A Semi-Interpenetrating Network Approach for Dimensionally Stabilizing Highly-Charged Anion Exchange Membranes for Alkaline Fuel Cells

There is a delicate balance between ion exchange capacity (IEC), conductivity, and dimensional stability in anion exchange membranes as higher charge content can lead to increased water uptake, causing excessive swelling and charge dilution. Using highly‐charged benzyltrimethylammonium polysulfone (IEC=2.99 mEq g−1) as a benchmark (which ruptured in water even at room temperature), we report the ability to dramatically decrease water uptake using a semi‐interpenetrating network wherein we reinforced the linear polyelectrolyte with a crosslinked poly(styrene‐co‐divinylbenzene) network. These membranes show enhanced dimensional stability as a result of lower water uptake (75 % vs. 301 % at 25 °C) while maintaining excellent hydroxide conductivity (up to 50 mS cm−1 at 25 °C). These improvements produced an enhanced alkaline fuel cell capable of generating 236 mW cm−2 peak power density at 80 °C. This method is easily adaptable and can be a viable strategy for stabilizing existing systems. A little restraint can work wonders: Increasing the ion exchange capacity of an anion exchange membrane often leads to higher conductivity at the expense of excessive swelling and decreased mechanical stability. We employ a semi‐interpenetrating network architecture to dimensionally stabilize highly‐charged benzyltrimethylammonium polysulfone membranes. These reinforced membranes exhibit excellent ionic conductivity and mechanical robustness.