Enhanced Selective Hydrogen Permeation through Graphdiyne Membrane: A Theoretical Study

Graphdiyne (GDY), with uniform pores and atomic thickness, is attracting widespread attention for application in H₂ separation in recent years. However, the challenge lies in the rational design of GDYs for fast and selective H₂ permeation. By MD and DFT calculations, several flexible GDYs were constructed to investigate the permeation properties of four pure gas (H₂, N₂, CO₂, and CH₄) and three equimolar binary mixtures (H₂/N₂, H₂/CO₂, and H₂/CH₄) in this study. When the pore size is smaller than 2.1 Å, the GDYs acted as an exceptional filter for H₂ with an approximately infinite H₂ selectivity. Beyond the size-sieving effect, in the separation process of binary mixtures, the blocking effect arising from the strong gas-membrane interaction was proven to greatly impede H₂ permeation. After understanding the mechanism, the H₂ permeance of the mixtures of H₂/CO₂ was further increased to 2.84 × 10⁵ GPU by reducing the blocking effect with the addition of a tiny amount of surface charges, without sacrificing the selectivity. This theoretical study provides an additional atomic understanding of H₂ permeation crossing GDYs, indicating that the GDY membrane could be a potential candidate for H₂ purification.