Hydrogen technology is a key pillar of a sustainable energy economy, offering pathways to reduce greenhouse gas emissions and mitigate risks associated with energy markets. The performance of hydrogen fuel cells and water electrolyzers is governed by electrochemical reactions occurring on nanostructured catalysts. During operation, these catalysts undergo continuous structural and morphological evolution, which critically determines both performance and long-term operational stability. Consequently, understanding the mechanisms of catalyst evolution under realistic operating conditions is essential for further progress in catalysis in general and hydrogen technologies in particular.

In this lecture, an advanced characterization approach operando small-angle X-ray scattering (SAXS) applied to nanostructured catalysts in functioning fuel cells and water electrolyzers is discussed. Operando X-ray scattering techniques provide direct, time-resolved insight into catalyst morphology evolution and enable quantitative correlation with electrochemical performance. In contrast to previously developed operando electrochemical cells, investigations performed in fully operational devices under realistic conditions allow a more complete understanding of catalyst degradation processes and structural transformation pathways. This approach delivers valuable information that is otherwise inaccessible in simplified model systems. Finally, current challenges and future directions in operando studies of electrochemical energy conversion devices are outlined.

e-mail: yurii.yakovlev@matfyz.cuni.cz