Aquivion-based anion exchange membranes: Synthesis optimization via dispersant agents and reaction time

Abstract

Alkaline membrane water electrolysis fed by renewable energy is a promising technology to produce “green” hydrogen for a variety of applications. Thanks to their unique characteristics of chemical, thermal and electrochemical stability, perfluorinated polymers are proposed as an alternative to hydrocarbon-based anion exchange membranes (AEMs) for applications in water electrolysers. A simple two-step functionalization reaction to introduce quaternary ammonium groups onto Aquivion® perfuorinated backbone is reported using a low toxicity dispersant. The most appropriate dispersant (Novec 7500) and reaction parameters (5 °C for 2 hrs) are selected. The complete conversion of the precursors into a quaternary ammonium salt is confirmed by a solid-state NMR study. Physico-chemical properties, thermal behavior and anion conductivity of the formed AEM are investigated. The phase separation characteristics of this perfluorinated polymer allow to reach a membrane ion mobility (μeff) 1.99 10−4 cm2 V−1 s−1, one order of magnitude higher than the FAA3-50 commercial membrane, meaning an enhanced ion dissociation. A very limited degradation of functional groups is demonstrated after immersion in alkaline solution, with only 2 % of ion exchange capacity (IEC) reduction against 14 % of the FAA3-50 commercial membrane. An electrolysis current density of 0.9 A cm−2 at 2.2 V and 90 °C, is achieved showing very promising applications for green hydrogen production.