Olha Mashtalir

Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide

Toward Titanium Carbide Batteries Many batteries and capacitors make use of lithium intercalation as a means of storing and transporting charge. Lithium is commonly used because it offers the best energy density, but also because there are difficulties in storing larger cations without disrupting the crystal structure of the host. Lukatskaya et al. (p. 1500) developed a series of MX compounds, where M represents a transition metal and X is carbon or nitrogen.The compound Ti3C2 forms a two dimensional layered structure, which is capable of accommodating a wide range of cations, including multivalent ones, either spontaneously or electrochemically The layered material Ti3C2 can intercalate much larger cations than Li+, allowing for energy storage applications. The 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.

Amine‐Assisted Delamination of Nb2C MXene for Li‐Ion Energy Storage Devices

2D Nb2CTx MXene flakes are produced using an amine-assisted delamination process. Upon mixing with carbon nanotubes and filtration, freestanding, flexible paper is produced. The latter exhibits high capacity and excellent stability when used as the electrode for Li-ion batteries and capacitors.

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.

In situ environmental transmission electron microscopy study of oxidation of two-dimensional Ti3C2 and formation of carbon-supported TiO2

Two-dimensional Ti3C2, also known as “MXene”, was oxidized in air under two different oxidizing regimes in order to produce carbon-supported TiO2. In situ TEM analysis coupled with Raman spectroscopy revealed the formation of either anatase nanoparticles or planar rutile nanocrystals, which were controlled by the time, temperature and heating rate.

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.

Solution-processed titanium carbide MXene films examined as highly transparent conductors

MXenes, a new family of two-dimensional structures, have recently gained significant attention due to their unique physical properties suitable for a wide range of potential applications. Here we introduce Ti3C2Tx delaminated monolayers as ultrathin transparent conductors with properties exceeding comparable reduced graphene oxide films. Solution processed Ti3C2Tx films exhibit sheet resistances as low as 437 Ω sq-1 with 77% transmittance at 550 nm. Field effect transistor measurements confirm that these films have a metallic nature, which makes them suitable as electrodes. We show using Kelvin Probe Atomic Force Microscopy that the work function of delaminated Ti3C2Tx flakes (with OH terminal groups) is 5.28 ± 0.03 eV. These results demonstrate that solution-processed Ti3C2Tx conducting films could open up a new direction for the next generation of transparent conductive electrodes.

Anodized Ti3SiC2 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, Ti3SiC2, 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(-2) (200 μA·cm(-2)) has been obtained, making this new material, free of additives and binders, a promising candidate as a negative electrode for Li-ion microbatteries.