Electrochemical Studies of Cu(I) and Cu(II) in an Aluminum Chloride‐N‐(n‐Butyl)Pyridinium Chloride Ionic Liquid

Abstract

A study of the Cu‐Cu(I)‐Cu(II) redox systems has been carried out in a butylpyridinium chloride‐aluminum chloride ionic liquid. Rotating disk (glassy carbon) and ring disk electrochemical studies were performed, as well as coulometric and potentiometric experiments. Cu(II) is reduced to both Cu(I) and Cu(0) in acidic (excess AlCl3 ) melts and the process is quasi‐reversible. Both Cu(I) and Cu(II) appear to adsorb at the glassy carbon electrodes in acidic melts. The reduction of Cu(II) appears reversible as determined by rotating disk voltammetry. In basic melts (excess butylpyridinium chloride), kinetic parameters for the slow electron transfer reduction of Cu(II) and oxidation of Cu(I) were evaluated. Both Cu(I) and Cu(II) appear to adhere to the Stokes‐Einstein equation in both acidic and basic melts, although the constancy of the viscosity‐diffusion coefficient product differs for each and changes as the melt is made either acidic or basic. Potentiometric measurements are interpreted as showing the presence of CuCl4−3 and CuCl6−4 in basic melts and perhaps false(normalCufalse(AlCl4)3−2 and normalCufalse(AlCl4)4−2 in acidic melts. Standard potentials for the various redox couples in acidic and basic melts were determined.

Electrodeposition of Metals in Ionic Liquids

“…In the case of a basic BPCl-AlCl 3 ionic liquid, NiCl 2 dissolves and forms a divalent nickel chlorocomplex anion, NiCl 2À 4 , which cannot be reduced to metallic Ni [46]. The electrodeposition of copper, Cu, has been studied in MPCl- [49], BPCl- [50], EMICl- [22,37,38,[51][52][53][54], and BMICl-AlCl 3 [55] ionic liquids. In the case of acidic ionic liquids, it is possible to introduce monovalent and divalent copper species, Cu(I) and Cu(II), by dissolving copper chloride and dichloride, respectively, and by the anodic dissolution of metallic copper.…”

“…The formal potentials of Cu(I)/Cu in an acidic MPCl-, BPCl-, EMICl-AlCl 3 are reported as 0.777 [49], 0.784 [50], and 0.837 [52] V, respectively. Cu(I) can be also obtained by the reduction of Cu(II), of which the formal potentials in the acidic MPCl-and BPCl-AlCl 3 are reported as 1.851 [49] and 1.825 [50] V, respectively. The nucleation and growth process of Cu are investigated on a single crystal Au electrode [55].…”

“…However, it is reported that the displacement of Al with Cu occurs when the Al-Cu alloy is immersed in the ionic liquid containing Cu(I) [54]. In the case of basic ionic liquids, it is possible to introduce the monovalent copper chlorocomplex anions, CuCl 2 and CuCl [50]. The formal potentials of Cu(I)/ Cu and Cu(II)/Cu(I) in the BPCl-AlCl 3 ionic liquid are reported as À0.647 and 0.046 V, respectively [50].…”

“…In the case of basic ionic liquids, it is possible to introduce the monovalent copper chlorocomplex anions, CuCl 2 and CuCl [50]. The formal potentials of Cu(I)/ Cu and Cu(II)/Cu(I) in the BPCl-AlCl 3 ionic liquid are reported as À0.647 and 0.046 V, respectively [50]. The electrodeposition of copper is also possible in a basic EMICl-AlCl ionic liquid [53].…”

How a Transition‐Metal(II) Chloride Interacts with a Eutectic AlCl3‐Based Ionic Liquid: Insights into the Speciation of the Electrolyte and Electrodeposition of Magnetic Materials

“…[5,6] Furthermore, organic chloroaluminates are excellent solvents for dissolving many metal halide salts and to electrodeposit them (e.g.,C u, Ni, Pd, andF e). [7][8][9][10][11][12] An issue associatedw ith anionic specieso fm etal ions for electro-deposition is that during the reduction reactiont he anionic speciesm ove against the electric field. [13] Cationicc omplexes of Al that contain neutral ligands are thus of fundamentali nterest for electrodeposition, butt hey have been rarely reported.…”