Molecularly Selective Electrochemical Recovery with Redox Polymers for Platinum Group Metals

The platinum group metals (PGMs) are precious metals with scarcity and have widespread use in jewelry, automotive converter, catalysts, pharmaceutical drugs, and fuel cells. 1 Because PGMs are keys for the energy transition towards renewables, creating a circular economy for PGMs can greatly contribute to the enduring sustainability of the energy industry. Electrosorption with redox materials has great application in low concentration desalination and ions recovery because of its low waste generation and nearly no chemical input during the operation. 2, 3 Furthermore, it has been proved that ferrocene-based redox polymer can recycle platinum-based catalysts with 99.5% recovery. 2 Nevertheless, the competitive electrosorption behavior between PGMs complexes with redox polymers is still unknown, which is critical to unlock more efficient pathways to purify PGMs particularly in the mining sector that separation of PGMs requires high energy and chemical input because of their similar physical and chemical properties. Here, we demonstrated for the first time an electrochemically reversible selective PGMs recovery system. Furthermore, because functional groups of redox polymers can affect the selectivity and the uptake of metal ions, 3 redox polymers with different functional groups and redox potential were designed, synthesized, and applied for selective electrosorption of PGMs ions. Results showed that our redox polymer has regeneration efficiency of 92% for iridium and 83% for ruthenium. Separation tests showed that the separation factor of platinum over rhodium in the Pt/Rh binary mixture can be up to 40 at open circuit potential and enhanced to higher than 100 by applying potential. For the real-world application, the electrosorption platform was applied for recycling catalytic converter and showed 38% recovery of iridium. Overall, our approach expands the scope of selective electrochemical recovery of PGMs, providing a platform with high energy-efficiency for the multicomponent recovery of PGMs from waste feedstocks. References Yakoumis, I.; Panou, M.; Moschovi, A. M.; Panias, D., Recovery of platinum group metals from spent automotive catalysts: A review. Cleaner Engineering and Technology 2021, 3 , 100112. Cotty, S.; Jeon, J.; Elbert, J.; Jeyaraj, V. S.; Mironenko, A. V.; Su, X., Electrochemical recycling of homogeneous catalysts. Sci. Adv. 2022, 8 (42), 12. Chen, R. L.; Feng, J. Y.; Jeon, J.; Sheehan, T.; Ruttiger, C.; Gallei, M.; Shukla, D.; Su, X., St