Functionalized Iron–Nitrogen–Carbon Electrocatalyst Provides a Reversible Electron Transfer Platform for Efficient Uranium Extraction from Seawater

Uranium extraction from seawater provides an opportunity for sustainable fuel supply to nuclear power plants. Herein, an adsorption-electrocatalysis strategy is demonstrated for efficient uranium extraction from seawater using a functionalized iron-nitrogen-carbon (Fe-Nx -C-R) catalyst, comprising N-doped carbon capsules supporting FeNx single-atom sites and surface chelating amidoxime groups (R). The amidoxime groups bring hydrophilicity to the adsorbent and offer surface-specific binding sites for UO22+ capture. The site-isolated FeNx centres reduce adsorbed UO22+ to UO2+ . Subsequently, through electrochemical reduction of the FeNx sites, unstable U(V) ions are reoxidized to U(VI) in the presence of Na+ resulting in the generation of solid Na2 O(UO3 ·H2 O)x , which can easily be collected. Fe-Nx -C-R reduced the uranium concentration in seawater from ≈3.5 ppb to below 0.5 ppb with a calculated capacity of ≈1.2 mg g-1 within 24 h. To the best of the knowledge, the developed system is the first to use the adsorption of uranyl ions and electrodeposition of solid Na2 O(UO3 .H2 O)x for the extraction of uranium from seawater. The important discoveries guide technology development for the efficient extraction of uranium from seawater.