1：Experimental Design and Method Selection:

First principles calculations using density functional theory (DFT) with the Vienna Ab Initio Simulation Package (VASP), employing the Perdew-Burke-Ernzerhof (PBE) functional for structural optimization and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for electronic structure and optical property calculations. Quantum-mechanical molecular dynamics (MD) simulations were used for stability testing.

2：Sample Selection and Data Sources:

Models of pristine h-BN and porous h-BN (p-BN) with carbon doping at concentrations of 16.67%, 33.3%, and 50.0 at%, created by replacing B and N atoms with C atoms in supercells.

3：67%, 3%, and 0 at%, created by replacing B and N atoms with C atoms in supercells. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Computational software (VASP) for simulations; no physical equipment or materials used as it is a theoretical study.

4：Experimental Procedures and Operational Workflow:

Structural optimization of h-BN and p-BN; introduction of carbon doping with various configurations; calculation of band structures, density of states, optical absorption coefficients, phonon spectra, and thermal stability via Born-Oppenheimer MD simulations; evaluation of band alignments for water splitting potentials.

5：Data Analysis Methods:

Analysis of band gaps, valence band maximum (VBM), conduction band minimum (CBM), optical absorption spectra, dynamic stability from phonon dispersions, and thermal stability from MD simulations.