Electrochemical behaviour of copper species in the 1-buthyl-3-methyl-imidazolium chloride (BMIMCl) ionic liquid on a Pt electrode

Abstract

The electrochemical behavior of Cu(I) and Cu(II) species in the ionic liquid 1-buthyl-3-methylimidazolium chloride, BMIMCl, on a platinum electrode in the interval of 333–363 K, has been investigated. Experiments per-formed in a controlled N2 atmosphere cell show that: (i) Cu(I) can be oxidized to Cu(II) and reduced to Cu(0), and (ii) Cu(II) can be reduced to Cu(I) by copper metal according to a comproportionation reaction whose constant has been calculated. The diffusion coefficients of Cu(I) and Cu(II) have been obtained by different electrochemical techniques. The dimensionless Schmidt numbers (Sc = ν/D) were also calculated to characterize the solute global mass transport through its environment. The kinetic parameters for the quasi-reversible electrochemical exchange Cu(II)/Cu(I) (i.e. the intrinsic rate constant of charge transfer, k0, and the charge transfer coefficient, α), as well as the reversible half wave potential, Er1/2, have been obtained for the first time in the mentioned ionic liquid, by simulation of the cyclic voltammograms and logarithmic analysis of the convoluted curves. The apparent standard potential of the electrochemical system Cu(I)/Cu(0) has been determined by potentiometry. Founding that nucleation and crystal growth plays an important role in the electrodeposition of metallic Cu onto the Pt surface. Experimental current–time transients followed the theoretical models based on instantaneous nucleation with three-dimensional growth of the nuclei at the studied temperatures. Electro-deposits of copper were obtained by potentiostatic electrolysis and analyzed by scanning electron microscopy with EDAX.