Cation Exchange and Systematic Evaluation of M ₄ C ₃ T _x MXenes for Hydrogen Evolution Reaction Electrocatalysis

Two-dimensional (2D) MXenes have recently attracted substantial attention as promising materials for hydrogen evolution reactions (HER) due to their electrocatalytically active basal plane and tunable electronic properties. In this study, we present a detailed synthesis protocol, preparation, and systematic evaluation of M 4 C 3 T x MXenes for HER activity. We use M 4 C 3 T x MXenes of group five transition metals, namely, V 4 C 3 T x, Nb 4 C 3 T x, and Ta 4 C 3 T x, as our model material system. We provide a detailed description of the synthesis of the MXenes’ precursor phases and their selective etching with hydrofluoric acid, followed by tetramethylammonium hydroxide (TMAOH)-assisted delamination to obtain single- to few-layered nanosheets. To prepare MXenes for HER testing, we present a universal ion-exchange process to replace the organic cations (tetramethylammonium) with lithium (Li + ) ions, effectively modifying the surface chemistry and interlayer spacing. Finally, we present details of the electrocatalytic HER evaluation study of the Li + -intercalated MXenes in 0.5 M H 2 SO 4 acidic conditions. Our study provides a systematic basis for understanding the preparation–composition–performance relationships in M 4 C 3 T x MXenes and conducting a comprehensive analysis of their HER performance, essential for MXene applications in energy conversion.