Distinctive Interactions of Cesium and Hexaniobate in Water

The Cs-effect states Cs⁺ has more covalent character in bonding interactions than the lighter alkalis. It is exploited in organic synthesis and influences behavior in water, most notably radioactive ¹³⁷Cs in nuclear wastes or the environment. Niobium polyoxometalates (Nb-POMs) provide a unique opportunity to probe aqueous phase ion-pairing responsible for cesium's solution behavior, because Nb-POMs are most soluble in conditions of maximum ion-association. Moreover, POMs broadly resemble metal-oxide surfaces representative of interfaces found in the environment and industrial processes. Aqueous dissolution calorimetry reveals that Cs−Nb-POM exhibits greater concentration dependence in its endothermic dissolution, compared to the lighter alkali analogues. This phenomenon is attributed to persistent ion-pairs upon dissolution, even in very dilute and otherwise ion-free solutions. While dissociation of these cation-anion interactions in the crystalline lattice is the dominant endothermic step of dissolution, deprotonation of the Nb-POM is the most exothermic. These studies highlight the importance of the competing effects of aqueous ion association and acid-base chemistry that control solubility of compounds from simple oxoanions to metal-oxo clusters to supramolecular assemblies to solid metal oxides.Keywords: polyoxometalate, cesium, thermochemistry, calorimetry, ion pair

Electrolytic Extraction of Copper, Molybdenum and Rhenium from Molten Sulfide Electrolyte

The validity of the electrochemical series for metal sulfides decomposition in their standard state has been tested experimentally at 1500 K for La₂S₃, Cu₂S, MoS₂, and ReS₂ in a molten electrolyte with the following molar composition: (BaS)₅₄₋(Cu₂S)₃₁₋(La₂S₃)₁₅ (electrolyte B). Voltammetry measurements indicated the presence of faradaic reactions in the investigated electrolyte with and without the addition of MoS₂ and/or ReS₂. Electrolysis experiments showed that the addition of La₂S₃ to BaS-Cu₂S increases the faradaic efficiency for liquid copper production with respect to a previously studied (BaS)₅₄₋(Cu₂S)₄₆ electrolyte, and enabled isolation of elemental sulfur as the anodic product. Electrochemical measurements suggested the need to take into account the activity of dissolved Cu₂S in order to explain the observed cell voltage during electrolysis. Electrolysis in the presence and absence of ReS₂ and/or MoS₂ confirmed their relative stability as predicted by assuming decomposition in their standard states. Analysis of the metal products electrowon from an electrolyte containing Cu₂S, MoS₂, and ReS₂ indicated the simultaneous production of solid and liquid phases with nonequilibrium compositions.Office of Naval Research (Contract N00014-12-1-0521

Fabrication and Performance of Reversible Micro-Tubular Solid Oxide Cells

https://kent-islandora.s3.us-east-2.amazonaws.com/node/17223/87033-thumbnail.jpgSolid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mode operation, where electricity is generated in a fuel cell mode and fuel is produced in an electrolysis mode. Our current work encompasses the design, fabrication, and performance analysis of a micro-tubular reversible SOC that is prepared through a single dip-coating technique with multiple dips using conventional materials. Electrochemical impedance and current-voltage responses were monitored from 700 to 800 °C. Maximum power densities of the cell achieved at 800, 750, and 700 °C, was 690, 546, and 418 mW cm−2, respectively. The reversible, dual mode operation of the SOC was evaluated by operating the cell using 50% H2O/H2 and ambient air. Accordingly, when the SOC was operated in the electrolysis mode at 1.3 V (the thermo-neutral voltage for steam electrolysis), current densities of −311, −487 and −684 mA cm−2 at 700, 750 and 800 °C, respectively, were observed. Hydrogen production rate was determined based on the current developed in the cell during the electrolysis operation. The stability of the cell was further evaluated by performing multiple transitions between fuel cell mode and electrolysis mode at 700 °C for a period of 500 h. In the stability test, the cell current decreased from 353 mA cm−2 to 243 mA cm−2 in the fuel cell mode operation at 0.7 V, while the same decreased from −250 mA cm−2 to −115 mA cm−2 in the electrolysis operation at 1.3 V.</p

SuresDistinctiveInteractionsCesiumHexaniobateInWaterSupportingInformation.pdf

The Cs-effect states Cs⁺ has more covalent character in bonding interactions than the lighter alkalis. It is exploited in organic synthesis and influences behavior in water, most notably radioactive ¹³⁷Cs in nuclear wastes or the environment. Niobium polyoxometalates (Nb-POMs) provide a unique opportunity to probe aqueous phase ion-pairing responsible for cesium's solution behavior, because Nb-POMs are most soluble in conditions of maximum ion-association. Moreover, POMs broadly resemble metal-oxide surfaces representative of interfaces found in the environment and industrial processes. Aqueous dissolution calorimetry reveals that Cs−Nb-POM exhibits greater concentration dependence in its endothermic dissolution, compared to the lighter alkali analogues. This phenomenon is attributed to persistent ion-pairs upon dissolution, even in very dilute and otherwise ion-free solutions. While dissociation of these cation-anion interactions in the crystalline lattice is the dominant endothermic step of dissolution, deprotonation of the Nb-POM is the most exothermic. These studies highlight the importance of the competing effects of aqueous ion association and acid-base chemistry that control solubility of compounds from simple oxoanions to metal-oxo clusters to supramolecular assemblies to solid metal oxides.Keywords: cesium, calorimetry, ion pairs, thermochemistry, polyoxometalateKeywords: cesium, calorimetry, ion pairs, thermochemistry, polyoxometalateKeywords: cesium, calorimetry, ion pairs, thermochemistry, polyoxometalateKeywords: cesium, calorimetry, ion pairs, thermochemistry, polyoxometalat

Energetics of Formation and Hydration of a Porous Metal Organic Nanotube

Hybrid materials, such as metal organic nanotubes (MON), are of interest because of their chemical tunability and permanent porosity. While an increasing number of compounds is being reported, very little is known about their thermodynamic stability. Herein, the energetics of a MON, (C₄H₁₂N₂)_0.5[(UO₂)­(H_ida)­(H_2ida)]·2H₂O (UMON, C₁₀H₂₁N₃UO₁₂) (ida = iminodiacetate), that possesses unique water exchange and uptake has been investigated by acid solution calorimetry, thermal analysis, and water adsorption calorimetry. The enthalpy of formation of UMON, C₁₀H₂₁N₃UO₁₂ (Δ<i>H</i>_f,rxn), from the dense components (uranium oxide (UO₃), piperazine (C₄H₁₀N₂), and iminodiacetic acid (C₄H₇NO₄) was −55.3 ± 0.9 kJ/mol, which was similar to values for other metal organic framework materials. The dehydration enthalpy to form an anhydrous UMON and gaseous H₂O at 37 °C from thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) experiments was 57.8 ± 1.9 kJ/mol of water. This value is somewhat higher than the vaporization enthalpy of water (44 kJ/mol) and suggests modest bonding interactions of H₂O with the inner walls of the nanotubes. Water adsorption calorimetry of (C₄H₁₂N₂)_0.5[(UO₂)­(H_ida)­(H_2ida)]·2H₂O indicated that the water molecules are confined inside the UMON material in two thermally distinct positions. The ice-like arrangement of the confined water molecules inside the nanotube impacts the energetics of the material and adds to the stabilization of the structure