Laying the foundation for digital material design of porous transport electrodes for PEM water electrolysis with multiscale tomography

We present the first multiscale identical location tomography of a porous transport electrode (PTE) of a proton exchange membrane water electrolyzer. The tomogram encompasses length scales between micrometer-thick fibers to nanopores in the catalyst layer (CL) with nanometer-thin binder coatings on the iridium-oxide particles. It was recorded using micro-computed tomography, focused ion beam scanning electron microscopy tomography, scanning transmission electron microscopy and spectroscopy, nitrogen adsorption, and supplemented by a modeling approach. The reconstruction of the PTE revealed a porosity of around 51% of the porous transport layer (PTL) and 61% of the CL. A thorough analysis of the CL allowed a comparison with the pristine catalyst powder and a realistic prediction of the transport parameters by modeling the binder thickness to a mean of 7 to 10.5 nm. Further, the overall transport parameters of the PTE were determined. The PTL had a higher permeability in the through-plane direction, whereas the CL showed isotropic transport properties. This study offers a comprehensive picture of the multiscale structure and properties of a PTE, which allows for a comparison with catalyst-coated membranes and computer-aided optimization of future PTEs.