Reverse electrodialysis for power production with ion-permselective spacers and its optimization

During the traditional reverse electrodialysis (RED) process, second only to concentration polarization phenomenon, the spacer shadow effect that blocks the ionic transport as a consequence of the use of non-permselective spacers has an undesirable impact on the practical power output. In this work, a configuration of ion-permselective spacer is proposed to eliminate the spacer shadow effect to improve the power density. By combining direct current and alternating current experimental methods, the spacer shadow and concentration polarization effects are measured. At the same time, their impact on stack resistance and power out are analyzed quantatively under different hydrodynamic conditions and spacer configurations to optimize the RED process performance. Compared with traditional spacers, the use of ion-permselective spacers makes the spacer shadow effect reduced by more than 95% inversely with a stronger concentration polarization phenomenon, which results in a higher power density due to remarkable decrease in stack resistance. In order to further suppress the concentration polarization, increasing flow rate and reducing pore size of channel are both feasible, which meanwhile leads to a further reduction in shadow effect. Yet, the variation of channel shape has little impact on the shadow and concentration polarization effects. The maximum power output of 0.81 W/m(2) is harvested with pore size of 4.5 mm and cell pair of 3 at flow rate of 40 L/h under the investigated conditions and is improved by 50% in comparison to non-permselective spacers. [GRAPHICS] .