Higher homologs of trialkyl phosphates have been proposed for the separation of U(VI) from fast reactor dissolver solution by liquid - liquid extraction. The electrochemical behaviour of U(VI) in tri-n-octyl phosphate (TOP) in the ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C(4)mimNTf(2)) was studied by cyclic voltammetry. The results were compared with those obtained with reference extractant, trin-butyl phosphate in C(4)mimNTf(2). The cyclic voltammogram of U(VI) in C(4)mimNTf(2) exhibited a prominent quasi-reversible reduction wave at 024 V(Vs. Fc/Fc(+)) was due to the reduction of U(VI) to U(V) and a couple of oxidation waves at +0.5 V(Vs. Fc/Fc(+)). The cathodic peak current was lowered and peak potential shifted cathodically in the presence of TBP and TOP due to the formation of co-ordinate complex of these ligands of with U(VI). The diffusion coefficient (D, cm(2)/s) of U(VI) and the heterogeneous charge transfer rate constant (k(s), cm/s) were determined for various systems and they increased with increase of temperature and decreased in the presence of ligands. Both these quantities decreased in the order U(VI) in C(4)mimNTf(2) > U(VI) - TBP in C(4)mimNTf(2) > U(VI) - TOP in C(4)mimNTf(2). The stability constant and the stoichiometry of U(VI) -TBP and U(VI) - TOP in ionic liquid medium was determined by cyclic voltammetry. (C) 2016 Elsevier B.V. All rights reserved.