Oxidative instability of ionomers in hydroxide-exchange-membrane electrolyzers

Hydroxide exchange membrane (HEM) electrolyzers can produce green H2 with only earth-abundant catalysts and electrolyte-free (nominally pure) water feed, significantly decreasing system cost and complexity. However, HEM technology suffers from short lifetimes, attributed in part to poor stability of anion-exchange polymers used in the membrane and catalyst layers. Here, we use electrochemical analysis and ex-situ characterization techniques to study anion exchange polymer degradation in electrolyzers. Using multiple ionomers, catalyst layer additives, and electrolyte feed, we show anode ionomer oxidation is the dominant degradation mechanism for all HEM-based electrolyzers tested. We show improved device stability using oxidation-resistant catalyst layer binders and offer new design strategies for advanced ionomer and catalyst layer development.