Critical aspects of membrane-free aqueous battery based on two immiscible neutral electrolytes


Redox Flow Batteries (RFB) stand out as a promising energy storage technology to mitigate the irregular energy generation from renewable sources. However, some hurdles limit their massive implementation including high cost of vanadium and the poor-performance of ion-selective membranes. Recently, we presented a revolutionary Membrane-Free Battery based on organic aqueous/nonaqueous immiscible electrolytes that eludes both separators and vanadium compounds. Here, we demonstrate the feasible application of this archetype in Aqueous Biphasic Systems (ABS) acting as an unprecedented Total Aqueous Membrane-Free Battery. After evaluating several organic molecules, methylviologen (MV) and 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) were selected as active species due to their optimum electrochemical behavior and selective partitioning between the phases. When connected electrically, this redox-active ABS becomes a Membrane-Free Battery with an open circuit voltage (OCV) of 1.23 V, high peak power density (23 mWcm(-2)) and excellent long-cycling performance (99.99% capacity retention over 550 cycles). Moreover, essential aspects of this technology such as the crossover, controlled here by partition coefficients, and the inherent self-discharge phenomena were addressed for the first time. These results point out the potential of this pioneering Total Aqueous Membrane-Free Battery as a new energy storage technology.



subject category

Chemistry; Science & Technology - Other Topics; Materials Science


Navalpotro, P; Trujillo, C; Montes, I; Neves, CMSS; Palma, J; Freire, MG; Coutinho, JAP; Marcilla, R

our authors


This work was partly developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013). C.M.S.S.N. also acknowledges FCT for the postdoctoral grant SFRH/BPD/109057/2015. MFreeB project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 726217). The results reflect only the authors' view and the Agency is not responsible for any use that may be made of the information they contain. We also gratefully acknowledge financial support from the Spanish Government through project SUSBAT (Ref. RTI2018-101049-B-I00) (MCIU/AEI/FEDER, UE). P.N. acknowledges the Spanish Government for the personnel grant through the FPI program (BES-2013-063098).

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