X-ray absorption spectroscopy and actinide electrochemistry: a setup dedicated to radioactive samples applied to neptunium chemistry

A spectroelectrochemical setup has been developed to investigate radioactive elements in small volumes (0.7 to 2 ml) under oxidation–reduction (redox) controlled conditions by X-ray absorption spectroscopy (XAS). The cell design is presented together with in situ XAS measurements performed during neptunium redox reactions. Cycling experiments on the NpO2 2+/NpO2 + redox couple were applied to qualify the cell electrodynamics using XANES measurements and its ability to probe modifications in the neptunyl hydration shell in a 1 mol l−1 HNO3 solution. The XAS results are in agreement with previous structural studies and the NpO2 2+/NpO2 + standard potential, determined using Nernst methods, is consistent with measurements based on other techniques. Subsequently, the NpO2 +, NpO2 2+ and Np4+ ion structures in solution were stabilized and measured using EXAFS. The resulting fit parameters are again compared with other results from the literature and with theoretical models in order to evaluate how this spectroelectrochemistry experiment succeeds or fails to stabilize the oxidation states of actinides. The experiment succeeded in: (i) implementing a robust and safe XAS device to investigate unstable radioactive species, (ii) evaluate in a reproducible manner the NpO2 2+/NpO2 + standard potential under dilute conditions and (iii) clarify mechanistic aspects of the actinyl hydration sphere in solution. In contrast, a detailed comparison of EXAFS fit parameters shows that this method is less appropriate than the majority of the previously reported chemical methods for the stabilization of the Np4+ ion.

The Correlation Between the Electronegativities and the Standard Potentials

Linear correlations are analyzed between the empirical electronegativities χa of metals and non-metals and their standard potentials Eo. The correlation intersection corresponds to the transfer from metals to non-metals, characterized by the intermediate electronegativity χa,interm and the standard potential Eo ~+ 0.5 V SHE which is close to Billiter potential +0.475 V SHE. It is concluded that χa,interm and Eo ~ +0.5 V SHE would define some hypothetical substance (neither metal nor non-metal) without its own chemical activity. This would be due to the intermediate non-specific (definite coulomb) bond of its outer electrons being insufficiently unstable (as metallic bonds) for breaking and insufficiently stable (as non-metallic bonds) for accepting electrons in half-reactions. Spontaneous half-reactions are analyzed as interactions of Red - and Ox - forms with water molecules on electrodes due to break Red + H2O → Ox + neinterm and formation Ox + neinterm + H2O → Red of specific (chemical) electron bonds, where neinterm are electrons in the absence of a specific bond with Ox-forms but at the definite coulomb bond with them. The instant division of electrons, ions, polarization water molecules of formed intermediate complexes leads to the appearance of double-electric layers on electrodes.

Surface-Functionalized Separator for Stable and Reliable Lithium Metal Batteries: A Review

Metallic Li has caught the attention of researchers studying future anodes for next-generation batteries, owing to its attractive properties: high theoretical capacity, highly negative standard potential, and very low density. However, inevitable issues, such as inhomogeneous Li deposition/dissolution and poor Coulombic efficiency, hinder the pragmatic use of Li anodes for commercial rechargeable batteries. As one of viable strategies, the surface functionalization of polymer separators has recently drawn significant attention from industries and academics to tackle the inherent issues of metallic Li anodes. In this article, separator-coating materials are classified into five or six categories to give a general guideline for fabricating functional separators compatible with post-lithium-ion batteries. The overall research trends and outlook for surface-functionalized separators are reviewed.

Electrochemical Processing and Thermal Properties of Functional Core/Multi-Shell ZnAl/Ni/NiP Microparticles

Electroless deposition on zinc and its alloys is challenging because of the negative standard potential of zinc, the formation of poor surface layers during oxidation in aqueous solutions, and extensive hydrogen evolution. Therefore, there are only few reports of electroless deposition on Zn and its alloys, neither of them on micro/nano powders. Here, we propose a two-step process that allows the formation of compact, uniform, and conformal Ni/NiP shell on Zn-based alloy microparticles without agglomeration. The process utilizes controlled galvanic displacement of Ni deposition in ethanol-based bath, followed by NiP autocatalytic deposition in an alkaline aqueous solution. The mechanism and effect of deposition conditions on the shell formation are discussed. Thermal stability and functional analysis of core-shell powder reveal a thermal storage capability of 98.5% with an encapsulation ratio of 66.5%. No significant morphological change of the core-shell powder and no apparent leakage of the ZnAl alloy through the Ni shell are evident following differential scanning calorimetry tests. Our two-step process paves the way to utilize electroless deposition for depositing metallic-based functional coatings on Zn-based bulk and powder materials.

Regulating the species and the counter-ions size of proton acids to prepare novel poly(4-aminodiphenylamine) nanomaterials towards supercapacitor

Poly(4-aminodiphenylamine) (P(4-ADPA)) is a kind of polyaniline derivative and is promising as one of the alternatives to polyaniline because its monomer has a lower oxidation standard potential for the oxidation...

Nernst equation applied to electrochemical systems and centenary of his Nobel Prize in chemistry

Walther Hermann Nernst received the Nobel Prize in Chemistry in 1920 for the formulation of the third law of thermodynamics, thus celebrating a century in this 2020 year. His work helped the establishment of modern physical chemistry, since he researched into fields, such as thermodynamics and electrochemistry, in which the Nernst equation is included. This paper reports on several experiments that used a Daniell galvanic cell working in different electrolyte concentrations for comparing results with the theoretical values calculated by the Nernst equation. The concentration and activity coefficients values employed for zinc sulfate and copper electrolytes showed activity can replaces concentrations in thermodynamic functions, and the results are entirely consistent with experimental data. The experimental electromotive force from standard Daniell cell, for ZnSO4 and CuSO4, with unitary activity and in different concentrations at room temperature is in agreement with those from theoretical calculations. Cu2+ ion concentrations and temperature were simultaneously varied; however, the cell potential cannot be included in calculations of Nernst equation for different temperatures than 25 °C because the standard potential value was set at 25 °C. The cell potential decreases drastically when the Cu2+ concentration was reduced and the temperature was above 80 oC.

Electrochemical Properties of NdCl3 and CeCl3 in Molten LiCl-KCl Eutectic Salt

NdCl3 and CeCl3 are characterized by the very close proximity of their standard reduction potentials. Thus, they represent the most challenging salt mixtures with respect to decoupling electrochemical responses and calculating concentrations. The goals of this study include the determination of the apparent standard potentials of both Nd3+/Nd2+ and Ce3+/Ce in LiCl-KCl-CeCl3 or NdCl3 mixtures. Matrix and concentration effects on fundamental electrochemical properties are of particular interest, as these thermodynamic properties will impact the ability to use voltammetry to measure concentrations in unknown samples. Several LiCl-KCl-CeCl3 or NdCl3 mixtures with NdCl3/CeCl3 concentrations ranging from 4 to 10 wt% at 753 to 793 K have been explored. For apparent standard potential values of CeCl3, a good agreement was obtained with the literature data, except above 773 K.

On the development of a gold-standard potential energy surface for the OH− + CH3I reaction

We develop the first accurate full-dimensional ab initio PES for the OH− + CH3I SN2 and proton-transfer reactions treating the failure of CCSD(T) at certain geometries.