Utilizing existing natural gas pipelines for hydrogen-blended natural gas (HBNG) transportation is an efficient and economical method for hydrogen energy delivery. To enhance the economic viability of hydrogen and meet diverse end-user requirements, research on hydrogen separation from HBNG is of significant importance. However, given the relatively low hydrogen concentration in HBNG (volume fraction ≤20%), palladium(Pd)-based membrane technology emerges as an ideal solution for this application scenario due to its unique hydrogen dissolution/diffusion mechanism that maintains exceptionally high hydrogen permeation selectivity even under low-concentration conditions. Silver (Ag) incorporation into Pd is a common strategy to enhance overall performance (improving hydrogen embrittlement and increasing permeability), while the specific mechanisms governing its impact on H₂/CH₄ separation require further investigation. This study employs molecular dynamics  and first-principles calculations to predict performances of pure Pd and Pd-silver (PdAg) alloy membranes for separation of H₂/CH₄. Calculations of adsorption properties, diffusion energy barriers, selectivity, and permeability indicate that PdAg alloy membranes exhibit superior hydrogen permeation performance compared to pure Pd membranes. Analysis reveals that Ag incorporation slightly reduces the hydrogen solubility coefficient, while the resultant lattice expansion effect significantly enhances the diffusion coefficient of hydrogen atoms. Both membranes maintain high H₂/CH₄ selectivity due to negligible methane solubility and permeability. These atomic-level insights elucidate fundamental separation mechanisms, providing critical theoretical guidance for designing high-performance membrane for low-concentration hydrogen separation.

Hydrogen separation, Hydrogen-blended natural gas, Molecular dynamics, Palladium membrane, PdAg alloy membrane, Permeability, Selectivity