Enhancing Capacitance Performance of Ti3C2Tx MXene as Electrode Materials of Supercapacitor: From Controlled Preparation to Composite Structure Construction

Abstract

Ti₃C₂T_x, a novel two-dimensional layer material, is widely used as electrode materials of supercapacitor due to its good metal conductivity, redox reaction active surface, and so on. However, there are many challenges to be addressed which impede Ti₃C₂T_x obtaining the ideal specific capacitance, such as restacking, re-crushing, and oxidation of titanium. Recently, many advances have been proposed to enhance capacitance performance of Ti₃C₂T_x. In this review, recent strategies for improving specific capacitance are summarized and compared, for example, film formation, surface modification, and composite method. Furthermore, in order to comprehend the mechanism of those efforts, this review analyzes the energy storage performance in different electrolytes and influencing factors. This review is expected to predict redouble research direction of Ti₃C₂T_x materials in supercapacitors.

Keywords: Capacitance performance; Electrode materials; MXene; Storage mechanism; Supercapacitor; Ti3C2Tx.

Fig. 1

Enhancing the capacitance of Ti₃C₂T_x as electrode materials of supercapacitors. a Structure of Ti₃C₂T_x [21]. b N-doped Ti₃C₂T_x [36]. c Ti₃C₂T_x/layered metallic double hydroxides [37]. d Ti₃C₂T_x/conductive polymers [41]. e Carbon-intercalated Ti₃C₂T_x composite paper [38]. f WO₃/Ti₃C₂T_x composite paper [39]. g 3D Ti₃C₂T_x aerogels [40]. Reproduced with permission from Refs. [, –40]

Fig. 2

Structure of Ti₃C₂T_x. a Atomic composition model of Ti₃C₂T_x [25]. b Schematic diagram of the process for etching and delamination of Mxene [51]. c Scanning electron microscopy (SEM) images of Ti₃AlC₂ particle and Ti₃C₂T_x [23]. Reproduced with permission from Refs. [23, 25, 51]

Fig. 3

Electrochemical performance of Ti₃C₂T_x at a scan rate of 5 mV s⁻¹. a Schematic illustration of ionic intercalation mechanism on the surface of the Ti₃C₂T_x. b CV curves of Ti₃C₂T_x in aqueous LiCl, NaCl, and KCl electrolyte at different potential windows. Reproduced with permission from Ref. [64]

Fig. 4

Pseudocapacitance of Ti₃C₂T_x in different electrolytes. a The change of surface group of Ti₃C₂T_x in H₂SO₄ [58]. b CV curves of Ti₃C₂T_x at a scan rate of 20 mV s⁻¹ [71]. c Gravimetric capacitances of Ti₃C₂T_x at different scan rates [75]. d CV curves of Ti₃C₂T_x at different scan rates in KOH electrolyte [75]. e Schematic of supercapacitor using Ti₃C₂T_x (pink, Ti; cyan, C; red, O) as negative electrode with solvated or desolvated states. Legend for the electrolyte: green, cation; orange, anion; yellow, solvent molecule [81]. Reproduced with permission from Refs. [58, 71, 75, 81]. (Color figure online)

Fig. 5

Ti₃C₂T_x film. a Schematic of the preparation of the nanoporous Ti₃C₂T_x films. b SEM image of nickel foam [92]. c CV curves of Ti₃C₂T_x film and modified nanoporous films at a scan rate of 10 mV s⁻¹. MP-MX_x means the nanoporous Ti₃C₂T_x film is obtained, where x is the mass ratio of Fe(OH)₃ hybrid [94]. Reproduced with permission from Refs. [92, 94]

Fig. 6

Ti₃C₂T_x aerogel. a SEM image of the Ti₃C₂T_x aerogel with different magnifications [40]. b Cross-sectional view of Ti₃C₂ aerogel, SEM image of Ti₃C₂ aerogel, and TEM of void walls. c CV and GCD curves of Ti₃C₂ aerogel, specific capacitance with different mass loadings, progression of the imaginary (C″) parts of the stack capacitance of Ti₃C₂ aerogel and areal capacitance with different mass loadings [96]. Reproduced with permission from Refs. [40, 96]

Fig. 7

Ti₃C₂T_x composited with PPy and MnO₂. a Schematic illustration of pyrrole polymerization using Ti₃C₂T_x. The surface groups on the latter contribute to the polymerization process [99]. b Cross-sectional SEM image, and TEM image of Ti₃C₂T_x/MnO₂ nanowires. c CV and GCD curves for different samples about Ti₃C₂T_x/MnO₂ nanowires [104]. Reproduced with permission from Refs. [99, 104]

Fig. 8

Ti₃C₂T_x-rHGO nanoporous network. a Cross section (i, ii) and SEM images (iii, iv) of Ti₃C₂T_x film (i, iii) and Ti₃C₂T_x-rHGO films (ii, iv). b CV and GCD curves of Ti₃C₂T_x films and Ti₃C₂T_x-rHGO and effects of areal mass loading on the volumetric capacitance. MX-rHGO_x, where x is the percentage of the weight of holey graphene oxide in the mixture. Reproduced with permission from Ref. [117]

Fig. 9

One-dimensional electrode materials of supercapacitors. a Morphology of electrospinning Ti₃C₂T_x composite [118]. b Schematic of the fabrication process of Ti₃C₂T_x fiber using biscrolling method. c Surface and cross-sectional morphologies of biscrolling Ti₃C₂T_x fiber. d CV curves obtained at 5 mV s⁻¹ and GCD curves obtained at 2 mA cm⁻² [120]. Reproduced with permission from Refs. [118, 120]

Fig. 10

N-doped Ti₃C₂T_x. a Schematic illustration of charge storage of hydrated electrolyte ions in N-doped Ti₃C₂T_x [122]. b Plan view of optical and SEM images of Ti₃C₂ and N-doped Ti₃C₂T_x using urea as the nitrogen source (UN-Ti₃C₂). c CV curves of the Ti₃C₂ films and N-doped Ti₃C₂ using different method, such as UN-Ti₃C₂, MN-Ti₃C₂ (nitrogen source is monoethanolamine), TN-Ti₃C₂ (solid solution method) [123]. Reproduced with permission from Refs. [122, 123]