Electrochemical behavior of Pd(II) and Rh(III) in [EMIm]NTf 2 ionic liquid

The electrochemical behavior of Pd(II) and Rh(III) in [EMIm]NTf2 ionic liquid has been studied on Pt working electrodes at 298 K by cyclic voltammetry (CV), polarization curve and galvanostatic transient techniques. Cyclic voltammogram of Pd(II) in [EMIm]NTf2 consists of two cathodic current peaks located at 1.37 V(Epc2), corresponding to Pd2+/Pd+, and at 0.69 V (Epc1) corresponding to Pd+/Pd. The transfer coefficient α was calculated by the Tafel extrapolation from the polarization curves to be 0.306, which is in agreement with the value reported in an aqueous solution system. For Rh(III) in [EMIm]NTf2, a cathodic current peak (Epc) was observed at -0.39 V, corresponding to Rh3+/Rh, and two oxidation peaks were observed at -0.13 V (Epa1) and 0.37 V (Epa2) during the reverse scan. A significantly negative shift in the cathodic peak potential was observed with the increase of the scan rate, indicating that the reduction of Pd(II) and Rh(III) on the Pt electrode involves kinetic complications. By using the galvanostatic transient technique, the diffusion coefficients of Pd(II) and Rh(III) in [EMIm]NTf2 ionic liquid solution were found to be ∼10-7 cm2/s. The potential difference between the reduction of Pd(II) to Pd and the reduction of Rh(III) to Rh obtained from the CV curves of the Pd(II) and Rh(III) co-existing [EMIm]NTf2 solution is found to be about 0.74 V, which makes it possible to electrodeposit Pd(II) and Rh(III) separately.