Dissociative mechanism from NH3 and CH4 on Ni-doped graphene: Tuning electronic and optical properties

Abstract

In this study, we employ a multi-scale computational modeling approach, combining density functional theory (DFT) and self-consistent charge density functional tight binding (SCC-DFTB), to investigate hydrogen (H${}_2$) production and dissociation mechanisms from ammonia (NH${}_3$) and methane (CH${}_4$) on pristine and nickel-doped graphene. These two-dimensional materials hold significant potential for applications in advanced gas sensing and catalysis. Our analysis reveals that Ni-doped graphene, validated through work function calculations, is a promising material for gas separation and hydrogen production. The samples with adsorbed molecules are characterized by calculating chemical potential, chemical hardness, electronegativity, electrophilicity, vibrational frequencies, adsorption and Gibbs energies by DFT calculations. Methane molecules preferentially adsorb at the hexagonal ring centers of graphene, while ammonia interacts more strongly with carbon atoms, highlighting distinct molecular doping mechanisms for CH${}_4$ and NH${}_3$. Dynamic simulations show that CH${}_4$ splits into CH${}_3$+H, with Ni-doped graphene facilitating enhanced hydrogen transmission, while NH${}_3$ dissociates into NH${}_2$+H, which may lead to N${}_2$H${}_4$ formation. Our non-equilibrium Green’s function (NEGF) simulations demonstrate increased H-atom transmission on Ni-doped graphene during gas interactions. These findings suggest that Ni-doped graphene is superior to pristine graphene for applications in gas separation, hydrogen production, and high-sensitivity sensors.