1：Experimental Design and Method Selection

Density functional theory (DFT) calculations were carried out using the plane-wave-based Vienna Ab initio Simulation Package (VASP), with a fixed 500 eV plane-wave kinetic energy cutoff. Generalized gradient approximation (GGA) was used for the exchange-correlation (XC) energy, within the Perdew–Burke–Ernzerhof (PBE) functional form. The screened HSE06 hybrid functional has been used to calculate more accurate electronic band structures.

2：Sample Selection and Data Sources

The electrons considered as in the valence are: 3d and 4s for Ni; 4d and 5s for Pd; 5d and 6s for Pt; 2s and 2p for N. Core electrons were approximated by projector augmented-wave pseudopotentials.

3：List of Experimental Equipment and Materials

Vienna Ab initio Simulation Package (VASP), PHONOPY code for phonon dispersion calculations.

4：Experimental Procedures and Operational Workflow

Structural optimization was obtained until the Hellmann-Feynman force acting on each atom was less than 0.01 eV/? in each direction. A 10 × 10 × 1 Monkhorst-Pack k-grid for Brillouin zone sampling was used for geometry optimization, which was enlarged to 16 × 16 × 1 for static total energy calculations. A vacuum slab of 20 ? along the z-axis was introduced for the 2D monolayers.

5：Data Analysis Methods

The phonon dispersion was calculated with the density functional perturbation theory (DFPT), using the PHONOPY code. AIMD simulations were performed to evaluate the thermal stabilities, where the PBE functional and the NVT canonical ensemble were used.