Aquivion-based anion exchange membranes: Synthesis optimization via dispersant agents and reaction time
Alessandra Carbone, Sabrina Campagna Zignani, Irene Gatto, Rolando Pedicini, Claudio Oldani, Alice S. Cattaneo, A.S. Aricò
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.