High performance water electrolysis using a poly(fluorene phenylpropylammonium) anion-exchange membrane with 2 M aqueous KOH

Abstract

Anion exchange membrane water electrolysis (AEMWE) has great potential to be established as a high-performance and low-capital cost technology for hydrogen production. High current densities can be achieved with a non-platinum group metal (non-PGM) catalyst. However, the harsh operation conditions require stable cell components. Here, we report on the use of a highly stable and ion conductive poly(fluorene alkylene) membrane (PdF–TMA) tethered with trimethylammonium cations via phenylpropyl side chains for AEMWE cells operating with 2 M aqueous KOH. The ether-free PdF–TMA polymer is efficiently prepared by polyhydroxyalkylation to reach a molecular weight of 236 kDa, a high thermal stability, and an ion-exchange capacity of 2.14 mequiv. g⁻¹ (OH⁻ form). Using commercial electrodes of NiFe₂O₄ (anode) and RANEY® nickel (cathode) and PdF–TMA as an AEM, the output current reached 1 A cm⁻² at voltages below 1.9 V at 60 °C. Also, PdF–TMA outperformed AEMION™ in terms of membrane resistance by almost 30% and, after 100 h at 0.5 A cm⁻², did not reveal any loss of conductivity, in contrast to AEMION™. Furthermore, both membranes were analysed by ¹H NMR spectroscopy after AEMWE tests and the PdF–TMA proved very stable even at 80 °C.