Flexible and conductive MXene films and nanocomposites with high capacitance

Abstract

MXenes, a new family of 2D materials, combine hydrophilic surfaces with metallic conductivity. Delamination of MXene produces single-layer nanosheets with thickness of about a nanometer and lateral size of the order of micrometers. The high aspect ratio of delaminated MXene renders it promising nanofiller in multifunctional polymer nanocomposites. Herein, Ti 3 C 2 T x MXene was mixed with either a charged polydiallyldimethylammonium chloride (PDDA) or an electrically neutral polyvinyl alcohol (PVA) to produce Ti 3 C 2 T x / polymer composites. The as-fabricated composites are flexible and have electrical conductivities as high as 2.2 × 10 4 S/m in the case of the Ti 3 C 2 T x /PVA composite film and 2.4 × 10 5 S/m for pure Ti 3 C 2 T x films. The tensile strength of the Ti 3 C 2 T x /PVA composites was significantly enhanced compared with pure Ti 3 C 2 T x or PVA films. The intercalation and confinement of the polymer between the MXene flakes not only increased flexibility but also enhanced cationic intercalation, offering an impressive volumetric capacitance of ∼530 F/cm 3 for MXene/PVA-KOH composite film at 2 mV/s. To our knowledge, this study is a first, but crucial, step in exploring the potential of using MXenes in polymer-based multifunctional nanocomposites for a host of applications, such as structural components, energy storage devices, wearable electronics, electrochemical actuators, and radiofrequency shielding, to name a few.he history of exfoliated, or delaminated, nanosheets (2D materials) dates back to the 1950s (1); however, few of the produced nanosheets are conductive. In recent years, 2D materials have been receiving increased attention, with graphene as the star material owing to its excellent electric, mechanical, and other properties (2-5). In 2011, our group reported on a new family of 2D early transition metal carbides, which combined metallic conductivity and hydrophilic surfaces (6). This novel 2D family was labeled MXenes to denote that they are produced by etching out the A layers from the layered M n+1 AX n phases (6-8) and their similarity to graphene (7).In the M n+1 AX n , or MAX, phases, "M" is an early transition metal, "A" is a group A (mainly groups 13-16) element, "X" is carbon and/or nitrogen, and n = 1, 2, or 3 (9). So far, the MXene family includes Ti 3 C 2 , Ti 2 C, (Ti 0.5, Nb 0.5 ) 2 C, (V 0.5 ,Cr 0.5 ) 3 C 2 , Ti 3 CN, Ta 4 C 3 (10), Nb 2 C, V 2 C (8), and Nb 4 C 3 (11). Because there are over 70 known MAX phases (9), many more MXenes can be expected. It is important to note here that MXene surfaces are terminated by O, OH, and/or F groups from the etching process. Henceforth, these terminated MXenes will be referred to as M n+1 X n T x , where T represents terminating groups (O, OH, and/or F) and x is the number of terminating groups.If they are not delaminated, MXenes are multilayered structures resembling those of exfoliated graphite, which have shown promising performance as electrodes in both lithium ion batteries and supercapacitors, as well as adsorbents for hea...

Effect of Postetch Annealing Gas Composition on the Structural and Electrochemical Properties of Ti2CTx MXene Electrodes for Supercapacitor Applications

“…In recent years, MXenes-a new family of 2D early transition metal carbides and carbonitrides, have been receiving significant research interest, by virtue of their excellent electrochemical energy storage properties, good electrical conductivity and superior mechanical properties [1][2][3][4][5] .…”

In Situ Formed Protective Barrier Enabled by Sulfur@Titanium Carbide (MXene) Ink for Achieving High‐Capacity, Long Lifetime Li‐S Batteries

“…The 70% S@Ti 3 C 2 T x film displays very high tensile strength (≈12.9 MPa) and Young's modulus (≈19.2 GPa; Figure 2f). In addition, the tensile strain of the film reaches 0.8%, higher than that of graphene oxide paper (<0.6%)52, 54 but lower than that of Ti 3 C 2 T x paper (≈6%) 55. This is because the large amount of nanocrystalline S in the composite (Figure S8b, Supporting Information) compromises the film's stretchability.…”

High-Voltage Symmetric Supercapacitor Based on 2D Titanium Carbide (MXene, Ti2CTx)/Carbon Nanosphere Composites in a Neutral Aqueous Electrolyte

“…MXene combined with nanocarbons 12,14,23,30,40,41 and polymers 17,23 were shown to yield better capacitance than pristine MXene but in a narrow voltage window (<1.0 V) in aqueous electrolytes 17,26,[28][29][30]41 or higher voltage window (>1.0 V) in organic electrolyte. 14,40 To date, nearly all reported works on MXene-based supercapacitors have been on the heavy MXene (Ti 3 C 2 T x ) rather than on the MXene type Ti 2 CT x , usually referred to as the lightest MXene.…”

“…Lukatskaya et al 38 indicated that the capacitance comes mainly from pseudocapacitive redox reactions of the Titanium. Gogotsi and co-workers 35,39 studied MXene as an anode material for Li-ion batteries (LiBs) and asymmetric cells and suggested the following lithiation and delithiation reactions taking place when Li + ions are inserted into the MXene matrix as described in Equation 1.Ling et al 23 and Zhao et al 38 also showed that expanding the interlayer gaps improves the capacity by facilitating ion transport. MXene combined with nanocarbons 12,14,23,30,40,41 and polymers 17,23 were shown to yield better capacitance than pristine MXene but in a narrow voltage window (<1.0 V) in aqueous electrolytes 17,26,[28][29][30]41 or higher voltage window (>1.0 V) in organic electrolyte.…”