Assembly of Nanofluidic MXene Fibers with Enhanced Ionic Transport and Capacitive Charge Storage by Flake Orientation

Abstract

MXenes are an emerging class of highly conductive two-dimensional (2D) materials with electrochemical storage features. Oriented macroscopic Ti3C2T x fibers can be fabricated from a colloidal 2D nematic phase dispersion. The layered conductive Ti3C2T x fibers are ideal candidates for constructing high-speed ionic transport channels to enhance the electrochemical capacitive charge storage performance. In this work, we assemble Ti3C2T x fibers with a high degree of flake orientation by a wet spinning process with controlled spinning speeds and morphology of the spinneret. In addition to the effects of cross-linking of magnesium ions between Ti3C2T x flakes, the electronic conductivity and mechanical strength of the as-prepared fibers have been improved to 7200 S cm–1 and 118 MPa, respectively. The oriented Ti3C2T x fibers present a volumetric capacitive charge storage capability of up to 1360 F cm–3 even in a Mg-ion based neutral electrolyte, with contributions from both nanofluidic ion transport and Mg-ion intercalation pseudocapacitance. The oriented 2D Ti3C2T x driven nanofluidic channels with great electronic conductivity and mechanical strength endows the MXene fibers with attributes for serving as conductive ionic cables and active materials for fiber-type capacitive electrochemical energy storage, biosensors, and potentially biocompatible fibrillar tissues.

Microfluidic Fabrication of Hierarchical‐Ordered ZIF‐L(Zn)@Ti3C2Tx Core–Sheath Fibers for High‐Performance Asymmetric Supercapacitors

“…Astonishingly, the ZIFÀ L(Zn)@Ti 3 C 2 T x fiber has a high capacitance of 1700 F cm À 3 at 1 A cm À 3 , more than 2 times that of the Ti 3 C 2 T x fiber (810 F cm À 3 ). To the best of our knowledge, our capacitive level is comparable with the best values among those reported (MXene/PEDOT:PSS fiber [39] of 614.5 F cm À 3 , MXene fiber [41] of 1360 F cm À 3 , MXene/rGO fiber [48] of 341 F cm À 3 , Biscrolled MXene/CNT yarn [37] of 1083 F cm À 3 , Ti 3 C 2 T x /ANF [34] of 807 F cm À 3 , MXene/CNT yarn [49] of 92 F cm À 3 , rGO/Ni cotton yarn [50] of 292.3 F cm À 3 , Graphene/CNTs [22] of 305 F cm À 3 (Table S2)). More significantly, even at such a high current density of 150 A cm À 3 , a good capacitance (845 F cm À 3 ) of the ZIFÀ L(Zn)@Ti 3 C 2 T x fiber can still be retained, whereas the Ti 3 C 2 T x fiber only preserves 59 F cm À 3 .…”

“…To further highlight the energy storage values, the energy densities under different power densities were calculated for comparison with recently reported literature (Figure 4d). Our maximum energy density reaches 19.0 mWh cm À 3 at a power density of 309 mW cm À 3 , which is one of the biggest levels compared with previously reported FESCs (MXene/PEDOT:PSS of 16.6 mWh cm À 3 , [44] MXene/rGO of 13.03 mWh cm À 3 , [38] RuO 2 @MXene of 13.5 mWh cm À 3 , [52] MXene of 10.61 mWh cm À 3 , [41] Graphene/PANI of 8.8 mWh cm À 3 , [53] Graphene/CNTs of 6.3 mWh cm À 3 , [22] MXene/TAEA of 5.1 mWh cm À 3 , [54] MXene/CNT of 2.55 mWh cm À 3 , [49] MnO 2 / /MXene@Fe 2 O 3 of 1.61 mWh cm À 3 [55] (Table S3)).…”

“…In this step, under the designed conical-cylindrical microchannels, the randomly arranged Ti 3 C 2 T x liquid crystals could be forced to yield the nanosheet orientation by strongly elongational flow along the axial directions, [25] resulting in the highly ordered alignment and anisotropic microstructure within fibers. Concomitantly, the Mg 2 + can greatly strengthen ionic crosslinking attractions among interlaminar Ti 3 C 2 T x nanoflakes through electrostatic interaction, [41] guaranteeing compact fibers with excellent interlayer connectivity, mechanical strength and electrical conductivity.…”

Relation between Charging Times and Storage Properties of Nanoporous Supercapacitors

“…We use the slit pore geometry shown in Figure 1, which describes the spatial structure of modern porous materials, such as graphene based electrodes [33,34] and graphene oxide (GO)/MXene fibers [35,36], exhibiting aligned slit-nanopores of width H comparable to electrolyte diameter d and length L H. The considered materials are used in supercapacitor's technologies as the porous electrodes which accumulate charge through electric double layer formation without chemical reactions. More precisely, these materials show promising applications for wearable electronics and smart textiles devices due to outstanding energy density and high flexibility [37].…”

Gelation‐Assisted Assembly of Large‐Area, Highly Aligned, and Environmentally Stable MXene Films with an Excellent Trade‐Off between Mechanical and Electrical Properties

“…The WAXS pattern of MAF‐0.25 displays narrower peaks compared to PMF (Figure 1e,f), corroborating that the MXene flakes in MAF‐0.25 are highly aligned in the in‐plane direction. [ 34 ] The corresponding Herman's orientation factor ( f ) determined from the azimuthal scan profile reaches 0.88 for MAF‐0.25, much larger than that of PMF (0.68). Notably, this Herman's orientation factor is larger than that of most previously reported MXene films prepared by various assembly methods.…”