Targeting at hydrogen purification, cross-linked organic-inorganic reverse-selective membranes containing poly(ethylene oxide) (PEO) are fabricated in situ by using functional oligomers (O,O'-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol: Jeffamine (R) ED-2003) with a high content of PEO and epoxy-functional silanes (3-glycidyloxypropyltrimethoxysilane: GOTMS). Changes in physicochemical properties due to varying silica content have been characterized; including a great decline in melting temperature; an improvement in glassy and degradation temperature, and the suppression of PEO crystallinity. The strong affinity between quadrupolar CO(2) and polar ethylene oxide (EO) groups enhances the CO(2)/H(2) separation performance of hybrid membranes, which can be further tuned by controlling the organic/inorganic ratio. The organic-inorganic hybrid membrane with 90 wt% of ED-2003 demonstrates an appealing CO(2) permeability of 367 Barrer with an attractive CO(2)/H(2) selectivity of 8.95 at 3.5 atm and 35 degrees C. The transport performance trend with composition variations is explained by analyzing the calculated solubility and diffusivity based on the solution-diffusion mechanism. Moreover, CO(2) permeability increases with applied pressure in pure gas tests because Of CO(2) plasticization phenomena, which is beneficial for CO(2)/H(2) separation. Attributing to CO(2) plasticization and CO(2) dominant sorption, the mixed gas test results of the membrane containing only 25 wt% ED-2003 show greatly improved CO(2)/H(2) selectivity of 13.2 with CO(2) permeability of 148 Barrer at 35 degrees C compared to pure gas results. Interestingly, at a stipulated CO(2) pressure, the inherent tension in cross-linked networks maintains the CO(2) permeability stable with the time. The cross-linked organic-inorganic membranes with enhancements in mechanical and thermal proper-ties are promising for industrial-scale hydrogen purification. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.