Hyperbranched Dual‐Cation Anion Exchange Membranes With Interconnected Ion Transport Channels for Fuel Cells

ABSTRACT Anion exchange membrane fuel cells (AEMFCs) hold great promise for low‐temperature energy conversion, but their development is hindered by the trade‐off between anion conductivity, chemical stability, and dimensional stability of anion exchange membranes (AEMs). To address this challenge, a series of hyperbranched dual‐cation AEMs (QPMTP‐Spir‐X) are designed and synthesized in this study by ultra‐strong acid‐catalyzed polymerization. The rigid 3D orthogonal structure of the spirobifluorene monomer enlarges the free volume and improves the ion transport efficiency. Optimized for optimal performance, the QPMTP‐Spir‐7 membrane exhibits a high hydroxide conductivity of 239.95 mS cm −1 at 80°C, which is accompanied by a low swelling (21.68%), as well as excellent mechanical properties and chemical stability. The QPMTP‐Spir‐7 membrane is assembled into an H 2 ‐O 2 AEMFC with a peak power density as high as 1.16 W cm −2 (80°C, 0/0 bar), which is nearly twice that of the commercial membrane PiperION A20 (0.56 W cm −2 ). This “hyperbranched dual‐cation” synergistic design effectively coordinates ionic conductivity and dimensional stability, providing a viable design idea for future high‐performance AEMs.