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Ion-Exchange Membranes for the Fabrication of Reverse Electrodialysis Device
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Osmotic Ballasts Enhance Faradaic Efficiency in Closed-Loop, Membrane-Based Energy Systems
Ryan S Kingsbury1, Orlando Coronell1
1Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
Environmental Science & Technology
|December 24, 2016
Summary
Adding neutral solutes as osmotic ballasts in closed-loop reverse electrodialysis (RED) systems significantly improves energy efficiency by mitigating water transport. This approach doubles faradaic efficiency and improves round-trip energy efficiency in RED energy storage.
Area of Science:
- Energy Storage and Conversion
- Electrochemistry
- Membrane Science
Background:
- Aqueous processes for energy storage, such as reverse electrodialysis (RED), rely on concentration differences across ion exchange membranes.
- These concentration differences create electrochemical potential and osmotic pressure, where water transport via osmosis negatively impacts system efficiency in closed-loop RED.
Purpose of the Study:
- To investigate the use of neutral, nonpermeating solutes as "osmotic ballasts" to mitigate water transport in closed-loop RED systems.
- To experimentally evaluate the impact of osmotic ballasts on system efficiency and performance.
Main Methods:
- Implementation of neutral, nonpermeating solutes (osmotic ballasts) in a closed-loop concentration battery based on RED.
- Experimental comparison of two proof-of-concept ballast molecules to assess their effect on water transport and system efficiency.
Main Results:
- Osmotic ballasts were shown to reduce, eliminate, or reverse net water transport through membranes during battery cycling.
- Faradaic and round-trip energy efficiency were more than doubled (from 18% to 50% and 7% to 15%, respectively) by mitigating osmosis.
- A slight negative impact on open circuit voltage was observed in the presence of ballasts.
Conclusions:
- Balancing osmotic pressure with noncharged solutes is a promising strategy for significantly reducing energy losses in closed-loop RED systems.
- Osmotic ballasts offer a viable method to enhance the efficiency of RED-based energy storage.
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