How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis

Cost reduction andfast scale-up of electrolyzer technologies areessential for decarbonizing several crucial branches of industry.For polymer electrolyte water electrolysis, this requires a dramaticreduction of the expensive and scarce iridium-based catalyst, makingits efficient utilization a key factor. The interfacial propertiesbetween the porous transport layer (PTL) and the catalyst layer (CL)are crucial for optimal catalyst utilization. Therefore, it is essentialto understand the relationship between this interface and electrochemicalperformance. In this study, we fabricated a matrix of two-dimensionalinterface layers with a well-known model structure, integrating themas an additional layer between the PTL and the CL. By characterizingthe performance and conducting an in-depth analysis of the overpotentials,we were able to estimate the catalyst utilization at different currentdensities, correlating them to the geometric properties of the modelPTLs. We found that large areas of the CL become inactive at increasingcurrent density either due to dry-out, oxygen saturation (under thePTL), or the high resistance of the CL away from the pore edges. Weexperimentally estimated the water penetration in the CL under thePTL to be & AP;20 & mu;m. Experimental results were corroboratedusing a 3D-multiphysics model to calculate the current distributionin the CL and estimate the impact of membrane dry-out. Finally, weobserved a strong pressure dependency on performance and high-frequencyresistance, which indicates that with the employed model PTLs, a significantgas phase accumulates in the CL under the lands, hindering the distributionof liquid water. The findings of this work can be extrapolated toimprove and engineer PTLs with advanced interface properties, helpingto reach the required target goals in cost and iridium loadings.