Interplay between Structure and Conduction Mechanism of Piperazinium-Functionalized Poly[Ethylene Pyrrole/Ethylene Ketone/Propylene Ketone] Anion Conducting Membranes.

Abstract

Anion exchange membranes (AEMs) have been proposed as potential alternatives to proton exchange membranes in electrochemical energy conversion and storage devices. Herein, the synthesis of a series of AEMs based on random piperazinium-methyl N-substituted poly[ethylene pyrrole/ethylene ketone/propylene ketone] (P-FPKK) and their structural characterization together with the elucidation of the ion conduction mechanism are reported. Different copolymers are prepared by a Paal-Knorr reaction of a poly(ethylene ketone/propylene ketone) copolymer precursor with 1-(2-aminoethyl) piperazine, modulating the molar ratios amine/(1,4-diketonic repeat units of copolymer) from ¼ to 3. The composition and structure are investigated by elemental analysis, attenuated total reflectance-Fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray diffraction. The degree of functionalization, f, plays a crucial role in controlling the thermal, morphological, and electrochemical properties of the P-FPKK_f(I)_g and P-FPKK_f(OH)_g membranes. P-FPKK_0.49(OH)_0.45 displays an ionic conductivity of 11.3 mS cm^-1 at 60 °C. After alkaline aging (1 m KOH at 60 °C for 336 h), retaining its structural integrity and 25% of its initial ionic conductivity value, suggesting them as possible candidates for testing in alkaline energy conversion and storage devices. Furthermore, broadband electrical spectroscopy studies reveal that the long-range charge migration processes are modulated by the segmental motion of the backbone chains of the copolymer matrix.