This study aimed to establish a closed-cycle operation technology with high thermal efficiency in the thermochemical sulfur-iodine cycle for large-scale hydrogen production. A series of experimental studies were performed to investigate the occurrence of side reactions in both the H 2 SO 4 and HI
x
phases from the H 2 SO 4 /HI/I 2 /H 2 O quaternary system within a constant temperature range of 323–363 K. The effects of iodine content, water content and reaction temperature on the side reactions were evaluated. The results showed that an increase in the reaction temperature promoted the side reactions. However, they were prevented as the iodine or water content increased. The occurrence of side reactions was faster in kinetics and more intense in the H 2 SO 4 phase than in the HI
x
phase. The sulfur or hydrogen sulfide formation reaction or the reverse Bunsen reaction was validated under certain conditions.
Ke Zhang,Xu Zhao,Sihan Chen,Liping Chang,Jiancheng Wang,Weiren Bao,Hui Wang
In chemical cycles to produce hydrogen , the H 2 S splitting cycle and the sulfur-iodine (S I) water splitting cycle both share the Bunsen reaction and HI decomposition. Therefore, they have to overcome the same challenges in the technology development, one of them being the complex and difficult separations of the mixed hydroiodic acid and sulfuric acid solution after the Bunsen reaction. To avoid the separations, this paper studies the electrolysis of the HI/H 2 SO 4 /H 2 O/toluene mixture, focusing on the electrochemical characterization of the Pt electrode by using linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The results show that hydrogen is identified from the gas generated from the cathode in electrolysis. Iodide oxidation is the main reaction in the anode chamber and no significant side reactions are observed. Iodine deposition on the anode surface increases the resistance to iodide diffusion to the anode. However, it can be mitigated by adding toluene in or applying stirring to the anolyte HI/H 2 SO 4 solution. The Pt cathode and sulfuric acid catholyte also work stably.
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