关键词: clathrate hydrate, hydrogen storage, diffusion, molecular dynamics

Abstract: Recently, a new phase C$_{1}'$ H$_{2}$ hydrate was experimentally identified. In this work, the diffusive behaviors of H$_{2}$ in C$_{1}'$ phase clathrate hydrate are explored using classic molecular dynamics (MD) simulations. It reveals that the cage occupancy by H$_{2}$ molecule negligibly influences the C$_{1}'$ phase clathrate structure but greatly dictates the diffusion coefficient of H$_{2}$ molecule. Due to the small cage size and small windows connecting the neighboring cages in C$_{1}'$ phase clathrate, non-occupancy of the neighboring cages is demanded to enable the diffusion of H$_{2}$ molecule that is primarily dominated by hopping mechanism. Moreover, the analysis of diffusive free energy landscape reveals lower energy barrier of H$_{2}$ molecule in C$_{1}'$ phase clathrate hydrate than that of other gases in conventional clathrate hydrates, and that H$_{2}$ molecule travels through the windows between neighboring cages with preferential molecular orientation. This study provides critical physical insights into the diffusion behaviors of H$_{2}$ in the C$_{1}'$ phase clathrate hydrate, and implies that the C$_{1}'$ clathrate hydrate is a promising solid structure for the next-generation H$_{2}$ storage.

Key words: clathrate hydrate, hydrogen storage, diffusion, molecular dynamics