The development of advanced electrochemical devices for energy conversion and storage requires fine tuning of electrode reactions, which can be accomplished by altering the electrode/solution interface structure. Particularly, in case of an alkali-salt electrolyte the electric double layer (EDL) composition can be managed by introducing organic cations (e.g. room temperature ionic liquid cations) that may possess polar fragments. To explore this approach, we develop a theoretical model predicting the 1 arXiv:2007.00378v1 [cond-mat.soft] 1 Jul 2020 efficient replacement of simple (alkali) cations with dipolar (organic) ones within the EDL. For the typical values of the molecular dipole moment (2 − 4 D) the effect manifests itself at the surface charge densities higher than 30 µC/cm 2. We show that the predicted behavior of the system is in qualitative agreement with the molecular dynamics simulation results.

We formulate a general mean-field theory for a flat electric double layer in ionic liquids and electrolyte solutions with ions possessing static polarizability and a permanent dipole moment on a charged electrode. We establish a new analytical expression for electric double-layer differential capacitance, determining it as an absolute value of the ratio of the local ionic charge density to the local electric field on an electrode surface. We demonstrate that this expression generalizes the analytical expressions previously reported by Kornyshev and Maggs and Podgornik. Using the obtained analytical expression, we explore new features of the differential capacitance behavior with an increase in the static polarizability and permanent dipole moment of cations. We relate these features to the behavior of ionic concentrations on the electrode. In particular, we elucidate the role of the competition between the dielectrophoretic attraction and Coulomb repulsion forces acting on polarizable or polar cations in the electric double layer in the behavior of the differential capacitance. The developed theoretical model and obtained theoretical findings could be relevant for different electrochemical applications, e.g., batteries, supercapacitors, catalysis, electrodeposition, etc.

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The intermetallic compound (IMC) PuPd 3 was synthesized by induction fusion of the components in a vacuum. The phase composition of the compound was confirmed by X-ray diffraction analysis. SEM analysis revealed the presence in the sample obtained of three metastable PuPd x phases (2.3 < x < 4.4) differing in the extent of enrichment in Pu. Data on the electrochemical properties of PuPd 3 in the 3LiCl-2KCl salt eutectic were obtained for the first time. Three main peaks of anodic oxidation are observed in the cyclic voltammogram of PuPd 3 at potentials of -1.74, -1.24, and -0.09 V (vs. Ag/AgCl). At potentials exceeding +0.6 V (vs. Ag/AgCl), PuPd 3 passes into the transpassive state. At lower potentials, anodic oxidation of IMC leads to the Pu dissolution in the form of Pu(III), but the simultaneously oxidized Pd is reduced on the electrode, which results in the enrichment of its surface in Pd.