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Reverse Electrodialysis is today recognized as one of the most promising technology to harvest Salinity Gradient Power (SGP-RE). However, the effectiveness of SGP-RE in real practice is still not clearly defined due to the lack of specific studies in literature, being in large part limited to investigations on pure NaCl solutions. In this work we experimentally investigated the effect of Mg2+, the most abundant cation in natural water after Na+, on SGP-RE performance by power measurements on a lab-scale stack prototype. Maximum power density ranged from 1.06 W/m(Mp)(2) (MP: membrane pair) - generated when feeding SGP-RE prototype with 0.5 molal//4 molal NaCl, to 0.06 W/m(Mp)(2) - measured when using 0.5 molal//4 molal MgCl2 solutions. Likewise, open circuit voltage decreased from 1.70 to 0.72 V. Evidence of uphill transport in the range of 0-30% MgCl2 was confirmed by Ion Chromatography analysis carried out on inlet and outlet streams of SGP-RE stack. Electrochemical Impedance Spectroscopy analysis revealed that cation exchange membrane resistance was critically affected by Mg2+ concentration: membrane resistance, from a value of 2.41 Omega cm(2) in pure NaCl solution, increased tenfold in pure MgCl2 solution. (C) 2016 Elsevier B.V. All rights reserved.

La1-xBa1+xGaO4-0 (LBG) compounds, based on unconnected GaO4 moieties, were recently proposed as proton conductors. Protonic defects in the lattice are inserted through self-doping with Ba2+, to create oxygen vacancies subsequently filled by hydroxyl ions. We present a combined structural analysis on self-doped LBG using X-ray diffraction (XRD) and X-ray absorption (EXAFS): these results unravel the finer structural details on the short-range and long-range scales, and they are correlated with the dynamical properties of protonic conduction coming from vibrational spectroscopy. The structure of the GaO4 groups is independent of the oxide composition. On hydration, an array of short intertetrahedral hydrogen bonds is formed, producing a contraction of the a axis. On the basis of thermogravimetric analysis, EXAFS, XRD and infrared spectroscopy (IR) results, we propose that the stiffness of the GaO4 tetrahedra hinders the intratetrahedral proton transfer, while the noticeable fraction of protons involved in strong hydrogen bonds limit the proton reorientational freedom.

Lanthanum barium gallate proton conductors are based on disconnected GaO4 groups. The insertion of hydroxyls in the LaBaGaO4 network proceeds through self-doping with Ba2+, consequent O2- vacancy formation to fulfill charge neutrality. With a structural investigation on self-doped LaBaGaO4 oxides using synchrotron XRD and EXAFS on the Ga K-edge, we find that: (a) the GaO4 tetrahedra retain their size throughout the whole series; (b) the GaO4 tetrahedra rotate as rigid bodies on hydration, leading to the formation of a network of shorter O-O configurations that are stabilized by hydrogen bonds; (c) contraction of the lattice occurs along the a unit cell axis, as a consequence of an overall structural rearrangement of the hydrated solid.