Seed assisted synthesis of an anionic metal–organic framework membrane for selective and permeable hydrogen separation

Abstract

Hydrogen selective metal–organic framework (MOF) membranes with excellent performance are still in high demand. Here, we are developing an anionic MOF material of CPM-5 into a membrane for H₂ separation. A well inter-grown CPM-5 membrane is successfully synthesized on a macroporous glass-frit disk by secondary growth assisted with a pre-deposited seed layer. The anionic framework of CPM-5 can interact strongly with CO₂, N₂ and CH₄ rather than H₂, shown by the isosteric heats of adsorption in a sequence of CO₂ (39.4 kJ mol⁻¹) > N₂ (28.4 kJ mol⁻¹) > CH₄ (25.1 kJ mol⁻¹) > H₂ (6.1 kJ mol⁻¹). The synthesized CPM-5 membrane is investigated for gas separation of H₂/CO₂, H₂/N₂ and H₂/CH₄. The results from binary gas permeation show separation factors of 39.4, 27.3 and 16.7 for H₂/CO₂, H₂/N₂ and H₂/CH₄, respectively; and a H₂ permeance of 11.2–12.0 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹. The selective separation of H₂ from CO₂, N₂ and CH₄ is governed by charge-induced adsorption, and verified by the gas adsorption results. The product of separation factor and H₂ permeance exceeds the latest upper bound of polymer membranes and surpasses that of most MOF membranes. In addition, the CPM-5 membrane is thermally stable, durable and reproducible, exhibiting great potential for industrial hydrogen recycling.