Preparation and properties of composite membranes composed of anion-exchange membranes and polypyrrole

Composite membranes composed of commercial anion exchange membranes and polypyrrole were prepared by chemical oxidation of pyrrole in the membrane matrix. Two different procedures were used: immersing the anion-exchange membranes equilibrated with a ferric chloride solution into an aqueous pyrrole solution; immersing the anion-exchange membranes equilibrated with the pyrrole solution into the ferric chloride solution. Polypyrrole homogeneously existed throughout the membranes in the former composite membranes, and the polymer existed on the membrane surfaces as layers in the latter membranes. Electrical conductivity parallel to the plane and that across a cross section of the membrane also demonstrated different morphology of the composite membranes. After evaluating the electrochemical properties of the composite membranes, transport properties in electrodialysis, transport number of sulfate ions, nitrate ions, and bromide ions relative to chloride ions and current efficiency were evaluated. Permeation of sulfate ions through the composite membranes was difficult; permeation of nitrate ions was enhanced by the existence of polypyrrole on and in the membranes and the relative transport number of bromide ions decreased depending on morphology of the membranes. The polypyrrole in the anion-exchange membranes markedly affected the transport number of anions relative to chloride ions.