A high-performance, H-2-permselective silica membrane derived from hexyltrimethoxysilane (HTMOS) was developed for application in the thermochemical water-splitting iodine-sulfur process. Silica membranes, referred to here as HTMOS membranes, were prepared via counter-diffusion chemical vapor deposition on gamma-alumina-coated alpha-alumina support tubes with outer diameters of 10 mm. Special attention was devoted to obtain high H-2/HI selectivity, high H-2 permeance, and good stability in the presence of corrosive HI gas. The effects of the deposition conditions, temperature, and period were investigated. The HTMOS membrane prepared at 450 degrees C for 5 min exhibited high H-2/HI selectivity (> 175) with H-2 permeance on the order of 10(-7) mol Pa-1 m(-2) s(-1). On the basis of stability experiments, it was found that the HTMOS membrane was stable upon HI exposure at a temperature of 400 degrees C for 11 h. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.