Two‐Dimensional Nb‐Based M ₄ C ₃ Solid Solutions (MXenes)

Herein, two new two‐dimensional Nb 4 C 3 ‐based solid solutions (MXenes), (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x and (Nb 0.8 ,Zr 0.2 ) 4 C 3 T x (where T is a surface termination) were synthesized—as confirmed by X‐ray diffraction—from their corresponding MAX phase precursors (Nb 0.8 ,Ti 0.2 ) 4 AlC 3 and (Nb 0.8 ,Zr 0.2 ) 4 AlC 3 . This is the first report on a Zr‐containing MXene. Intercalation of Li ions into these two compositions, and Nb 4 C 3 T x was studied to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb 4 C 3 T x , but were not present in Nb 2 CT x . After 20 cycles at a rate of C/4, the specific capacities of (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x and (Nb 0.8 ,Zr 0.2 ) 4 C 3 T x were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb 4 C 3 T x .