Understanding the use of carbon-based porous transport layers at the cathode in PEM water electrolysis

Cost reduction of cell components is a major issue in PEM water electrolysis. For the anode, titanium materials with noble metal coatings represent the state of the art. For the cathode, the use of carbon-based porous transport layers, also known as gas diffusion layers (GDLs), is gaining prominence due to their significantly lower costs compared to titanium-based materials. In PEM fuel cells, carbon-based GDLs are well-established, with advancements in contact and gas/water transport achieved through micro porous layers and hydrophobic treatments. In contrast, in PEM water electrolysis, topics like interfacial contact, compression behavior, and the use of additives for carbon-based GDLs have not been widely discussed in the literature yet. With this work, we present a fundamental performance investigation of these aspects. We investigate cell performance using voltage breakdown analysis and electrochemical impedance spectroscopy, combined with subsequent Distribution of Relaxation Time analysis. Our findings highlight the effect of GDL compression and underscore the necessity of coated flow fields at the cathode. PTFE additives were found to have minimal influence on cell behavior, regardless of the presence or absence of water flow at the cathode. However, the use of micro porous layers demonstrated positive effects, particularly for ultra-low cathode catalyst loadings.