Loosened Hydrophobic Microphase to Facilitate Ion Channel Formation in Anion Exchange Membrane for Fuel Cell Applications

Abstract

Constructing well-defined ion channels can contribute to high conductivity and stability of anion exchange membranes (AEMs) for fuel cells. Herein, high performance AEMs are designed by incorporating spiro-adamantane-fluorene (SAF) unit into poly (aryl indole) backbone, which is then grafted with di-cation side chains. Featuring integrated high degree of bulkiness and rigidity, the SAF unit gives rise to decreased backbone packing density and suitably loosened hydrophobic microphase, thus lowers the resistance of cation aggregation during microphase separation, and facilitates ion cluster connection (when hydrated) to create continuous pathways for faster OH- diffusion as revealed by molecular dynamic simulation and conductivity measurements. The optimized AEM displays a high hydroxide conductivity of 161.9 mS cm-1 (at 80 ºC, and medium IEC of 2.32 mmol g-1); its H2/O2 fuel cell yields an outstanding peak power density of 2.07 W cm-2 at 80 ºC; the AEM remains stable after prolonged (> 400 h) fuel cell operation at 60 ºC and 200 mA cm-2. This work reveals the important role of loosened hydrophobic microphase for ion channel formation, and provides a new guide for AEM design toward better balanced conductivity and stability; it may potentially contribute to further advancement of alkali membrane fuel cells.

Keywords: anion exchange membrane, bulky-rigid unit, loose hydrophobic microphase, ion channel, Fuel Cell