Defect size engineering in pyridinic-N-doped graphene surfaces for hydrogen sulfide adsorption and dissociation: A first-principles study

To guide the metal-free design of H2S capture and conversion materials, we elucidate how defect-size engineering at pyridinic-N sites in graphene controls H2S adsorption and dissociation. Using dispersion-corrected DFT (PBE-D3), CI-NEB, machine learning force field accelerated ab initio molecular dynamics (MLFF-AIMD) at 500 K, we compare six vacancy models (nC6, n = 1, 2, 3, 6, 7, ∞). The initial adsorption is a dispersion-dominated physisorption, with Ead narrowly distributed around −0.4 to −0.3 eV and only a weak dependence on defect size. Energy decomposition reveals component compensation: as the defect enlarges, the non-dispersion contribution stabilizes systematically whereas the dispersion term weakens, keeping Ead nearly constant. Geometrically and electronically, larger defects induce pre-activation—pre-elongation of the S–H bond, shortening of the N···H distance, and enhanced H-1s/N-2p overlap—which stabilizes the transition state and lowers the barrier: 0.87 ± 0.05 eV for 1C6–6C6, dropping to ≈0.79 eV (7C6) and 0.61 eV (∞C6). MLFF-AIMD (500 K, 10 ps) further confirms that H2S remains adsorbed on 1C6 without desorption, evidencing finite-temperature stability despite the physisorptive nature. These results establish a clear guideline: enlarging the vacancy around pyridinic-N preserves weak initial binding while systematically reducing the dissociation barrier, offering a practical route to high-performance, metal-free desulfurization and catalysis.