Reverse electrodialysis (RED) has received considerable attention as a technique for extracting energy from salinity gradients, but studies have generally been limited to the generation of power from natural gradients, such as seawater and river water. In this work, we consider the potential of RED for energy storage using reversible desalination. We present the experimental performance of a rechargeable concentration battery system based on closed-loop, reversible electrodialysis (ED). Further, we develop a nonsteady state mass transport model based on chemical thermodynamics that successfully predicts the performance of the system. A single charge-discharge cycle of the battery was performed at several different current densities, beginning at 33% and ending at 40%-90% state of charge. The experimental round-trip energy efficiency ranged from 21.2% to 34.0%, with maximum current (faradaic) and voltage (ohmic) efficiencies of 58.9% and 78.5%, respectively. Upon calibration, our mass transport model is able to predict the majority of these results within experimental error. The combination of experimental and theoretical results indicate that resistance of the ion exchange membranes and transport of water by osmosis are the dominant sources of ohmic and faradaic energy losses, respectively. Our results demonstrate that a functioning battery can be constructed using existing (reverse) electrodialysis technology. Such a battery is somewhat unique among energy storage technologies in that the energy storage capacity (Wh) is fully decoupled from its power capacity (W); a trait shared only by redox flow batteries. Future improvements in ion exchange materials and optimization of system conditions will increase the energy efficiency, power density, and energy density of the process.

Energy storage by reversible desalination: A concentration battery based on electrodialysis

251st National Meeting (2016)

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