An alternative cation exchange membrane morphology for reverse electrodialysis

Introduction Reverse electrodialysis (RED) is a promising membrane-based technology that can extract the salinity gradient power from solutions at different concentration by forming a controlled mixing environment with the help of anion and cation exchange membranes (AEM and CEM) [1]. Majority of the membranes investigated for RED were commercial electrodialysis (ED) membranes due to similarity of the two processes. However, RED requirements substantially differ from ED. ED membranes are designed to maintain their electrochemical and mechanical properties under severe conditions, whereas RED process conditions are milder [2]. Liquid indued phase separation (LIPS) method can be an alternative IEM preparation method for RED by forming asymmetric more open structures that can reduce the membrane ionic resistance, while permselectivity can be maintained by the presence of a top dense layer. In this study, a novel tailor made CEM was designed from sulfonated polyethersulfone (sPES) and its electrochemical performance was compared with two commercial membranes. Material and Methods LIPS method was used to prepare sPES-CEM. Electrochemical characterization of the membranes was carried out with a potentiostat/galvanostat as described previously, and power density estimated from permselectivity and resistance data by using half-cell method for 100µm compartment thickness [3]. Results Tailor made sPES membrane had 0.84 permselectivity while 1.00 and 0.95 were permselectivity values for CMX and Fuji-CEM, respectively. Contrarily, sPES areal resistance resulted in better performance: CMX resistance was around 2.2 Ohm?cm2 while sPES and Fuji-CEM resistances were 21% and 52% (I suggest to insert the values) of CMX, respectively. Moreover, sPES exhibited the best performance in terms of power density, 4.84 W/m2 (I suggest to insert the values also of the other two systems). For sPES membrane, the trade-off between permselectivity and resistance was favorable considering the higher power density achievable. Conclusions sPES-CEM prepared by LIPS method revealed that it can be a good alternative to conventional CEMs for RED. It might open a new scenario for the IEM preparation for RED but also for other electromembrane processes for energy conversion. References 1.Avci, A. H.; Sarkar, P.; Tufa, R. A.; Messana, D.; Argurio, P.; Fontananova, E.; Curcio, E. Effect of Mg2+ ions on energy generation by Reverse Electrodialysis, J. Memb. Sci., 520 (2016) 499-506. 2.Guler, E.; Zhang, Y.; Saakes, M.; Nijmeijer, K. Tailor-made anion-exchange membranes for salinity gradient power generation using reverse electrodialysis, ChemSusChem., 5 (2012) 2262-2270. 3.Fontananova E.; Messana D.; Tufa R. A.; Nicotera I.; Kosma V.; Curcio E.; van Baak, W.; Drioli, E.; Di Profio, G. Effect of solution concentration and composition on the electrochemical properties of ion exchange membranes for energy conversion, J. Power Sources, 340 (2017) 282-293.