Influence of solution concentration and salt types on the performance of reverse electrodialysis cells

The influence of salt concentrations on the performance of reverse electrodialysis (RED) stacks has rarely been investigated using thermolytic salts such as NH₄HCO₃, that can be regenerated using waste heat and can be set at any desired concentration below saturation limits. Here, power densities produced by a RED stack were first investigated using different NaCl concentrations, and then tested using NH₄HCO₃. The power produced by the RED stack increased with NaCl concentrations from 0.6M to 3.6M in the HC (high concentration) solution, but it did not increase at higher salt concentrations due to limited ion exchange membrane capacity. NaCl concentrations larger than 0.14M in the LC (low concentration) solution decreased power primarily as a result of lower salinity ratios (<25). However, LC concentrations up to 0.14M NaCl did not appreciably affect power output due to a trade-off between decreased internal resistances with higher solution conductivities and lower salinity ratios. Power densities using NH₄HCO₃ solutions were slightly lower on the basis of identical molar concentrations, but similar on the basis of matched solution conductivities.