Abstract
A thermochemical water–splitting iodine–sulfur (IS) process enables us to provide the carbon–free hydrogen (H2) at high–efficiency levels using high–temperature heat sources, such as high–temperature gas–cooled reactors, solar heat, and more. Recently, Japan Atomic Energy Agency constructed the H2 production test facility made of the industrial– available corrosion–resistant components, and demonstrated the operations for 150 h at the rate of ca. 30 L/h. In addition, the cation exchange membranes (CEMs) for the HI mediated electro–electrodialysis (EED) were developed by a radiation graft polymerization method in order to improve the IS process efficiency. High proton (H+) conductivity and selectivity are required for the performance of CEMs to reduce the consumption energy for EED. The H+ conductivity of the radiation grafted CEMs was successfully improved by controlling the grafting amount, compared with that of the commercially–available membrane, Nafion®. Moreover, the H+ selectivity and water transport of the developed CEMs was improved by introducing divinylbenzene as the crosslinker. The crosslinkers suppress the permeation of water and I– ions except for H+ caused by the inhibition of the membrane swelling. Currently, the further improvement of the membrane performance is underway by using the ion–track grafting technique.
