A successful demonstration of closed-loop thermochemical Iodine–Sulfur (IS) cycle for hydrogen production remains challenging owing to the lack of detailed data on thermodynamic estimates, recuperator system, reactor designs, product separation, and materials of construction. This review identifies and details the technological challenges in the most energy-consuming sulfuric acid decomposition step with a focus on the thermodynamic behavior of the fluids, acid concentration system, reactor designs, SO₂–O₂ separation, energy consumption, and materials of construction. The state-of-art and directions for future development are also discussed in detail. The results show that the thermodynamic properties can be estimated accurately using an electrolyte NRTL model. The compression-cooling process is found to be a better alternative for separating SO₂–O₂. However, the high energy requirement for cooling remains a tall challenge. Hastelloy C-276 and SiC are suitable materials for the construction of the equipment in the high temperature range while, SiC, Teflon, and glass are suitable in the low temperature range.

由于缺乏关于热力学估计、换热器系统、反应器设计、产品分离和结构材料的详细数据，用于制氢的闭环热化学碘 - 硫 (IS) 循环的成功演示仍然具有挑战性。本综述确定并详细说明了最耗能的硫酸分解步骤中的技术挑战，重点关注流体的热力学行为、酸浓缩系统、反应器设计、SO ₂ –O ₂分离、能源消耗和建筑材料。还详细讨论了最新技术和未来发展方向。结果表明，使用电解质 NRTL 模型可以准确地估计热力学性质。发现压缩冷却过程是分离 SO ₂ –O ₂的更好选择。然而，冷却的高能量需求仍然是一个巨大的挑战。Hastelloy C-276 和 SiC 是适合在高温范围内构建设备的材料，而 SiC、Teflon 和玻璃则适合在低温范围内构建。