M5X4 - A Family of MXenes

MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes are the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X, Tx) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4. Only one M5X4Tx MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two new phase-pure M5AX4 mixed transition metal MAX-phases, (TiTa)5AlC4 and (TiNb)5AlC4, and their successful topochemical transformation into (TiTa)5C4Tx and (TiNb)5C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M5AX4 MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, opening the door to exciting new applications for MXenes.