X-ray transparent proton-exchange membrane fuel cell design for in situ wide and small angle scattering tomography

We have constructed a 5 cm2 proton exchange membrane hydrogen fuel cell optimized for transparency of high energy X-rays. This cell allows for in situ elastic scattering measurements (WAXS, SAXS) during electrochemical operation with minimal trade-offs in cell performance vs benchtop designs, and is capable of reaching auto- motive current densities. A key feature is that the beam enters the cell at grazing incidence to the electrodes, massively increasing the effective pathlength and therefore the signal-to-background ratio. The 360∘ trans- parency in the plane of the sample permits imaging coupled with advanced techniques, such as X-ray diffraction computed tomography.