Effect of interfacial state in bipolar membrane on rectification and water splitting

Abstract

The effect of polymer component and structure in the membrane interface on rectification and water splitting is discussed in order to examine the water splitting mechanism. Various types of bipolar membranes which had different amino groups in the anion exchange layer, different polyelectrolytes in the membrane interface, and different interface thickness of polystyrene were prepared. The current–voltage characteristics and membrane resistance were measured. If the space between the cation and anion exchange layers was produced, the water splitting effect was reduced. Water splitting effect was accelerated even if a quaternary amino group was inserted in the interface region instead of a secondary or ternary amino group, which implied that the water dissociation occurred not only due to the catalytic effect of the secondary or ternary amino group but also to the electric field. It was evidenced that the membrane which had a thick interface region showed a high conductivity before the critical point of thickness of the interface region, which meant an increase in the reactive region of the water. It was proved that if the anion exchange layer was composed of only binary or ternary amino groups, the water splitting effect was also reduced due to the low anion selectivity.