Ultrafine\nParticle RecyclingEfficiency of\nthe Hydrophobic Double Emulsion Technique for the Selective Agglomeration\nand Froth Flotation of Ultrafine Cathode Catalyst Particles from PEM\nWater Electrolyzers

On account of the use of platinum group metals (PGMs)\nas active\nmaterials in proton exchange membrane water electrolyzer (PEMEL) cells,\ndevelopment of recycling processes for fine catalyst materials is\nindispensable for further scale-up of hydrogen production. By applying\na contrast in (de)wetting ability of the materials, ultrafine particles\nhave the potential to be separated for recycling. The limitation of\nparticle size in froth flotation technology can be overcome by adding\noil droplets to the system. This study investigates the selective\nseparation of ultrafine particles by applying hydrophobic high internal\nphase (HIP) water-in-oil emulsion containing only 5% of organic liquid\nemulsified as a double emulsion in the particle dispersion. Hydrophobic\ncathode particles (i.e., carbon black) are selectively agglomerated\nin this system, allowing 90% of the feed to be recovered in the froth\nphase. The recovery rate was also significantly higher than that using\nthe same amount of pure oil promoter, kerosene. In the binary particle\nsystem, 70% of the target particles are recovered with 90% grade by\nadding 2.8% hydrophobic double emulsion.