HIx concentration by electro-electrodialysis using stacked cells for thermochemical water-splitting IS process

In the thermochemical water-splitting iodine–sulfur process for hydrogen production, efficient concentration/separation of HI from HIx solution, a mixture of HI–H2O–I2, is very important. In this paper, an experimental study on concentrating HI in HIx using stacked electro-electrodialysis (EED) cells was carried out under the conditions of 1atm, 80 °C and the current density of 0.10 A/cm2. The performance of EED stacks including 1, 2 and 4 EED units was evaluated. The results showed that multi-unit EED cells could concentrate HI in catholyte much faster than single-unit cells. The apparent transport number (t+) of all the experiments were very close to 1, while the ratio of permeated quantities of water to H+ (β) changed in a relatively larger range of 1.98–2.89. Although the current efficiency will degrade faster when using a multi-unit stack than a single-unit cell at the late stage of EED process, at high iodine content multi-unit stack could maintain quite high current efficiency.

► Studies conducted on stacked EED cells including 1, 2 and 4 EED units. ► Multi-unit EED stacks could concentrate HI much faster than a single-unit cell. ► The calculated apparent proton transport numbers were very close to 1.0. ► At high I2 content multi-unit stack could maintain quite high current efficiency.