Highly Stable Poly(diphenyl sulfide piperidine) Anion Exchange Membrane Grafting with Flexible Side-Chain Cationic Group for Water Electrolysis

Abstract

Aryl-piperidine polymers are preferred for anion exchange membranes (AEMs) due to their excellent designability and alkaline resistance stability. In the present work, a poly(diphenyl sulfide piperidine) polymer backbone, distinct from the conventional poly(biphenyl piperidine), is synthesized via a superacid-catalyzed reaction. Subsequently, a series of AEMs (PPSP-xPip) are achieved by grafting cationic groups with long flexible alkyl chains onto the main chain. All membranes demonstrate good membrane-forming ability and toughness with elongation at break ranging from 16.8 to 34.5%. The OH^– conductivity of them is in the range of 88.4–117.1 mS cm^–1 at 80 °C, attributed to the high water uptake and the favorable microphase separation structure. The representative PPSP-35Pip membrane exhibits high alkaline stability with 89% of the conductivity retention ratio in 2 M NaOH after 520 h at 80 °C. The current density of its water electrolyzer cell reaches 0.619 A cm^–2 in 2 M NaOH electrolyte at 2.0 V. After 520 h of endurance testing, the water electrolyzer maintains excellent stability with the voltage fluctuation of only 1.07%.