composition, structure and properties of these novel materials and possible routes of its modification. The research was focused on 2D titanium carbide, Ti3C2Tx, chosen as the representative of the MXene family. The kinetic study of Ti3C2Tx synthesis discovered the main synthesis parameters, viz. temperature, time and particle size, that affect the etching process and define the quality of final product. MXenes were found to be able to spontaneously accommodate various ions and small organic molecules between the layers leading to preopening of the structure. A major challenge of large scale production of delaminated, atomically thin 2D MXene layers was solved with two delamination techniques involving dimethyl sulfoxide and isopropyl amine pre-intercalation followed by sonication in water. Ti3C2Tx was also found to possess adsorptive and photocatalytic properties, revealing its potential for environmental applications. It also showed limited stability in water and in the presence of oxygen, providing important practical information on proper handling and storage of MXene materials. Completion of this work allowed the performance of energy storage devices to be improved significantly, viz. Li-ion batteries and electrochemical capacitors, and gave rise to many other potential applications such as MXene-polymer composites, sorption, and catalysis. More importantly, it opened a path to the large-scale synthesis of thin, single-layer MXene sheets and led to establishing MXenes as fully-fledged members of the growing family of 2D materials.Ph.D., Materials Science -- Drexel University, 201
Intercalation and Delamination of Layered Carbides and Carbonitrides
Intercalation and delamination of two-dimensional solids in many cases is a requisite step for exploiting their unique properties. Herein we report on the intercalation of two-dimensional Ti3C2, Ti3 CN and TiNbC - so called MXenes. Intercalation of hydrazine, and its co-intercalation with N,N-dimethylformamide, resulted in increases of the c-lattice parameters of surface functionalized f-Ti3C2, from 19.5 to 25.48 and 26.8 Ã…, respectively. Urea is also intercalated into f-Ti3C2. Molecular dynamics simulations suggest that a hydrazine monolayer intercalates between f-Ti3C2 layers. Hydrazine is also intercalated into f-Ti3 CN and f-TiNbC. When dimethyl sulphoxide is intercalated into f-Ti3C2, followed by sonication in water, the f-Ti3C2 is delaminated forming a stable colloidal solution that is in turn filtered to produce MXene \u27paper\u27. The latter shows excellent Li-ion capacity at extremely high charging rates
Dye Adsorption and Decomposition on Two-Dimensional Titanium Carbide in Aqueous Media
Recently a large family of two-dimensional (2D) layered early transition metal carbides and carbonitrides-labelled MXene-possessing metallic conductivity and hydrophilic surfaces was discovered. Herein we report on the adsorption and photocatalytic decomposition of organic molecules in aqueous environments containing Ti3C2Tx, a representative of the MXene family. This material possesses excellent adsorption toward cationic dyes, best described by a Freundlich isotherm. We also found that the material may undergo structural changes in aqueous media
High-Purity Lithium Metal Films from Aqueous Mineral Solutions
Lithium metal is a leading candidate
for next-generation electrochemical
energy storage and therefore a key material for the future sustainable
energy economy. Lithium has a high specific energy, low toxicity,
and relatively favorable abundance. The majority of lithium production
originates from salt lakes and is based on long (>12 months) periods
of evaporation to concentrate the lithium salt, followed by molten
electrolysis. Purity requires separation from base metals (Na, K,
Ca, Mg, etc.), which is a time-consuming, energy-intensive process,
with little control over the microstructure. Here, we show how a membrane-mediated
electrolytic cell can be used to produce lithium thin films (5–30
μm) on copper substrates at room temperature. Purity with respect
to base metals content is extremely high. The cell design allows an
aqueous solution to be a continuous feedstock, advocating a quick,
low-energy-consumption, one-step-to-product process. The film morphology
is controlled by varying the current densities in a narrow window
(1–10 mA/cm<sup>2</sup>), to produce uniform nanorods, spheres,
and cubes, with significant influence over the physical and electrochemical
properties
Anodized Ti<sub>3</sub>SiC<sub>2</sub> As an Anode Material for Li-ion Microbatteries
We
report on the synthesis of an anode material for Li-ion batteries
by anodization of a common MAX phase, Ti<sub>3</sub>SiC<sub>2</sub>, in an aqueous electrolyte containing hydrofluoric acid (HF). The
anodization led to the formation of a porous film containing anatase,
a small quantity of free carbon, and silica. By varying the anodization
parameters, various oxide morphologies were produced. The highest
areal capacity was achieved by anodization at 60 V in an aqueous electrolyte
containing 0.1 v/v HF for 3 h at room temperature. After 140 cycles
performed at multiple applied current densities, an areal capacity
of 380 μAh·cm<sup>–2</sup> (200 μA·cm<sup>–2</sup>) has been obtained, making this new material, free
of additives and binders, a promising candidate as a negative electrode
for Li-ion microbatteries
Carbon Pipette-Based Electrochemical Nanosampler
Sampling ultrasmall volumes of liquids
for analysis is essential
in a number of fields from cell biology to microfluidics to nanotechnology
and electrochemical energy storage. In this article, we demonstrate
the possibility of using nanometer-sized quartz pipettes with a layer
of carbon deposited on the inner wall for sampling attoliter-to-picoliter
volumes of fluids and determining redox species by voltammetry and
coulometry. Very fast mass-transport inside the carbon-coated nanocavity
allows for rapid exhaustive electrolysis of the sampled material.
By using a carbon pipette as the tip in the scanning electrochemical
microscope (SECM), it can be precisely positioned at the sampling
location. The developed device is potentially useful for solution
sampling from biological cells, micropores, and other microscopic
objects
Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide
International audienceThe intercalation of ions into layered compounds has long been exploited in energy storage devices such as batteries and electrochemical capacitors. However, few host materials are known for ions much larger than lithium. We demonstrate the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers. MXenes combine 2D conductive carbide layers with a hydrophilic, primarily hydroxyl-terminated surface. A variety of cations, including Na+, K+, NH4+, Mg2+, and Al3+, can also be intercalated electrochemically, offering capacitance in excess of 300 farads per cubic centimeter (much higher than that of porous carbons). This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions
Synthesis of Carbon/Sulfur Nanolaminates by Electrochemical Extraction of Titanium from Ti 2 SC
International audienceHerein we electrochemically and selectively extract Ti from the MAX phase Ti2SC to form carbon/sulfur (C/S) nanolaminates at room temperature. The products are composed of multi-layers of C/S flakes, with predominantly amorphous and some graphene-like structures. Covalent bonding between C and S is observed in the nanolaminates, which render the latter promising candidates as electrode materials for Li-S batteries. We also show that it is possible to extract Ti from other MAX phases, such as Ti3AlC2, Ti3SnC2, and Ti2GeC, suggesting that electrochemical etching can be a powerful method to selectively extract the M elements from the MAX phases, to produce AX layered structures, that cannot be made otherwise. The latter hold promise for a variety of applications, such as energy storage, catalysis, etc