Nafion vs. Fumion: Impact of Ionomers on the Alkaline Oxygen Evolution Reaction

Abstract

As demand for renewable energy sources grows, it is increasingly important to develop cost-effective, stable, and efficient alternatives to fossil fuels. Alkaline water electrolysis provides an especially promising solution to this challenge. Alkaline water electrolyzers, while promising, continue to pose a number of barriers to their widespread commercial implementation. Powder-based electrocatalysts, for example, rely partially on ionomers, or charged binder materials, for their stability and ionic conductivity. Notably, the charge of the ionomer should be considered in the context of the oxygen evolution reaction, whose reactant is negatively charged hydroxide. Despite this, a negatively charged, proton-conducting ionomer, Nafion, is used as a binding agent in most alkaline electrolyzers. This discrepancy motivates a systematic evaluation of anion-conducting ionomers as electrode binders in alkaline oxygen evolution electrocatalysis to improve hydroxide transport and enable more reliable catalyst screening. Here, we compare the activity and stability of an Ir/C electrocatalyst prepared with Nafion, Fumion, and a 1:1 Nafion:Fumion mixed binder to clarify the role of ionomer charge. While Fumion-containing electrodes exhibit high apparent current densities during cyclic voltammetry and chronopotentiometry, a substantial portion of this response arises from ionomer degradation rather than sustained catalytic activity. In contrast, mixed-ionomer electrodes achieve high current densities while maintaining stability comparable to Nafion-bound electrodes. These findings highlight the critical influence of anion-exchange ionomers on both measured activity and stability and underscore the need to reevaluate electrocatalysts previously benchmarked using Nafion-based electrodes.