The iodine-sulfur thermochemical cycle (IS cycle) can be applied to realize water decomposition and hydrogen production by using the solar energy or the nuclear heat from High Temperature Gas-cooled Reactor as heat source. Among the three reactions of the IS process (Bunsen reaction, H2SO4 decomposition and HI decomposition), the HI decomposition has the slowest reaction rate and the lowest thermodynamic equilibrium conversion (about 23% at 500 degrees C). In order to make HI decompose at the workable reaction rate, catalysts had to be applied in the reaction system. This paper outlines our study on the monometallic and bimetallic catalysts for HI decomposition at INET (Institute of Nuclear and New Energy Technology, Tsinghua University, China). The influences of different supports, transition metals, bimetallic compositions, reaction time on the catalytic performance for HI decomposition were investigated. The optimized catalyst of 2.5 wt.%Pt -2.5 wt.%Ir/C was proposed and adopted to catalyze the HI decomposition in the close cycle operation of IS-100 facility with the H-2 production rate of 100 NL/h. Both the conversion of HI (21%) and the H-2 production rate (60 NL/h) reached the technical targets of the nuclear hydrogen project (National S&T Major Projects 2010zx06901: Research on key technologies of hydrogen production from high temperature gas cooled reactor). (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.