Halogenated Ti3C2 MXenes with Electrochemically Active Terminals for High-Performance Zinc Ion Batteries

The class of two-dimensional metal carbides and nitrides known as MXenes offer a distinct manner of property tailoring for a wide range of applications. The ability to tune the surface chemistry for expanding the property space of MXenes is thus an important topic, although experimental exploration of surface terminals remains a challenge. Here, we synthesized Ti 3 C 2 MXene with unitary, binary, and ternary halogen terminals, e . g ., −Cl, −Br, −I, −BrI, and −ClBrI, to investigate the effect of surface chemistry on the properties of MXenes. The electrochemical activity of Br and I elements results in the extraordinary electrochemical performance of the MXenes as cathodes for aqueous zinc ion batteries. The −Br- and −I-containing MXenes, e.g ., Ti 3 C 2 Br 2 and Ti 3 C 2 I 2, exhibit distinct discharge platforms with considerable capacities of 97.6 and 135 mAh·g –1 . Ti 3 C 2 (BrI) and Ti 3 C 2 (ClBrI) exhibit dual discharge platforms with capacities of 117.2 and 106.7 mAh·g –1 . In contrast, the previously discovered MXenes Ti 3 C 2 Cl 2 and Ti 3 C 2 (OF) exhibit no discharge platforms and only ∼50% of capacities and energy densities of Ti 3 C 2 Br 2 . These results emphasize the effectiveness of the Lewis-acidic-melt etching route for tuning the surface chemistry of MXenes and also show promise for expanding the MXene family toward various applications.