Deconvoluting Degradation Mechanisms in Anion Exchange Membrane Water Electrolysis Using Operando X-ray Microtomography

Anion exchange membrane water electrolysers are held back by the low durability of the ionomer in the membrane and catalyst layers. Studying ionomer degradation in these systems is challenging because the main mechanisms - which result in catalyst detachment, membrane thinning, and loss of cationic functionality - have opposing effects on the cell potential. Electrochemical measurements alone are therefore insufficient for elucidating the underlying causes of degradation. To address this, a bespoke miniature-electrolyser-cell is developed for X-ray microtomography imaging of membrane electrode assemblies at 1.6 µm resolution. This setup enables the study of the entire active volume of the electrolyser under static and operando conditions and is validated against standard 5 cm² laboratory cells. An operando investigation of degradation in Fumasep-based catalyst-coated membranes reveals both significant membrane thinning and loss of membrane ionic conductivity during stability testing, leading to increased ohmic resistance and cell potential. In contrast, a Selemion membrane shows minimal changes in thickness and conductivity and is significantly more stable compared to Fumasep when exposed to synchrotron radiation. This platform has relevance for operando studies of electrochemical materials and devices generally, including proton exchange membrane electrolysers, fuel cells, and CO₂ electrolysers using both lab-based and synchrotron X-ray sources.