Abstract
The performance of anion-exchange membranes (AEMs) in Reverse Electrodialysis is hampered by both presence of multivalent ions and fouling phenomena, thus leading to reduced net power density. Therefore, we propose a monolayer surface modification procedure to functionalize Ralex-AEMs with poly(acrylic) acid (PAA) in order to (i) render a monovalent permselectivity, and (ii) minimize organic fouling. Membrane surface modification was carried out by putting heterogeneous AEMs in contact with a PAA-based aqueous solution for 24 h. The resulting modified membranes were firstly characterized by contact angle, water uptake, ion exchange capacity, fixed charge density, and swelling degree measurements, whereas their electrochemical responses were evaluated through cyclic voltammetry. Besides, their membrane electro-resistance was also studied via electrochemical impedance spectroscopy analyses. Finally, membrane permselectivity and fouling behavior in the presence of humic acid were evaluated through mass transport experiments using model NaCl containing solutions. The use of modified PAA-AEMs resulted in a significantly enhanced monovalent permselectivity (sulfate rejection improved by >35%) and membrane hydrophilicity (contact angle decreased by >15%) in comparison with the behavior of unmodified Ralex-AEMs, without compromising the membrane electro-resistance after modification, thus demonstrating the technical feasibility of the proposed membrane modification procedure. This study may therefore provide a feasible way for achieving an improved Reverse Electrodialysis process efficiency.
Highlights
The continuous rise of worldwide electricity demand has led to an increasing global interest in the study and development of green technologies capable of generating sustainable and renewable power [1,2]
Γd,anion-exchange membranes (AEMs) cd where OCV represents the open circuit voltage, N is the number of cell pairs, R the universal gas constant, T the absolute temperature, F the Faraday constant, α is equal to the permselectivity of the corresponding ion exchange membrane, γ represents the activity coefficient, c is the molar concentration, and z is equal to the valence of the anion/cation that crosses the corresponding membrane
36–38% compared to their thicknesses at dry conditions, which demonstrates the essential role of the membrane operating conditions for improved Reverse Electrodialysis (RED) performance, improved performance, since higher thicknesses might result in increased membrane electrosince higher thicknesses might result in increased membrane electro-resistance, reducing the resistance, thuspower reducing the obtainable net power density
Summary
The continuous rise of worldwide electricity demand has led to an increasing global interest in the study and development of green technologies capable of generating sustainable and renewable power [1,2]. In this respect, Reverse Electrodialysis (RED) represents an attractive technology due to the possibility of harvesting renewable energy from salinity gradients (e.g., between seawater and river water) through the use of alternating anion exchange membranes (AEMs) and cation exchange membranes (CEMs) forming cell pairs, where the different compartments between these membranes are fed with streams of different salinity (feedwaters with high and low salt concentration) [3,4,5]. The development of mono-selective AEMs and CEMs is crucial for an improved RED process efficiency
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