<i>In-operando</i> two-dimensional X-ray imaging of CO ₂ electrolyzer

Membrane–electrode assembly (MEA)-based electrochemical devices offer a promising pathway toward sustainable chemical production. However, achieving high-resolution in-operando characterization of an MEA cross-section remains a significant challenge. In this work, we developed and demonstrated an in-operando two-dimensional (2D) X-ray diffraction imaging technique to visualize and analyze the internal processes of an MEA-based CO₂ electrolyzer. By combining a serpentine scanning strategy with synchrotron-based wide-angle X-ray scattering, we achieved spatially resolved mapping of key components and chemical species within the MEA, with particular focus on comparing the corresponding regions at the land and channel areas of the flow field. Our results reveal that salt formation initiates and accumulates preferentially within the gas diffusion layer at the channel region, in contrast to the land region. Structural modeling and diffusion length analysis based on the 2D X-ray diffraction maps indicate that faster CO₂ transport in the channel region, enabled by shorter diffusion pathways, leads to more substantial salt formation. This study highlights the utility of in-operando 2D X-ray diffraction imaging as a powerful diagnostic tool in MEA systems.