MXene-Based Nanocomposites for Supercapacitors: Fundamentals and Applications

Abstract

MXene-based nanocomposite materials with other 2D materials have made a large impact in the field of energy storage, particularly in the area of supercapacitors. Combining conductive 2D MXene with other 2D materials, such as transition metal oxide, transition metal dichalcogenides, and layered double hydroxide, improves the electrochemical energy storage properties of resulting MXene-based nanocomposites. The interface of MXene and 2D nanocomposite materials allows an improved electrochemical performance for energy storage applications. In this review, state-of-the-art research progress in 2D/2D MXene-based nanocomposite synthesis, structural and morphological properties, and electrochemical performance for supercapacitors is explored. 2D MXene nanocomposites electrochemical properties in terms of specific capacitance, energy, power densities, and stability are discussed. This study shows that this rapidly developing field has an important impact on the next-generation supercapacitor.

Keywords: 2D materials; MAX; energy storage.

Figure 1

a) History of MXene synthesis during the last 12 years. b) Various major applications of MXene‐based nanocomposites.

Figure 2

MXene synthesis approaches. Top‐down approaches: a) conventional HF etching process for MXene synthesis wherein Ti₃AlC₂ was added into hydrofluoric (HF) acid (Re‐draw from reference paper).^{[ 40 ]} HF‐free etching MXene synthesis process included b) acid/salt etching process in which a combined FeF₃ and HCl solution was used for MXene synthesis (Re‐draw from reference paper),^{[ 41 ]} c) fluorine‐free strategies in the presence of NaOH–water solution with different experimental conditions: (1) at lower temperature: formation of insoluble Al (oxide) hydroxide; (2) at higher temperature and low NaOH concentrations: dissolve Al (oxide) hydroxide in NaOH; (3) higher temperatures and higher NaOH concentrations: completely dissolve the Al(oxide) hydroxides in NaOH solution (the Bayer process) (Re‐draw from reference paper),^{[ 42 ]} d) fluorine‐free anodic etching in binary solution of NH₄Cl and tetramethylammonium hydroxide with applied potential of +5 V,) (Re‐draw from reference paper)^{[ 43 ]} e) fluorine‐free MXene etching using iodine in anhydrous acetonitrile solution followed by delamination in HCl solution (Re‐draw from reference paper),^{[ 45 ]} f) ion‐induced etching, e.g., HF etching of MXene followed by stirring in different metal ion solutions (e.g., Mn, Ni, Co) (Re‐draw from reference paper),^{[ 46 ]} and g) large‐scale MXene synthesis process, including several steps and an internal system connected with a cooling jacket and tank to allow uniform temperature controlled via a programmable computer. There is automatics attached to gas, drying process, and adjustable pressure, as a result, permit homogeneous feeding of MAX powder. Reproduced with permission.^{[ 47 ]} Copyright 2020, John Wiley and Sons. Bottom‐down approaches h) gas‐phase chemical vapor deposition (CVD) synthesis in which TiCl₃ powders were added to the reactor and then converted into a gaseous precursor, TiCl₃(g). Additionally, treatment in an argon (Ar) atmosphere, followed by a reaction with methane at 770 °C results in the formation of Ti₂CCl₂ powders (Re‐draw from reference paper).^{[ 48 ]}

Figure 3

In situ XRD analysis for MXene intercalation in the potential range of −1 to −0.2 V in 1 M KOH electrolyte, wherein a) vertical lines indicate the initial peak position (0002) of the MXene electrodes before cell assembly while inclined vertical arrows demonstrate the shift in (0002) peak position. Insets explain the expansion and shrinking of c lattice parameters during cycling. Reproduced with permission.^{[ 66 ]} Copyright 2013, The American Association for the Advancement of Science. Intercalation of electrolyte ion on exfoliated and multi‐layered nanosheet of MXenes presented in b) by an illustration of MXene multilayer covering shallow and deep adsorption sites, which is closer to gap opening and interior part. c) Capacitance of MXene/carbon measured at scan rates of 2 and 20 mV s⁻¹ in 1 M MgCl₂ electrolyte, corresponding to deep and shallow adsorption sites. Reproduced with permission.^{[ 68 ]} Copyright 2015, John Wiley and Sons. d) Electrochemical in situ X‐ray data of the Ti edge energy versus potential show that a potential sweep between 0.275 and −0.35 V shifts the Ti edge to lower energy, indicating a reduction in its average oxidation state. Reproduced with permission.^{[ 69 ]} Copyright 2015, John Wiley and Sons.

Figure 4

Different synthesis methods for MXene‐based nanocomposites: a) Schematic of Teflon‐lined stainless‐steel autoclave for hydrothermal method (Re‐draw from reference paper).^{[ 82 ]} b) Representative configuration of an electrodeposition method with Pt: counter; Ag/AgCl: reference and substrate: working electrode (Re‐draw from reference paper).^{[ 83} , ^{84 ]} c) Schematic of vacuum‐assisted filtration method for synthesis of solid material in the presence of an external vacuum pump.^{[ 87 ]} d) Schematic of brush painting method using conducting ink (Re‐draw from reference paper).^{[ 90 ]}

Figure 5

Synthesis of MXene and transition metal oxide composites‐based nanocomposite with an example preparation of MXene/Fe₂O₃ using vacuum filtration (Re‐draw from reference paper).^{[ 109 ]} in which a solution containing MXene and FeOOH suspension was vacuum‐filtered through cellulose paper.

Figure 6

Synthesis of MXene and transition metal dichalcogenide‐based nanocomposite using hydrothermal methods. a) Illustration of synthesis for MoS₂/MXene nanocomposite using magneto‐hydrothermal synthesis under an applied magnetic field of 9T, resulting in an MXene nanosheet covered by a MoS₂ nanosheet (Re‐draw from reference paper).^{[ 129 ]} b) Schematic of synthesis for NiS₂/MXene composite using hydrothermal method. After the hydrothermal process, randomly distributed nanocube‐like NiS₂ nanostructures assembled over the MXene surface (Re‐draw from reference paper).^{[ 136 ]}

Figure 7

Synthesis of MXene and layered double hydroxide‐based nanocomposite using solution reaction and etching methods. a) Schematic illustration of preparation of cobalt−nickel layered double hydroxides (CoNi‐LDH) on MXene‐carbon nanofibers (MX‐CNF). MXene and carbon nanofibers (MX‐CNF) obtained by electrospinning, followed by the formation Co‐MOF@MX‐CNF and CoNi‐LDH@MX‐CNF electrodes using solution and etching reaction methods (Re‐draw from reference paper).^{[ 159 ]} b) Schematic illustration of cobalt‐nickel double hydroxide@MXene (CoNi‐DH@MXene) electrode synthesis using room temperature solution and etching methods (Re‐draw from reference paper).^{[ 160 ]}