Scaling the thickness of a material to an atomically thin limit leads to the emergence of distinct physical properties that are unachievable in its bulk counterpart. Here, we predict the existence of superconducting state with a critical temperature $\left(T_{\mathrm{c}}\right)$ of 1.50 K in a stable atomically thin two-dimensional (2D) crystal of scandium (Sc), referred to as “scandiene.” Unlike its metallic bulk counterpart, the emergence of superconductivity in scandiene is driven by an overall softening of phonons and an increased electronic density of states at the Fermi level. Hydrogenation of scandiene can give rise to the formation of two phases, i.e., electride and nonelectride ${\mathrm{Sc}}_2\mathrm{H}$. The $T_{\mathrm{c}}$ of both electride and nonelectride ${\mathrm{Sc}}_2\mathrm{H}$ remains measurable, with approximate values of 1.76 and 1.54 K, respectively. Notably, in the ${\mathrm{Sc}}_2\mathrm{H}$ electride, strong electron-phonon coupling between interstitial anionic electrons and low-frequency acoustic modes dominated by Sc atoms significantly enhances the $T_{\mathrm{c}}$ up to 15.0 K under 8% biaxial tensile strain. These findings not only expand the family of 2D monoelemental materials but also establish avenues for exploring superconductivity in the 2D limit.

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• Chemical bonding
• Electronic structure
• First-principles calculations
• Superconductivity
• BCS theory