Two-dimensional superconductors have garnered significant attention due to their exceptional quantum properties, particularly tunable superconductivity, which holds great potential for advanced quantum technologies. In this study, first-principles calculations reveal two stable transition metal mononitride monolayers—1T- and $1H\text{−}{\mathrm{Mo}}_2{\mathrm{N}}_2$—featuring chemically distinct Mo- and N-terminated surfaces. Electron-phonon coupling calculations predict the superconducting transition temperatures $\left(T_{\mathrm{c}}\right)$ of $\sim 13.6$ K for the 1T phase and $\sim 13.5$ K for the 1H phase. The coupling between Mo $d_{z^2}$ orbital electrons at the Fermi level and out-of-plane acoustic phonon modes associated with Mo atoms is identified as a key contributor to superconductivity. Hydrogenation on the Mo-terminated surface boosts $T_{\mathrm{c}}$ to 25.4 K in 1T phase, driven by the increase of Mo $d_{z^2}$ electronic states at the Fermi level and the softening of the out-of-plane acoustic mode induced by the activation of Mo-H bond stretching vibrations. In contrast, hydrogenation on the N-terminated surface suppresses superconductivity due to the inhibition of out-of-plane Mo vibrations. Furthermore, double-sided hydrogenation on both surfaces reduces $T_{\mathrm{c}}$ to 16.9 K in the 1T phase and 8.2 K in the 1H phase. These findings provide valuable insights into tunable superconductivity in two-dimensional materials through targeted site-dependent hydrogenation.

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• Superconductivity
• 2-dimensional systems
• First-principles calculations