Achieving High Pseudocapacitance of 2D Titanium Carbide (MXene) by Cation Intercalation and Surface Modification

Abstract

Supercapacitors attract great interest because of the increasing and urgent demand for environment‐friendly high‐power energy sources. Ti3C2, a member of MXene family, is a promising electrode material for supercapacitors owing to its excellent chemical and physical properties. However, the highest gravimetric capacitance of the MXene‐based electrodes is still relatively low (245 F g−1) and the key challenge to improve this is to exploit more pseudocapacitance by increasing the active site concentration. Here, a method to significantly improve the gravimetric capacitance of Ti3C2Tx MXenes by cation intercalation and surface modification is reported. After K+ intercalation and terminal groups (OH−/F−) removing , the intercalation pseudocapacitance is three times higher than the pristine MXene, and MXene sheets exhibit a significant enhancement (about 211% of the origin) in the gravimetric capacitance (517 F g−1 at a discharge rate of 1 A g−1). Moreover, the as‐prepared electrodes show above 99% retention over 10 000 cycles. This improved electrochemical performance is attributed to the large interlayer voids of Ti3C2 and lowest terminated surface group concentration. This study demonstrates a new strategy applicable to other MXenes (Ti2CTx, Nb2CTx, etc.) in maximizing their potential applications in energy storage.

MXene‐Based Composites: Synthesis and Applications in Rechargeable Batteries and Supercapacitors

“…Moreover, the method can also increase the layer spacing of MXenes. [83] Figure 11e shows that the capacitance of 400-KOH-Ti 3 C 2 is significantly increased, especially when expressed as the ratio of inserted capacitance, due to the increase of the interlayer spacing.…”

“…[225] As for MXenes materials, the major 2D M n+1 X n candidates show high metallic conductivity, and the 2D M n+1 X n T x varieties display semimetallic conductivity from the presence of the T groups. [83] It is well known that the structure of the ultrathin layers benefits performance for transferring and storing Li + ions. However the electron delocalization is affected by the functionalized groups.…”

“…[276,277] One type is biased toward physical effects, and the capacitors store charges via a static electric field. [83,278] In an aqueous electrolyte, on the one hand, metal ions can combine with water molecules to form an electric double layer structure on the surface of MXenes. This type of SCs is called an electrical double layer capacitor (EDLC).…”

“…In addition to forming MXene-based composites to increase capacitance, optimization can also be achieved by doping [245,287,288] or surface modification, [83,108,289] whereby the conductivity of the doped MXene typically increases. [122,123] Furthermore, the introduction of doped precursors can increase the interlayer spacing of an MXene.…”

“…Figure 12k shows a thin layer of Ti 3 C 2 T x distributed on the carbon fiber. [83] Copyright 2017, John Wiley and Sons. Mater.…”