The Proton exchange membrane fuel cell (PEMFC) is an electrochemical converter which produces electricity and heat from hydrogen and oxygen, with water as the only by product. It is a promising, but still expensive, technology. The need of improvement is still important and equally important is the need of understanding. The active layer (AL) of the PEMFC is probably the most critical component of this technology, but also the least understood. In particular, the water content in the proton conducting ionomer and in the pores of this material are largely unknown, despite the fact that it has a strong influence on the performance and durability. Thus, it is currently a subject at the forefront of the research. This proposal aims to quantifying the amount of water in both phases within the AL simultaneously and operando using Small Angle Neutron Scattering (SANS), since no other technic can provide such information. This requires a dedicated cell whose constraints have been identified, a small beam and consequently high neutron flux along with an efficient spectrometer. The crucial information will allow to raise bottlenecks to go toward the design more efficient electrodes.