Department 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.
Environ Sci Technol. 2017 Feb 7;51(3):1910-1917. doi: 10.1021/acs.est.6b03720. Epub 2017 Jan 11.
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.
基于反向电渗析（RED）的用于能量存储和转换的水相过程需要在离子交换膜两侧存在显著的浓度差，从而产生电化学势差和渗透压差。在我们最近证明的作为一种新的储能方式的闭环 RED 中，渗透压导致的水传输对系统的法拉第效率有非常显著的负面影响。在这项工作中，我们在基于 RED 的闭环浓度电池中使用中性、不可渗透的溶质作为“渗透压压舱物”。我们展示了比较两种概念验证压舱物分子的实验结果，并表明在电池循环过程中，压舱物会减少、消除或反转膜中水的净传输。通过缓解渗透压，法拉第效率和往返能量效率分别从 18%提高到 50%和从 7%提高到 15%，尽管在这个非优化系统中，压舱物的存在对开路电压有轻微的负面影响。我们的结果表明，使用非带电溶质平衡渗透压是一种很有前途的方法，可以显著降低闭环 RED 系统中的法拉第能量损失。
