Highly Conducting Poly(arylene-imidazolium) Anion Exchange Membranes Containing Thin-Span Channels Constructed by Cation–Dipole Interaction

Abstract

The membrane-based alkaline electrolyzer and fuel cell system has a significant drawback because it uses a concentrated, corrosive alkaline electrolyte. The anion exchange membranes (AEMs) also have lower conductivity than proton exchange membranes (PEMs) because OH– ions have a lower penetration coefficient. In this study, intending to prepare AEMs with high ionic conductivity in low concentrations of alkaline solution, two imidazolium diol monomers have been synthesized as unique candidates for the synthesis of stable anion exchange polymers. Then a strategy for designing AEMs with ion-conducting channels using a strong cation-dipole interaction between imidazolium cations and polar poly(vinylpyrrolidone) (PVP) (PAIm1/PVP blend membrane and Cross-PAIm1-PVP membrane) was reported. At 25 °C, the PAIm1/PVP blend and Cross-PAIm1-PVP membrane have ionic conductivities of 77.1, 104.9 mS cm–1 in water (Cl– form), and 315, 356.1 mS cm–1 in KOH 0.2 M, respectively. Also, a semicrystalline poly(arylene-imidazolium)2 (PAIm2) was synthesized and blended with PVP to increase the ions’ orientation for boosted ion conductivity. The ionic conductivity of the PAIm2/PVP blend membrane is 25.9 mS cm–1 in water (Cl– form) and 86.1 mS cm–1 in KOH 0.2 M at 25 °C. In addition, the prepared membranes in direct ethanol fuel cells (DEFCs) show preferable behavior in single-cell performance, with a peak power density (Pmax) of 17.7, 11.1, and 9.1 mW cm–2 at 30 °C for PAIm1/PVP, PAIm2/PVP, and Cross-PAIm1-PVP membranes, respectively. The results demonstrate that the prepared AEMs can use in electrolyzers and fuel cells.