Synthesis, Characterization, and Electrochemical Behavior of Layered Vanadium Nitride MXene.

Abstract

MXenes have been extensively studied for over a decade, with numerous compositions successfully synthesized. However, the top-down synthesis of vanadium nitride (V₂NT_x) has remained elusive despite its predicted superior electrochemical performance and stability in aqueous environments. In this work, we demonstrate the synthesis of V₂NT_x MNene by utilizing our oxygen-assisted molten salt etching (O₂-MSE) method. We additionally demonstrate the versatility of our synthesis approach on the corresponding carbide phase (V₂CT_x), confirming its applicability across MAX phases regardless of the X element. Comprehensive structural, physical, chemical, and electrochemical characterizations confirm the MNene's crystallinity, high surface area, tunable surface chemistry, layered morphology, and superior electrochemical performance compared to its carbide counterpart. As a proof of concept, synthesized V₂NT_x MNene and V₂CT_x MXene were tested as electrodes in an electrochemical device using aqueous electrolytes. The results reveal that the MNene outperforms the carbide in terms of higher capacity, enhanced cycling stability, and better overall performance compared to the carbide phase. For example, in an acidic electrolyte (1 M H₂SO₄), V₂NT_x achieved a specific capacity of 123 mAh g^-1, surpassing the 93 mAh g^-1 of V₂CT_x. Further analysis reveals the enhanced electrochemical performance of V₂NT_x MNene is attributed to the -O and/or -OH surface groups, which undergo more reversible redox reactions in acidic environments compared to alkaline media, which is in contrast to conventional bulk VN (nonlayered) material. In summary, we report the synthesis of layered vanadium MNene via the O₂-MSE method, demonstrating its stability, electrochemical activity, and surface chemistry that enhances energy storage and conversion.