Ultrafine Particle Recycling─Efficiency of the Hydrophobic Double Emulsion Technique for the Selective Agglomeration and Froth Flotation of Ultrafine Cathode Catalyst Particles from PEM Water Electrolyzers

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