Experimental and numerical comparison of water transport in untreated and treated diffusion layers of proton exchange membrane (PEM) fuel cells

► Fluorescence microscopy is used for ex-situ visualization of flow in GDLs. ► A pore-network model is developed to study saturation in treated and untreated GDLs. ► Three different flow characteristics are identified for treated and untreated GDLs. ► Water rapidly invades the exposed areas and develops new passages in untreated GDLs. ► Water prefers to flow through a limited number of initial passages in treated GDLs.