Rational Selection of Transition Metals in M₄C₃ MXenes to Control the Electrocatalytic Hydrogen Evolution Reaction

2D MXenes have shown great promise as active materials in electrocatalytic hydrogen evolution reaction (HER). In this work, we present the selection of transition metal elements (V, Nb, Ta) in three M₄C₃T<i>_x</i> MXenes (V₄C₃T<i>_x</i>, Nb₄C₃T<i>_x</i>, Ta₄C₃T<i>_x</i>) to control their electrocatalytic performance for HER using an experimental approach. We synthesized V₄C₃T<i>_x</i>, Nb₄C₃T<i>_x</i>, Ta₄C₃T<i>_x</i> MXenes from their parent MAX phases via a selective etching route using hydrofluoric acid, followed by an organic intercalant (tetramethylammonium hydroxide)-assisted delamination. Further, we used an ion exchange process to modify the MXenes’ surface chemistry and interlayer spacing by replacing (TMA⁺) with Li⁺ cations. By comparing the electrocatalytic HER performance of the resulting V₄C₃T<i>_x</i>, Nb₄C₃T<i>_x</i>, Ta₄C₃T<i>_x</i> MXenes, we demonstrate the role of exposed transition metals (V, Nb, Ta) on the basal plane. Notably, V₄C₃T<i>_x</i> MXenes exhibit the lowest HER overpotential of ~ 248 mV at 10 mA/cm² under acidic conditions (0.5 M H₂SO₄), surpassing Nb₄C₃T<i>_x</i> (~ 317 mV at 10 mA/cm²) and Ta₄C₃T<i>_x</i> MXenes (~ 426 mV at 10 mA/cm²). This improved performance can be attributed to the catalytically active vanadium basal planes in V₄C₃T<i>_x</i>. Our findings provide insight into the design of efficient and cost-effective catalysts through the rational selection of transition metals in MXenes for application as HER catalysts and tailoring electrocatalytic properties of 2D materials for sustainable energy applications.