(Keynote) Understanding How Porous Transport Layer Properties and Electrode Structure Affect the OER Electrode in an Anion Exchange Membrane Electrolyzer

Water electrolysis to produce hydrogen is gaining significant attention due to a significant decrease in the cost of renewable energy sources such as solar, wind, and tidal etc. Among the existing water electrolysis technologies, anion exchange membrane water electrolysis has recently emerged due to its potential advantages over proton exchange membrane electrolysis and traditional alkaline electrolysis. Anion exchange membrane electrolyzers (AEMELs) can allow for the use of PGM-free electrocatalysts and low-cost component materials due to its less corrosive alkaline environment while also enabling electrochemical H₂ compression.

In an operating AEMEL, the anode electrode – where the oxygen evolution reaction (OER) occurs – controls a majority of the cell's behavior. Recent work has shown that the most statistically relevant variables controlling the cell behavior are the catalyst choice, electrode structure and the properties of the porous transport layer (PTL). While the catalyst has been widely studied in the literature, significantly less attention has been paid to the catalyst layer design and the role of the PTL in dictating performance. The PTL is one of the most important components in AEM electrolyzer as it facilitates (i) water transport from the pores of the PTL through catalyst layer to the membrane towards hydrogen evolution reaction (HER) electrode, (ii) electron transport from the grains of the PTL through the catalyst material to the reaction sites in the catalyst layer, (iii) hydroxide transport from membrane to the reaction sites in the catalyst layer, and (iv) oxygen bubble removal from the reaction sites in the catalyst layer to the pores of the PTL.

In this study, various PTLs with different properties (e.g. material, fabrication methods, features size and thickness) were used to support the catalyst layer in operating AEMELs. It was found that higher porosity facilitates multiphase (O₂, H₂O, OH^-) transport, however, catalyst layer adhesion deceases, resulting in higher contact resistance increasing cell overpotentials. It was also found that nickel based PTLs perform relatively better than stainless steel. Moreover, fiber felts offer slightly lower overpotentials compared to sintered structures likely offering enhanced surface area for catalyst deposition and access to the active sites. Furthermore, an increase in thickness did not affect transient voltage response, though it had a negative effect on durability – likely due to low permeability, O₂ blocking the pathways while increasing overall cell resistance. The experimental findings presented here would provide important insights for development of PTL materials and structures for efficient and low-cost water electrolysis.