Effect of pinholes in Nb4C3 MXene sheets on its electrochemical behavior in aqueous electrolytes

Two-dimensional (2D) niobium carbide, Nb 4 C 3 T x (T x : O, OH, and F), a representative member of the 43 MXene structural motif, has shown promising electrochemical performance in acidic electrolytes.The capacitive performance of Nb 4 C 3 T x in neutral aqueous electrolytes has been reported as moderate, but little effort has been made to improve it.In this paper, we report a method to introduce nanopores (pinholes) in Nb 4 C 3 T x MXene flakes by adjusting the etching time.The pinholes generated during the etching process improve ion diffusion pathways, which are otherwise hindered by the restacking of the 2D flakes.The "holey Nb 4 C 3 T x " shows a 50 % improved rate capability at charge/discharge time scales of 1-2 s in 1 M Li 2 SO 4 , Na 2 SO 4 , and (NH 4 ) 2 SO 4 electrolytes.Our strategy of controlling the permeability of Nb 4 C 3 T x sheets can potentially be applied to other MXenes, providing guidance for improving the capacitance and rate capability of 2D materials.