Electro-electrodialysis of HI–I2–H2O mixture using radiation-grafted polymer electrolyte membranes

In the thermochemical water-splitting iodine–sulfur process for hydrogen production, new polymer electrolyte membranes were applied in an electro-membrane process (electro-electrodialysis, EED) to increase the HI molality of HIx solution (HI + I2 + H2O mixture) to be over quasi-azeotropic. Radiation grafting of a styrene monomer into a poly(ethylene-co-tetrafluoroethylene) base film and subsequent sulfonation provided electrolyte membranes that had ion exchange capacities (IECs) of 1.1–1.6 mmol/g. With the EED of the HIx solutions using [HI] = [I2] = 10 mol/kg at 40 °C the transport number of protons, ratio of permeated quantities of water to the protons, and current efficiency all appeared to depend on the IEC of the resulting membranes. When compared to Nafion, the self-made membranes exhibited lower electric cell resistance, and thereby decreasing up to 32% of the overall energy required in the concentration operation.