The preparation of chemically modified electrode surfaces that feature well-defined molecular species mitigates many challenges associated with characterization of surface composition and enables study of solid-liquid interfaces with some of the advantages of homogeneous chemistry. In this presentation, we will describe the surface immobilization and characterization of uranyl (UO<sub>2</sub><sup>2+</sup>) complexes on carbon electrodes. Enabled by a custom-tailored ligand framework, electrochemical studies show that uranyl can be cycled through multiple oxidation states on our electrodes and that the intact complex remains persistently bound to the electrode surface under a variety of conditions. Electrodes can also be functionalized with a metal-free ligand, enabling uranyl capture from solution and comparative work on interfacial actinide partitioning. X-ray photoelectron (XP) spectroscopy has been used to aid in the identification of surface-bound species and confirm the robustness of our surface modification strategy. Insights from the XP spectra of our uranyl complexes also aid understanding of molecular uranium spectroscopy, including updated relative sensitivity factors and quantification of chemical-shift effects for the molecular uranyl species. Our latest work will be discussed, including studies aimed at tracking differences between interfacial electrochemical processes and those allowed to occur in solution further from the electrode surface.

Immobilization of molecular uranium complexes on carbon electrodes

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