Explication of Water Splitting Mechanism and Fundamental Research of Materials and Systems Designs in Bipolar Membranes

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The bipolar membrane is a layered structure involving a cation selective membrane joined to an anion selective one. Water splitting has to be accompanied with water dissociation into hydrogen and hydroxide ions caused in the boundary surface between anion and cation layers and successive ion diffusion through charged layers. It is of practical interest in a new process for the commercial production of acid and base. As a result of the impedance measurements of the bipolar membranes under the constant d.c. biased voltages, it was observed that the electric conductivity and the electric capacity under reverse-biased voltage showed quite different behavior from all the other applied voltage and membrane conditions. The reduction in both the specific electric conductivity and the dielectric constant of the intermediate layer was implied by the impedance results that were analyzed using equivalent circuits.The current-voltage characteristics of bipolar membrane/LiCl + alcohol systems were measured and compared with those of the LiCl + water system. In this study, methanol, ethanol, 1-propanol, ethylene glycol and propylene glycol were examined and lithium chloride was employed as an electrolyte. The current-voltage curves suggested that the dissociation into the cation and the anion had occurred also in the methanol system in the interface between the anion exchange and cation exchange layers. The product in the anion exchange layer side was analyzed in the LiCl + methanol system to prove the generation of lithium methoxide. In addition, the difference in the current-voltage characteristics in the other LiCl + alcohol systems to be compared with the LiCl + methanol system and the effect of water as an impurity were discussed.