Decomposition of hydrogen iodide (HI) is one of the key reactions in the sulfur-iodine (S-I) thermochemical water splitting promising for the massive hydrogen production. Much effort has been made to explore the preparation of high performance catalyst for this hydrogen-producing reaction. Although platinum has long been found to be an efficient metallic catalyst, it was prone to agglomerate at elevated temperature resulting in a decrease in the hydrogen yield. A series of bimetallic Pt-Ir/C catalysts were prepared by electroless plating to investigate the effect of Ir/Pt molar ratio on the HI conversion compared with Pt/C and Ir/C catalysts. The physical properties and morphology of the catalysts were characterized by BET, XRD, TEM and ICP-AES. The synergistic effect of platinum and iridium with respect to HI decomposition was confirmed by the fact that the bimetallic Pt-Ir/C-0.77 catalyst with 1 wt% Pt loading and 0.77 wt% Ir loading showed much higher catalytic activity and thermostability compared with Pt/C and Ir/C catalyst. Based on the experimental results obtained, it may be concluded that the bimetallic Pt-Ir/C catalyst was supposed to be a cost-effective and high performance catalyst promising to be employed for the hydrogen production via the S-I thermochemical water splitting cycle. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.