Ionomer-Dependent Oxygen Evolution Reaction in a Half-Cell and a Liquid Electrolyzer

Abstract

Electrocatalytic oxygen evolution reaction (OER) is an important area of research due to its significance in water electrolysis, which contributes to the clean-energy storage and conversion techniques. OER exhibits irreversible and sluggish kinetics, which necessitates a high overpotential to achieve the desired reaction rate. In an alkaline medium, non-precious metals (such as Ni, Fe, Co) or metal-free materials (such as 3d-transition metal oxides and heteroatom-doped carbons) can replace expensive iridium and ruthenium oxides, which is otherwise required in an acidic medium to facilitate the reaction. However, developing new catalysts for alkaline OER is limited by the scaling relations among adsorption energetics of key intermediates (i.e., OOH*, OH*, and O*).The electrochemical reaction kinetics depends critically on the nature of the interface between catalyst and the electrolyte where an electrical double layer (EDL) forms during OER. The current understanding of the EDL structure involves the interfacial interactions between adsorbates and catalyst layer (CL) which can be modified to improve the reaction efficiency. Ionomers are essential components of the CL and are vital in uniformly dispersing catalyst particles in ink solution. The ionomers also act as binder for the catalyst particles in the CL, helping to improve the electrode’s durability and stability over time. In addition, despite the fact that ionomers affect the properties of EDL, the impact of ionomer on the reaction pathway is often overlooked in electrocatalytic research.In this study, we investigate the role of ionomer in the catalyst layer by comparing different polymer dispersions, including PTFE, Nafion, and commercial As-4. The results indicate that the Nafion-contained CL performs better than other polymer CLs in TF-RDE/RRDE, as it facilitates direct O*-O* coupling. In contrast, anionic ionomer demonstrates superior long-term stability in alkaline liquid electrolyzers, despite oxidization degradation.