Electrochemical behaviour of some copper(II) salts in 20 wt.% propylene carbonate + ethylene carbonate: Standard potential of the Cu~(2+)/Cu system at 25 ℃

摘要

The behaviour of Cu(ClO_4)_2, CuCl_2 and CuBr_2 in 20 wt.% propylene carbonate (PC) + ethylene carbonate (EC) has been studied to conductivity, potentiometry and voltammetry. The conductance behavior of copper(II) halides in 20 wt.% PC + EC is explained on the basis of the equilibrium 3CUX_2<=>Cu~(2+) + 2CuX_3 and 2CuX_2<=>(CuX_2)_2. A copper indicator electrode in conjunction with a Hg/HgCl_2(s) in 20 wt.% PC + EC reference electrode was used for the potential measurements. The results of the potentiometric measurements, combined with those of the conductance measurements, provided the standard potential, E°, of the reaction Cu~(2+) + 2e~-<=>Cu(s) versus SHE in 20 wt.% PC + EC at 25 ℃, which is found to be 0.400 ± 0.002 V. Sampled dc and cyclic voltammetric measurements were also undertaken with these Cu(II) salts in 20 wt.% PC + EC using Pt working and counter electrodes and Hg/HgCl_2(s) in 20 wt.% PC + EC as athe reference electrode. These voltammetric measurements yielded the standard potential value (0.394 ± 0.003 V vs. SHE) of the system, which is in agreement with the value obtained by the potentiometric method.