The Polarographic Behavior of the Neptunium (III)—Neptunium (IV) Couple in Chloride and Perchlorate Solution

XANES Spectroelectrochemistry: A New Method for Determining Formal Potentials

“…From the plot shown in Figure , it is clear that there is not a measurable deviation from linearity across the measured range, which indicates that there is no significant irreversibility in the reactions. Deviations from expected slope are not uncommon in Nernstian analyses and do not necessarily support previous arguments that the two Np couples under investigation are not entirely reversible. ,, Instead, the result could reflect other artifacts, such as small changes in activity coefficients over the range of the experiments. It should be noted that there is a difference in the integrated absorption intensities between the oxidized and reduced forms of Np in both redox couples that could influence the slope.…”

“…The Np(III) and Np(IV) edges in XANES spectra are more separated than the Np(V) and Np(VI) spectra, which overlap enough to render their quantitative separation difficult. The electrolytic preparation of valence-specific Np ions in a 1 M perchloric acid solution is well documented. − The pH of the HClO 4 solution allows both redox couples to be accessed in the same solution with no observable hydrolysis or precipitation. , These two different couples provide good examples of the use of XANES spectroelectrochemistry in the determination of formal reduction potentials. Previous work to determine Np formal potentials has relied on polarography or potentiometric titrations or optical spectroscopy to determine the valence-specific concentrations of Np.…”

Standard Potentials of the (MO2 2+/MO2 -) and (M4+/M3+ ) Redox Systems for Neptuniumand Plutonium

“…(5) allow to determine the standard potential and the specific interaction coefficients Δ e = e(Ox, CIO4) -e (Red, CIO4) ( Table 3).…”

“…HlNDMAN and KRITCHEVSKY [5] made some Polarographie measurements on the (Np(IV)/ Np(III)) couple in perchloric and hydrochloric acids at 25 °C. They found the system to be irreversible in HQO4 medium but it was reversible in HCl medium giving a formal potential of 0.142 ± 0.005 V/NHE in 1 Μ HCl.…”