Gas diffusion layers and their optimal usage in PEM water electrolysis

Carbon-based gas diffusion layers (GDLs) employed at the cathode can reduce costs in PEM water electrolysis stacks compared to titanium-based materials [1]. For PEM fuel cells, carbon-based GDLs have been widely investigated regarding their compression behavior, hydrophobic additives, and micro porous layers (MPLs) [2-4]. Contrary to this, studies on their application in PEM water electrolysis are lacking [5]. In this study, we present a comprehensive investigation to better understand the use of carbon-based GDLs focusing on compression behavior and the role of MPLs in improving the interface towards cathode catalyst layer. To achieve this, cell compression was varied between 0 % and 80 % with post-mortem analysis conducted using confocal laser scanning microscopy (CLSM). Electrochemical characterization was carried out for each compression level. Figure 1 a) shows the cell’s overpotentials at 3 Acm^(-2), revealing an increase in ohmic resistance for cases at under and over compression levels, along with higher kinetic overpotentials at 80 % compression. The effect of an MPL with low cathode catalyst loading (<0.06 mg_Ptcm^(-2)) is presented through polarization curve measurements, see Figure 1 b). A substantial performance increase can be seen when the MPL is used, which can be attributed to improved contact and enhanced catalyst utilization. Through further voltage breakdown analysis and electrochemical impedance spectroscopy (EIS), followed by Distribution of Relaxation Time (DRT) analysis, we provide fundamental understanding on the use of carbon-based GDL materials.