Hydroxide Conducting Naphthalene-Containing Polymers and Membranes Via Polyhydroxyalkylations

Anion exchange membranes (AEMs) are critical components of alkaline membrane water electrolyzers and fuel cells that are under development today [1,2]. Consequently, there is a strong demand for highly conductive and alkali-stable AEMs. In this context, polyhydroxyalkylation has emerged as one of the most efficient synthetic pathways to chemically resistant polymer backbones for AEMs. In these Friedel-Crafts type polycondensations, an electron-rich aromatic compound reacts with an activated ketone or aldehyde to produce an aryl-ether-free polymer. The desired quaternary ammonium cations are then usually introduced through a Menshutkin reaction [3,4]. In the current work, we have employed naphthalene-based compounds as monomers in polyhydroxyalkylations to prepare a series of high-molecular weight poly(naphthalene alkylene)s with various naphthalene contents. These polymers were then quaternized and cast into AEMs. Here, we will discuss the influence of the naphthalene monomer type and content on AEM properties such as solubility, water uptake, ion conductivity, ionic clustering, thermal and alkaline stability, and also the prospects of using these AEMs in electrochemical systems. References: [1] Chen, N., Wang, H.H., Kim, S.P. et al. Poly(fluorenyl aryl piperidinium) membranes and ionomers for anion exchange membrane fuel cells. Nat. Commun. 12 , 2367 (2021). [2] Li, D., Park, E.J., Zhu, W. et al. Highly quaternized polystyrene ionomers for high performance anion exchange membrane water electrolysers. Nat. Energy 5 , 378–385 (2020). [3] Olsson, J.S., Pham, T.H., Jannasch, P., Poly(arylene piperidinium) hydroxide ion exchange membranes: synthesis, alkaline stability, and conductivity. Adv. Funct. Mater. 28 , 1702758 (2017). [4] Pan, D., Bakvand, P.M., Pham, T.H., Jannasch, P. Improving poly(arylene piperidinium) anion exchange membranes by monomer design. J. Mater. Chem. A 10 , 16478–16489 (2022).