Performance Degradation in Alkaline-Membrane Electrolyzers

Abstract

Anion exchange membrane (AEM) electrolysis uses a hydroxide-conducting polymer membrane providing a basic environment for the anodic oxygen evolution reaction (OER) and thus an environment that is suitable for earth-abundant catalyst materials. Currently, concentrated KOH is often added to the system to reduce interface resistive losses, with the unintended consequence of increased corrosion and complicating system design. In contrast, K2CO3 provides high conductivity and is nominally non-corrosive. Surprisingly, a rapid AEM stack failure has also been observed for several catalysts during testing in 1 wt. % K2CO3. This failure mechanism remains unclear. Here, I will present the results of a carbonate-induced degradation study performed in collaboration with Proton OnSite (Nel Hydrogen) using analytical and surface characterization techniques. Our results obtained via XPS and three-electrode measurements taken together show that the ionomer degrades during electrolysis into oxidized fragments and that the rate of degradation appears to be catalyst-dependent: some catalyst show a lower rate of ionomer oxidation than others. We hypothesize this difference is related to the ability to form a non-conductive shell during OER. The shell may prevent direct electrical contact of the ionomer with the highly oxidizing catalyst surface during OER. Our findings not only elucidate degradation mechanisms, but also point towards degradation mitigation strategies, such as the informed sculpting of the binder/catalyst interface specifically targeting the conductivity of the catalyst shell. In the remainder of the presentation, I will discuss analogous degradation studies with a pure water feed, and present a preliminary model of degradation phenomena in alkaline membrane electrolyzers. Figure 1