Branched poly(p-terphenylene 3-piperidinium)s for anion exchange membrane water electrolysis

Anion exchange membranes (AEMs) are central to clean-energy electrochemical technologies, yet achieving high hydroxide conductivity together with dimensional and alkaline stability remains challenging. Here we implement a straightforward branching strategy in poly(arylene 3-piperidinium)s by incorporating two trifunctional units, i.e., triptycene and 1,3,5-triphenylbenzene, into the polymer backbone. This architecture suppresses water uptake and swelling without compromising the membrane's ion-transport efficiency and chemical durability. Compared to linear membranes, the branched membranes exhibit a 34−36% reduction in water absorption. Triptycene-based branched AEMs achieved superior performance, including suppressed swelling (<18% at 80 °C), high conductivity up to 191 mS cm −1  at 80 °C, and improved alkaline stability, remaining intact in 1 M NaOH for at least 2000 h. Importantly, a water electrolyzer based on B-PT3Pip-3%Trip demonstrated a current density of 6.9 A cm −2  at 2.0 V and 80 °C, and can operate stably under 1 A cm −2  at 60 °C for 1000 h with a voltage decay of only 81 μV h −1 . The synthetic simplicity of the branching strategy, together with the combination of suppressed swelling, high conductivity, and long-term durability, makes branched poly(arylene 3-piperidinium) AEMs highly promising for AEM water electrolysis applications.