Supercapacitors with enhanced energy storage and hydrogen evolution reaction performance via sequential alkali-modified MXenes

Abstract

Ti₃C₂T_x MXene has emerged as a promising material among various 2D MXenes for energy storage and conversion applications due to its exceptional conductivity, large surface area, and tunable surface chemistry. However, challenges such as low specific capacitance due to layer stacking and limited active sites hinder their utilization in supercapacitors and hydrogen evolution reaction (HER) applications. Herein, we investigate the potential of hydrothermal-assisted sequential alkali modification of MXenes to address these challenges to enhance their performance. Hydrothermal sequential alkali treatment introduces –O and –OH functional groups on the MXene surface, improving electrochemical properties and stability. The specific surface area of KOH-treated MXene increases more than threefold to 19.3 m² g⁻¹ compared to 6.4 m² g⁻¹ in pristine MXene. KOH treatment reduces F-termination, which is advantageous for electrochemical performance enhancement. The KOH-treated MXene-based supercapacitors exhibited a gravimetric capacitance of 681 F g⁻¹ at a 10 mV s⁻¹ scan rate, significantly higher than the 392 F g⁻¹ of pristine MXene. These supercapacitors also demonstrated a cyclic stability of ∼90% after 5000 cycles. The overpotential of hydrothermally KOH-treated MXene is 214 mV compared to 238 mV for pristine MXene and a Tafel slope of 131 mV per decade compared to 175 mV per decade demonstrates the advantage of sequential KOH treatment to MXenes in HER applications.