Objective: Here we report on an innovative synthesis of polymer/palladium asymmetric membrane that allows a control of the membrane morphology, the specific location of in situ grown Pd nanoparticles within the membrane and significant enhancement of H-2 permeance values with respect to the reference polymer membrane. Materials and method: Nanocomposite asymmetric films have been prepared from polyetherimide and palladium acetate for Pd amount ranging from 0 to 15 wt%. In this work, we have at first demonstrated that polyetherimide/palladium acetate membranes of different porous microstructures could be successfully prepared from a cononsolvent process. The influence of the composition of the PEI solution and of the cononsolvent immersion bath on the precursor membrane morphology was studied. Pd nanoparticles were then in situ grown within the membranes by two different post-treatments, an annealing treatment with a final step at 220 degrees C or a chemical treatment consisting in immersing the precursor membranes in a methanol/sodium borohydride solution. Results: In this work, we have at first demonstrated that polyetherimide/palladium acetate membranes of different porous microstructures could be successfully prepared from a cononsolvent process. The structure and the repartition of the nanoparticles, determined from XRD and TEM characterizations, were discussed as a function of the in situ generation routes. The gas permeance was determined for H-2 and CO2 and the ideal H-2/CO2 selectivity factor was analysed for the two nanocomposite series. The nanocomposite membrane series prepared from the annealing post-treatment exhibited particularly interesting properties towards H-2 separation applications. (C) 2014 Elsevier B.V. All rights reserved.