In Situ Ice Template Approach to Fabricate 3D Flexible MXene Film‐Based Electrode for High Performance Supercapacitors

Abstract

MXenes with metallic conductivity, high pseudo-capacitance and 2D structure, are promising flexible electrode materials for supercapacitors, but suffer from the restacking issue, which hinders ion accessibility and causes sluggish ion kinetics. Herein, a simple in situ ice template strategy is proposed to fabricate free-standing, flexible 3D porous Ti 3 C 2 T x /carbon nanotubes (CNTs) film (3D-PMCF) by freeze-drying Ti 3 C 2 T x-based hydro-films without any postprocessing. During the freeze-drying process, small ice grains are in situ transformed from the residual water molecules in the Ti 3 C 2 T x interlayer and then act as a self-sacrifice template to construct a 3D porous network. CNTs introduced in the hydro-film increase the amount of interlayer water and the resultant porosity. The 3D structure of Ti 3 C 2 T x significantly increases the exposed surface active sites and accelerates the ion transport, meanwhile maintaining good flexibility. Consequently, the flexible 3D-PMCF film delivers a capacitance of 375 F g −1 at 5 mV s −1 and retains 251.2 F g −1 at 1000 mV s −1 with excellent cycling stability, much superior to the conventional densely stacked Ti 3 C 2 T x film. Being assembled into a symmetric supercapacitor, an energy density of 9.2 Wh kg −1 is realized. This work demonstrates a simple and efficient route for constructing high-performance and flexible 3D MXene film electrodes for supercapacitors.

Freeze‐assisted Tape Casting of Vertically Aligned MXene Films for High Rate Performance Supercapacitors

“…[30] Ice-templating has been employed to develop high-performance supercapacitor films with MXene, such as in the work demonstrated by Zhang Peng et al which showcases a Ti 3 C 2 T x /CNT film with an internal porous network, exposing a greater amount of surface active sites. [31,32] FaTC is a popular manufacturing method for functionally graded structures and porous ceramics. [33][34][35][36][37][38] For example, Yu Chen et al [33] fabricated functionally graded acicular electrodes for solid oxide fuel cells using this method, achieving enhanced electrochemical performance.…”

Recent Advances in Functional 2D MXene‐Based Nanostructures for Next‐Generation Devices

“…[113][114][115][116][117][118][119] The synergistic effects are expected for 2D MXene/1D nanomaterial heterostructures to combine both structural advantages of 1D nanostructure and 2D MXene for desirable performances. [32,33,54,[66][67][68][69][120][121][122] For example, Xiao et al [66] anchored well-defined CdS nanorods on ultrathin Ti 3 C 2 T x nanosheets through electrostatically driven assembly and hydrothermal methods (Figure 6a). The SEM image shows that CdS nanorods are tightly anchored on the surface of 2D MXene Ti 3 C 2 T x nanosheets ( Figure 6b).…”

“…© 2020 Wiley-VCH GmbH or MXenes incorporated into heterostructures is a decisive strategy. [32,34,49,83,[175][176][177] In 2018, Yoon et al [83] reported that an N-doped Ti 2 CT x with different N doping contents was successfully synthesized by sequential intercalation and decomposition of carbon nitride through a simple exfoliation and thermal annealing method. The cyclic voltammetry (CV) curves for pristine Ti 2 CT x , N-doped Ti 2 CT x at 500 °C, N-doped Ti 2 CT x at 700 °C, N-doped Ti 2 CT x at 900 °C, and Ti 2 CT x at 900 °C without NH 2 CN in 6 m KOH electrolyte at a scan rate of 100 mV s −1 exhibit that the CV curve shape of N-doped Ti 2 CT x becomes more and more rectangular as the annealing temperature increases, and its corresponding areas also become larger (Figure 10a).…”

“…Besides, it should be pointed out that at 10 A g −1 , the specific capacitance of N-doped Ti 2 CT x at 900 °C electrode only reduces by 13.8% in comparison to that at 1 A g −1 , while pristine Ti 2 CT x , N-doped Ti 2 CT x at 500 °C, N-doped Ti 2 CT x at 700 °C, and Ti 2 CT x at 900 °C without NH 2 CN decline by 50.5%, 48.6%, 48.9%, and 38.6%, respectively, suggesting that the as-prepared N-doped Ti 2 CT x at 900 °C electrode has the best rate capability. [83] Moreover, in 2020, Zhang et al [32] reported that the free-standing, flexible 3D porous MXene Ti 3 C 2 T x /CNTs film was successfully fabricated by freeze-drying MXene Ti 3 C 2 T x -based hydro-films without post-processing. The variations of specific capacitance as a function of scan rate in the range from 5 to 10 000 mV s −1 exhibit that the as-fabricated 3D porous Ti 3 C 2 T x /CNT electrode has the highest specific capacitance of 372 F g −1 at a scan rate of 5 mV s −1 , outperforming the porous MXene Ti 3 C 2 T x electrode and dense MXene Ti 3 C 2 T x electrode (Figure 10d).…”

Self-propagating fabrication of 3D porous MXene-rGO film electrode for high-performance supercapacitors

“…Since they were firstly reported in 2011, MXenes have attracted much attention due to their unique structure and surface chemistry [ 2 , 3 ]. Especially for the application in supercapacitors, MXenes are promising electrode materials because they exhibit much higher pseudocapacitance, larger density and metallic conductivity compared with carbon materials used in the conventional electric double layer capacitors (EDLCs) [2][3][4][5][6] . Furthermore, with the 2D lamellar structure, MXenes can be fabricated into flexible and freestanding electrodes without current collector and binder, implying great potential in flexible energy storage devices [ 1 , 7-10 ].…”