Nowadays, anion exchange membranes (AEMs) are used in various electrochemical devices, such as fuel cells, electrolyzers, and redox flow batteries. Particularly, AEMs are polymers characterized by the presence of positively charged functional groups and have attracted great interest due to the promise of low-cost sources of renewable energy for the future. However, the membranes that have undergone the most development and have been most widely commercialized to date are proton exchange membranes (PEM), specifically Nafion, due to their good chemical and mechanical stability. Nevertheless, the complexity of the synthesis and high costs are issues that have led scientific convenience to opt for other polymeric membranes, like sulfonated nonfluorinated hydrocarbon polymers, as poly(arylene ether ketone)s (PAEKs) or poly(arylene ether sulfone)s (PAESs) that combine lower cost and display high chemical and mechanical stabilities.
Nevertheless, there are different problems and challenges associated with the development of AEMs since materials with high chemical stability at high pH levels as well as high conductivities are required. One of the strategies used to achieve high ionic conductivity is by increasing the ion exchange capacity (IEC) of the membrane (IEC); however, this results in excess of water uptake (WU), leading to a drastic decrease in mechanical properties. Currently, there are different types of AEMs, and the most common are those based on polysulfones and poly(ethylene oxide)s. However, these types of materials have a limitation since they have ether bonds in the main chain that are susceptible to degradation. Therefore, the development of new polymer-forming reactions that allow obtaining materials with high chemical, mechanical, and thermal stabilities is essential. On the other hand, polymers without ether bonds in the main chain have been reported, obtained through polycondensation reactions for its use as AEMs, allowing the development of new structures, achieving an adequate balance between hydration, conductivity, and thermal, mechanical, and chemical stability.
In this study, we present a convenient and scalable chemical methodology to introduce new functionalities in different polymers via postpolymerization modification that enable suitable ionic conductivity and chemical stability for anion exchange membranes applications
Novel polymeric materials were obtained through a systematic study of the polyhydroxyalkylation reaction in superacid medium of carbonyl compounds with activated and non-activated aromatic compounds with modulable functionalities.
The proposed materials focus on structures with positive charges provided mainly by quaternary ammonium, imidazolium and pyridinium groups, confer high ionic conductivities, ideal for ion exchange membranes in storage or electrochemical energy devices.
A novel linear, soluble, high-molecular-weight polymers has been obtained using a superacid-catalyzed polyhydroxyalkylation reaction. The reactions were performed at room temperature in the Brønsted superacid trifluoromethanesulfonic acid (CF3SO3H, TFSA) in a mixture with methylene chloride. The obtained materials were functionalized by nucleophilic substitution reactions with the aim of introducing different amino-quaternary groups (positive charges) and were also characterized by FT-IR, NMR-H1, NMR-C13, DSC, TGA and viscosity. The AEMs were prepared using the casting method and their morphological, mechanical, water-uptake (WU), ion exchange capacity (IEC) and ionic conductivity properties were determined.
The authors gratefully acknowledge the financial support from Secihti MADTEC-2025-M-222, as well as E. R. Morales, G. Cedillo V., and S. López Morales for help with polymer characterizations. The authors thank Josué Romero from LUME RRID:SCR_024400 for TEM image acquisition and technical support.