Application of novel hydrophobic binders for the selective agglomeration of fine particles for the recycling of PEM water electrolyzers

With the tremendous increase of hydrogen production via water electrolysis technology, the development of a recycling process for valuable raw materials is emerging as an important issue for a functional circular economy. Especially, platinum group metals such as Iridium oxide and platinum particles on carbon black are used as active materials in the polymer electrolyte membrane (PEM) water electrolyzer. Since the size range of those particles is well below 100 µm, the development of mechanical separation technologies has not been well established. Conventional mechanical separation processes, such as flotation, are not effective for particles in the submicron scale.
According to previous investigations, each material on both electrodes shows a contrast in surface properties in terms of (de)wett(ing)ability. Cathode materials such as carbon black exhibit a hydrophobic character, while anode materials like Iridium oxide show a rather good affinity for water. For this study, pure particle fractions of carbon black and titanium oxide are used as representative materials.
Oil agglomeration is one of the widespread technologies to recover hydrophobic particles. As reported by Kim Van Netten in 2017, the separation of fine coal particles from a suspension was achieved by using a new type of hydrophobic binder comprising only 5 % of organic liquid. In this study, this novel organic emulsion system is applied to separate ultra-fine carbon black particles selectively and to assess the functionality of the emulsion to develop a process for PEM recycling. Those water-in-oil-in-water emulsion droplets enable to reach the agglomeration of carbon black particles in a few seconds which is a promising pre-treatment result for subsequent enrichment.