The effect of ionomer content in catalyst layers in anion-exchange membrane water electrolyzers prepared with reinforced membranes (Aemion+™)†

Abstract

Anion-exchange membrane water electrolyzers (AEMWEs) have seen a significant rise in performance and durability in recent years. However, systematic studies of membrane-electrode assembly parameters such as ionomer and catalyst contents are scarcely available. In this work, we provide an electrochemical and microscopic analysis of ionomer content in anode and cathode catalyst layers to provide insight into their impact on AEMWE performance and stability. The results are based on catalyst-coated membranes (CCMs) using commercially-available, reinforced Aemion+? membranes (Ionomr Innovations Inc.) and Aemion+? ionomer binder in the catalyst layers reaching a performance of 1 A cm^?2 at a voltage below 2 V. The ionomer content in the cathode catalyst layer was shown to have minimal influence on performance and to allow stable performance in AEMWE using both 10 wt% and 20 wt%. Varying the ionomer content in the anode catalyst layer resulted in an optimized content of 7 wt% ionomer, providing a sufficiently low content to avoid mass transport limitation, and sufficiently high content to properly bind the catalyst as observed in a constant current hold stability test. Performance was found to be stable over a range of 0.001–1 M KOH in the feed solution with slight improvement for higher KOH contents. This study highlights the importance of balancing the demands of catalyst utilization and mass transport with mechanical and hydrolytic stability of the catalyst layers.