Topotactic transformation and molten salt electrodeposition: Upcycling spent catalysts into platinum nanospheres

Spent catalysts are vital platinum resources yet hazardous wastes, threatening irreversible environmental harm if mishandled. This study introduces a strategy for upcycling platinum from spent catalysts into nanospheres. Demonstrated using a simulated system and validated with a real spent catalyst, the designed Pt→Li 2 Pt→Li 2 PtO 3 pathway enables the topotactic conversion of Li 2 Pt to Li 2 PtO 3 via oxygen intercalation, thereby reconstructing the electronic structure of platinum. Zintl-phase Li 2 Pt intermediate enhanced the oxidation kinetics. Li 2 PtO 3 stabilized platinum in the +4 state and facilitated its dissolution in the molten salt. Preferential Li + dissolution triggered lattice destabilization and the release of Pt 4+ . Pt 4+ coordination evolved from O 2− to Cl − -dominated soluble complexes through mixed-coordination intermediates like [PtOCl y ] (y− 2 )− . Electrochemical analysis confirmed a two-step reduction mechanism, which suppressed explosive nucleation and dendritic growth. Electrodeposition at 1.0 V produced uniform platinum nanospheres. This study develops a clean and efficient upcycling strategy for spent catalysts, which provides a viable solution for the sustainable utilization of strategic metal resources.