The transition to a sustainable energy landscape hinges on the development of materials that operate efficiently and reliably under demanding conditions. Batteries, electrocatalysts, solid-state ionic conductors, and other energy-related systems exhibit complex, dynamic transformations during operation, spanning multiple length and time scales. Capturing these changes in real time is essential for understanding degradation pathways, reaction mechanisms, and performance limits. In this context, synchrotron-based X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) have emerged as uniquely powerful and complementary tools for the in situ/operando characterization of energy materials.

In this talk, it will be highlighted how combining XAS and XRD under working conditions enables a general picture of structure–property relationships in energy devices. XAS provides element-specific insight into local structure and electronic state, allowing us to follow changes in oxidation state, coordination environment, and disorder around selected atomic species. Operando XAS measurements during cycling or under applied potential reveal, for instance, how redox processes evolve under different potentials, how active sites evolve, and how intermediate species form and disappear [1]. XRD, on the other hand, probes long-range order, phase evolution, and strain, making it possible to track crystallographic transformations, phase coexistence, and lattice responses to electrochemical, thermal, or mechanical stimuli.

I will discuss case studies where the coordinated use of synchrotron XAS and XRD in custom-designed in situ/operando cells has clarified key questions in energy conversion and storage[2]. Examples include the identification of metastable phases in intercalation electrodes, the correlation between local redox reactions and bulk phase transitions in complex oxides, and the structural fingerprints of degradation in electrocatalysts exposed to reactive gas or liquid environments. These examples will illustrate how carefully engineered sample environments—electrochemical cells, gas-flow reactors, solid-state devices—are crucial to bridge the gap between idealized measurements and realistic working conditions, while maintaining adequate X-ray transparency, stability, and time resolution.

Overall, this contribution aims to showcase how in situ/operando synchrotron XAS and XRD are reshaping our understanding of energy-related materials, moving from static snapshots to dynamic, mechanism-oriented pictures. By providing actionable guidelines on experimental design, cell development, and data interpretation, the talk will highlight current capabilities, typical pitfalls, and future opportunities for the community working at the interface between synchrotron science and energy technologies.