Tröger’s Base Microporous Anion Exchange Membranes with Hyperbranched Structure for Fuel Cells

The application of anion exchange membranes (AEMs) in alkaline fuel cells is profoundly affected by its performance. In this work, Tröger’s base microporous AEMs with hyperbranched structure (QA-BTB-x%) are prepared by superacid catalysis. The introduction of the hyperbranched structure can enhance the free volume of the AEMs, which will improve the water uptake (WU) of the AEMs and thus promote the transport of OH–. By increasing the content of the branching agent from 0% to 8%, the WU of the AEMs gradually increased from 41.7% to 62.6% at 80 °C. The maximum OH– conductivity of the QA-BTB-5% AEMs can reach to 95.2 mS cm–1 in ultrapure water at 80 °C with a low swelling ratio (14.9% at 80 °C). Small angle X-ray scattering (SAXS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) show that the QA-BTB-5% AEMs has a good microphase separation structure that is beneficial for OH– transport. After a long-term alkaline stability test, the QA-BTB-5% still has a high OH– conductivity. The maximum power density of the QA-BTB-5%-based single cell can reach to 548 mW cm–2 in H2/O2. All of the results demonstrate obvious performance enhancements of AEMs upon the introduction of hyperbranched structure into the polymer backbone.