Two‐Dimensional Quaternary Alloys of (RuMoVNb)Se ₂ for Superior Hydrogen Evolution Reaction Catalysis

ABSTRACT Alloying 2D transition metal dichalcogenides offers a promising strategy to broaden their applications. Herein, (RuMoVNb)Se 2 quaternary alloy nanosheets ( x Ru = 0–1) were synthesized via colloidal reactions. Incorporation of Ru into the (MoVNb)Se 2 maintained exclusively 2D layered structure over wide composition range, accompanied by a phase evolution from the hexagonal 2H to 1T. The quaternary alloying results in more metallic electronic structures than the ternary alloying. First‐principles calculations supported the homogenous atomic mixing of quaternary alloys and the favored 2H → 1T phase transition at higher x Ru . Compared to (MoVNb)Se 2 , the quaternary alloys exhibited significantly enhanced electrocatalytic activity toward the hydrogen evolution reaction (HER) across alkaline, acidic, and neutral electrolytes. Gibbs free energy calculations show that Ru atoms optimize hydrogen adsorption, directly correlating with the improved HER performance. In situ X‐ray absorption fine structure data (in 1 M KOH) reveal electrolyte adsorption on Ru as key to superior HER catalysis.