Boosting Hydrogen Production from Hydrogen Iodide Decomposition over Activated Carbon by Targeted Removal of Oxygen Functional Groups: Evidence from Experiments and DFT Calculations

In the thermochemical sulfur–iodine water splitting cycle for hydrogen production, the hydrogen iodide (HI) decomposition reaction serves as the rate-determining step, and its high efficiency relies on the precise design of active sites on the catalyst. This paper combines experimental characterization with density functional theory (DFT) calculations, focusing on activated carbon catalysts. By regulating the types and contents of oxygen-containing functional groups through H2 reduction treatment at different temperatures, the influence of oxygen-containing functional groups on HI decomposition was investigated. The results show that H2 reduction treatment can gradually remove oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups on the surface of activated carbon without significantly affecting the pore structure. Catalytic activity tests conducted under the typical reaction temperature of 500 °C confirmed that as the content of oxygen-containing functional groups decreases, the HI decomposition efficiency increases. DFT calculations further revealed the role of oxygen-containing functional groups: they inhibit the chemisorption of reactant HI on unsaturated carbon atoms and alter the desorption activation energy of product H2, thereby affecting the overall reaction process. This study provides important theoretical guidance and experimental basis for designing efficient HI decomposition catalysts.