Plasma-driven synthesis of nitrogen-doped graphene: unveiling the reaction mechanism and kinetic insights

Abstract

Context

The rotating arc plasma technique for the synthesis of nitrogen-doped graphene capitalizes on the distinctive attributes of plasma, presenting a straightforward, efficient, and catalyst-free strategy for the production of nitrogen-doped graphene. However, experimental outcomes generally fail to elucidate the atomic-level mechanism behind this process. Our research utilizes molecular dynamics simulations to explore theoretically the formation of radicals during the plasma-driven reaction between methane (CH₄) and nitrogen (N₂). The simulations present a complex reaction system comprising nine principal species: CH₄, CH₃, CN, CH₂, HCN, CH, N₂, H₂ and H. Notably, HCN and CN emerge as pivotal precursors for nitrogen doping. Optimal nitrogen concentrations enhance the synthesis of these precursors, whereas excessive nitrogen suppresses the formation of C₂ species, impacting the yield of nitrogen-doped graphene. Conversely, higher methane concentrations stimulate the generation of carbon radicals, augmenting the production of HCN and CN and thus, influencing the properties of the synthesized material. This work is expected to lay a theoretical foundation for the refinement of nitrogen-doped graphene synthesis processes.

Methods

In this investigation, we employed the LAMMPS software package to explore the formation of free radicals during the methane–nitrogen reaction via molecular dynamics (MD) simulations. These simulations were conducted under an NVT ensemble, maintaining a constant temperature of 3500 K with a time step of 0.1 fs over a duration of 1000 ps. To reduce the variability and enhance the reliability of the simulation outcomes, each simulation was meticulously conducted three times under identical parameters for subsequent statistical analysis.