Synergistic etching and intercalation enables ultrathin Ti 3 C 2 T x and Nb 2 CT x MXene nanosheets

Abstract Transition metal‐containing MXene has shown great potential in the promising research fields, and its performance strongly depends on the composition, structure, dimension, and surface chemistry. Thus, rational design and controllable synthesis of ultrathin two‐dimensional (2D) MXene nanosheets with uniform surface terminations are of great importance. However, the use of 2D MXene, particularly in solar‐powered photocatalysis and electrocatalysis, is restricted by the formation of thick, multi‐layered MXene flakes with a small interlayer spacing produced from the conventional hydrofluoric acid (HF) etching method. In this work, we report a few‐layer MXene nanosheets by solely employing a mixture of lithium fluoride and hydrochloric acid as the etching reagent. Synergic etching and intercalation technique endows MXene with ultrathin 2D nanostructures; moreover, the use of fluoride salt, rather than harmful HF, offers a safer and environmentally‐friendly synthetic route for scalable green production of 2D MXene. Both the obtained Ti 3 C 2 T x and Nb 2 CT x nanosheets show a highly efficient photoelectrochemical performance superior to highly stacked MXene flakes. This work highlights a mild, simultaneous etching and delamination strategy for the development of high quality of 2D MXene nanosheets.