Preparation of high-conductivity QPPO (quaternary-aminated poly (2,6-dimethyl-1,4-phenyleneoxide)) membranes by electrical treatment

Anion exchange membranes (AEMs) have been studied to improve conductivity for their high performance in energy conversion systems such as reverse electrodialysis, alkaline polymer fuel cells, and redox flow batteries. The functional groups with positive charge on backbones in AEMs form ion channels, which is the most significant factor in determining the conductivity of anions through the membrane. A typical method frequently used to enhance ionic conductivity is increasing the ion exchange capacity (IEC). However, AEMs with excessive amounts of positively charged functional groups may reduce ion selectivity or increase ion crossover by weakening mechanical properties due to high water uptake and the swelling ratio. To overcome this problem, we studied in this paper the alignment of ion channels for quaternary-aminated poly (2,6-dimethyl-1,4-phenyleneoxide) (QPPO) by applying an electric field to improve conductivity while retaining ion permselectivity with reasonable mechanical properties. We observed that the conductivity of the aligned QPPO membranes was enhanced up to three times using the same ion exchange material. Further, characteristic changes in the AEMs were investigated for the aligned ion channels using X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), and atomic force microscopy (AFM).