High-resolution x-ray microscopy and nano-CT provides a new approach to non-invasively and non-destructively study nano-structures in situ and in operando. Combined with tunable synchrotron x-ray sources, the elemental and certain chemical compositions can also be mapped dynamically in 3D. These capabilities are valuable for studying electrochemical systems, particularly those involving electrochemical reactions with porous structures at tens of nm to micron scale. The paper gives an introduction of this technique with several examples.