Thermochemical Water-Splitting for Hydrogen Production by Antimony-Iodine Processes

A new thermochemical water-splitting process named \u22Sb-I Process\u22 was proposed on the basis of thermodynamic considerations and some preliminary experiments. The process consists of three reactions which eventually produce hydrogen from water via HI intermediate. Subsequent examinations, however, showed that this process embraced a difficulty in the separation of HI gas from the reaction system. To overcome this difficulty, the process was subjected to modification in two ways. First the electrolysis of the aqueous HI solution was combined with the original process to eliminate the HI separation step. The overall efficiency for this \u22Sb-I Hybrid Process\u22 was estimated to be 33～37％ when the recovery of heat was assumed to be 80％. The second modification was carried out by introducing calcium as an additional reaction medium. The resulting modified process, \u22Sb-I-Ca Process\u22, consists of five reactions. It was found that all reaction- and separation-steps in this process could be conducted without serious difficulties. From a flow diagram made on the basis of the experimental results, the overall efficiency was estimated to be about 39％ with an assumption of 80％ heat recovery