Operando scanning small- and wide-angle X-ray scattering (SAXS&WAXS) at the cSAXS beamline of the Swiss Light Source was employed in this study to examine the water saturation of polymer electrolyte fuel cell (PEFC) component, particularly in the nanoscale pore space of catalyst layers (CL) and the membrane hydration state. A small beam size (≈7x30 microns) and ≈0.6 microns through-plane step size enabled to resolve of the bulk CLs (Pt/C Ketjen Black based, 0.1 mgPt/cm2; ≈7 microns thick) separated by a 15-micron membrane. Additionally, it allows for precise registration in case of membrane swelling during operation, which is a prerequisite for the analysis of the operando scattering data. Due to the difference in electron density variation between solid-void and solid-liquid interfaces, any change in CL saturation results in different scattering intensity profiles, which can be quantified by Invariant calculations (see Fig. 1a & b).The presentation will give insights into CL saturation evolution concerning relative humidity, operating pressure and current density. Differences in the CL saturation, and membrane hydration indicated by a change in d-spacing of the ionomer peak (1), were observed between wet nitrogen flushing and cell operation (see Fig. 1c & d). However, the cathode microporous layer (MPL) saturation seems to be unaffected for a Li100-based MPL on a Freudenberg H14 gas diffusion layer (GDL) substrate. The length scale-specific scattering data will provide a better understanding of mass transport in PEFC’s materials and allow us to push material design development forward. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at beamline cSAXS of the Swiss Light Source.