Composite membranes with a highly selective polymer skin for hydrogen separation

•Asymmetric membranes were prepared by spin coating 6FDA-durene onto ZIF-8/6FDA-durene.•6FDA-durene layer on the membrane was cross-linked by reacting with EDA vapor.•Modified membranes showed improved H2 gas selectivity without loss in H2 permeability.•ZIF-8 loading in the substrate affected the permeability of the modified membranes.•H2/CO2, H2/N2, and H2/CH4 separation values surpassed the 2008 Robeson upper bound.

This study reports the fabrication of a highly hydrogen selective cross-linked polymer skin on a highly permeable mixed matrix membrane. Selective polymer skins were prepared by spin coating a thin layer of 6FDA-durene polymer onto ZIF-8/6FDA-durene mixed matrix membranes followed by subsequent cross-linking of the 6FDA-durene layer with ethylene diamine (EDA) vapor. Resultant membrane yielded significantly high gas pair selectivities for the separation of H2/CO2, H2/N2 and H2/CH4 of 29, 341, and 278, respectively, while also maintaining a high hydrogen permeability of 500 Barrers. The superior separation performances of this system surpass the current permeability–selectivity tradeoff limits (Robeson 2008 upper bound) for H2/CO2, H2/N2, and H2/CH4 separations. The present work elucidates the potential of fabricating a highly selective layer (thin skin) on a highly permeable membrane to obtain high permeability and high selectivity simultaneously.