Osmotic Ballasts Enhance Faradaic Efficiency in Closed-Loop, Membrane-Based Energy Systems

Ryan S. Kingsbury, Orlando Coronell

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Aqueous processes for energy storage and conversion based on reverse electrodialysis (RED) require a significant concentration difference across ion exchange membranes, creating both an electrochemical potential and an osmotic pressure difference. In closed-loop RED, which we recently demonstrated as a new means of energy storage, the transport of water by osmosis has a very significant negative impact on the faradaic efficiency of the system. In this work, we use neutral, nonpermeating solutes as "osmotic ballasts" in a closed-loop concentration battery based on RED. We present experimental results comparing two proof-of-concept ballast molecules, and show that the ballasts reduce, eliminate, or reverse the net transport of water through the membranes when cycling the battery. By mitigating osmosis, faradaic and round-trip energy efficiency are more than doubled, from 18% to 50%, and 7% to 15%, respectively in this nonoptimized system. However, the presence of the ballasts has a slightly negative impact on the open circuit voltage. Our results suggest that balancing osmotic pressure using noncharged solutes is a promising approach for significantly reducing faradaic energy losses in closed-loop RED systems. (Figure Presented).

Original languageEnglish (US)
Pages (from-to)1910-1917
Number of pages8
JournalEnvironmental Science and Technology
Issue number3
StatePublished - Feb 7 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Environmental Chemistry


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