A Multi‐Scale Structural Engineering Strategy for High‐Performance MXene Hydrogel Supercapacitor Electrode

Abstract

MXenes as an emerging two-dimensional (2D) material have attracted tremendous interest in electrochemical energy-storage systems such as supercapacitors. Nevertheless, 2D MXene flakes intrinsically tend to lie flat on the substrate when self-assembling as electrodes, leading to the highly tortuous ion pathways orthogonal to the current collector and hindering ion accessibility. Herein, a facile strategy toward multi-scale structural engineering is proposed to fabricate high-performance MXene hydrogel supercapacitor electrodes. By unidirectional freezing of the MXene slurry followed by a designed thawing process in the sulfuric acid electrolyte, the hydrogel electrode is endowed with a three-dimensional (3D) open macrostructure impregnated with sufficient electrolyte and H + -intercalated microstructure, which provide abundant active sites for ion storage. Meanwhile, the ordered channels bring through-electrode ion and electron transportation pathways that facilitate electrolyte infiltration and mass exchange between electrolyte and electrode. Furthermore, this strategy can also be extended to the fabrication of a 3D-printed all-MXene micro-supercapacitor (MSC), delivering an ultrahigh areal capacitance of 2.0 F cm -2 at 1.2 mA cm -2 and retaining 1.2 F cm -2 at 60 mA cm -2 together with record-high energy density (0.1 mWh cm -2 at 0.38 mW cm -2 ).

Mechanically Stable All Flexible Supercapacitors with Fracture and Fatigue Resistance under Harsh Temperatures

“…[15][16][17][18] Therefore, mechanical stability proposes further new requirements for the rational design of supercapacitors. [19,20] The efficient strategies, such as planar interdigital micro-supercapacitors, [21] sandwich-like stacked, [22] and fiber-based supercapacitors [16] have demonstrated some incredible features of flexibility. However, the stacked or assembled strategy dramatically increased the interlayer interface resistance and squandered the use of the non-active substance, thus deteriorating the device performance.…”

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

“…APP, consisting of polyphosphate main chains and lateral groups of ammonia ions, has been recognized as a kind of non-toxic, biodegradable, and cost-effective inorganic polymer, [36] and its poly-ionic nature renders APP an ideal bonding agent. Largeflake Ti 3 C 2 T x MXene was prepared by our recently developed freeze-and-thaw-assisted method, [9,19] and has an average lateral size of ≈8.3 μm and a thickness of ≈1.6 nm (Figure S1a-c, Supporting Information), as indicated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The single crystallinity of the as-synthesized MXene flakes was verified by high-resolution TEM (HRTEM) and selected area electron diffraction (SAED) (Figure S2, Supporting Information).…”

“…[1,2] The dimensionality reduction of MAX brings myriad possibilities in creating 2D materials with emergent properties. [3][4][5] Among the current 2D material family, transition metal carbides and nitrides (MXenes) stand out because they own a unique set of innate characteristics (e.g., metallic conductivity [6] and solution processability [7] ) that render them promising for various applications, such as energy storage, [8][9][10] sensing, [11] electrocatalysis, [12,13] and electromagnetic interference (EMI) shielding. [14][15][16] In most cases, the assembly of MXene flakes into freestanding, macroscopic films is a prerequisite to realizing these applications.…”

MXene reinforced organohydrogels with ultra-stability, high sensitivity and anti-freezing ability for flexible strain sensors

“…Hydrogels are a kind of three-dimensional network structure material which contains a large amount of water. [1][2][3] Due to their biocompatibility and excellent mechanical stability, hydrogels have been employed as flexible sensing materials and used in wearable devices, [4][5][6][7][8][9] electronic skin, 10,11 supercapacitors, 12,13 and soft robots. 14,15 MXenes are a kind of transition metal carbide two-dimensional nanomaterial with a graphene-like structure, 16 which have unique properties of metallic conductivity, hydrophilicity, good processability and high specific surface area.…”