Halogenated TiC 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 TiC MXene with unitary, binary, and ternary halogen terminals, .., -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, ., TiCBr and TiCI, exhibit distinct discharge platforms with considerable capacities of 97.6 and 135 mAh·g. TiC(BrI) and TiC(ClBrI) exhibit dual discharge platforms with capacities of 117.2 and 106.7 mAh·g. In contrast, the previously discovered MXenes TiCCl and TiC(OF) exhibit no discharge platforms and only ∼50% of capacities and energy densities of TiCBr. 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.