Unraveling Alkaline Oxygen Evolution Reaction: From Ionomer Binder Materials to Electrode Engineering

The ionomer binder plays a vital role in efficient and robust oxygen evolution reaction (OER) within the catalyst layer (CL). In addition to binding catalyst particles, the ionomer functions as a transport medium for ions and water while interacting with the catalyst, directly influencing the electrochemical activity. Although its effect on the electrical double layer is well-studied, the ionomer's impact on the reaction pathway is often overlooked. In addition, the physical and chemical stabilities of the ionomer in the CL significantly affect the long-term performance and durability of the electrochemical cell. Thus, optimizing the design of anion exchange ionomers has become increasingly important. In the rotating disk electrode system, Nafion binder demonstrates the highest initial activity due to its excellent interfacial compatibility with Ir black catalysts during the alkaline OER process. However, when scaling up to a gas diffusion electrode system to investigate long-term durability, Nafion exhibits rapid degradation, posing a major limitation for its use in alkaline water electrolyzers. This work highlights the importance of using a highly conductive and durable binder to maximize the catalyst performance for an effective OER. We systematically compare the performance of electrodes using three different ionomers, Nafion, PTFE, and AS-4, while also evaluating the impact of various catalyst and ionomer loading modes on the reaction efficiency. The findings of this study offer valuable insights into the role of ionomers, highlighting their critical importance in the development of high-performance alkaline ionomers.