Gallenene as a Dual‐Functional Material for Sodium‐Ion Batteries and Hydrogen Evolution: A First‐Principles Study

Alkali metal Na‐ion batteries (NIBs) present an eco‐friendly and cost‐effective alternative to lithium‐ion batteries. However, the limited availability of high‐performance anode materials continues to hinder their widespread adoption. In this study, we theoretically investigate the potential of a two‐dimensional elemental monolayer of gallium, known as gallenene (Ga 100 ‐ML), as a promising anode material for NIBs and as an electrocatalyst for the hydrogen evolution reaction (HER). The structural, dynamical, and thermal stability of Ga 100 ‐ML is confirmed through formation and cohesive energy calculations, phonon dispersion analysis, in‐plane stiffness evaluation, and ab initio molecular dynamics simulations. Electronic structure analysis reveals its metallic nature, and adsorption studies show that up to 45 Na atoms can be stably accommodated, corresponding to a high theoretical storage capacity of 961.30 mAh/g and a low diffusion barrier of 0.36 eV. Furthermore, HER activity is significantly enhanced upon Pt decoration, achieving a minimum Gibbs free energy of hydrogen adsorption of −0.12 eV. These results highlight Ga 100 ‐ML as a promising candidate for dual applications in NIBs and catalyst for HER.