Membrane-Free Redox Flow Batteries

Project Information

MFreeB

Grant agreement ID: 726217

DOI

10.3030/726217

Project closed

EC signature date 29 March 2017

Start date 1 June 2017

End date 30 November 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 998 407,01

EU contribution

€ 1 998 407,00

Coordinated by

Fundacion IMDEA Energia
Spain

Periodic Reporting for period 5 - MFreeB (Membrane-Free Redox Flow Batteries)

Reporting period: 2023-12-01 to 2024-11-30

Summary of the context and overall objectives of the project

Renewable energy implementation requires efficient and affordable energy storage systems, such as Redox Flow Batteries (RFBs). Current Vanadium RFBs face challenges including the high cost and toxicity of vanadium components and the expensive, low-performance ion-selective membranes.
The MFreeB project aims to remove the membrane of RFBs by developing a versatile and scalable Membrane-Free RFB using immiscible electrolytes and replacing the metallic species by cheap and abundant organic molecules. Specific objectives are:
-Development of Metal-free redox couples with high solubility, optimum redox potential, fast kinetics and multi-electron exchange and electrolytes to be applied in a Membrane-Free RFB.
-Investigation of the Immiscibility and Partition Coefficients of catholyte and anolyte enabling spontaneous separation of the two electrolytes.
-Enhancing energy density through higher solubility, increased operating voltage, and multi-electron transfer.
-Increase the power density by removing the membrane that provokes high internal resistance.
-Innovative Membrane-Free RFB will reduce both operational and maintenance cost.

The main conclusions are:
-Validated Membrane-Free Batteries: Successfully demonstrated the concept under static and flowing conditions.
-Proven Versatility: Demonstrated flexibility with various electrolyte combinations and diverse active species.
-Advances in Molecular Modeling: Enabled optimization of organic active species' properties, including redox potential, solubility, and partition coefficients.
-Innovative Reactor Design: Patented a reactor design supported by fluid-dynamic simulations, proving feasibility for flow batteries.
-Enhanced Electrolyte Interphase Understanding: Developed novel techniques to analyze interfacial processes in immiscible electrolytes.
-Improved Lab Prototype Performance: Enhanced energy density and power density through optimized cell designs and electrolytes.
-Significant Knowledge: Advanced the development of efficient, cost-effective, and sustainable battery technologies.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work performed during the whole project is detailed below:
1. Proof of concept of Static Membrane-Free Battery (MFreeBat)
A static membrane-free battery was demonstrated using immiscible electrolytes.
Exploitation: Patent: ESP201630327. Granted. Licensed to a company.
Dissemination: Marcilla, R et al. Angew. Chemie, 2017, 56,12460-12465
2. Versatility of the Membrane-Free Battery concept
The versatility of MFreeBat was tested by > 10 redox electrolytes paired in several immiscible anolyte/ catholyte systems.
Dissemination:Marcilla, R et al. ACS Appl. Mater. Interfaces, 2018, 10, 48, 41246-41256
3. Feasibility of aqueous biphasic system as Static MFreeBat
Aqueous Biphasic Systems (ABS), were used for the first time as MFreeBat electrolytes. Dissemination: Marcilla R. et al. Adv. Science, 2018, 5, 1800576
4. Identification of critical aspects in aqueous MFreeBats
Crossover and self-discharge challenges were addressed, with self-discharge identified as a key issue of the technology.
Dissemination: Marcilla R. et al. Energy Storage Mater., 2020, 26,400-407
Exploitation: Patent App.: EP23382722. Licensed to a company
5. Molecular Modelling
Computational methods predicted electrochemical properties of organic redox compounds, such as redox potentials, and Molecular Dynamics analyzed interactions between redox molecules and supporting salts.
Dissemination: Marcilla R. et al. Sust. Energy & Fuel. 2020, 4, 5513-5521; ChemSusChem, 2023, e202201984; J. Mater. Chem. A, 2021,9, 505-514
6. Development of lab prototype of Membrane-Free Redox Flow battery
Fluid-dynamic simulations led to a patented membrane-free flow reactor design that maintains a stable liquid-liquid interface, enabling operation under flowing conditions. Flowing conditions improved battery performance.
Exploitation : Patent: WO2021209585B1. Granted. Licensed to a company
Dissemination: Marcilla R. et al. Inter. J. Heat and Mass Transfer, 2021, 170, 121022, Marcilla R. et al. Energy Storage Mater. 56 ,2023, 403–411; J.Power Sources, 2024, 608, 234660 ; APL Energy, 2025, 3, 012001; under revision in Angew. Chemie

In summary, the project results were exploited through 16 publications and 3 patents (all licensed to a European start-up due to the significant industrial interest). Dissemination efforts include over 50 activities such as conferences, WS, training sessions, and social media engagement targeting diverse audiences (scientific, industrial, and public) to maximize the project's impact and visibility.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project achieved significant progress, surpassing the state of the art in several areas which underscore the project's contribution to the development of efficient, versatile, and sustainable membrane-free battery technologies:
1.Feasibility demonstration of the membrane-free battery with organic redox molecules as active species.
2.Versatility demonstration of the concept using different electrolytes and organic species.
3.Study of ABS as redox immiscible electrolytes and their application in membrane-free batteries.
4.Perform molecular modeling studies to evaluate the tunability of active species properties.
5.Design of a new reactor for flowing conditions guided by fluid-dynamic studies and simulations.
6.Application of new methodologies such as Electrochemical Scanning Microscopy to provide insights into the mechanism of Self-discharge at the liquid-liquid interface.
7.Development of an aqueous Zn hybrid membrane-redox flow batteries with high coulombic efficiency.
8.Investigation of aqueous triphasic systems as an alternative to biphasic ones to mitigate the self-discharge reaction in the battery.

scheme of an aqueous membrane-free flow battery with organic active species