The heterogeneous rate constant k(0) of the ferrocene/ferrocenium (Fc/Fc(+)) redox couple and the diffusivities (D-Fc and D-Fc(+)) of the two species were measured in a toluene/trihexyl(tetradecyl) phosphonium tris(pentafluoroethyl) trifluorophosphate solution. This ionic liquid allowed to increase sufficiently the solution conductivity so that those measurements could be performed using a rotating disk electrode. For a 0.1 mol L-1 ionic liquid concentration, the results obtained from regression on electrochemical impedance data provided: k(0) = (4.82 +/- 0.38) 10(-5) m s(-1), D-Fc = (1.43 +/- 0.33) x 10(-9) m(2) s(-1); D-Fc(+) = (0.98 +/- 0.23) x 10(-9) m(2) s(-1). The capacitance values close to the rest potential were in the range of 1 mu F cm(-2) in agreement with a nonspecific adsorption of the solvent and with the large size of phosphonium cations. (C) 2013 Elsevier B.V. All rights reserved.