Furthermore, the transferred charges of the oxidation and the reduction peaks were similar (Figure ), suggesting no significant disproportionation of the U(V) upon its formation on the Ti electrode. emerged, which could be assigned to uraninite structures. This finding suggests that the PEC extracted U present in the form of uraninite. Although uraninite is nominally UO2 with a fluorite-type (CaF2) structure, its actual stoichiometry can vary significantly (UO2+x, 0≤x≤0.61) due to the variance of the oxidation state of U . XPS high-resolution U4f scan was then performed to further confirm the oxidation state of the extracted U. The spectrum shows two major peaks separated from each other by 10.8 eV (Figure ). These two peaks could be assigned to the U4f7/2 and U4f5/2, respectively, and the separation of these two peaks was due to the spin-orbit split . Additionally, two small peaks at 399.7 eV and 388.8 eV were also observed (Figure ), which could be assigned to the satellite peaks of U(V) . Furthermore, the U4f5/2 and U4f7/2 peaks were fit , and the results show two strong peaks at 391.8 eV and 381.0 eV, both separated from their corresponding satellite peak by 7.8 eV. Based on these data, the two U4f peaks could both be assigned to U(V) . The absence of spectral patterns of either U(VI) or U(IV) shows that the PEC extracted U was pentavalent, consistent with the CV characterization. A few studies have shown that U(V) could be stabilized by coordination with iron oxides, carbonate or organic ligands . However, iron oxides and carbonate were not detected by the XRD analysis, and Fe and organic ligands were absent in the synthetic Ucontaining water. In comparison, the PC extracted U was a mixture of U(IV) and U(VI) (Figure ). Hence, one hypothetical explanation could be the stabilization of U(V) in UO2.5 uraninite structure on the surface of the Ti electrode, which needs further investigations.