Fluorine-Free Fabrication of MXene via Photo-Fenton Approach for Advanced Lithium–Sulfur Batteries

The mainstream synthesis method for MXene is using aqueous fluorine-containing acidic solutions to eliminate the A-element layers from their MAX phases. However, this strategy is environmentally hazardous and impairs the material performance (e.g., supercapacitor and Li-S batteries) owing to the presence of -F terminations. Herein, we exploit a low-temperature "soft chemistry" approach based on photo-Fenton (P.F.) reaction for the fabrication of F-free Ti3C2 (Ff-Ti3C2) with high purity of 95%. It is confirmed that the continuous generation of highly reactive oxygen species (HO• and O2•- radicals) during the P.F. reaction weakens the metallic Ti-Al bonds in the MAX phase and promotes the formation of high concentration OH- anions, which are conducive to the sequential topochemical deintercalation of Al layers. Moreover, the strengthened charge accumulation on the Ff-Ti3C2 surface creates rich electron "reservoirs" for actuating the Li-S chemistry, which not only strengthens the host-guest interactions but also propels the kinetics of the polysulfide conversion. Taking advantage of the superior mechanical robustness, better electrolyte wettability, and improved electrocatalytic activity, the resultant Ff-Ti3C2 can be used as an ideal sulfur host and Li-S chemistry mediator for advanced flexible Li-S batteries.