Improving water management in fuel cells through microporous layer modifications: Fast operando tomographic imaging of liquid water

Polymer electrolyte fuel cells (PEFCs) have been actively developed for a wide range of power generation applications. At the high power densities required for automotive applications, sophisticated water management is vital to further improve cell performance. In particular, the gas diffusion layer (GDL), which includes a micro porous layer (MPL), plays a crucial role in optimizing both water drainage and gas transport between the catalyst layer and gas channels. The present work studied the effect of cathode MPL porosity on the water distribution in the GDL. The results show that cells in which MPL materials have larger, micron-sized pores exhibit better performance. Advanced 4D operando X-ray imaging (3D structure plus time) was employed to analyse the water content in GDLs, and demonstrated that the superior performance of cells with large MPL pores is due to the efficient formation of water pathways. These pathways are based on water clusters allowing percolation in the through-plane direction from the bottom to the top of the GDL. Such pathways decrease the liquid water level in the entire cathode GDL. Especially, large MPL pores merge numerous small liquid water pathways in the catalyst layer and stabilize them morphologically, thus creating primary pathways for effective water drainage.