Progress of 2D MXene as an Electrode Architecture for Advanced Supercapacitors: A Comprehensive Review

Abstract

Supercapacitors, designed to store more energy and be proficient in accumulating more energy than conventional batteries with numerous charge-discharge cycles, have been developed in response to the growing demand for energy. Transition metal carbides/nitrides called MXenes have been the focus of researchers' cutting-edge research in energy storage. The 2D-layered MXenes are a hopeful contender for the electrode material due to their unique properties, such as high conductivity, hydrophilicity, tunable surface functional groups, better mechanical properties, and outstanding electrochemical performance. This newly developed pseudocapacitive substance benefits electrochemical energy storage because it is rich in interlayer ion diffusion pathways and ion storage sites. Making MXene involves etching the MAX phase precursor with suitable etchants, but different etching methods have distinct effects on the morphology and electrochemical properties. It is an overview of the recent progress of MXene and its structure, synthesis, and unique properties. There is a strong emphasis on the effects of shape, size, electrode design, electrolyte behavior, and other variables on the charge storage mechanism and electrochemical performance of MXene-based supercapacitors. The electrochemical application of MXene and the remarkable research achievements in MXene-based composites are an intense focus. Finally, in light of further research and potential applications, the challenges and future perspectives that MXenes face and the prospects that MXenes present have been highlighted.

Figure 1

Schematic diagram of a supercapacitor.

Figure 2

Periodic table illustrating the elements of the MAX phase and MXene.

Figure 3

Schematic representation of etching.

Figure 4

XRD pattern of (a) MAX powder (Ti₃AlC₂) in comparison with MXene, indicating the peak shift and (b) magnified image showing the peak shift after MXene formation. Reproduced from ref (89). Copyright 2021 American Chemical Society.

Figure 5

Scanning electron micrographs of the (a) MAX phase (Ti₃AlC₂) and (b) accordion-like structure of exfoliated MXene. Reproduced from ref (89). Copyright 2021 American Chemical Society.

Figure 6

Diagram of (a) EDLC, (b) pseudocapacitor, and (c) hybrid capacitor.

Figure 7

Electrochemical testing of Ti₃C₂T_x-CNTs and Ti₃C₂T_x-based single mSC devices. (A) CV curves at 10 mv/s, (B) GCD curves at 0.5 mA/cm², (C) rate capacity, (D) EIS, (E) Ragone plots, and (F) cycling stability for 5000 times. Reproduced from ref (127). Copyright 2021 American Chemical Society.

Figure 8

D-Ti₃C₂T_x and N-d-Ti₃C₂T_x/MoO_x films with different mass loadings of MoO_x nanoparticles: (a) CV curves at 20 mV s^–1, (b) GCD curves at 5 A g^–1, and (c,d) gravimetric and volumetric capacity at different scan rates. Reproduced from ref (140). Copyright 2021 Elsevier.

Figure 9

(a) CV curves of a Ti₃C₂T_x/PANI electrode. (b) Comparison of the CV Ti₃C₂T_x/PANI and Ti₃C₂T_x electrodes. (c) Gravimetric capacitance of electrodes with different thicknesses and mass loadings. (d) Galvanostatic charge/discharge profiles of the Ti₃C₂T_x/PANI electrode. (e) Specific capacitances of the Ti₃C₂T_x/PANI electrode. (f) EIS of Ti₃C₂T_x/PANI electrodes. Reproduced from ref (151). Copyright 2018 Royal Society of Chemistry.

Figure 10

Rate performance of the TH-800, TD-800, and Ti₃C₂T_x-800 electrodes. Reproduced from ref (160). Copyright 2018 Royal Society of Chemistry.

Figure 11

Scan rate dependence of volumetric capacitance of a 1.2 μm (Mo_2/3, Y_(1–x)/3)2C) film and a 2 μm Mo_1.33C film in 1 M H₂SO₄ and 6 M KOH. Reproduced from ref (165). Copyright 2018 American Chemical Society.

Figure 12

CVs of 1.7-IL-Ti₃C₂T_x/GCE at 2 mV s^–1 in 3 M H₂SO₄ and 3 M H₂SO₄–0.8 M [Emim]H₂SO₄. Reproduced from ref (173). Copyright 2020 Royal Society of Chemistry.

Figure 13

Electrochemical performance of a 1.2 μm thick film of (Mo_2/3, Y_(1–x)/3)₂C: (a) 1 M H₂SO₄ and (b) 6 M KOH. Reproduced from ref (165). Copyright 2018 American Chemical Society.

Figure 14

Areal capacitances of the Ti₃C₂T_x film and Ti₃C₂T_x/PDA-2, 5, and 10 composite film electrodes as a function of the scan rate. Reproduced from ref (176). Copyright 2019 Elsevier.

Figure 15

CV curves of (a) electrodes made using large flakes (average size of ∼3 μm) and (b) small flakes (average size of ∼0.18 μm). Reproduced from ref (181). Copyright 2018 American Chemical Society.