Wettability based separation of ionomer-containing ultrafine particles for PEM water electrolyzer recycling

Abstract

As green hydrogen production via proton exchange membrane water electrolyzers (PEMELs) continues to scale up, the development of effective recycling processes for end-of-life components is becoming increasingly important. In PEMELs, ultrafine catalyst particles exhibit significant differences in hydrophobicity, which serve as a basis for selective separation. In this study, two separation techniques based on hydrophobicity differences (liquid–liquid particle separation and emulsion-based froth flotation) were proposed for particle recovery. Since catalyst inks contain amphiphilic ionomers as binders in addition to the particles, their influence on wettability-based separation was investigated. To clarify this effect, we investigated the physicochemical characteristics of ionomer-coated particles. Key parameters such as particle size, surface area (BET), and zeta potential were measured, and their impact on wettability was assessed. The results show that ionomer adsorption leads to a notable reduction in the hydrophobicity contrast, thereby hindering their selective separation. To address this issue, a dispersant was introduced to both separation processes. This addition improved the recovery performance, under conditions where the hydrophobicity difference was reduced (LLPS: recovery increased from 10 % to 70 %, froth flotation: approx. 15 % improvement). Although the addition of dispersants improved the recovery performance, the separation efficiency remained lower than that observed under ionomer-free conditions (over 95 % of recoveries in both processes). The findings highlight the complex interactions between particles, ionomers, and reagents in dispersion systems. Further investigation into these interactions is necessary to develop more robust and scalable recycling strategies. A deeper understanding of the physicochemical mechanisms will provide valuable insight into the design of selective separation processes for catalyst recovery in PEMEL systems.