Generation of Light-Induced Electrical Potential from Ion Exchange Membranes Containing 4,4'-Bipyridine Moiety
The effect of various swelling solvents for anion exchange membranes having a viologen moiety as the anion exchange groups on photovoltage was examined to obtain a high photovoltage and to clarify the mechanism of charge transfer. Anion exchange membranes having a viologen moiety, based on a copolymer membrane of chloromethylstyrene and divinylbenzene and a film of chloromethylated polysulfone, were swelled with various solvents, and clamped between two ITO electrodes (indium-tin oxide electrodes), and a xenon lamp irradiated the membrane from one side. In general, the solvents that swelled the membranes well and provided a high photovoltage included ethylene glycols, 1,3-dioxolane, 1,3-dioxane, and 1-methyl-2-pyrrolidone. Especially, the membrane swelled with 1,3-dioxolane generated a high photovoltage. It is thought from these results that methylene groups neighboring oxygen and between two oxygens, which is an electron acceptor, are related to the charge transfer in the system. When the cell was assembled by sandwiching a cation exchange membrane (as a separator) between two anion exchange membranes with a viologen moiety, the photovoltage significantly decreased with an increase in repeat time of the irradiation and interruption. On the other hand, the voltage of the cell having of an anion exchange membrane separator did not significantly decrease with the same procedure. When non-ion-exchanged chloride ions were added to the cell, the generation of the photovoltage became high compared to the cell without the ions. It was concluded from these results that chloride ions also play an important role in the charge transfer in the cell.
Sata
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Faculty of Engineering, Yamaguchi University, Tokiwadai 2557, Ube City, 755, Japan