Experimental Investigation on the Concentration Polarization and Power Output of a Reverse Electrodialysis Stack With Permselective Spacers for Different Factors

The use of permselective spacers in reverse electrodialysis (RED) stack introduces a more severe concentration polarization phenomenon at membrane–solution interfaces in spite of effectively suppressing the spacer shadow effect. In this paper, the concentration polarization phenomenon in RED with permselective spacers is analyzed for different membrane types, numbers of cell pairs, solution concentrations, and temperatures by measuring non-ohmic resistance based on direct and alternating current methods combined with theoretical formula. Experiments on direct current method are further made to determine the influence of concentration polarization on power output and power generation performance of stack for different factors. The results show that the non-ohmic resistance accounts for less than 40% of the total stack resistance. Increasing the flowrate and solution temperature effectively suppresses the concentration polarization in stack and thus is beneficial to improving the power output. However, the membrane type, number of cell pairs, and solution concentration hardly affect concentration polarization. In spite of this, these factors all have a considerable impact on the power generation performance of the stack. Among them, increasing the concentration of concentrated and diluted solutions is most beneficial to improving the power density.