Yair Cohen

Polyamide RO membranes are widely used for seawater desalination owing to their high salt rejection and water permeability; however, improved selectivity–permeability trade-off is still desired. “Molecular plugs,” small molecules immobilized within the polyamide structure, offer an attractive approach; however, their overall effect on polyamide physicochemical properties poses many questions. Here, we analyze the effect of decylamine, a promising plug, and a few charged and uncharged mimics on polyamide films using several in situ techniques. Electrochemical impedance spectroscopy (EIS) reveals a complex pH-dependent response, whereby, upon exposure to amine solution, conductivity first rapidly drops; however, under alkaline conditions, when amine is uncharged, the trend subsequently slowly reverses, and conductivity increases. This slow reversal was observed for noncharged alcohols of similar size as well, but not for larger surfactant molecules. The reversal was assigned to the uptake of plug molecules within polyamide, as opposed to the fast initial drop assigned to surface adsorption. EIS and quartz-crystal microbalance (QCM) results showed that exposure to decylamine under alkaline conditions ultimately led to an irreversible decrease in conductivity, that is, stronger ion rejection, remaining after re-exposure of polyamide to amine-free buffer. This suggests that plug uptake within polyamide resulted in polymer stress, indeed observed in surface stress measurements, and subsequent relaxation. The results indicate that the moderate size of decylamine and conditions minimizing its charge were optimal for irreversible change; however, charge interactions helped maximize its binding within polymer and induce the desired sustained change in selectivity. The results have many potential implications for improving current membrane desalination technology and increasing inherent membrane selectivity toward hard-to-remove species.

Although the affinity of metallocorroles to axial ligands is quite low, this is not the case when the chelated element is phosphorus. This work is hence focused on the mechanism of ligand exchange of six‐coordinate phosphorus corroles as a tool for affecting their chemical and physical properties. These fundamental investigations allowed for the development of facile methodologies for the synthesis of a large series of complexes and the establishment of several new structure/activity profiles that may be used to understand and predict spectroscopic features and for tailor‐made modification of photophysical and electrochemical properties. This is exemplified by the facile access to complexes with terminal groups that are of large potential for practical applications based on click chemistry, optical imaging, and surface science.

Temperature-dependent electrochemical impedance spectroscopy and cyclic voltammetry are employed to study changes in the order and interactions in molten alkali-halide salt binary-mixtures. Nyquist plots of KCl-LiCl, KCl-NaCl and KBr-NaBr equimolar mixtures at 700°C are characterized by a small semicircle at high-frequencies and a larger low-frequencies semicircle. Two peaks with well-separated time constants are present in the Bode phase plots. Those are referred to the interfacial and double-layer properties at high frequencies and to the bulk electrical properties away from the electrode at low frequencies. Along the measured temperatures (700–800°C), the KCl-NaCl mixture is featured with a low-frequencies peak only below ∼750°C, which diminishes at higher temperatures, as may point on a dispersion of the ionic structure. The entropies of the mixtures are calculated from the change of the electrochemical windows with temperature. The entropy of KCl-NaCl increases drastically along heating, implying on a drastic change in the order and interactions in the melt. In contrast, the KX-LiX (X = Cl, Br, I) entropies do not change. It is suggested that the stability of the ionic structure of the molten salt mixtures with temperature is a result of collaborative asymmetric polarization interactions among the different ions in the melt.

In situ electrochemical stress measurements are used to interrogate changes in oxide structure before and during the oxygen evolution reaction (OER) from Ir, Ni, Co, Au, and Pt electrodes in alkaline electrolyte. Stress evolution during potential cycling reports on changes in oxidation state and oxide forms. Hysteresis observed in the potential-dependent stress from Ir, Au, and Pt electrodes is associated with chemical irreversibility in electrode composition and roughness. Alternatively, Ni and Co exhibit reversible conversion between hydroxide and oxyhydroxide forms during cycling. From the experimentally determined stress, charge passed during electrode oxidation, and Young’s modulus, the change in strain exhibited by Ni and Co electrodes during hydroxide-oxyhydroxide conversion is calculated to be 7.0% and 8.4%, respectively. We also show that the magnitude of change in stress is proportional to the amount of material that is further oxidized.

The complex electrochemical impedance spectra of tungsten – (KCl-LiCl) interface at 700–800°C consist of two well-separated semicircles. One at high frequencies and reflects charge transfer resistance and interfacial capacitance. The second is at low frequencies and is attributed to the electrical properties of the melt. Similar spectra are measured for tungsten – (KCl-NaCl) interface. The low-frequencies semicircle though is reduced above 750°C. Entropy estimations from cyclic voltammetry measurements indicate an increase in the entropy of KCl-NaCl at ∼750°C and a possible change in the inter-ionic order and interactions. Asymmetric anion polarization interactions are suggested to be involved.