Concentration of HI in Iodine–Sulfur cycle using EED stack

Concentration and separation of HI is very important for the efficient hydrogen production of Iodine–Sulfur thermochemical cycle, because of the presence of HI–H2O azeotropy at HI:H2O = ∼1:5 (molar ratio). Electro-electrodialysis (EED) has been proved to be very promising in concentrating HI, while the researches on stacked EED cells, which are essential for large scale application of EED process, has not been reported. In this study, EED stacks including 1, 2 and 4 cell units (50 mm × 50 mm effective membrane area) were designed and applied for the concentration of HI in HIx solution (HI–H2O–I2 mixture), using Nafion membrane and graphite electrodes. At 60 °C and 0.10 A/cm2, the performance of the stacks was evaluated, and the effects of initial composition of HIx and EED unit quantity on the HI concentrating capacity and cell voltage were discussed.