Electroreduction Mechanism of UO₂Cl₂ and Nucleation and Morphology of Uranium Dioxide at Different Conditions

To investigate the electroreduction mechanism of UO₂Cl₂ and the nucleation mode and morphology of uranium dioxide, the electrochemical behavior of UO₂²⁺ on the tungsten (W) electrode was studied in LiCl-KCl molten salt by cyclic voltammetry. The results demonstrated that UO₂²⁺ underwent two sequential single-electron transfers to form UO₂. Prior to its reduction to UO₂⁺, UO₂²⁺ was initially converted into a low-coordination complex ion. Besides the reduction peak of bulk UO₂, a peak associated with the strong adsorption of UO₂ on the electrode surface was also observed. The nucleation mode of UO₂ was examined by chronoamperometry, revealing that the nucleation mechanism was related to UO₂Cl₂ concentration. The influence of current densities on nucleation morphology was studied using an atomic force microscope and found the nuclei was smaller and denser at higher current density. The deposits obtained by galvanostatic electrolysis at different current densities were examined by scanning electron microscopy-energy-dispersive X-ray spectroscopy and X-ray diffraction, showing that a regular octahedral UO₂ was formed at low current density, while a dendritic UO₂ was formed at high current density. A two-step electrolysis with an initial high current density followed by a low current density was conducted, and a dense UO₂ with a lychee-like morphology was produced.