Control of ion exchange capacity in block copolymer binders enables high hydroxide conductivity at low swelling and improves catalyst activity for AEM water electrolysis

Abstract

The development of membranes for anion exchange membrane water electrolysis (AEMWE) has recently been extremely fruitful, but less effort has been devoted to specific tailoring of polymeric binders to enhance catalyst utilization and electrical conductivity within the catalyst layer. Herein we report a simple one-pot synthesis of block copolymers (BCP) for application as anode binders in AEMWE. The BCPs contain hydrophilic poly(biphenyl piperidinium) and hydrophobic blocks based on meta-terphenyl and 2,2,2-trifluoroacetophenone of varying fractions. The synthetic approach provides facile access to ionomers with largely varied ion exchange capacities (IECs) between 0.94 and 2.68 meq. g−1, giving rise to binders with extremely low swelling yet efficient hydroxide transport. The least hydrophilic BCP with ∼25 wt-% hydrophilic fraction and an IEC of 0.94 meq. g−1 exhibits a high hydroxide conductivity of σOH = 174 mS cm−1 at 80 °C at a low water uptake of 13% at 80 °C, and almost temperature-independent swelling. The low water uptake enables increased catalyst utilization in nickel-iron layered double-hydroxide-based anodes, which, in combination with the high hydroxide conductivity, results in an improved AEMWE performance. AEMWE single cells exhibit current densities of 3800 mA cm−2 at 2 V, not achieved neither by using statistical copolymer analogs nor commercial-type binders.