Probing membrane and interface properties in concentrated electrolyte solutions

Reverse electrodialysis with saline waters and concentrated brines: A laboratory investigation towards technology scale-up

“…Such trend is related to the reduction in the residence time, leading to a larger average salinity gradient between compartments, and the improvement of mixing phenomena inside compartments, although these latter play a minor role when seawater and brine are used [34]. For such highly saline solutions, the minor contribution of polarization phenomena and the resistance of the boundary layer have been also observed by EIS measurements [32]. However, the most important influence of velocity is observed for the net power density and the yield.…”

“…This is quite surprising, considering the expected effect of membranes thickness and also the nominal values of IEMs areal resistance (lower for the thinner membranes in river water -seawater conditions). This finding can likely be attributed to a different behaviour of the two membranes when in contact with highly concentrated solutions, which can generate swelling and ions sorption phenomena, affecting the ionic conductivity of the IEMs [32] and eventually leading to a lower actual resistance of the thicker membranes.…”

“…A similar increase of power density has been observed (Figure 8) for the different membranes, ranging from 40% to 50% of the reference value. Such increase can be related to the strong dependence of membrane resistance on the system temperature, which can lead to a reduction between 30% and 50% when increasing the temperature from 20°C to 40°C [32]. The effect of temperature is also beneficial in increasing the conductivity of both solutions.…”

Progress and prospects in reverse electrodialysis for salinity gradient energy conversion and storage

“…Moreover, when ions are transported through the membrane from the HCC to LCC driven by an electrochemical potential gradient, the flux difference between the co-ion and the counter-ion along with the difference in transport number of the ions between the membrane and solution phase determines the formation of a diffusion boundary layer (DBL), having a thickness of several hundred of micrometers [119,120]. The diffusion boundary layer non-ohmic resistance is due to change in salt concentration in the unstirred (stagnant) liquid films close to the membrane surfaces [72,[121][122][123]. Thus, the internal stack resistance of RED is accounted by several resistances as described next.…”

Potential of brackish water and brine for energy generation by salinity gradient power-reverse electrodialysis (SGP-RE)

“…An enhancement in the electrical resistance of the membranes with the concentration of the electrolyte solution was also because of the increase in Donnan adsorbed salts and shrinking of the membranes. 20 A systematic investigation of this aspect, based on the electrochemical impedance spectroscopy, 13,14 will be the objective of future communications. Table 3.…”