Electrochemical from aqueous solutions

Ouyang, J.Y., and Y.F. Li. 1997. Great improvement of polypyrrole films prepared electrochemically from aqueous solutions by adding nonaphenol polyethyleneoxy(10)ether. Polymer 38 3997. 

Electrowinning from Aqueous Solutions. Electrowinriing is the recovery of a metal by electrochemical reduction of one of its compounds dissolved in a suitable electrolyte. Various types of solutions can be used, but sulfuric acid and sulfate solutions are preferred because these are less corrosive than others and the reagents are fairly cheap. From an electrochemical viewpoint, the high mobiUty of the hydrogen ion leads to high conductivity and low ohmic losses, and the sulfate ion is electrochemicaHy inert under normal conditions. 

Interest in using ionic liquid (IL) media as alternatives to traditional organic solvents in synthesis [1 ], in liquid/liquid separations from aqueous solutions [5-9], and as liquid electrolytes for electrochemical processes, including electrosynthesis, primarily focus on the unique combination of properties exhibited by ILs that differentiate them from molecular solvents. 

MoUn AN, Dikusar Al (1995) Electrochemical deposition of PbSe thin films from aqueous solutions. Thin Solid Films 265 3-9... 

Froment M, Bernard MC, Cortes R, Makili B, Lincot D (1995) Study of CdS epitaxial films chemically deposited from aqueous solutions on InP single crystals. J Electrochem Soc 142 2642-2649... 

It has been pointed out that metals residing below the position held by manganese (and, therefore, much below hydrogen) in the electrochemical series (Table 6.11) cannot be electrodeposited from aqueous solutions of their salts. These metals are called base metals or reactive metals and can be electrodeposited only from nonaqueous electrolytes such as solutions in organic solvents and molten salts. As with an aqueous electrolyte, there is a minimum voltage which is required to bring about the electrolysis of a molten salt. 

Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

Reviewed here are surface electrochemical studies of organic molecules adsorbed at well-defined Pt(lll) electrode surfaces from aqueous solution. Emphasis is placed upon studies of nicotinic acid (NA), pyridine (PYR), and nine related pyridine carboxylic acids. 

Electrochemical deposition of metals and alloys involves the reduction of metal ions from aqueous, organic, and fused-salt electrolytes. In this book we treat deposition from aqueous solutions only. The reduction of metal ions in aqueous solution is... 

Electrodeposition of Pa metal has been performed from both aqueous and nonaqueous solutions. An isopropanol solution of 10-20 p,gmL Pa from 8M HCl/0.01 M HE/Pa stock was employed for quantitative electrodeposition [41]. The cell consisted of a gold-plated A1 cathode and a Pt wire anode. During deposition the current was maintained at 1 mA, which produced a potential of 400-600 V during the 90-min electrolysis. The progress of the electrolysis was externally monitored by alpha-counting of the electrolysis solution before and during the electrodeposition. Deposition studies of metal from aqueous solutions are more common. Pa was electrodeposited on platinum in 95% yield at tracer concentrations from an electrolyte of [NH4]C1/HC1 [42]. Electrochemical and chemical conditions of the plating process were described for Pu solutions, which served as a model for the other actinide elements studied. Another tracer... 

Example 7a is the idea behind the electrochemical series, a list of elements whose ions will displace the ions of another element from solution, as shown in Table 3. At comparable concentrations, ions of elements with larger negative reduction potentials (more easily oxidized) will displace those of elements with smaller negative reduction potentials from solution. In the short electrochemical series shown in Table 3, an element will displace the ions of any element lower in the list from aqueous solution. In some cases, however, the displacement reactions may be slow due to kinetic factors. 

An oxoaquaruthenium(IV) complex of a macrocyclic mixed N,0-donor ligand, [RuIV(N202)(0)(H20)]2+ (N202 = l,12-dimethyl-3,4 9,10-dibenzo-l,12-diaza-5,8-dioxacyclopentadecane), has been prepared by electrochemical oxidation of rRuin(N202)(0H)(0H2)]2+ and characterized by X-ray crystallography (Fig. 2) (46). Isolation of this complex from aqueous solution has been taken as an indication of a very small equilibrium constant for the reaction... 

Harrington T, Pletcher D. The removal of low levels of organics from aqueous solutions using Fe(II) and hydrogen peroxide formed in situ at gas diffusion electrodes. J Electrochem Soc 1999 146(8) 2983-2989. 

Ponce de Leon C, Pletcher D. Removal of formaldehyde from aqueous solutions via oxygen reduction using a reticulated vitreous carbon cathode. J Appl Electrochem 1995 25 307-314. 

---