Interfacial selective separation of fine particles for the recycling of PEM electrolyzer exploiting particle-fluid interactions in multiphase systems

For large-scale of green hydrogen production via water electrolysis, catalysts containing critical materials in a submicron down to nanometer scale have advantages as active materials in the application. The circularity of critical raw materials such as PGM after the utilization phase becomes and thus recycling processes for end-of-life water electrolyzers need to be developed.
In the range of ultra-fine particle systems (0.1 to 10 µm), established techniques like flotation have challenges for their efficient separation. Liquid-liquid phase transfer is one possible alternative approach for the selective separation of such fine particles. In this phase transfer process, the interactions between particles and oil droplets are greater than those between particles and air bubbles in classic flotation. Hence, particles can be enriched much more efficiently at the oil-water interfaces.
In this study, titanium oxide TiO2 and carbon black are separated representing anode and cathode material in polymer electrolyte membrane (PEM) water electrolyzer respectively. Wettability characterization studies revealed their significant contrast in hydrophobicity. TiO2 exhibits a rather hydrophilic surface while carbon black shows hydrophobic characteristic, however there are still many unknown properties of the surface characteristics of various carbon black variants.
By using the analytic particle solvent extraction (APSE) method, particle mixtures can be transferred into organic and aqueous phases respectively, and selectively separated with high recovery. This approach provides a contribution to scale-up the recycling processes of PEM water electrolyzers.