Electrochemical studies on uranyl(VI) chloride complexes in ionic liquid, 1-butyl-3-methylimidazolium chloride

UV-visible absorption spectra of solutions prepared by dissolving Cs2UO2Cl4 or UO2Cl2·nH2O into 1-butyl-3-methylimidazolium chloride (BMICl) have been measured. As a result, it was clarified that uranyl species in BMICl exist as [UO2Cl4]2-. Cyclic voltammograms of [UO2Cl4]2- in BMICl were measured at 80±1degC using a glassy-carbon working electrode, a platinum wire counterelectrode, and a Ag/AgCl reference electrode with a liquid junction filled with BMIBF4 in a glove box under Ar atmosphere. Peaks corresponding to one redox couple were observed around -0.73 (Epc) and -0.65 V (Epa). The potential differences between two peaks (δEp) at scan rates in the range from 10 to 50 mV s-1 are 70-80 mV, and are almost consistent with the theoretical ΔEp value (67 mV) for the reversible one-electron-transfer reaction at 80degC. Furthermore, the (Epc+Epa)/2 value is constant, -0.690 V, regardless of the scan rate. From these results, it is concluded that [UO2Cl4]2- in BMICl is reduced to [UO2Cl4]3- quasi-reversibly. (author)