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

Two-dimensional (2D) niobium carbide, Nb₄C₃T_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 Nb₄C₃T_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 Nb₄C₃T_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 Nb₄C₃T_x” shows a 50 % improved rate capability at charge/discharge time scales of 1–2 s in 1 M Li₂SO₄, Na₂SO₄, and (NH₄)₂SO₄ electrolytes. Our strategy of controlling the permeability of Nb₄C₃T_x sheets can potentially be applied to other MXenes, providing guidance for improving the capacitance and rate capability of 2D materials.