The decomposition of hydrogen iodide in the thermochemical water splitting iodine sulfur process at an intermediate temperature (400 degrees C) using a catalytic membrane reactor was reported here, for the first time. The performance of a catalytic membrane reactor based on a hexyltrimethoxysilane-derived silica membranes (H-2 permeance of 9.4 x 10(-7) mol Pa-1 m(-2) s(-1) and H-2/N-2 selectivity of over 80.0.) was evaluated at 400 degrees C by varying the HI flow rates of 2.6, 4.7, 6.9, 8.4, and 9.7 mL min(-1). The silica membranes were prepared by counter-diffusion chemical vapor deposition method on gamma-alumina alpha-coated alumina tubes. Hydrogen was successfully extracted from the membrane reactor using the silica membrane at 400 degrees C. A significant increase in HI conversion was achieved. The conversion achieved at an HI flow rate of 2.6 mL min(-1) was approximately 0.60, which was greater than the equilibrium conversion in HI decomposition (0.22). (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.