Cation Exchange and Systematic Evaluation of M₄C₃T_<i>x</i> 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 M₄C₃T_<i>x</i> MXenes for HER activity. We use M₄C₃T_<i>x</i> MXenes of group five transition metals, namely, V₄C₃T_<i>x</i>, Nb₄C₃T_<i>x</i>, and Ta₄C₃T_<i>x</i>, 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 H₂SO₄ acidic conditions. Our study provides a systematic basis for understanding the preparation–composition–performance relationships in M₄C₃T_<i>x</i> MXenes and conducting a comprehensive analysis of their HER performance, essential for MXene applications in energy conversion.