Organic electrochemistry has its origin in 1830 with Michael Faraday [ 1 ], but electrochemistry in general was discovered in 1800 when Alessandro Volta discovered the voltaic pile, the first electrochemical cell (Figure 1 ) [ 2
Authors:C. Kremer, S. Domínguez, M. Pérez-Sánchez, A. Mederos and E. Kremer
The heavy use of99mTc in nuclear medicine and the recent development of188Re radiopharmaceuticals have encouraged the comparative study of Tc and Re coordination compounds. In this work, the electrochemistry of [MVO2 (amine)2]+ (M=Tc, Re; amine = ethylenediamine, 1,3-diaminopropane, diethylenetriamine, triethylenetetramine) complexes is studied by cyclic voltammetry and the results are compared. The voltammograms of these compounds, obtained at different pH values, show that [ReO2(amine)2]+ cations are thermodynamically stable even when protonated. On the other hand, analogous Tc compounds are not so stable and easily decompose if existing as [TcO(OH) (amine)2]2+.
A study of the electrochemistry of uranium in LiF–BeF2 system important for molten salt reactor concept was conducted at W and Ni electrodes. Cyclic voltammetry and chronopotentiometry
methods were used. Two-step reduction mechanism for U4+ ions involving one electron exchange in soluble/soluble U4+/U3+ system and three electron exchange in the second step were found on W electrode. Both processes were identified as reversible
and diffusion-controlled. Based on voltammetric and chronopotentiometric measurements, the diffusion coefficient of U4+ ions at 813 K was calculated: D(U4+) = 1.26 × 10−6 cm2 s−1 and D(U4+) = 1.28 × 10−6 cm2 s−1, respectively. Formation of U–Ni alloys was observed on Ni electrode.
Authors:L. Martinot, L. Lopes, J. Marien and C. Jérôme
Molten salts have been widely used for the electrochemical preparation of lanthanum and uranium metals at high temperature. In this paper we demonstrate the feasibility of a similar process in dimethylformamide (DMF) and in the mixture g-butyrolactone/tetrahydrofuran (g-BL/THF). The best conditions for the preparation were deduced from preliminary transient electrochemistry experiments and from secondary ions mass spectrometry (SIMS) measurements involving SIMS mappings and SIMS depth profile analyses.
The electrochemical behaviour of uranium has been studied in basic, NaCl-saturated NaAlCl4 melts at 175°C. Solutions of UO3 exhibit two oxidation/reduction waves (cyclic voltammetry). The first wave corresponds to the U(VI)/U(IV) redox couple and is irreversible (slow electron transfer). The second wave corresponds to the deposition and stripping of an insoluble U(III) compound (U(IV)/U(III)). Solutions of UO2 or UCl4 and U(IV) solutions prepared by exhaustive electrolysis of UO3 behave identically. The cyclic voltammograms of U(IV) solutions are the same as those of UO3, but they show additional anodic peaks. Analysis of the peak currents (cyclic voltammetry), the limiting currents (pulse polarography) and the non-linear log i-t curves (anodic controlled potential coulometry) leads to the conclusion that uranium (IV) in the basic chloroaluminate melt exists as two different species in slow equilibrium with one another, of which only one species can be oxidized to U(VI). E.m.f. measurements of U(VI)-U(IV) mixtures indicate that the electron transfer process involves the formation of an intermediate U(V) species in a disproportionation equilibrium.
The electrochemical behaviour of PrF3 was studied in the LiF–CaF2 (79/21 molar ratio) at 1,213 K. Inert (W) and reactive (Ni) electrodes were used. Pr(III) ions are reduced in a single, three
electron exchange. The redox potential of the Pr(III)/Pr couple at the inert electrode was observed very close to the decomposition
potential of the LiF–CaF2 melt. Experiments using reactive working electrode were done. The results show the potential shift connected to the alloying
reactions of Pr and Ni. Deposition of Pr–Ni layer was confirmed by SEM-EDX analysis. Conclusions for the Pr separation possibilities
from spent nuclear fuel were done.
Authors:K. Heckner, G. Majoros, A. Kraft and R. Landsberg
The lowering of the photocorrosion ofn-GaP in 1M KOH in the presence of several redox systems was investigated using neutron activation analysis. After thermal neutron irradiation of GaP and annihilation of irradiation induced defects by annealing processes the photodissolution was investigated by measuring the activity of the corresponding electrolyte solutions. The dependence of the stabilization of the photoelectrode on concentration and redox potential of the reduced form of the redox couples I–, Fe (CN)
was measured. It was found that the stabilization is growing with growing concentration and lowering of the redox potential of the corresponding redox couple.
The electrochemical reduction of hexavalent and tetravalent uranium is investigated in ethylammonium nitrate at 298 K and in the acetamide-KSCN eutectic at 400 K. The transient techniques describe a two-step reduction of UO
in acetamide-KSCN while only one step is observed in ethylammonium nitrate. The reduction of tetravalent uranium proceeds in one step giving trivalent uranium in the two media. In any cases, additional kinetic phenomena are the source of difficulties for the understanding of the reactions. In controlled potential electrolysis, side-reactions between the reduced species and the solvent impede completely the mechanism foreseen by transient methods.