Fig. 3: Schematic illustration of the uranium electrodeposition.

a Cyclic voltammograms of simulated seawater using PEDOT@sp²c-COF-AO coated glassy carbon electrode as a working electrode (black) and uranium spiked simulated seawater (400 ppm) using sp²c-COF-AO (olive) and PEDOT@sp²c-COF-AO (orange) coated glassy carbon as working electrodes, respectively. b Schematic illustration of uranium extraction processes in this work. In step I, under the current condition, UO₂²⁺ or H⁺ gets reduced into UO₂ or H₂ on the cathode; meanwhile, negative Cl⁻ or OH⁻ is oxidized to Cl₂ or O₂ on the anode side. In step II, under the electroless condition, spontaneous redox reactions occurred, whereby the generated Cl₂ or O₂ was reduced at the graphite rod to compensate for the oxidation of the UO₂ into UO₃, forming a galvanic cell (yellow, U⁴⁺; organ, U⁶⁺; red, O; olive, Cl; white, H).